JPH06141184A - Method and device for encoding/decoding multilever picture data - Google Patents

Abstract

PURPOSE:To efficiently encode multilevel picture data without damaging the reproducibility of a multilevel picture by detecting the picture element, where the density level is changed, as a change point with respect to each line of multilevel picture data and encoding the change point of the encoding line by two-dimensional displacement of differences in position and density level from the change point of an already encoded reference line. CONSTITUTION:A change point detecting part 4 is provided which detects the position of a picture element which is different from the picture element, which just precedes it in the scanning order, by density level with respect to each line at the time of defining each line of multilevel picture data, which is obtained by sampling in picture element units, as the encoding line. A distance detecting part 12 which compares the change point on the encoding line with that on the reference line as an already encoded line to obtain a position difference DELTAa and a level difference detecting part 13 which obtains a density level difference DELTAn are provided. These position difference DELTAa and density level difference DELTAn are recognized as two-dimensional displacement, and a preliminarily determined code V corresponding to this displacement is obtained to encode the change point on the encoding line.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multivalued image data encoding method and device for highly efficient encoding and storing or transmitting multivalued image data obtained by scanning an image and sampling in pixel units. The present invention also relates to a method and apparatus for restoring multi-valued image data related thereto.

[0002]

2. Description of the Related Art As a method of encoding multi-valued image data,
Bit plane coding methods and block coding methods are well known. The bit plane coding method is a method of two-dimensional data compression of a multi-valued image, in which the density level of each pixel is expressed by a binary code, and two-dimensional MR (Modified. Read) Encode. In this encoding method, although the two-dimensional correlation of high-order bits is high, the correlation of low-order bits is small and the compression rate is not so good.

The block coding method is a method of compressing a one-dimensional or two-dimensional data of a multi-tone image, and a certain section (in the one-dimensional compression) or a certain area (in the two-dimensional compression) of the image. ), And the difference between the average density level and the density level of each pixel is sequentially encoded for each section or each area.

In this method, since the section or region is set irrespective of the change characteristic of the image, even if there is a correlation in the image characteristic before and after the division boundary, it cannot be utilized, and the compression efficiency is not always good. As another multi-valued image coding method, the boundary of the gradation level of the quantized coding line is
There is a method of encoding the positional relationship with the boundary position of the reference line by an MR (Modified Read) method which is often used for encoding a binary image.

However, since this method applies the above-mentioned MR method, the boundary position when the level on one side of the gradation level boundary of the coding line and the corresponding level on the one side of the boundary of the reference line are the same. Is encoded with a vertical code. Therefore, for a multi-valued image in which the boundary of the gradation level (which can also be called a change point where the gradation level changes) changes frequently with respect to the reference line both in terms of position and gradation level (density level). As a result, high coding efficiency cannot always be obtained.

As a related multilevel image encoding method,
There are methods described in JP-B-4-7871 and JP-B-3-22752.

[0007]

SUMMARY OF THE INVENTION In consideration of the above points, an object of the present invention is to encode multi-valued image data suitable for high-efficiency encoding of multi-valued images such as documents including multi-valued images such as photographs. A method and apparatus for converting the multi-valued image data, and a method and apparatus for restoring multi-valued image data related thereto.

Specifically, by performing coding using the density level correlation not only in the main scanning direction of the image but also in the sub scanning direction, high coding efficiency can be expected without impairing reproducibility. An object of the present invention is to provide a multivalued image data encoding method and device, which can be expected to reduce transmission time and storage capacity, and a related multivalued image data restoration method and device.

[0009]

A first means for achieving the above object is to provide a pixel whose density level changes for each line of multi-valued image data obtained by scanning an image and sampling in pixel units. Is detected as a change point, and the change point of the encoded line is converted into a two-dimensional displacement (Δa, Δn) of the difference Δa in position with the change point of the already encoded reference line and the difference Δn in density level. Corresponding code V (Δa, Δn)
That is, the multi-valued image data encoding method and apparatus are adapted to be encoded by.

A second solution is that, for multi-valued image data obtained by scanning an image and sampling in pixel units, the target pixel is a character / line drawing based on the density levels of the target pixel and its peripheral pixels. An image area discriminating means for discriminating whether or not the pixel belongs to a region, and when the discrimination result is affirmative, the target pixel is changed to white (minimum density level) or black (maximum density level) depending on the density level of the target pixel. Binary quantization,

If the result of the determination is negative, a binarization processing means for outputting the density level of the pixel of interest as it is is provided, and a pixel whose density level changes for each line of the output image data of the binarization processing means. Is detected as a change point,
A code V (Δ) corresponding to a two-dimensional displacement (Δa, Δn) of the difference Δa in position between the change point of the encoded line and the change point of the already encoded reference line and the difference Δn in density level.
a, Δn) is a multivalued image data encoding method and apparatus.

A third solving means is that, for multi-valued image data obtained by scanning an image and sampling in pixel units, the target pixel is a character / line drawing based on the density levels of the target pixel and its peripheral pixels. Image area discrimination means for discriminating whether or not it belongs to a binary image area such as or a multi-valued image area such as a photograph, and multi-valued image data read according to the image area determination result 2 of the binary image data surface in which the pixels in the value image area are set to the minimum density level (white) and the multivalued image data surface in which the pixels in the binary image area are set to the minimum density level (white).
Separated into faces,

The image on the binary image data surface is binary-quantized,
A multi-valued image encoded by the first encoding method, an image on the multi-valued image data surface is encoded by the second encoding method, and the encoded data is alternately transmitted from the head encoding line of each surface. That is, the data encoding method and device are used.

A fourth solving means is that, for multi-valued image data obtained by scanning an image and sampling in pixel units, the target pixel is a character / line drawing based on the density levels of the target pixel and its peripheral pixels. An image area discriminating means for discriminating whether or not the pixel belongs to a region, and when the discrimination result is affirmative, the target pixel is changed to white (minimum density level) or black (maximum density level) depending on the density level of the target pixel. Binarization processing means for binarizing is provided,

Pixel sequences having a positive determination result of the image area determining means are binary-coded by the MR encoding method, and pixel sequences having a negative determination result are multi-value encoded, and the binary-encoded code sequence and multi-value are encoded. This is to provide a multivalued image data encoding method and device in which an identification code for identifying the encoding method is added to the head of the encoded code string.

A fifth solving means is a multi-valued image data decoding means for decoding the M-level encoded multi-valued image data fetched through a storage medium or a transmission medium, and a multi-valued image data decoding means. The multi-valued image of M gradations decoded by the means is requantized to N gradations (N ≦ M), the quantization error at the time of requantization is diffused to the peripheral pixels, and the average density level before and after the quantization. Has N-value error diffusion means for matching

When the gradation expression number n per pixel of the multi-valued image display or printing means is n ≦ M, the gradation number of requantization of the N-value error diffusion means is n corresponding to the gradation expression number n. And then
This is to provide a multivalued image data restoration method and device for requantizing an M gradation decoded multivalued image into n gradations.

[0018]

According to the first solving means of the present invention, in a multi-valued image such as a photograph, the density level of each pixel changes slowly, and the density level of the pixel of interest is almost equal to the density levels of the surrounding pixels, and the difference is small. It utilizes the characteristic that even if there is, it is very small.

Due to the properties of the multi-valued image described above, the position of the changing point on the encoded line where the density changes exists near the position of the already changing point on the reference line, and both changing points are present. There is a high probability that the difference in the concentration level of is also small.

Therefore, in the first solving means, a pixel whose density changes on the encoding line is detected as a change point, and this change point is located at a position difference Δa from the change point on the reference line and a difference between the density levels. Corresponding to the two-dimensional displacement (Δa, Δn) of Δn, by assigning and encoding codewords having shorter codeword lengths as the frequency of occurrence is high, high coding efficiency is achieved without impairing reproducibility. Can be expected.

A second solving means is to set the pixels of the area discriminated as the binary image area by the image area discriminating means to white (minimum density level) or black (maximum density level) depending on the density level of the pixel. Since the value is converted into a value, there are two types of change points in this area, a change pixel from white to black and a change pixel from black to white, and the sign of the maximum positive or negative value of Δn in the density level difference code L (Δn) If a word is assigned to a code word having a short code length, this binary image area can be coded by the multi-valued image coding method of the first solving means with almost the same coding efficiency as the conventional MR code.

That is, a high coding efficiency of the multi-valued image area can be expected, and the binary image area can be made into a sharp binary image by edge enhancement, and the same high coding efficiency as the conventional one can be obtained. .

A third solving means is a binary image in which an image in which a binary image and a multivalued image are mixed is discriminated between a binary image area and a multivalued image area by the image area discrimination means, and the multivalued image area is whitened. Plane and the binary image area are separated into two white-valued multi-valued image planes, and the images of these two planes are encoded by encoding methods with high encoding efficiency corresponding to the nature of the image, so that the total is obtained. High encoding efficiency can be expected, the memory capacity for image storage can be reduced, and the transmission time can be shortened for image transmission.

Further, images having different properties are separated and stored,
Since the data is transmitted, various correction processing can be performed independently on the binary image and the multivalued image at the time of image restoration.

A fourth solving means discriminates a binary image area and a multivalued image area by an image area discriminating means in an image in which a binary image and a multivalued image are mixed, and a binary image area in an encoding line. Is binarized by the MR encoding method, the multi-valued image area is multi-valued, the identification code of the encoding method is added to the head of the binary and multi-valued code sequence, and the data is stored and transmitted. So

Similar to the third solving means, it is possible to perform coding with a coding method having a high coding efficiency corresponding to the nature of each image, so that a high coding efficiency can be expected as a whole, and the memory capacity for image storage is reduced. It is possible to reduce the transmission time in image transmission.

A fifth solution is that the multi-value coded image or the received multi-value image corresponds to the display / print gradation number n of the display or printer by n-value by the N-value error diffusion method. Since it is quantized into and displays and prints a multi-valued image,
It is possible to obtain the best multi-valued image that makes full use of the display / print gradation capability.

[0028]

Embodiments of the present invention will be described below with reference to the drawings.

[First Embodiment] FIG. 1 is a block diagram showing the configuration of the first embodiment of the present invention. In the figure,
1 is an input terminal for multi-valued image data, 2 is a sync signal input terminal synchronized with the input timing of multi-valued image data for capturing multi-valued image data, and 3 is a multi-valued one for storing at least one line of multi-valued image data The image line memory 4 is a change point detection unit that detects the position on the line of a change point (change pixel) where the density changes from the multivalued image data and the density level thereof.

Reference numeral 5 is a change point a0, a at which the coding line is coded.
A coded change point memory unit that stores the positions of 1 and a2 and a density level; 6 is a coded line change point memory that temporarily stores information about the change point of the coded line detected by the change point detection unit 5;
Reference numeral 7 is a reference line change point memory for storing information of already encoded change points of the reference line, and 8 is a reference line change point memory 7 for determining reference change points b1 and b2 of the reference line based on the change point a0. B1b2 detecting section for detecting, 9 is reference change point b
A reference change point memory unit that stores information of 1 and b2.

Reference numeral 10 is a pass mode discriminating section for discriminating whether or not the mode is the pass mode based on the positional relationship between the change points a1 and b2, 11 is a vertical mode encoding section, and 12 to 15 are vertical mode encoding sections 11
12 is an a1b1 distance detection unit that detects the positional relationship between the change points a1 and b1 and the distance, 13 is an a1b1 level difference detection unit that detects the difference in density level between the change points a1 and b1, and 14 is
A vertical mode determination unit that determines whether or not the mode is the vertical mode based on the detection results of the a1b1 distance detection unit 12 and the a1b1 level difference detection unit 13, and 15 is a1b1 distance detection unit 12 and a1b1 level difference detection unit 1.
3 is a vertical mode code table for outputting a code corresponding to this two-dimensional displacement based on the detection result of No. 3.

Reference numeral 16 is a horizontal mode encoding unit, and 17 to 24.
Is an element that constitutes the horizontal mode encoding unit 16, 17 is an a0a1 distance detection unit that detects the distance between the change points a0 and a1, and 18 is an a0a1 level difference detection unit that detects the density level difference between the change points a0 and a1, Reference numeral 19 denotes an a1a2 distance detecting unit that detects the distance between the changing points a1 and a2, and 20 denotes a1a2 that detects the difference in density level between the changing points a1 and a2.
Level difference detectors, 21 and 22 are selectors, 23 is a run length code table that outputs a code corresponding to the distance (corresponding to the run length) between two change points, and 24 is a density level difference between two change points. It is a level difference code table which outputs a corresponding code.

Reference numeral 25 is an EOL0 code generator that outputs a code EOL0 indicating the beginning of a two-dimensional encoded data string, 26 is a P code generator that outputs a code P indicating a pass mode, and 27 is a code H indicating a horizontal mode. An H code generating section for outputting, 28 is an EOL1 code generating section for outputting a code EOL1 indicating the head of the one-dimensional encoded data sequence, and 29 is 15 corresponding to the discrimination results of the pass mode discriminating section 10 and the vertical mode discriminating section 14. , 23, 24, 2
A two-dimensional code synthesizing unit that selectively takes in the respective codes output from Nos. 5, 26 and 27, arranges them in a predetermined order, and outputs them.

Numeral 30 is a one-dimensional code synthesizing section for taking in the codes outputted from the run length code table 23, the level difference code table 24 and the EOL1 code generating section 28, arranging them in a predetermined order and outputting them, and 31 is a two-dimensional code synthesizing section. A selector that selects and outputs one of the outputs of the unit 29 and the one-dimensional code synthesis unit 30, 32 is an output terminal of the encoding device, 33 is a selector,
Reference numeral 34 is an address control unit that controls the address of the multi-valued image line memory, 34 is a control unit that controls the operation of each unit, and 36.
Is a K line counter that counts the number of lines coded based on the sync signal of the sync signal input terminal 2, and 37 is a code that switches between one-dimensional and two-dimensional coding methods based on the value of the K line counter. It is a switching unit.

Next, the operation of the first embodiment will be described with reference to FIG. The encoding apparatus of this embodiment uses multi-valued image data in line units supplied from the multi-valued image data input terminal 1 on the basis of a synchronization signal supplied to the terminal 2 for each pixel unit. It is temporarily stored in a predetermined area of the memory 3.

Assuming that the density level of the pixel at the position i from the head pixel on the line is N (i), the address control unit 34 sets the address value to 0 at the head of the line and increments by 1 each time one pixel is fetched. Address values of areas to be stored are generated corresponding to the arrangement order of pixels on a line, and the density level of each pixel for one line is stored in the multi-valued image line memory 3.

The encoding apparatus of this embodiment encodes the multi-valued image data for one line stored in the multi-valued image line memory 3 as an encoding line by the encoding method described later, and when the encoding is completed. , Input multi-valued image data of a new line to be encoded from the input terminal 1.

The k-line counter 36 counts the number of input lines, and the coding-method switching unit 37 switches the coding method for each k-line including the leading line. That is, the first line is one-dimensionally encoded, the subsequent (k-1) line is two-dimensionally encoded, and the next line is one-dimensionally encoded again, so that the one-dimensional encoding process is performed every k lines. .

The one-dimensional coding result is the one-dimensional code synthesizing unit 30.
Is output to the output terminal 32 via the selector 31.
The two-dimensional coding result is output from the two-dimensional code synthesizing unit 29 to the output terminal 32 via the selector 31. When the coding of the line for one page is completed, the one-dimensional code synthesizing unit 30
The EOL1 code is fetched from the EOL1 code generation unit 28, and 6 consecutive codes (RTC code indicating the end of the page) of this code are output to the output terminal 32 via the selector 31.

(One-dimensional encoding operation) First, the one-dimensional encoding operation will be described. The change point detection unit 4 reads from the head pixel of the line from the multi-valued image line memory 3, detects a pixel whose density level changes as a change point, and detects the position i of the change point (the address value supplied from the address control unit 34). ) And the density level N (i) are encoded.
Supply to. For example, when the density levels N (i-1) and N (i) of the pixel position (i-1) and the pixel of i are different, the pixel of the pixel position i is detected as the change point.

However, the change point detection unit 4 detects the change point on the assumption that a white (minimum density level) pixel is virtually present immediately before the head pixel of the line. Also, assuming that a white (minimum density level) pixel exists immediately after the last pixel of the line, this virtual pixel is detected as a virtual change pixel (virtual change point) without depending on the density level of the last pixel of the line. To do.

FIG. 2 shows how the change point detection section 4 detects a change point. In this figure, the number of pixels in one line is 14 for convenience of explanation. Each small frame shows one pixel, and the numerical value in the frame shows the density level of that pixel. 0 means white, and the larger the value of the density level, the darker it is. The numerical value at the top of the frame indicates the position of each pixel, s is a virtual white pixel provided immediately before the first pixel of the line, and e is a virtual change pixel (point) provided immediately after the last pixel of the line.

In the case of (1) in FIG. 2, the pixel positions 3, 4, 5, 8, 9 and the virtual change pixel e are detected as change points as indicated by the arrows. In the case of (2) in FIG. 2, pixel positions 0, 3, 9 and the virtual change pixel e are detected as change points.

If the change points detected by the change point detection unit 4 are cj, j = 1,2, N from the beginning of each line (where N is the number of detected change points), the position of each change point cj Pj and concentration level N (Pj
) Information becomes a pair and the encoding change point memory unit 5 is arranged in order.
Is supplied to.

Hereinafter, the change point cj is expressed as cj = (Pj, N (Pj)).

The encoding change point memory unit 5 is provided with an encoding change point.
It consists of a0 memory, a1 memory and a2 memory.
Address value of change point (position Pj stored in the order of a2 memory)
), The input change point information is stored. That is, when the change point of the change point a0 memory is cj, the change point cj + 1 is stored in the change point a1 memory, and the change point cj + 2 is stored in the change point a2 memory.

In the case of one-dimensional encoding, a change point a0 memory and a change point a1 memory are used, and input change point information is stored in two memories according to the positional relationship of the change points described above. However, the information of the first change point c1 of the line is stored in the a1 memory, and the a0 memory is located immediately before the first pixel of the line, and the virtual white pixel with the run length of 0 and the density level of 0 (white) is virtually changed. Initialized to be a point. That is, position P0 = 0
(Same position as the line top pixel), Density level N (P0)
It is initialized as = 0 (white).

Therefore, the change point cj is in the a0 memory, and the change point cj + 1 (j = 0,1,2, N: N is the number of detected change points in the a1 memory, where c0 is the virtual change point. ) Is stored each time a change point is input. This state is shown in FIG. The input change points c1, c2, ..., C6 to the encoding change point memory unit 5 in FIG.
Change point detected in the coding line shown in (1) of
c1, c2, ..., c6.

In the case of one-dimensional coding, the horizontal mode coding section 16 uses the a0 memory and a1 of the coding change point memory section 5.
The horizontal mode is sequentially encoded based on the change point information that is output from the memory and is adjacent in the detection order. a0 memory output change point is cj, a1 memory output change point is cj + 1 cj = {Pj, N (Pj)} cj + 1 = {Pj + 1, N (Pj + 1)} where {a , N (a)} a indicates the position on the line, and N
(a) shows the density level value of the pixel at the position a on the line.

When Pj <Pj + 1, the a0a1 distance detector 17 calculates (Pj + 1-Pj) and detects the distance Δaj from the change point cj to cj + 1. .DELTA.aj = Pj + 1-Pj That is, the run length .DELTA.aj of the pixel row of the same density level that continues from the change point cj to the pixel immediately before the change point cj + 1 is detected.

The a0a1 level difference detection unit 18 uses N (Pj + 1)-
N (Pj) is calculated to detect the density level difference Δnj between the pixels at the change point cj and the change point cj + 1. Δnj = N (Pj + 1) -N (Pj) If the density level value of the multi-valued image data is changed from the minimum 0 (white) to the maximum n (black), the density level difference can take values from -n to n. .

FIG. 4 is an explanatory diagram showing the operation of detecting the run length and the density level difference between the change points of the horizontal mode encoding unit 16 (FIG. 1) during the one-dimensional encoding and the one-dimensional encoded code string. is there. In (b) of (1) and (2) of FIG.
Of the run length between the change points by the a0a1 distance detection unit 17 of
The state of the detection result of the density level difference between the change points by the level difference detection unit 18 is shown. The change point sequence is the change point sequence detected in the coding line shown in FIG.

The run length Δa0 between the change points detected by the a0a1 distance detector 17 is sequentially supplied to the run length coding table 23 via the selector 21 and converted into a code R (Δa0) corresponding to the run length Δa0. To be converted. Code R (Δa0)
Is the MH (Modified Huffman) used in facsimiles
Like a code, it is configured by a code in which a short code word is assigned to a run length that frequently occurs. You may comprise with a makeup code and a termination code like MH code.

The density level difference Δn0 between the change points detected by the a0a1 level difference detecting section 18 is sequentially supplied to the level difference encoding table 24 via the selector 22, and the code L (Δn0 corresponding to the level difference Δn0 is supplied. ) Is converted to. Similarly to the above, the code L (Δn0) is also configured by a code in which a short code is assigned to a level difference having a high occurrence frequency.

In other words, in the one-dimensional encoding, the change point is represented by R (Δa0) and L (Δn0) corresponding to the run length Δa0 and the density level difference Δn0 between the adjacent change points, respectively. It is encoded as Δa0) + L (Δn0).

The output code R (Δ
a0) and the output code L (Δn of the level difference code table 24
0) is supplied to the one-dimensional code synthesis unit 30. The one-dimensional code synthesizing unit 30 takes in the code EOL1 from the EOL1 code generating unit 28 at the head of the one-dimensional coded line, takes in the codes R (Δa0) and L (Δn0) that are sequentially supplied thereafter, and arranges them in a predetermined array. And output.

FIG. 4C shows an example of the one-dimensional coded sequence output from the one-dimensional coded synthesis section 30. Figure 4 (d)
To the run length codeword as shown in (2) of FIG.
10 shows an encoded data string when the black run length code word and the level difference code word of the H code are the code words shown in (1) of FIG. Further, as shown in FIG. 4B, the sum of run lengths by the code R (Δa0) of one line corresponds to the number of pixels of one line, and the sum of the code L (Δn0) of one line is the minimum density. The level becomes 0 (white).

This is to detect an error during transmission or during storage / reproduction by checking both when decoding one line. The one-dimensional code string output from the one-dimensional code synthesizing unit 30 is output from the output terminal 32 of the present encoding device via the selector 31, and is stored in a transmission device or a storage device. The selector 31 is set to 1 when one-dimensionally encoded by the encoding method switching unit 37 described above.
It is controlled so that the code string from the dimensional code synthesis unit 30 is selected.

The selectors 21 and 22 are controlled by the encoding switching section 37 and the control section 35 (control lines are not shown). At the time of one-dimensional encoding, the selector 21 uses a0
Select the output of the a1 distance detector 17 so that the selector 2
2 is controlled to select the output of the a1a2 distance detector 19.

(Two-dimensional encoding operation) When the one-dimensional encoding is performed as described above, the next consecutive (k-1) lines are two-dimensional encoded. Before two-dimensional encoding,
The change point information (the position i of each change point and the density level N (i) of the pixel) of the coded line (including the one-dimensional coded line) is transferred to the next line via the coded line change point memory 6. Upon encoding the line, it is supplied to and stored in the reference line change point memory 7. That is, the reference line change point memory 7
Stores information about the change point of the reference line encoded immediately before the line to be encoded.

FIG. 5 shows how the change point detected in the coded line shown in (1) of FIG. 2 is stored in the reference line change point memory 7. Aj in the figure indicates the address value of the memory that stores the jth change point information detected from the beginning of the line. This address value is increased by a predetermined value for each change point, and the next change point information is stored in the corresponding area.

EOF (End of File) is a code indicating the end of the reference line change point information. Therefore, the b1b2 detecting means 8 reads the information (position and density level) of the corresponding change point by increasing the address value from the head address value A1 at every predetermined value. If the read information is the EOF code, it is detected that there is no change point on the reference line thereafter.

These address controls are controlled by a reference line change point memory / address controller (not shown). The coding line change point memory 6 also stores the change point information of the detected coding line in a similar format.

The two-dimensional encoding is performed by the multivalued image line memory 3
The new coded line is encoded based on the change point information stored in the reference line change point memory 7. First,
The principle of two-dimensional encoding will be described. In the case of two-dimensional coding, the coding change points a0, a1, which are the change points on the coding line.
The a2 and the reference change points b and b2 which are the change points on the reference line are defined as follows.

(Definition of terms) Change point: A pixel in which the density level of the pixel on the line is different from the density level of the immediately preceding pixel. Encoding change point a0 ... A change point on the encoding line that defines another change point. At the beginning of the line, a virtual pixel placed immediately before the beginning pixel of the line. The subsequent position of a0 is defined by the immediately preceding coding mode (described later).

Encoding change point a1 ... The first change point on the encoding line to the right of a0. Coding change point a2 ... The first change point on the coding line to the right of the a1. Reference change point b1 ・ ・ ・ A0 on the reference line to the right of the a0
And a pixel with a different density level, if there is one, its first change point, and if it does not exist, the virtual change point immediately after the last pixel on the reference line. Reference change point b2 ... A change point on the reference line to the right of the b1. If it exists, the first change point thereof, and if it does not exist, a virtual change point immediately after the last pixel on the reference line.

The change point information corresponding to the above is detected by the change point detection unit 4 from the pixel line of the encoded line of the multi-valued image line memory 3 to detect the coded change points a0, a1 and a2, and the reference line change The reference change points b and b2 are detected by the b1b2 detection unit 8 from the change point information of the reference line stored in the point memory 7, and the corresponding memories of the encoding change point memory unit 5 and the reference change point memory unit 9 are detected. Remember. The coding change points are coded by the following procedure in accordance with the position and the density level difference from these reference change points.

(Procedure A) If b2 exists on the left side of a1, pass mode coding is performed, and a0 is moved to the pixel position on the coding line immediately below b2. However, if b2 exists immediately above a1, the procedure goes to step B without performing the pass mode coding.

(Procedure B) When b2 does not exist on the left side of a1, the distance Δa between a1 and b1 and the concentration level difference Δn between a1 and b1.
Is detected by Δa = Pa1−Pb1 Δn = N (Pa1) −N (Pb1), and 2 of the position difference Δa and the concentration level difference Δn is detected.
If the dimensional displacement (Δa, Δn) is within the specified range,
Performs vertical mode encoding and shifts a0 to position a1. When the two-dimensional displacement (Δa, Δn) is not within the predetermined range, horizontal mode coding is performed to shift a0 to the position of a2.

(Processing of start pixel and end pixel) is performed as follows. The first a0 of each encoded line is virtually placed immediately before the first pixel and is set as a white pixel (minimum density level).
Further, the coding of each coding line is continued until the position of the virtual change pixel (minimum density level) located immediately after the last existing pixel is coded.

The pass mode encoding outputs only the code P indicating the pass mode, and does not encode the change point. That is,
Pass mode code word: P Vertical mode coding is performed by the distance Δa between the coding change point a1 and the reference change point b1 and the two-dimensional displacement (Δa, Δ) of the density level difference Δn.
The coding change point a1 is coded with the code V (Δa, Δn) corresponding to (n). That is, vertical mode code word: V (Δa, Δn)

The horizontal mode coding is performed by the code H indicating the horizontal mode coding and the run length Δa from the coding change points a0 to a1.
The sign R (Δa0) indicating 0 and the density level difference Δ between a0 and a1
The code L (Δn0) indicating n0, the code R (Δa1) indicating the run length Δa1 from the code change points a1 to a2, and the code L (Δn1) indicating the density level difference Δn1 between a1 and a2 are encoded. The change points a1 and a2 are encoded. That is, horizontal mode code word: H + R (Δa0) + L (Δn0) + R (Δa1) + L (Δn1)

FIG. 6 shows the flow of the coding procedure of the present coding apparatus, particularly the flow of the two-dimensional coding procedure. Figure 6
In the above, the encoding change point a2 is detected when the vertical mode determination is negative, but a2 may be detected in advance when a1 is detected.

The operation of the above two-dimensional encoding will be described using a specific example. If the pixel row of the already encoded reference line and the pixel row of the encoding line to be newly encoded are pixel rows as shown in (1-2) and (2) of FIG. Based on the reference line change point information already detected and stored in the reference line change point memory 7, the coding line is coded as follows.

The pixel line of the reference line of (1-2) of FIG. 7 is the same as (1) of FIG. 2 and (1) of FIG. The change point information shown in (1-1) of FIG. 7 is stored.

As described in the one-dimensional encoding, the changing point detecting section 4 detects a pixel whose density level changes as a changing point. In the case of the coded line of FIG. 7, the pixel at pixel position 3 is first detected as the change point. Next, the pixel at the pixel position 4 is detected as the change point.

When these two change points are supplied to the encoding change point memory unit 5, the encoding change point memory unit 5 stores the first change point information in the a1 memory and the next change point information in the a2 memory. Remember. Also, at the beginning of the line, in the case of two-dimensional encoding, the a0 memory is set to the position and the density level of the virtual pixel of the minimum density level (white) virtually provided immediately before the beginning of the line. It is initialized.

That is, at the head of the line, the information of the virtual pixel arranged immediately before the head pixel of the line is stored in the a0 memory of the coding change point memory unit 5, and the first (first detected) information is stored in the a1 memory. Change point information, the second (the next detected) change point information is stored in the a2 memory.

Based on the position information of the changing point of the a0 memory, the b1b2 detecting section 8 determines the first changing point b1 (reference changing point b1) on the reference line on the right side (larger in address) than the changing point. ) And a change point b2 (reference change point b2) on the right side of the line) are detected from the reference line change point memory 7 and supplied to the reference change point memory unit 9. In this case, the change point position of a0 memory is s =
Therefore, if bi = (Pj, N (Pj), the reference change point b1 = (3,2) and the reference change point b2 = (4,3) are detected, and b1 is stored in the reference change point memory unit 9. The b1 memory and the b2 memory are stored in the b2 memory of the reference change point memory unit 9, respectively.

A0, a1, of the encoding change point memory unit 5 at this time
The relationship between the pixel positions of the a2 memory and the coding change points a0, a1, a2 of the b1 and b2 memories of the reference change point memory unit 9 and the reference change points b1 and b2 is shown in 1) of (3) of FIG. Show. In case of 1)

A0 = (0,0) a1 = (3,1) b1 = (3,2) a2 = (4,2) b2 = (4,3).

The pass mode discriminating unit 10 determines whether or not the pass mode is determined from the positional relationship between the encoding change point a1 of the a1 memory of the encoding change point memory unit 5 and the reference change point b2 of the b2 memory of the reference change point memory 9. Determine whether. That is, it is detected whether or not the reference change point b2 is on the left side (smaller in address) of the position of the coding change point a1. In the case of 1) in (3) of FIG. 7, b2 is a1.
It does not correspond to the pass mode because it is on the right side of. The negative determination result of the pass mode determination unit 10 is supplied to the two-dimensional code synthesis unit 29.

The vertical mode coding unit 11 determines the coding change point.
After determining whether or not the mode is the vertical mode based on the information of a1 and the reference change point b1, the coding change point a1 is encoded by the vertical mode code when the vertical mode is applicable. The position of a1 is Pa1, the density level is N (Pa1), the position of b1 is Pb1, the density level is N (P1).
b1) and the encoding change point a1 = (Pa1, N (Pa1)) and the reference change point b1 = (Pb1, N (Pb1)),

The a1b1 distance detector 12 detects Δa = Pa1−Pb1 as the positional distance (including direction) Δa between a1 and b1. The a1b1 level difference detection unit 13 detects Δn = N (Pa1) −N (Pb1) as the density level difference Δn between a1 and b1.

In the case of 1) in (3) of FIG. 7, a1 = (3,1), b1 =
Since it is (3,2), the distance Δa = 3-3 = 0 level difference Δn = 1-2 = -1 two-dimensional displacement (Δa, Δn) = (0, -1).

The vertical mode discriminating unit 14 determines whether the two-dimensional displacement (Δa, Δn) between the detection result Δa of the a1b1 distance detecting unit 12 and the detection result Δn of the a1b1 level difference detecting unit 13 is within a predetermined range. Determine whether.

2 of the distance Δa between a1 and b1 and the density level difference Δn
The coding efficiency at the time of two-dimensional coding differs depending on how far the vertical mode is set with respect to the dimensional displacement (Δa, Δn). Two-dimensional displacement (Δa, Δ
n) with a high frequency of occurrence should be in vertical mode, short code words should be assigned in order of frequency of occurrence, and those with a low frequency of occurrence should be coded in horizontal mode.

Otherwise, if a two-dimensional displacement having a low frequency of occurrence is included in the vertical mode and the number of cases in the vertical mode is increased, the code word length of the displacement having a low frequency of occurrence becomes longer, and the code word length becomes longer than that of the horizontal mode coding. Is longer and the coding efficiency is lower. Two-dimensional displacement (Δa, Δn
Various settings can be made for the area of). An example is shown in FIG.
Shown in.

FIG. 8 (a) shows a case of encoding in the vertical mode 2
The region of the dimensional displacement is a region in which the distance Δa is in the range of −3 to 3 and the density level difference Δn is in the range of −3 to 3. In this case, it is assumed that the distance Δa and the concentration level difference Δn change independently. (b) is the distance Δ
It is assumed that there is a high probability that the difference in concentration level will become smaller as the absolute value of a becomes larger.

FIG. 8C shows the distance Δa and the density level difference Δ.
n is assumed to be high when one is large and the other is small. In Fig. 8, the range is from -3 to 3, but the range is not limited to this value, and Fig. 8 shows the shape of the two-dimensional displacement region encoded in the vertical mode. Is. Here, for convenience of explanation, the region shown in FIG. 8B will be described as a region to be encoded in the vertical mode. That is, the encoding change point a1 is set in the range where the distance Δa is in the range of -1 to 1 and the concentration level difference Δn is in the range of -1 to 1, and in the range where Δa is in the range of -3 to 3 and Δn = 0. Encode in vertical mode.

In the case of 1) in (3) of FIG. 7, the distance Δa = 0
, The level difference Δn = −1, the two-dimensional displacement (0, −1) is within the above-described vertical mode coding area, and therefore the vertical mode determination result is affirmative. Therefore, two-dimensional displacement (0, -1)
Is a corresponding code word V (0, 0 in the vertical mode code table 15).
-1) is encoded. Further, the vertical mode determination result is supplied to the two-dimensional code synthesis unit 29.

The vertical mode code table 15 inputs the two-dimensional displacement (Δa, Δn) of the distance Δa and the density level difference Δn, and the code V corresponding to the two-dimensional displacement (Δa, Δn) of this input. (Δa, Δn) is output and supplied to the two-dimensional code synthesis unit 29.

In the case of 1) in (3) of FIG. 7, the code V (0,-
1) is output. The vertical mode coding is a code configuration in which short code words are assigned in descending order of occurrence frequency in the vertical mode region shown in FIG. 8 (b), and is similar to the vertical mode code in the binary MR coding method, for example. Composed of things.

When the coding change point a1 is coded in the vertical mode as described above, the new coding change point a0 is modified to the pixel of the previous a1 and a1, a2 and b1 and b2 are detected by the change point detection section 4 and the b1b2 detection section 8 and stored in a predetermined memory of the encoded change point memory section 5 and the reference change point memory section 9. The positional relationship between the new coding change point and the reference change point is shown in 2) of (3) of FIG.

In the case of 2), a0 = (3,1) a1 = (4,2) b1 = (4,3) a2 = (5,4) b2 = (5,4).

Also in this case 2), the determination result of the pass mode determination unit 10 is negative because b2 is located on the right side of a1, and a1b1 distance Δa = 4-4 = 0 a1b1 level difference Δn = 2-3 = -1 Two-dimensional displacement (Δa, Δn) = (0, -1) and the two-dimensional displacement is encoded in the vertical mode because it is within the vertical mode encoding area, and the code V (0, -1) is two-dimensional. It is supplied to the code synthesis unit 29.

Since a1 is encoded in the vertical mode, a new a0 is similarly corrected to the position of the previous a1 and the encoding change point and the reference change point are updated. The update result is shown in (3) of FIG.
Shown in 3). In the case of 3), a0 = (4,2) a1 = (5,4) b1 = (5,4) a2 = (10,0) b2 = (8,2).

Also in this case 3), the determination result of the pass mode determination unit 10 is negative because b2 is located on the right side of a1, and a1b1 distance Δa = 5-5 = 0 a1b1 level difference Δn = 4-4 = 0 Two-dimensional displacement (Δa, Δn) = (0,0), and even in the case of 3), V (0,0) is encoded in the vertical mode.

The next coding change point and reference change point are as shown in 4) of (3) of FIG. In the case of 4), a0 = (5,4) a1 = (10,0) b1 = (8,2) a2 = (14,0) b2 = (9,0).

In this case, since b2 is located on the left side of a1, the mode is the pass mode, and the determination result of the pass mode determination unit 10 is 2
It is supplied to the dimensional code synthesis unit 29. After the pass mode coding, the new a0 is corrected to the position of the previous b2, and the coding change point and the reference change point are updated based on this a0. The update result is shown in 5) of (3) in FIG.

In the case of 5), a0 = (9,4) a1 = (10,0) b1 = (14,0) a2 = (14,0) (b2 = (14,0)).

In this case as well, the determination result of the pass mode determination unit 10 is negative because b2 is located on the right side of a1, and a1b1 distance Δa = 10-14 = -4 a1b1 level difference Δn = 0-0 = 0 2 Since the dimensional displacement (Δa, Δn) = (− 4,0) and the two-dimensional displacement is outside the vertical mode coding region, the negative discrimination result of the vertical mode discrimination unit 14 to that effect is the two-dimensional code synthesis. Is supplied to the unit 29.

Then, in the horizontal mode encoding section 16, the encoding change points a1 and a2 are encoded in the horizontal mode.
The horizontal mode encoding unit 16 first determines the distance Δa0 between a0 and a1 in the a0a1 distance detection unit 17 as follows: Δa0 = Pa1-Pa0 = 10-9 =
1 That is, the run lengths of pixel rows of the same density level that continue from the pixel immediately before a0 to a1 are detected and supplied to the run length code table 23 via the selector 21.

The run length code table 23 has a code R (Δa0) corresponding to the input run length Δa0, as in the one-dimensional coding.
= Output R (1). a0a1 The level difference detection unit 18 uses a0
Δn0 = N (a1)-N
(A0) = 0-4 = -4 is detected and supplied to the level difference code table 24 via the selector 22. The level difference code table 24 outputs the code L (Δn0) = L (−4) corresponding to the input density level difference Δn0, as in the one-dimensional encoding.

The output codes R (1) and L (-4) of the run length code table 23 and the level difference code table 24 are supplied to the two-dimensional code synthesis section 29, respectively. Further, the a1a2 distance detecting unit 19 determines that the distance Δa1 between a1 and a2 is Δa1 = Pa2-
That is, Pa1 = 14-10 = 4 That is, the run lengths of the pixel rows of the same density level that continue from the pixel immediately before a1 to a2 are detected and supplied to the run length code table 23 via the selector 21.

The run length code table 23 outputs the code R (Δa1) = R (4) corresponding to this run length. Also,
The a1a2 level detector 20 detects Δn1 = N (a2) −N (a1) = 0-0 = 0 as the density level difference Δn1 between a1 and a2, and supplies it to the level difference code table 24 via the selector 22. To do. The level difference code table 24 outputs the code L (Δn1) = L (0) corresponding to the input density level difference Δn1.
These run length code R (4) and level difference code L (0)
Are supplied to the two-dimensional code synthesis unit 29, respectively.

That is, the horizontal mode encoding unit 16 at the time of two-dimensional encoding sets the encoding change points a1 and a2 to the run length Δa0 between a0 and a1, the density level difference Δn0, and the run length between a1 and a2. R (Δa0) + L with the corresponding code for Δa1 and the density level difference Δn1
Encoding is performed as (Δn0) + R (Δa1) + L (Δn1).

In the case of 5), R (1) + L (-4) + R (4
) + L (0). When this horizontal mode encoding is completed, the new a0 is corrected to the position of the previous a2. At this time,
Since the new position of a0 corresponds to the virtual pixel position at the end, the coding of this coding line ends.

The two-dimensional code synthesizing unit 29 sets the EOL0 code indicating that the subsequent code string is a two-dimensional coded code string at the head of each two-dimensional code line to the EOL0 code generating unit 25. Take in more.

Then, thereafter, the P code generation unit 2 is determined according to the determination results of the pass mode determination unit 10 and the vertical mode determination unit 14.
6, the P code indicating the pass mode, the vertical code V (Δa, Δn) output from the vertical mode encoder 11, the H code indicating the horizontal mode from the H code generator 27, and the horizontal mode encoder 16 Horizontal code output from R (Δa0) + L (
Δn0) + R (Δa1) + L (Δn1) (where Δa0 is the distance between a0 and a1, Δn0 is the concentration level difference between a0 and a1, Δa1 is the distance between a1 and a2, Δn1 is the concentration level difference between a1 and a2) ) Is selectively taken in, each code is arranged in the order of encoding, and is output from the output end 32 of the present encoding device via the selector 31.

Specifically, 0) The code EOL0 from the EOL0 code generator 25 is fetched at the head of the two-dimensional coding line. 1) If the determination result of the pass mode determination unit 10 is affirmative, the code P from the P code generation unit 26 is fetched.

2) When the determination result of the pass mode determination unit 10 is negative and the determination result of the vertical mode determination unit 14 is affirmative, the vertical code V (Δa, Δ) from the vertical mode encoding unit 11 is obtained.
n) is taken in. 3) When the determination results of the pass mode determination unit 10 and the vertical mode determination unit 14 are both negative, the code H from the H code generation unit 27 and the horizontal code R (Δ from the horizontal mode encoding unit 16
Take in a0) + L (Δn0) + R (Δa1) + L (Δn1).

The two-dimensional code string of the two-dimensional coding result of the coding line of (2) with respect to the reference line of (1-2) of FIG. 7 is shown in FIG.
(4) of.

FIG. 9 collectively shows the code words corresponding to each coding mode in the two-dimensional coding. The code word in the vertical mode is the case where the area of the two-dimensional displacement (Δa, Δn) in the vertical mode is set to the area shown in (b) of FIG.
Here is an example. Here, the vertical codewords V (-3,0), V (-2,0), V (-1,0), V (0,0), V (1,0) at the density level difference Δn = 0 ,
V (2,0) and V (3,0) are matched with the vertical mode code words V-3, V-2, V-1, V0, V1, V2 and V3 of the MR coding method.

As a result, common use with a conventional facsimile encoding device is achieved, the increase in the scale of the multivalued image encoding device according to the present invention is avoided, and the application to conventional facsimiles is facilitated. .

In FIG. 10A, the density level difference code L
An example of (Δn) is shown. This code word is assigned as the occurrence frequency is smaller as the absolute value of the density level difference Δn is larger, and is not limited to this. For example, when the absolute value of the density level difference Δn is equal to or larger than a predetermined value, the level difference itself may be encoded by a binary code. In this case, a normal code or a binary code may be distinguished by adding a code indicating the binary code before the binary code. FIG. 7 (5) shows an encoded data string in the case of the code word shown in FIGS. 9 and 10.

(Effects of First Embodiment) As described above, in the first embodiment of the present invention, in a multi-valued image such as a photograph, the density level change in pixel units is gentle, and The density level of is almost equal to the density level of the surrounding pixels, and even if there is a difference, it is slight.

That is, according to the first embodiment of the present invention, the position of the changing point on the encoded line where the density changes exists near the position of the already changed encoded point on the reference line,
Moreover, by utilizing the property that the difference in density level between both change points is small, the two-dimensional displacement (Δa, Δn) of the difference Δa between the position of the change point on the reference line and the change point on the coding line and the difference Δn of the density level is used. ), A code word having a shorter code word length is assigned to a higher occurrence frequency, and a coding change point is coded, whereby a high compression rate can be expected without impairing reproducibility.

The encoding system of the present invention is based on the monochrome binary MR encoding system in the conventional facsimile.
Since it is extended to multi-valued images, it has a high affinity with the conventional MR system, and it is necessary to increase the device scale so much when adding a facsimile function for encoding and transmitting multi-valued images as they are at multi-valued levels. There is an advantage that can be realized.

Further, in the above description, the case of the image information not including the color information has been described. However, in the color image, the individual color components of R, G, B or Y, I, Q are
Alternatively, by applying the above-described multi-level encoding method only to a specific color component, it is possible to perform high-efficiency encoding or high-efficiency transmission of a color image.

[Second Embodiment] FIG. 11 shows a second embodiment of the present invention.
3 is a block diagram showing the configuration of the embodiment of FIG. The second embodiment is applied to an image transmission device (for example, a facsimile device) that reads and encodes a multivalued image such as a character / line drawing or a photograph and stores or transmits it.

In FIG. 11, reference numeral 50 denotes a document reading 1
A dimension reading sensor, 51 is an ADC (analog-digital converter) that digitizes the output of the reading sensor 50, 52 is a shading correction unit that corrects variations in pixel sensitivity of the reading sensor 50 and unevenness of a light source that illuminates an original, 53 Is a front line multi-valued image memory that temporarily stores at least one line of image data after shading correction, 54 is a white peak detection unit that detects the white peak value of the document from the image data output from the shading correction unit 52,
Is.

Reference numeral 55 designates an edge emphasizing portion for emphasizing the edge portion of the line drawing on the basis of the density levels of the pixel of interest of the current line, its peripheral pixels and the peripheral pixels supplied from the preceding line multi-valued image memory 53. Is a smoothing unit that smoothes the density level of the pixel of interest based on the density levels of the pixel of interest, surrounding pixels before and after it, and peripheral pixels supplied from the preceding line multi-valued image memory 53. A gamma correction unit for converting a subsequent density level into a predetermined level according to the level.

Reference numeral 58 denotes a target pixel of a binary image such as a character or line drawing based on the density levels of the target pixel of the current line and its surrounding pixels and the peripheral pixels supplied from the preceding line multi-valued image memory 53. An image area discrimination unit that discriminates between a pixel in a region and a pixel in a region of a multivalued image such as a photograph, 59 is a binary / multivalued quantizer, and 60 and 61 are binary / multivalued quantizers 59. 60 is a binary quantizing unit that performs binary quantization (whether it is the maximum density level or the minimum density level) on the output value of the edge emphasizing unit 55 according to the detection value of the white peak detecting unit 54.
Reference numeral 1 denotes a selector for selecting and outputting either the output of the binary quantizing unit 60 or the gamma correcting unit 57 to the image area discriminating unit 58 according to the discrimination result.

Reference numeral 62 is a line buffer memory for temporarily storing the image data output from the selector 61, and 63 is a multi-function image data encoding apparatus (shown in FIG. 1) of the first embodiment. The value encoding unit 66 is a storage memory that stores the multilevel encoded data output from the output terminal 32 of the multilevel encoding unit 63. Reference numeral 64 is a modem that modulates multi-level encoded data in the storage memory and sends it to the line 65.

Reference numeral 68 decodes the received multilevel coded data received from the line 65, demodulated by the modem 64 and temporarily stored in the storage memory 66, and reversely decodes the multilevel coded unit 63 to restore a multilevel image. The multi-level decoding unit 69 quantizes the density level of each pixel of the decoded multi-valued image data into an N value, diffuses an error at the time of quantization to peripheral pixels, and inputs the average density level and the N value. N for making the average density levels after quantization approximately equal
A value error diffusion unit, 70 is a display that displays an image of the N-value error diffusion result, 71 is a printer that prints the N-value error diffusion result, and 72 is the display gradation number n per pixel of the display 70 and the printer 71. And an N value control unit for changing the N value of the N value error diffusion unit 69 for displaying and printing respectively.

In the second embodiment, the image signal read by the reading sensor 50 is used by the image area discrimination unit 58 to determine whether the pixel of interest belongs to a binary image area such as a character or line drawing, or a multivalued image such as a photograph. If the pixel of interest belongs to a binary image area, the pixel of interest is binary quantized into white (minimum density level) or black (maximum density level) according to the density level of the pixel of interest,

If the pixel belongs to the multi-valued image area, the binary / multi-valued quantizer 59 outputs the density level of the pixel of interest as it is.
Is selectively binary-quantized by the multi-value encoding unit 63 that performs the multi-value encoding shown in the first embodiment on the selectively binary-quantized image data. To do. Then, it is temporarily stored in the storage memory 66 or is transmitted from the line 65 to the partner receiving device via the modem 63.

When multi-value coded image data is received, the multi-value decoding unit 68 decodes the image data, and then the N-value error diffusion unit 69 displays the display 70 and the printer 7.
Corresponding to the number n of gradation expression abilities of 1, pseudo halftoning with n gradations per pixel is performed, and display or printing is performed.

The operation of the second embodiment will be described. The reading sensor 50 reads the document in line units, and outputs the reading level (analog value) in pixel units in synchronization with the reading clock from the operation timing control unit 67. The ADC digitally quantizes the read level of each pixel in synchronization with the read clock, and supplies it to the shading correction unit 52.

The shading correction unit 52 corrects the variation in the sensitivity of the pixels of the reading sensor 50 and the unevenness of the light source that illuminates the original. Therefore, the shading correction unit 52
Stores in advance image data for one line (referred to as a shading waveform) in which a white reference document is read by the reading sensor 50 and quantized, and is stored on the line of the document (main scanning) based on the shading waveform. Corresponding to the position above)
The quantized value (density level) of the read pixel is corrected.

The shading correction result is supplied to the white peak detecting section 54, the edge enhancing section 55, the smoothing section 56, the preceding line multi-valued image memory 53 and the image area determining section 58. The pixel data of each part is fetched in synchronization with a control timing signal (not shown).

The previous line multi-valued image memory 53 sequentially takes in the shading correction results, and temporarily stores the image data for at least one line before the current line input. The front line multi-valued image memory 53 stores the data of the pixels around the target pixel of the previous line corresponding to the position of the target pixel of the current line in the edge emphasizing unit 55 and the smoothing unit 56.
And to the image area determination unit 58.

As shown in (1) of FIG. 12, the edge emphasizing unit 55 sets the weighting factor a, for the density level of the hatched current pixel of the current line and its peripheral pixels as shown in the figure.
Multiply b, c, d, e, and f, and determine the density level of the pixel of interest as the sum of them. The weighting factor is a negative value for the surrounding pixels
(a, b, c, d, f) is given to the pixel of interest with a positive value (e), and the weighting coefficients are distributed so that the sum becomes 1.

As a result, if the difference between the density levels of the target pixel and the peripheral pixels is large, the difference is further emphasized, and as a result, the black and white change boundary portion such as a line drawing is emphasized. The edge emphasis result is supplied to the binary quantization unit 60 that constitutes the binary / multi-valued quantization unit 59, and is quantized into a binary value (maximum density level or minimum density level).

The white peak detector 54 has a peak value on the white side of the density level of the input pixel (minimum value at the density level).
To detect. The responsivity of the detection is fast for the change to the white side, and has a characteristic that the peak value is gently changed to the black side when the density level is on the black side from the detected peak value. The white peak detection result is supplied to the binary quantization unit 59.

The binary quantizing unit 60 changes the binarization threshold value according to the white peak value of the detection result of the white peak detecting unit 54, and binary-quantizes the edge-emphasized image data. That is, when the white peak value is the minimum density level value (pure white), the threshold value is an intermediate density level between pure white and pure black, and when the white peak value changes to the black side, the threshold value is also black at a predetermined ratio. Change to the side. This regards the background density of the original as white,
This is for binarizing characters / line drawings on the background density.

The binary quantization result of the binary quantization section 60 is supplied to one input terminal of the selector 61. Smoothing unit 56
As shown in (2) of FIG. 12, the weighting factors a, b, c, d, e, for the density level of the hatched target pixel of the current line and its surrounding pixels are shown in the figure. Multiply by f and determine the density level of the pixel of interest as the sum. The weighting coefficient is given a positive value with respect to the pixel of interest and the peripheral pixels, and the weighting coefficient is distributed so that the total sum becomes 1. As a result, changes in the density level of each pixel are smoothed. The degree of smoothing depends on how the weighting factors are given.

The area of the peripheral pixels of the smoothing filter is not limited to (2) in FIG. 12, but in the case of a multi-valued image consisting of halftone dots, the period of the halftone dots is covered. It is necessary to perform smoothing so as to detect the average density within the halftone dot period by using the surrounding pixel area. Here, for convenience of explanation, in order to show the principle, a 3 * 2 pixel region as shown in the figure is used.

The gamma correction unit 57 corrects the density level of the smoothed image data according to the input density level, as shown in (3) of FIG. The figure shows three types of correction characteristics. This is performed in consideration of the recording characteristics of the multivalued image density characteristics and the sharpness of the image after recording. The correction result of the gamma correction unit 57 is supplied to the other input terminal of the selector 61.

As shown in (1) of FIG. 13, the image area determination unit 58 determines the target pixel (H) of the current line, the peripheral pixels (F, G, I, J) of the current line and the peripheral pixels of the previous line. Based on the density levels of (A, B, C, D, E), the pixel of interest belongs to a binary image area such as a character or line drawing, or to a multi-valued image area such as a photograph (including a halftone image). Detects if it belongs.

As shown in (2), (3) and (4) of FIG. 13, the discrimination method is to move the smoothing filter equivalent to that shown in (2) of FIG. The density levels N (G), N (H), and N (I) of the smoothing result are obtained,
If either the difference between N (H) and N (G) or the difference between N (H) and N (I) is greater than or equal to a predetermined value, it is determined that the pixel of interest belongs to the binary image area. Is determined to belong to the multi-valued image area.

The determination based on the density level after smoothing is performed in order to avoid erroneous determination of a change in the density level of black in the halftone dot image and white between the halftone dots as a binary image area. is there. Therefore, like the smoothing filter of the smoothing unit 56, the smoothing filter here also detects the average density level within the halftone dot period.

The image area determination is not limited to the above method, but various determination methods can be used. For example, Japanese Patent Laid-Open No. 2-292956 and Japanese Patent Publication No.
-62355, paying attention to the periodicity of the halftone dots, first detecting the halftone dot image area, and thereafter,
As described in Japanese Patent No. 115975, the difference between the density level change amount of a line drawing and a photograph (excluding a halftone dot image) and the change frequency is used to discriminate between a line drawing and a photographic image. The value image area may be distinguished from a multivalued image area such as a photograph (including a halftone image).

When the area of the target pixel is discriminated in this way, the discrimination result is supplied to the control terminal of the selector 61. When the image area discrimination result is a binary image area, the selector 61 selects the binary quantization result of the binary quantization unit 60 and supplies it to the line buffer memory 62. When the image area determination result is the multi-valued image area, the correction result of the gamma correction unit 57 is selected and supplied to the line buffer memory 62.

The line buffer memory 62 serves as a buffer that absorbs the difference between the reading speed of the reading sensor 50 and the sending speed of the multi-level encoding unit 63 and the modem 64 to the line 65. This line buffer memory 62
When the storage amount of the above is more than a certain amount, the operation timing control unit 67 temporarily stops the line reading of the reading sensor 50, and when the storage amount of the line buffer memory 62 encoded by the multi-level encoding unit 63 becomes less than the certain amount. Resume reading.

Storage and reading in the line buffer memory 62 are controlled by the control timing of the operation timing controller 67. The read control timing is also supplied to the multi-level encoding unit 63. Line buffer memory 6
The second output image data is supplied to the multi-level encoding unit 63 and multi-level encoded. The encoding method of the multi-level encoder 63 is the encoding method described in the first embodiment. The configuration of the multi-level encoding unit 63 is the configuration shown in FIG.

Since the binary image area is binary-quantized into the minimum density level (white) and the maximum density level (black), the changing point in the binary image area is from the change pixel from white to black and from black. It becomes a pixel that changes to white. The change in the concentration level has the maximum positive and negative values. Difference in density level and two in one-dimensional encoding
The code corresponding to the density level difference at the time of horizontal mode coding at the time of dimensional coding is set to a code word length corresponding to the occurrence frequency of this maximum density level change. Encoding can be performed with almost the same high encoding efficiency.

In vertical mode coding at the time of two-dimensional coding, the change point a1 of the coding line to white (black) is
The reference line is encoded by the difference between the position of the reference change point b1 to white (black) and the density level. However, since the difference between the density levels is 0, the code corresponding to the position difference results. Encoded in words. This is consistent with the conventional MR encoding method.

The frequency of occurrence of each code word varies depending on the image to be handled and the image including the binary image area in the code table in each of these coding modes.
The codeword length of the codeword may be determined in correspondence with the image to be handled, and assuming an image to be handled to some extent, in accordance with the occurrence frequency at that time. As a result, in the binary image area, it is possible to perform encoding with almost the same high encoding efficiency as the conventional MR encoding.

As described above, the multi-valued image area is
Since the change point where the density level changes is encoded by the code word corresponding to the two-dimensional displacement of the difference between the position of the reference line and the reference change point and the difference of the density level, a multi-valued image with a gentle change in density is enhanced. It can be encoded with encoding efficiency. The multilevel encoding result is temporarily stored in the storage memory 66 and is stored in the modem 64.
Is sent to the line 65 via. The above is the operations of reading, image processing, encoding, accumulating, and transmitting in the second embodiment.

Next, the operation at the time of receiving a multi-value encoded image will be described. The multi-level coded data received from the line 65 and demodulated by the modem 64 is decoded into multi-level image data by the multi-level decoding unit 68 via the storage memory 66. This decoding method is a decoding method for the coding method of the multi-level coding unit 63.

FIG. 14 is a block diagram showing the structure of the multilevel decoding unit 68. In the figure, 6801 is a multi-level encoded data input terminal of the multi-level decoding unit 68, 6802 is a shift register that stores multi-level encoded data in bit units, and 6803 is EOL1 / that detects EOL1 code and EOL0 code. 0 code detector.

Reference numeral 6804 denotes a two-dimensional coding mode code detecting section for detecting the P code and the H code indicating the coding mode in the two-dimensional coding, and 6805 denotes the vertical mode coded data V.
Vertical mode decoding unit for detecting and decoding (Δa, Δn), 6
Reference numeral 806 denotes horizontal mode encoded data R (Δa0), L (Δn
0), R (Δa1), L (Δn1) to R (Δa0), L (Δn
0), R (Δa1), and L (Δn1) in this order, and the horizontal mode decoding unit performs decoding.

Reference numeral 6807 denotes a reference change point a0 memory for storing a reference change point a0 which serves as a reference for decoding a decoding line, and 681.
0 is the reference change point b from the previous line change point memory 6811.
B1b2 detection unit for detecting 1, b2 corresponding to the reference change point a0, 6
Reference change point b1 809 temporarily stores reference change points b1 and b2.
b2 memory, 6808 is standard change point a0, reference change point b1, b2
And the detection result of the two-dimensional encoding mode detection unit 6804 and the vertical mode decoding unit 680 which is output corresponding to the detection result.
5 and the decoding result of the horizontal mode decoding unit 6806,
A change point calculation unit that calculates change points a1 and a2.

Reference numeral 6812 denotes a current line change point memory for temporarily storing the change point of the current line (decoding line) calculated by the change point calculation unit 6808, 6824 denotes a line end detection unit for detecting the end of the line of the decoded line, Reference numeral 6815 denotes a reception error detection unit that detects a reception error of the one-dimensional encoded line, and reference numerals 6816 to 6821 denote reception error detection units 6815.
6816 is a run length sum detection unit that detects a sum of run lengths of a one-dimensional encoded line, and 6817 detects a match between the sum of run lengths and a predetermined pixel value r of one line. A coincidence detection unit, 6819 detects the total sum of the density level differences between the change points of the one-dimensional encoded lines for one line, and a total difference detection unit 6820 detects whether the total level difference value is 0 or not. The coincidence detection unit 6821 is an AND logic unit that detects whether the detection results of the coincidence detection units 6817 and 6820 are both positive.

6813 is a current line change point memory 6812
A pixel restoration unit that restores the multi-valued pixel row of the decoded line based on the change point information of the, 6814 is a multi-valued image line memory that stores the restored multi-valued pixel row of the decoded line, 682
Reference numeral 2 is an output terminal of the multi-level decoding unit 68, and 6823 is a control unit for controlling the operation of each unit.

Next, the operation of the multi-level decoding unit 68 will be described with reference to the operation flow charts of FIGS. FIG. 15 is a flowchart showing the overall operation of the multi-level decoding unit 68.

The multi-level decoding unit 68 loads the multi-level encoded data into the multi-level code shift register 6802 supplied from the input terminal 6801 in bit units. EOL1 / 0 detector 68
03 detects the EOL1 code and the EOL0 code from the output of the multilevel code shift register 6802. Until any of these codes is detected, the internal data of the multi-level code shift register 6802 is shifted bit by bit, and at the same time, the input terminal 6801
Take in more new data.

When the EOL1 / 0 detection unit 6803 detects the EOL1 code, the multilevel decoding unit 68 performs a one-dimensional decoding process on the coded data for one line following the EOL1 code. After the one-dimensional decoding process, if there is no reception error and the RTC code (page end code) is not detected in this one-dimensional decoding process (if the page is not the end), EOL1 / 0 is set again.
The detector 6803 detects the EOL1 code and the EOL0 code.

When the detected code is the EOL0 code, the subsequent coded data is subjected to the two-dimensional decoding process. The EOL1 code and the EOL0 code are used as the head of each line, and the decoding processing is performed in line units until the page end signal (RTC code) is detected. Although not shown in FIG. 11, the RTC code detection is performed by the RTC detector.

When an error such as a reception error is detected in the one-dimensional decoding process and the two-dimensional decoding process,
Performs predetermined error processing, and the EOL1 / 0 detection unit 6803
New coded data is fetched from the coded data input terminal until the EOL1 code is detected.

When the EOL1 code is detected, one-dimensional coding processing is performed. In the processing corresponding to this error, the two-dimensional coding processing encodes the change point of the coding line with the change point of the previous line (reference line) as a reference, so that the decoding of the one-dimensional coding line and the two-dimensional coding are performed. In decoding the coded line,
If there is an error, this error will be propagated to the next line. Therefore, until the next one-dimensional coded line is detected, the last correctly decoded line is repeatedly output, and the error may occur. Perform processing to avoid displaying / printing. Such processing is performed under the control of the operation control unit 6823 based on the error detection result of each unit.

(One-Dimensional Decoding Processing) Next, the operation of the one-dimensional decoding processing after detecting the EOL1 code will be described. FIG. 16 shows the operation procedure of the one-dimensional decoding process.

Upon detecting the EOL1 code, the EOL1 / 0 detection unit 6803 detects the reference change point a0 memory 6807, the run length total sum detection unit 6816, and the level difference total detection unit prior to the one-dimensional decoding processing of the one-dimensional encoded line. 6819 is initialized. The reference change point a0 memory 6807 stores the pixel position as Pj,
Assuming that the density level at the pixel position Pj is N (Pj), the stored value a0 is initialized to the virtual change pixel as a0 = (P0, N (P0)) = (0,0).

Here, j means the j-th change point from the beginning of the decoding line. The run length sum detection unit 6816 sets the detection value suma = 0, and the level difference sum detection unit 6819 sets the detection value su.
It is initialized to mn = 0. Further, the EOL1 / 0 detection unit 6803
The horizontal mode decoding unit 6806 is instructed to start the one-dimensional decoding process.

The horizontal mode decoding unit 6806 in the one-dimensional decoding processing fetches the coded data from the multi-level coding shift register 6802, and first, the run length code R (Δ
aj) is detected. Here, Δaj is the run length between the j-th and j + 1-th change points. This detection is based on a run length decoding table ((2) in FIG. 10) in which each run length code and the corresponding run length are associated with the input and the output, and the unit of bit from the multi-level code shift register 6803 is selected. The run length code R (Δaj) existing in the run length decoding table is detected from the code string, and the corresponding run length Δaj is obtained. Then, the obtained run length Δaj is supplied to the change point calculation unit 6808.

Next, the horizontal mode decoding unit 6806 similarly uses the encoded data sequence after the run length code detection as shown in FIG.
Based on the level difference decoding table shown in (1) of 0, the level difference code L (Δnj) is detected, and the corresponding level difference Δnj is detected.
Is supplied to the change point calculation unit 6808. Δnj is the j-th
This is the density level difference between the j + 1th change point.

In this way, the detection of the run length Δaj and the level difference Δnj is repeated in pairs until the end of the line. In detecting the run length and level difference, if the run length code or level difference code corresponding to each table could not be detected, it is considered that a code error occurred during reception or during storage / reproduction in the storage memory. The determination is made, the error flag is set, and the one-dimensional decoding process is ended.

Specifically, the horizontal mode decoding unit 6806 notifies the operation control unit 6823 of the error, and the operation control unit 6823 controls the entire operation at the time of error as in the procedure of FIG. Here, assuming that the coded data string of the one-dimensional coding line is the coded data string shown in (d) of (1) of FIG. 4, the horizontal mode decoding unit 6806 causes the run length to be "10" after EOL1 coding. As the code, the subsequent "0011" is detected as a level difference code, and the corresponding run length Δa1 = 3 and level difference Δn1 = 2 are supplied to the change point calculation unit 6808.

This detection is sequentially repeated and the detection result is supplied to the change point calculation unit 6808. In the case of this code string, the run length and level difference detection results are as shown in (b) of (1) of FIG. The change point calculation unit 6808 supplies the run length Δaj and the level difference Δ supplied as a pair from the horizontal mode decoding unit 6806.
The change points are calculated sequentially based on nj.

Specifically, the run length Δa1 supplied first
Based on the level difference Δn1, the reference change point a0, the position P0 of the reference pixel in the memory, and the density level N (P0), the first calculated change point C1
Position P1 and density level N (P1) are calculated as P1 = P0 + .DELTA.a1 N (P1) = N (P0) +. DELTA.n1 C1 = (P1, N (P1)).

Then, the information of the calculated change point is supplied to the current line change point memory 6812, and the reference change point is stored.
The value a0 stored in the a0 memory 6807 is updated as a0 = C1.

As described above, the change point calculation unit 6808 sequentially supplies the run length Δaj and the level difference Δnj supplied from the horizontal mode decoding unit 6806 in pairs, and the stored value a0 a0 = (Pj, Pj, N (Pj)), the j + 1th change point Cj + 1 is calculated as Pj + 1 = Pj + Δaj N (Pj + 1) = N (Pj) + Δnj Cj + 1 = (Pj + 1, N (Pj + 1) )) Is calculated and the result is calculated as the current line change point memory 6812.
To the reference change point a0 memory 6807 and Cj
Update to +1 change point information.

This change point calculation is performed by the line end detection unit 68.
At 24, it is detected whether or not the position Pj of the storage change point of the reference change point a0 memory 6807 is equal to or more than the predetermined pixel number r of one line, and the operation is continued until the detection result becomes affirmative. Alternatively, FIG.
As shown in the flow chart of FIG. 5, the line end may be determined when the sum value sum of run lengths suma is equal to or greater than r.

As a result of calculation of the change point Cj for one line,
For the code string of (d) in (1) of FIG. 4, the change points of the current line change point memory 6812 are as shown in FIG.
The position Pj of Cj and the density level N (Pj) are stored as a pair. The pixel restoration unit 6813, based on the change point information of the current line change point memory 6812 detected by the reception error detection unit 6815 described later that there is no error, converts the multi-valued pixel row of the decoding line into the multi-valued image line. Restored on memory 6814.

When the change point information stored in the current line change point memory 6812 is shown in FIG. 5, a multi-valued pixel row is restored as follows. First, the first change point C1 = (P
The pixel row up to the pixel immediately before the position P1 = 3 of 1, N (P1)) = (3,2) is set to the pixel row of the density level 0. Change point C1 position P1 = 3
From the next change point C2 = (4,3) to the pixel immediately before the position P2 = 4 is set to the pixel of the density level N (P1)) = 2, and the change point
The pixel from the C2 position P2 = 4 to the pixel immediately before the change point C3 position P3 = 5 is set to the pixel of the density level N (P2) = 3.

In this way, the change points Cj = (Pj, N
Change point Cj + 1 = (Pj + 1, N from position Pj of (Pj))
Up to the pixel immediately before the position Pj + 1 of (Pj + 1)) is restored with the pixel of the density level N (Pj). This pixel restoration unit 68
The pixel restoration result by 13 is as shown in FIG.

The reception error detection unit 6815 uses the run length Δaj and the level difference Δnj between the respective change points output from the horizontal mode decoding unit 6806 during the one-dimensional decoding process, in the one-dimensional encoded data string. The error of is detected as follows. The run length sum detection unit 6816 sequentially adds Δaj to the run length sum detection value suma initialized at the beginning of the line to detect the sum of run lengths for one line. Also, the level difference sum detection unit 6819 sequentially adds Δnj to the level difference sum detection value sumn initialized at the beginning of the line to detect the sum of the level differences for one line.

The coincidence detection unit 6817 has a run length sum detection value.
The match between the suma and the predetermined pixel number r of one line is detected, and the match detection unit 6820 detects whether the level difference sum total detection value sumn is 0 or not. At the time of one-dimensional encoding, the distance (run length) between the change points and the density level difference are encoded, including the white virtual pixel arranged immediately before the beginning of the line and the white virtual change point immediately after the end of the line. Therefore, the total run length should be the number r of pixels in one line, and the total sum of the density level differences should be zero.

Therefore, when the detection result of at least one coincidence detection value is negative, it is determined that there is an error in the one-dimensional encoded data, and the operation control unit 6823 is notified of this. The operation control unit 6823 stops the operation of the pixel restoration unit 6813 until the calculation of the change point of the next one-dimensional decoding line having no reception error is completed. That is, the pixel restoration unit restores the pixels of the error-free decoded line on the multi-valued image line memory 6814.

When the pixel restoration of the decoded line is completed, the change point information of the current line change point memory 6812 is stored in the previous line change point memory 681 for decoding of the next encoded line.
1 and stored in a similar format.

(Two-dimensional decoding process) Next, the operation of the two-dimensional decoding process after detection of the EOL0 code will be described. FIG. 17 shows the operation procedure of the two-dimensional decoding process.

Upon detecting the EOL0 code, the EOL1 / 0 detection unit 6803 changes the stored value a0 of the reference change point a0 memory in the same manner as in the one-dimensional decoding process prior to the two-dimensional decoding process of the two-dimensional coding line. , A0 = (Pa0, N (Pa0)) = (0,
0), and initializes to a virtual change pixel.

The b1b2 detection unit 6810 has a multi-level encoding unit 63.
Similar to the b1b2 detection section 8 of the reference change point a0 change point of the memory
The reference change points b1 and b2 are detected from the previous line change point memory 6811 based on a0, and the change point information is used as the reference change point b1b2.
The data is stored in the b1 memory and the b2 memory of the memory 6809. Further, when the EOL1 / 0 detection unit 6803 detects the EOL0 code,
The two-dimensional coding mode code detection unit 6804 is instructed to start operation. The two-dimensional coding mode code detection unit 6804 uses the EO
It is detected whether the code string following the L0 code is a P code (a code indicating the pass mode), an H code (a code indicating the horizontal mode), or any other code (a vertical code word encoded in the vertical mode).

Hereinafter, the two-dimensional coding mode code detection unit 68
The operation of 04 when (1) the P code is detected, (2) when the H code is detected, and (3) when it is not the P or H code will be described. (1) When the P code is detected,
The change point calculation unit 6808 is informed of that fact. When the P code is detected (in the case of pass mode decoding), the change point calculation unit 6808 sets the standard change point a0 and the reference change point b2 to a0 = (Pa0, N (Pa0)) b2 = (Pb2, N (Pb2) )

Then, the new reference change point a0 is set to be the same as the old a0, the position is set to the position of b2, and the reference change point a0 memory 6807 is expressed as a0 = (Pb2, N (Pa0)). The stored value of is updated. (This is a process corresponding to "immediately below a0 = b2" in FIG. 17)

(2) When the H code is detected, the horizontal mode decoding process is performed by the horizontal mode decoding procedure shown in FIG. 18, and the reference change point a0 is updated with a2 described later. Specifically, the two-dimensional coding mode code detection unit 6804 instructs the horizontal mode decoding unit 6806 to start operation. The horizontal mode decoding unit 6806 determines the run length code R (Δa0) and the level difference code L (Δn0) from the code string following the H code in the run length decoding table and the level difference decoding as in the one-dimensional decoding process. Detected based on the table, the corresponding run length Δa
0 and the level difference Δn0 are supplied to the change point calculation unit 6808.

Similarly to the above, the run length code R (Δa1) and the level difference code L (Δn1) are detected from the subsequent code string, and the run length Δa1 and the level difference Δn1 are supplied to the change point calculation unit 6808. When the change point calculation unit 6808 detects the H code (in the case of horizontal mode decoding), the reference change point a0, that is, a0 =
From (Pa0, N (Pa0)) and Δa0 and Δn0, the change point a1 is calculated as a1 = (Pa0 + Δa0, N (Pa0) + Δn0) = (Pa1, N (Pa1)),

Further, from a1 and Δa1 and Δn1, the change point
a2 is a2 = (Pa1 + Δa1, N (Pa1) + Δn1) = (Pa
2, N (Pa2)). This calculation result is supplied to the current line change point memory 6812, and the change point a2 information is stored in the reference change point a0 memory 6807 as a new reference change point a0.

(3) If the code is not a P or H code, vertical mode decoding processing is performed in the vertical mode decoding procedure shown in FIG. 19, and the reference change point a0 is updated with a1 described later. Specifically, the two-dimensional coding mode code detection unit 6804 instructs the vertical mode decoding unit 6805 to start operation. The vertical mode decoding unit 6805 receives the vertical code V (Δa, Δn) and the two-dimensional displacement (Δa, Δn) shown in FIG. 9 from the encoded data string.
), The vertical code is detected based on the corresponding vertical decoding table, and the corresponding two-dimensional displacement (Δa, Δn) is supplied to the change point calculation unit 6808.

If it is not a P or H code (in the case of vertical mode decoding), change point calculation section 6808 determines change point a1 from b1 = (Pb1, N (Pb1)) as reference change point b1 and Δa and Δn. It is calculated as a1 = (Pb1 + Δa, N (Pb1) + Δn) = (Pa1, N (Pa1)).

This change point a1 information is supplied to the current line change point memory 6812 and a new reference change point a0 is set.
Is stored in the reference change point a0 memory 6807 as As described above, in the two-dimensional decoding process, the two-dimensional coding mode code detection unit 6804 detects the coding mode, performs the corresponding decoding process, calculates the change point, and stores the change point in the current line change point memory. The reference change point a0 is stored in the 6812 and the reference change point a0 is updated, and the b1b2 detection unit 6810 detects the reference change points b1 and b2 corresponding to this a0 and prepares for the next decoding process.
This repetition is repeated by the line end detection unit 6824 until the position of the reference change point a0 becomes equal to or greater than the predetermined number of pixels r in one line.

When the horizontal mode decoding unit 6806 and the vertical mode decoding unit 6805 cannot detect the corresponding codes, the operation control unit 6823 is notified that a reception error of the encoded data string has occurred. Based on the change point information stored in the current line change point memory 6812 of the error-free decoded line, the operation control unit 6823 causes the pixel restoration unit 6813 to create a pixel row in the multi-valued image line memory 6814. Restore.

Assuming that the coded data string of the two-dimensional coded line is (5) in FIG. 7 and the change point of the reference line is (1-1) in the figure, the above two-dimensional decoding process results in The pixel row shown in (2) will be restored. As described above, the multi-valued image restored by the multi-valued decoding unit 68 is supplied to the N-valued error diffusion unit 69 line by line, and is displayed on the display 7.
0 and the n-value quantization corresponding to the gradation display capability n per pixel of the printer 71.

FIG. 20 is a block diagram showing the structure of the N-value error diffusion unit 69. In the figure, 6901 is an input terminal for multi-valued image data of the N-value error diffusion section 69, 6902 is an n-value control signal input terminal for controlling the quantization number N, 6903 is an addition section, 6904 is an N-value quantization section, Reference numeral 6905 denotes an error calculation unit that calculates the difference between the input density level value of the N-value quantization unit 6904 and the density level value after quantization.

Reference numeral 6906 denotes an error diffusion filter section, 6907.
To 6913 are elements constituting the error diffusion filter unit 6906, and 6907 is an error line memory for storing the quantization error of each pixel for at least one line, 6908, 6
Reference numeral 909 denotes a delay unit for timing adjustment, 691
0, 6911 and 6912 are weighting units that output correction values corresponding to the quantization error values of the respective inputs, 6913 is an addition unit that adds the outputs of the weighting units 6910 and 6912 and 6913, and 6914 is an N-value error diffusion unit 69. Output terminal.

The N-value error diffusion unit 69 takes in the multi-valued image data Xi, j (i is the sub-scanning direction position, j is the main scanning direction position) from the multi-valued image data input terminal 6901, and the adding unit 69
03, the output value ESi, j of the error diffusion filter unit 6906
And is supplied to the N-value quantization unit 6904. The N-value quantizer 6904 quantizes the input value Di, j into an n-value corresponding to the n-value control value n supplied from the n-value control signal input terminal 6902.

The error calculation unit 6905 has an N-value quantization unit 690.
The difference Ei, j between the input value Di, j of 4 and the quantized value Yi, j is
= Di, j-Yi, j, and the error diffusion filter unit 69
Supply to 06. This quantization error Ei, j is
It is supplied to the weighting unit 6910 via 08 and is also supplied to the error line memory 6907 for temporary storage.

The error line memory 6907 stores the input pixel value.
Quantization error Ei- of the previous line corresponding to pixel position j of Xi, j
1, j and Ei-1, j + 1 are output, Ei-1, j is sent to the weighting unit 6911 via the delay 6909, and Ei-1, j + 1 is sent to the weighting unit 6
Supply to 912. The weighting units 6910, 6911 and 6912 output a correction value obtained by multiplying the quantization error value of each input by the correction coefficient a, b, c. The output values of these weighting units are added by the addition unit 6913, and added by the addition unit 6903 to the input value Xi, j.

Let ESi, j be the output value of the error diffusion filter 6906 (output value of the adder 6913), ESi, j = a * Ei, j-1 + b * Ei-1, j + c * Ei-1 , j + 1 However, a + b + c ≦ 1, and the output value Di, j of the adder 6903 becomes Di, j = Xi, j + Ei, j. This Di, j is quantized into an n value by the N-value quantization unit 6904, and the quantized value Yi, j is output from the output terminal 6914.

FIG. 21 is an explanatory diagram showing the operation of the N-value error diffusion section 69, and in particular the manner of error diffusion by the error diffusion filter section 6906, where i is the sub-scanning direction position and j is the main scanning direction position. . As shown in (a) in the figure, if the pixel of interest to be quantized is Si, j (x mark), the quantization error of the pixels Si-1, j on the previous line shown in (1) (stored in the error line memory Value) Ei-1, j is corrected by the correction coefficient b and the target pixel Si, j
Is added to the density level of.

Similarly, the quantization errors Ei-1, j + 1 of the pixels Si-1, j + 1 on the previous line are corrected by the correction coefficient c and added to the target pixel. Further, the pixel Si, j-1 immediately before the pixel of interest on the current line is
The quantization error Ei, j-1 of is added to the pixel of interest. In other words, as shown in (b) in the figure, the quantization error of the target pixel (marked by x) corrected by the correction coefficients a, b, c is distributed to the peripheral pixels. Since the quantization error is diffused to the peripheral pixels in this way, the average densities of the images before and after the N-value quantization can be matched.

FIG. 22 is a block diagram showing the structure of N-value quantization section 6904. In the figure, 69041 is N
An input terminal of the value quantization unit 6904, 69042 is a binary quantization table that quantizes the input value Di, j of the input terminal 69041 into a binary value, and 69043 is a ternary quantization table that quantizes Di, j into a ternary value. , 69044 quantizes Di, j into N values N
A value quantization table, 69045 is a selector for selecting and outputting the quantization output of each table as the quantization output of the n-value quantization table corresponding to the value n of the n-value control value input terminal 6902, 6914 is an N-value quantization The output terminal of the unit 69.

Although only two, three and N-value quantization tables are shown in the figure, in reality, there are a plurality of quantization tables from 2 to N. The quantized input value Di, j is input to each quantization table and each n-value quantized value is selected by the selector 69045.
Is supplied to. For example, when the quantized input value is 0 to 255, the ternary quantization table 69043 outputs any one of three values (0, 128, 255) corresponding to the input value. The selector 69045 has n values corresponding to the n-value control value n.
Select the quantized value Yi, j in the value quantization table and output terminal 6
Output to 914.

The n-value control value n is supplied from the N-value control unit 72. The N-value control unit 72 outputs an n-value according to the gradation expression capability per pixel of the connected display 70 and printer 71.

For example, if the number of gradations of the display 70 is nd
, The number of gradations of the printer 71 is np, and the N-value error diffusion unit 69
If the number of input grayscales is set to ni and np <nd ≤ ni, the control value n is set to nd when the multi-valued image is reproduced and displayed on the display 70, and the multi-valued image is reproduced and printed by the printer 71. Set the control value n to np.

As described above, since the multivalued image is reproduced by quantizing in accordance with the number of gradations of the display and the printer, it is possible to obtain the multivalued image which maximizes the display and printing capabilities of the display 70 and the printer 71. it can. (Effect of the second embodiment)

As described above, in the second embodiment of the present invention, (1) a pixel in a binary image area such as a character / line drawing is white (minimum density level) or black depending on the density level of the pixel. Since the value is binarized to (maximum density level), there are two types of change points in this area, a change pixel from white to black and a change pixel from black to white, and Δn in the density level difference code L (Δn) By assigning the code word for the positive and negative maximum values of the code word of the short code length, this binary image area is almost the same coding efficiency as the conventional MR code in the multi-valued image coding method of the first embodiment. Can be encoded with.

That is, it is possible to expect a high coding efficiency in the multi-valued image area, and the binary image area is made into a sharp binary image by edge emphasis, and moreover, a high coding efficiency similar to the conventional one can be obtained. . In addition, (2) the multi-value encoded image or the received multi-valued image is displayed,
Corresponding to the number n of display / print gradation levels of a printer, the multi-value image is displayed / printed by quantizing to n values by the N-value error diffusion method. Can be obtained.

[Third Embodiment] FIG. 23 shows the third embodiment of the present invention.
3 is a block diagram showing the configuration of the embodiment of FIG. The third embodiment is an image transmission apparatus (for example, a facsimile apparatus) that reads and encodes a multivalued image such as a character / line drawing or a photograph and stores or transmits it.

Specifically, as shown in (1) of FIG. 24, a multi-valued image original in which a binary image area and a multi-valued image area are mixed is read, and the multi-valued image area shown in (2) is whitened. The binary image and the binary image area shown in (3) are separated into two surfaces of a whitened multivalued image, and the separated binary image surface is subjected to conventional MR encoding to separate the separated multivalued image surface into The multi-valued image encoding method shown in the first embodiment is used for encoding, and binary MR encoded line data and multi-valued encoded line data are paired to form one line for transmission. .

In FIG. 23, those having the same functions as those in the second embodiment of FIG. 11 are designated by the same reference numerals. 8
When the image area determination result of the pixel of interest by the image area determination unit 58 is a binary image, 0 selects and outputs the binary quantization value of the binary quantization unit 60, and when the determination result is a multi-valued image, the minimum value is set. The selector 81 for selectively outputting the density level (white), 81 outputs the minimum density level (white) when the image area determination result is binary,
When the determination result is a multi-valued image, the selector selectively outputs the correction result of the gamma correction unit 57.

Reference numeral 82 is a binary line buffer memory for temporarily storing the output value of the selector 80 in pixel units, and reference numeral 83 is an output from the binary line buffer memory 82 in the conventional MR encoding method (referred to as binary MR encoding). A binary MR encoding unit that encodes in accordance with 1., a selector 84 that selects and outputs the encoding result of the binary MR encoding unit 83 and the multilevel encoding result, and 85 is a binary MR encoding from the storage memory 66. A binary MR decoding unit that decodes data, and 86 is a binary line memory that stores at least one line of the decoding result of the binary MR decoding unit (1 bit per pixel).

87 is the output value of the binary line memory 86 (1
/ 0) corresponding to the maximum density level or the minimum density level, and 88 adds the output density level value of the density recovery section 87 and the output density level value of the N-value error diffusion section 69 in pixel units. It is a density addition unit that outputs the output.

The operation of the third embodiment will be described. Here, the part different from the operation of the second embodiment will be mainly described.
An image area determination unit based on the reading result of this reading line and the preceding line is shown in FIG. 25, where the density level of the reading line is read by the reading sensor 50 and subjected to shading correction after A / D conversion. The determination result of 58 is (2) in FIG.
Given the determination result shown, the selector 80 and the selector 81
Is controlled as follows in accordance with this image area determination result.

As shown in (3) of FIG. 25, the selector 80 is edge-enhanced by the edge emphasizing section 55 and binary-quantized by the binary quantizing section 60 when the image area determination result is a binary image area. The selected result is output. When the image area determination result is a multi-valued image area, white (minimum density level) is selected and output.
That is, the selector 80 outputs the binary image data (1 bit per pixel) in which the multi-valued image area is whitened.

As shown in (4) of FIG. 25, the selector 81 selects and outputs white (minimum density level) when the image area determination result is a binary image area. When the image area determination result is a multi-valued image area, it is smoothed by the smoothing unit 56 and the gamma correction unit 5
In step 7, the result of density correction is selected and output. That is, the selector 81 outputs multi-valued image data (a plurality of bits per pixel) in which the binary image area is whitened.

The output of the selector 80 is temporarily stored in the binary line buffer memory, and the output of the selector 81 is temporarily stored in the line buffer memory 62. The binary MR encoding unit 83 MR-encodes the binary image data output from the binary line buffer memory 82 on a line-by-line basis. MR
The (Modified Read) encoding is a binary image encoding method generally used in a facsimile or the like, and the description thereof is omitted here.

The multi-value encoding unit 63 multi-value encodes the multi-valued image data output from the line buffer memory 62 on a line-by-line basis. The coding method is the coding method described in the first embodiment. 23 (4) and (5) show the states of binary MR coding and multilevel coding for each reading line. (4) is binary MR coding, and (5) is multi-level coding 1
2 shows a line for two-dimensional encoding. The figure shows the case where the k factor value = 4.

As shown in the figure, the binary image data of line i is subjected to one-dimensional coding (so-called M
H-encoding), and multi-valued image data is one-dimensionally encoded in multi-valued encoding. Next line i + 1, i + 2, i +
The binary image data of No. 3 is subjected to two-dimensional encoding (MR) in binary MR encoding, and the multi-valued image data is subjected to two-dimensional encoding in multi-level encoding. The above four lines are repeated.

As shown in (1) of FIG. 26, the binary MR encoded data (a) by the binary MR encoding unit 83 of each reading line i and the multivalued encoded data ( 26A is supplied to the storage memory 66 through the selector 84 in the order shown in FIG. That is,
Following the binary MR encoded data, the multilevel encoded data is temporarily stored in the storage memory 66 via the selector 84 for each reading line.

In the figure, EOL1 is a code indicating that the subsequent encoded data sequence is a one-dimensionally encoded encoded data sequence in binary MR encoding, and EOL0 is a subsequent encoding in binary MR encoding. A code indicating that the data string is a two-dimensional coded coded data string, and EOLM1 is a code indicating that the subsequent coded data string is a one-dimensional coded coded data string in multi-level coding. , EOLM0 is a code indicating that the subsequent encoded data sequence is a two-dimensionally encoded data sequence in multi-level encoding.

These encoded data strings are
In the case of transmission, the data is sent from the storage memory 66 to the line 65 via the modem 64 in the order shown in (2) of FIG.
When the multi-valued image coded as described above is received, the received coded data is sent to the binary MR coding unit 85 and the multi-level decoding unit 68 for decoding via the storage memory 66. 26
It is supplied in the order of (2).

Also, in the case where the image is encoded by its own device, temporarily stored in the storage memory 66, and restored offline (so-called offline COPY operation), the same is read from the storage memory 66 in the order of (2), Binary MR encoding unit 8
5 and the multilevel decoding unit 68.

The binary MR decoding unit 85 uses the EOL1 code and
EOL0 code is detected and the subsequent encoded data string is binary MR
Decrypt. After detecting the EOL1 code, the subsequent encoded data string is subjected to one-dimensional decoding processing (so-called MH decoding), and after detecting the EOL0 code, the subsequent encoded data string is
Two-dimensional decoding processing (MR decoding) is performed. The decryption result is 2
The value line memory 86 is temporarily stored line by line.

The binary image data in the binary line memory 86 (1 bit per pixel represents white / black) is converted into the minimum density level value by the density restoring unit 87 in correspondence with the stored value of each pixel. (White) or the maximum density level value (black) is restored. The minimum density level value and the maximum density level value are the same as the minimum density level value and the maximum density level value in the encoding of the multi-valued image.
When encoding from (white) to density level 63 (black),
The minimum density level value is 0 and the maximum density level value is 63. The density restoration result of the binary image by the density restoration unit 87 is supplied to the density addition unit 88.

The multi-level decoding unit 68 uses the EOLM1 code and EO
The LM0 code is detected, and the multilevel decoding unit 68 shown in FIG.
The detection code of the EOL1 / 0 code detection unit 6803 of
EOLM1 code, EOL0 code is changed to EOLM0 code) and the subsequent encoded data string is multi-value decoded. After detecting the EOLM1 code, the subsequent encoded data sequence is subjected to one-dimensional decoding processing, and after detecting the EOLM0 code, the subsequent encoded data sequence is subjected to two-dimensional decoding processing.

The result of the multi-value decoding by the multi-value decoding unit 68 is requantized into an n-value by the N-value error diffusion unit 69 in correspondence with the n-value control value n from the N-value control unit 72. And is supplied to the density addition unit 88. In the density addition unit 88, the n-value quantized multivalued image data of the decoded line i from the N-value error diffusion unit 69 (which can take values from the minimum density level to the maximum density level) and the binary line memory The binary image data of the decoded line i (which takes either the minimum density level or the maximum density level) temporarily stored in 86 and density-restored by the density restoration unit 87 is added to the corresponding pixel unit. It

As a result, the binary image and the multi-valued image are separated, and those originally encoded are combined here to restore the read image or the received image. The output of the density addition unit 88 is the display 70 or the printer 7.
1 and the image is reproduced.

FIG. 27 shows how a binary image and a multi-valued image are decoded and then combined. (1) is a binary MR decoding result, and each pixel is represented by 1 bit indicating whether it is a white pixel or a black pixel. In the figure, black pixels are indicated by 1 and white pixels are indicated by 0. (2) is the density restoration result, which is the maximum density level value for black pixels and the minimum density level value for white pixels. (3) is the N-value error diffusion result, and (4) is the density addition result of the binary image area of (2) and the multi-valued image area of (3) by the density addition unit 88.

FIG. 27 (5) shows the result of requantization of the multi-valued image when the n value in the N-value error diffusion unit 69 is made smaller (coarse) than in the case of (3). 2 of (2)
It is the result of adding the densities of the value image and the multivalued image of (5) and combining the two.

(Effect of the Third Embodiment) As described above, in the third embodiment, an image in which a binary image and a multivalued image are mixed is separated into a binary image area and a multivalued image area, Since the binary image plane in which the multi-valued image area is whitened and the multi-valued image plane in which the binary image area is whitened can be coded by a coding method having a high coding efficiency corresponding to the property of the image, respectively, a high total coding is possible. Efficiency can be expected, the memory capacity for image storage can be reduced, and the transmission time for image transmission can be shortened.

In particular, since there is no change point in the coding of the whitened area, there is no increase in the code amount due to the whitened area in the two-dimensional coding. At the time of one-dimensional encoding, a code expressing the run length of this white area is required, but the increase rate can be made minute by increasing the k factor value. Rather, it can be expected that the total coding efficiency can be improved by adopting a coding method corresponding to each image property.

Further, since the binary image area and the multi-valued image area are separated and stored or transmitted, the density characteristic (so-called gamma characteristic) of the multi-valued image is restored at the time of image restoration on the display 70 or printer 71 on the receiving side. It is also possible to modify the processing so as to match the density characteristics of the above or according to the preference of the receiving side. In addition, the density of the binary image can be changed independently of the density of the multi-valued image. In this way, since images having different properties are separated and stored and transmitted, various correction processes can be performed independently on a binary image and a multivalued image at the time of image restoration.

The multi-level coding and multi-level decoding method is not limited to the above-mentioned coding method, and various multi-level coding methods can be used. For example, 8 such as DCT (Discrete Cosine Transform)
* The multi-valued image area may be encoded by using an encoding method in units of 8 pixels.

FIG. 28 shows that the binary image area has the above-mentioned binary MR.
FIG. 7 shows a state of encoding of a read line when encoding is performed by encoding and a multi-valued image area is encoded by DCT. DCT
As shown in (2), multi-valued image coding by
The pixel group in this is 8 *
DCT coding is performed in units of 8, and the DCT coding result for 8 lines is followed by the coded data for 8 lines of binary coding and the corresponding DCT for 8 lines as shown in (3).
Similar effects can be obtained by storing and transmitting encoded data.

[Fourth Embodiment] In the above-described embodiment, the multivalued image area is separated into two surfaces, a whitened binary image surface and a whitened multivalued image surface. Even if the encoding method is changed between the binary image area and the multi-valued image area, the same effect can be expected.

FIG. 29 is a diagram showing this encoding method.
For a mixed image of binary and multi-valued images of (1), as shown in (2) of FIG. 29, the corresponding encoding process is changed within a line according to the image area determination result, and the encoding process is performed. . here,
The case where the k factor value = 4 is shown, and the lines i and i + are shown.
4. ． As described above, one-dimensional encoding is performed for every four lines.

In line i + 1 of (2) in FIG. 29, the multi-valued encoding process suddenly starts from the two-dimensional encoding process without passing through the one-dimensional encoding process. This situation occurred because there was no multi-valued image area, although it was the line to be processed.) Two-dimensional multi-level encoding is performed after the binarization processing of the binary image of the previous line (minimum density level). Or the maximum density level quantized data), the corresponding reference change points b1 and b2 are obtained,
Multi-value code the current line i + 1.

Further, when the multi-valued image area of the previous line, such as line i + 6, ends and becomes a binary image area in the current line, and when this is subjected to binary two-dimensional encoding, it is a binary 2
In the dimensional coding, since there is no concept of multivalued density level differences between change points, vertical coding cannot be performed, but binary two-dimensional coding is performed by coding the corresponding pixel column in the horizontal mode. be able to.

An example of the encoded data string of each line which has been encoded in this way is shown in (3) of FIG. In the figure
For EOL1 and EOL0 codes, the subsequent encoded data string is binary 1
Dimension, a code that is a two-dimensional encoded data string and that indicates the beginning of a new line. EOL1-C and EOL0-C codes are
A code indicating that the subsequent coded data string is a binary one-dimensional, two-dimensional coded data string, but is not the beginning of a new line. The EOLM1 and EOLM0 codes are codes that indicate that the subsequent coded data string is a multi-valued one-dimensional, two-dimensional coded data string and is the head of a new line. EOLM1-C, EO
The LM0-C code is a code indicating that the subsequent coded data string is a binary one-dimensional, two-dimensional coded data string, but is not the beginning of a new line.

These encoded data strings are stored or transmitted in the order of reading lines as shown in (3) of FIG. Decoding of this coded image data is performed by EOL1 and EO.
By detecting the L0, EOLM1, and EOLM0 signs,
The decoding of a new line is started, various EOL codes are detected, and the decoding process is performed by the corresponding decoding method.

In the binary image area, the density is restored to a value of either the minimum density level or the maximum density level, and in the multi-valued area, the image data of the decoding line in which the decoded density level is left unchanged is transferred to the N-value error diffusion unit. To re-quantize to n value and display / print on display or printer to reproduce image.
Whether the binary image area is the minimum density level or the maximum density level
Since the values are quantized and the density is restored, no quantization error occurs even if the N-value error diffusion process is performed, and the input binary image does not change. The image in the multi-valued image area is only n-value quantized.

[0245]

As described above, according to the present invention,
(1-1) In a multi-valued image such as a photograph, the position of the changing point on the coding line where the density changes exists near the position of the already changing point on the reference line, and both changes Utilizing the property that the difference in concentration level between points is small,
Two-dimensional displacement (Δa, Δn) of the difference Δa between the change point on the reference line and the change point on the encoding line and the difference Δn between the density levels.
), A code word having a shorter code word length is assigned and coded with a higher occurrence frequency, so that a multi-valued image can be coded with high coding efficiency without impairing reproducibility.

(1-2) Since the encoding method of the present invention is an extension of the conventional MR encoding method of monochrome binary in a facsimile to a multi-valued image, the conventional MR
It has a high affinity with the system and has an advantage that it can be realized without increasing the device scale so much when adding a facsimile function for encoding and transmitting a multi-valued image as it is at a multi-valued level.

Further, (2-1) the binary image area is detected,
By binary-quantizing to the minimum density level (white) or the maximum density level (black), an image in which a binary image and a multivalued image are mixed can be coded with high coding efficiency.

Further, (2-2) the multi-value coded image or the received multi-valued image corresponds to the display / print gradation number n of the display or printer by n-value by the N-value error diffusion method. Since the multi-valued image is quantized and displayed / printed, it is possible to obtain the best multi-valued image utilizing the display / print gradation capability.

Further, (3-1) an image in which a binary image and a multivalued image are mixed is separated into a binary image region and a multivalued image region,
Since the binary image plane in which the multi-valued image area is whitened and the multi-valued image plane in which the binary image area is whitened can be coded by a coding method having a high coding efficiency corresponding to the property of the image, respectively, a high total coding is possible. Efficiency can be expected, the memory capacity for image storage can be reduced, and the transmission time for image transmission can be shortened.

(3-2) Since images having different properties are separated and stored and transmitted, various correction processes can be independently performed on the binary image and the multivalued image at the time of image restoration.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of a multi-valued image encoding device as a first embodiment of the present invention.

FIG. 2 is an explanatory diagram illustrating a change point detection operation of a change point detection unit 4 in FIG.

FIG. 3a of the encoding change point memory unit 5 at the time of one-dimensional encoding
It is explanatory drawing which shows the memory | storage operation of the change point information of 0, a1 memory.

FIG. 4 is an explanatory diagram showing an operation of detecting a run length and a density level difference between changing points of the horizontal mode encoding unit 16 at the time of one-dimensional encoding, and a one-dimensional encoded code string.

FIG. 5 is an explanatory diagram showing a method of storing change point information in a reference line change point memory and a coded line change point memory.

FIG. 6 is a flowchart showing a procedure of an operation of one-dimensional and two-dimensional encoding according to the first embodiment of the present invention.

FIG. 7 is an explanatory diagram showing a two-dimensional encoding operation and a two-dimensional encoded code string according to the first embodiment of this invention.

FIG. 8 is an explanatory diagram showing an example of a two-dimensional displacement area encoded in the vertical mode.

FIG. 9 is an explanatory diagram showing a coding mode, a pixel to be coded, and a code word at the time of two-dimensional coding.

FIG. 10 is an explanatory diagram showing an example of a density level difference code according to the first embodiment.

FIG. 11 is a block diagram showing a configuration of a multi-value image transmission device as a second embodiment of the present invention.

12 is an explanatory diagram illustrating operations of an edge enhancement unit 55, a smoothing unit 56, and a gamma correction unit 57 in FIG.

13 is an explanatory diagram illustrating an operation of the image area determination unit 58 in FIG.

14 is an explanatory diagram showing a configuration of a multilevel decoding unit 68 in FIG.

FIG. 15 is a flowchart showing a multilevel decoding procedure of a multilevel decoding unit 68 according to the second embodiment.

FIG. 16 is a flowchart showing a one-dimensional decoding procedure of the multilevel decoding unit 68.

FIG. 17 is a flowchart showing a two-dimensional decoding procedure of the multilevel decoding unit 68.

FIG. 18 is a flowchart showing a horizontal mode decoding procedure of the multilevel decoding unit 68.

FIG. 19 is a flowchart showing a vertical mode decoding procedure of the multilevel decoding unit 68.

20 is a block diagram showing a configuration of an N-value error diffusion unit 69 in FIG.

FIG. 21 is an explanatory diagram showing how a quantization error is diffused.

FIG. 22 is a block diagram showing the configuration of an N-value quantization unit 6904.

FIG. 23 is a block diagram showing a configuration of a multi-value image transmission device as a third embodiment of the present invention.

[Fig. 24] Fig. 24 is an explanatory diagram illustrating a manner in which a binary image area and a multivalued image area are separated and a read image is separated into two surfaces of a binary image and a multivalued image surface and an encoding method for each surface.

FIG. 25 is an explanatory diagram showing a manner in which a reading line is separated into a binary image surface and a multivalued image surface according to an image area determination result.

[Fig. 26] Fig. 26 is an explanatory diagram illustrating an example of encoded data on a binary image plane and a multivalued image plane, and the order of storage and transmission thereof.

[Fig. 27] Fig. 27 is an explanatory diagram illustrating a decoding result of a decoding line of a binary image plane, a decoding result of a decoding line of a multi-valued image plane, and a combination state thereof by density addition.

[Fig. 28] MR encoding of a binary image plane, DC of a multi-valued image plane
FIG. 3 is an explanatory diagram showing a state of encoding when performing T encoding, and a transmission order when accumulating or transmitting each encoding result.

FIG. 29 shows how a coding method is changed when a coding method is changed between a binary image area and a multivalued image area in a read line, and an identification code for identifying the coding method is added when transmitting a coding result. It is an explanatory view shown.

[Explanation of symbols]

1 ... Multi-valued image input terminal, 3 ... Multi-valued image line memory, 4 ... Change point detection section, 5 ... Encoding change point memory section, 7 ... Reference line change point memory, 8 ... b1b2 detection unit, 9 ... Reference change point memory unit, 10 ... Path mode determination unit, 11 ... Vertical mode encoding unit, 14 ... Vertical mode determination unit, 12 ... a1b1 distance detector, 13 ... a1b1 level difference detector, 15 ... Vertical mode code table, 16 ...
・ Horizontal mode coding unit, 17 ... a0a1 distance detection unit, 18
... a0a1 level difference detection unit, 23 ... run length code table, 24 ... level difference code table, 25 ... EOL0 code generation unit, 26 ... P code generation unit, 27 ... H Code generation unit, 28 ... EOL1 code generation unit, 29 ... Two-dimensional code synthesis unit, 30 ... One-dimensional code synthesis unit, 32 ... Output terminal of multi-level coding device, 50 ... Reading sensor 52 ... Shading correction unit 53 ... Front line multi-valued image memory 54
・ ・ ・ White peak detection unit, 55 ・ ・ ・ Edge enhancement unit, 56 ・ ・ ・
Smoothing unit, 57 ... Gamma correction unit, 58 ... Image area determination unit, 59 ... Binary / multi-valued quantization unit, 60 ... Binary quantization unit, 61 ... Selector, 63 ... Multi-level encoding unit, 66 ...
Storage memory, 64 ... Modem, 68 ... Multi-level decoding section, 69 ... N-value error diffusion section, 70 ... Display,
71 ... Printer, 72 ... N-value control unit, 6803 ...
EOL1 / 0 code detection unit, 6804 ... Two-dimensional coding mode code detection unit, 6805 ... Vertical mode decoding unit, 6806 ...
Horizontal mode decoding unit, 6807 ... Standard change point a0 memory, 6808 ... Change point calculation unit, 6809 ... Reference change point b1b2 memory, 6810 ... b1b2 detection unit, 6811 ...
Previous line change point memory, 6813 ... Pixel restoration unit, 68
15 ... Reception error detection unit, 6816 ... Run length total detection unit, 6819 ... Level difference total detection unit, 6904 ...
N-value quantizer, 6905 ... Error calculator, 6907 ...
Error line memory, 6903, 6913 ... Adder unit, 6
910, 6911, 6912 ... Weighting unit, 6904
2 ... Binary quantization table, 69043 ... Tri-valued quantization table, 69044 ... N-valued quantization table, 690
2 ... n-value control value input terminal, 69045 ... selector,
80, 81 ... Selector, 83 ... Binary MR encoding unit,
85 ... Binary MR decoding unit, 87 ... Density restoration unit, 88 ...
・ Concentration adder

Claims (30)

[Claims] 1. When each line of multi-valued image data obtained by scanning an image and sampling in pixel units is used as an encoding line, the density level of each line is the same as that of the immediately preceding pixel in the scanning order, Detecting the position of a different pixel as a change point, comparing the change point on the encoded line with the change point on the reference line, which is an already encoded line, and obtaining the position difference Δa; The step of obtaining the level difference Δn and the step V of obtaining the position difference Δa and the concentration level difference Δn as a two-dimensional displacement (Δa, Δn) and obtaining a predetermined code V (Δa, Δn) corresponding thereto Accordingly, the method of encoding multi-valued image data comprises the step of encoding the change points on the encoding line. 2. When each line of multi-valued image data obtained by scanning an image and sampling in pixel units is used as an encoding line, the density level of each line is that of the immediately preceding pixel in the scanning order, By detecting the position of a different pixel as a change point, a change point on the coding line is a0, a reference change point serving as a reference for defining another change point, and the reference change on the coding line. Seen in the scanning direction from the point a0 (hereinafter,
Detecting these change points with the first change point being the right side (a1), the first change point on the right side from the change point a1 on the encoding line, and a2, and the already encoded line. On the line, a change point on the right side of the corresponding position of the reference change point a0 and having a density level different from that of the change point a0 is b1, and the first change on the right side of the change point b1 on the reference line. The point is designated as b2, the step of detecting these change points, the step of obtaining the position difference Δa and the density level difference Δn on the respective lines of the change points a1 and b1, respectively, and the obtained position difference Δa. The difference Δn between the concentration levels is used as a two-dimensional displacement (Δa, Δn) to determine whether or not the difference is within a predetermined range, and when the difference is within a predetermined range, the two-dimensional Displacement ( Predetermined code V (Δ) corresponding to Δa, Δn)
a, Δn) to encode the change point a1, and then the encoded change point a1 as a new reference change point a0 and the change point a2 as a new change point a1.
A multi-valued image data encoding method comprising the steps of repeating the above procedure. 3. When each line of multi-valued image data obtained by scanning an image and sampling in pixel units is used as an encoding line, the density level of each line is that of the immediately preceding pixel in the scanning order, By detecting the position of a different pixel as a change point, a change point on the coding line is a0, a reference change point serving as a reference for defining another change point, and the reference change on the coding line. Seen in the scanning direction from the point a0 (hereinafter,
Detecting these change points with the first change point being the right side (a1), the first change point on the right side from the change point a1 on the encoding line, and a2, and the already encoded line. On the line, a change point on the right side of the corresponding position of the reference change point a0 and having a density level different from that of the change point a0 is b1, and the first change on the right side of the change point b1 on the reference line. The point where b2 is the point of detection of these change points, and the position of the change point b2 on the line is the change point a.
A first determination step of determining whether or not the position is on the left side of the position of 1 on the line; and, if the first determination result is affirmative, encoding that effect with a specific code P, Subsequently, selecting a pixel position on the coding line that is the same as the position of the change point b2 on the reference line as a new reference change point a0, and the positions of the change points a1 and b1 on the respective lines. Difference Δa and density level difference Δn, and whether the calculated position difference Δa and density level difference Δn are two-dimensional displacements (Δa, Δn) and whether they are within a predetermined range. And a second determination step for determining whether or not the first determination result is negative and the second determination result is positive, the predetermined determination corresponding to the two-dimensional displacement (Δa, Δn). The change point is calculated by obtaining the code V (Δa, Δn) A method for encoding a 1, followed by the change point a1 obtained by coding the new reference change point a0,
A step of repeating the above procedure with the change point a2 as a new change point a1, and when the first determination result is negative and the second determination result is also negative, a specific code H indicating that , A code R (Δa indicating the run length Δa0 from the change points a0 to a1
0) and the code L (Δn0) indicating the density difference Δn0 between the change points a0 and a1, the code R (Δa1) indicating the run length Δa1 from the change points a1 to a2, and the change point a.
The step of encoding the change points a1 and a2 with the code L (Δn1) indicating the density difference Δn1 between 1 and a2, and then the above procedure is repeated with the change point a2 as a new reference change point a0. A multi-valued image data encoding method comprising the steps of: 4. The multivalued image data encoding method according to claim 2, wherein the difference Δa between the positions of the change points a1 and b1.
And the density level difference Δn has a two-dimensional displacement (Δa, Δn) within a predetermined range, the change point a1 is set to the two-dimensional displacement (Δa, Δn). In the code V (Δa, Δn) to be encoded correspondingly, Δa
Is any of the values -3, -2, -1, 0, 1, 2, 3 and the code when Δn = 0 is the standard encoding method for binary black and white MR
A multivalued image data encoding method, which is characterized by matching a code in a vertical mode of a (modified read) code. 5. The multi-valued image data encoding method according to claim 2, 3 or 4, wherein among all the lines to be encoded, the first line and the K-th line thereafter (where K is an integer) ), The column of pixel positions detected as change points on the line is defined as c0, c1, c2, c3, c4 ,, cN (N is an arbitrary integer), these change point sequences c0, c1, c2, c
Let 3, c4 ,,, cN be the run length Δ from the change point cj to cj + 1
The symbol R (Δaj) indicating aj and the symbol L (Δnj) indicating the density difference Δnj between the change points cj and cj + 1 (where j = 0 ,,,
N-1), and the code EOL1 indicating that the code string is added to the head of the code string. 6. Multi-valued image data obtained by scanning an image and sampling in pixel units is taken in, and the minimum density level is white or the maximum density level is black depending on the density level of each pixel data. A step of performing binary quantization, an output step of taking in the multi-valued image data and outputting each pixel data without changing its density level, and a step of taking in the multi-valued image data and selecting a pixel as a target pixel therein Regarding the data, based on the respective density levels of the pixel data and the pixel data located in the periphery of the pixel data, it is possible to determine whether or not the pixel data of interest belongs to a character / line drawing area or not. A step of selecting the binary quantized output when the image area discrimination result is affirmative, and a negative step when the image area discrimination result is negative; When each line of the image data that is the output is used as a coded line, the density level of each line is different from that of the immediately preceding pixel in the scanning order, and the position of a different pixel is detected as a change point. The change point on the conversion line is compared with the change point on the reference line, which is an already encoded line, to obtain the position difference Δa, to obtain the density level difference Δn, and The change point on the encoding line is encoded by obtaining the predetermined code V (Δa, Δn) corresponding to the difference Δa and the difference Δn between the density levels as a two-dimensional displacement (Δa, Δn). A multivalued image data encoding method comprising the steps of: 7. Multi-valued image data obtained by scanning an image and sampling in pixel units is taken in, and the minimum density level is white or the maximum density level is black depending on the density level of each pixel data. A step of performing binary quantization, an output step of taking in the multi-valued image data and outputting each pixel data without changing its density level, and a step of taking in the multi-valued image data and selecting a pixel as a target pixel therein Regarding the data, based on the respective density levels of the pixel data and the pixel data located in the periphery of the pixel data, it is possible to determine whether or not the pixel data of interest belongs to a character / line drawing area or not. A step of selecting the binary quantized output when the image area discrimination result is affirmative, and a negative step when the image area discrimination result is negative; When each line of the image data that is the output is a coded line, the density level of each line is different from that of the immediately preceding pixel in the scanning order, and the position of a different pixel is detected as a change point. At the change point on the encoding line, a reference change point serving as a reference for defining another change point is a0, and the reference change point a0 on the encoding line is viewed in the scanning direction (hereinafter,
Detecting these change points with the first change point being the right side (a1), the first change point on the right side from the change point a1 on the encoding line, and a2, and the already encoded line. On the line, a change point on the right side of the corresponding position of the reference change point a0 and having a density level different from that of the change point a0 is b1, and the first change on the right side of the change point b1 on the reference line. The point is designated as b2, the step of detecting these change points, the step of obtaining the position difference Δa and the density level difference Δn on the respective lines of the change points a1 and b1, respectively, and the obtained position difference Δa. The difference Δn between the concentration levels is used as a two-dimensional displacement (Δa, Δn) to determine whether or not the difference is within a predetermined range, and when the difference is within a predetermined range, the two-dimensional Displacement ( Predetermined code V (Δ) corresponding to Δa, Δn)
a, Δn) to encode the change point a1, and then the encoded change point a1 as a new reference change point a0 and the change point a2 as a new change point a1.
A multi-valued image data encoding method comprising the steps of repeating the above procedure. 8. Multi-valued image data obtained by scanning an image and sampling in pixel units is taken, and the minimum density level is white or the maximum density level is black depending on the density level of each pixel data. A step of performing binary quantization, an output step of taking in the multi-valued image data and outputting each pixel data without changing its density level, and a step of taking in the multi-valued image data and selecting a pixel as a target pixel therein Regarding the data, based on the respective density levels of the pixel data and the pixel data located in the periphery of the pixel data, it is possible to determine whether or not the pixel data of interest belongs to a character / line drawing area or not. A step of selecting the binary quantized output when the image area discrimination result is affirmative, and a negative step when the image area discrimination result is negative; When each line of the image data that is the output is a coded line, the density level of each line is different from that of the immediately preceding pixel in the scanning order, and the position of a different pixel is detected as a change point. At the change point on the encoding line, a reference change point serving as a reference for defining another change point is a0, and the reference change point a0 on the encoding line is viewed in the scanning direction (hereinafter,
Detecting these change points with the first change point being the right side (a1), the first change point on the right side from the change point a1 on the encoding line, and a2, and the already encoded line. On the line, a change point on the right side of the corresponding position of the reference change point a0 and having a density level different from that of the change point a0 is b1, and the first change on the right side of the change point b1 on the reference line. The point where b2 is the point of detection of these change points, and the position of the change point b2 on the line is the change point a.
A first determination step of determining whether or not the position is on the left side of the position of 1 on the line; and, if the first determination result is affirmative, encoding that effect with a specific code P, Subsequently, selecting a pixel position on the coding line that is the same as the position of the change point b2 on the reference line as a new reference change point a0, and the positions of the change points a1 and b1 on the respective lines. Difference Δa and density level difference Δn, and whether the calculated position difference Δa and density level difference Δn are two-dimensional displacements (Δa, Δn) and whether they are within a predetermined range. And a second determination step for determining whether or not the first determination result is negative and the second determination result is positive, the predetermined determination corresponding to the two-dimensional displacement (Δa, Δn). The change point is calculated by obtaining the code V (Δa, Δn) A method for encoding a 1, followed by the change point a1 obtained by coding the new reference change point a0,
A step of repeating the above procedure with the change point a2 as a new change point a1, and when the first determination result is negative and the second determination result is also negative, a specific code H indicating that , A code R (Δa indicating the run length Δa0 from the change points a0 to a1
0) and the code L (Δn0) indicating the density difference Δn0 between the change points a0 and a1, the code R (Δa1) indicating the run length Δa1 from the change points a1 to a2, and the change point a.
The step of encoding the change points a1 and a2 with the code L (Δn1) indicating the density difference Δn1 between 1 and a2, and then the above procedure is repeated with the change point a2 as a new reference change point a0. A multi-valued image data encoding method comprising the steps of: 9. Multi-valued image data obtained by scanning an image and sampling in pixel units, and regarding the pixel data selected as a pixel of interest therein, the pixel data and pixel data located in the periphery thereof, Based on each density level of the
An image area discrimination step of discriminating whether the image belongs to a value image area or a multivalued image area such as a photograph, and the multivalued image data obtained by scanning the image and sampling pixel by pixel is taken in, Using the image area discrimination result, the captured multi-valued image data is set to white, which is the minimum density level, of the image data belonging to the multi-valued image area such as a photograph, and the binary image area such as a character or line drawing. The step of creating a first image data surface with the image data belonging to the same as is, and the same multi-valued image data captured by using the image area discrimination result, Creating a second image data surface in which the image data belonging to the same is left as it is, and the image data belonging to the binary image area such as a character and a line drawing is white which is the minimum density level; Belong to A first encoding step of binary-quantizing image data and encoding the image data by a first encoding method; and image data belonging to the second image data plane, which is different from the first encoding method. A second encoding step of encoding with the second encoding method, and the first image data surface and the second image data surface,
A method for encoding multi-valued image data, comprising the step of alternately transmitting encoded data from a head encoding line. 10. The multi-valued image data encoding method according to claim 9, wherein the second encoding method is the method of claim 1,
2. A multivalued image data encoding method comprising the encoding method described in 2, 3, 4, or 5. 11. The multi-valued image data encoding method according to claim 9 or 10, wherein identification is performed to identify an encoded data sequence by the first encoding method and an encoded data sequence by the second encoding method. A multi-valued image data encoding method, wherein a code is added to the head of each encoded data string. 12. Multi-valued image data obtained by scanning an image and sampling in pixel units, and regarding the pixel data selected as a pixel of interest therein, the pixel data and pixel data located in the periphery thereof, An image area determination step of determining whether or not the pixel data of interest belongs to a character / line drawing area based on each of the density levels of, and if the determination result is affirmative, A binarization processing step of binarizing the pixel data into white, which is the minimum density level, or black, which is the maximum density level, according to the density level; and an image data string binarized by the binarization processing step. Is binary-coded by an MR coding method, and if the determination result is negative, a multi-value coding step of coding the pixel data string by a multi-value coding method, and the binarization Value encoding code string And a step of adding an identification code for identifying an encoding method to the head of each of the multi-level encoded code string, the multi-level image data encoding method. 13. The method for encoding multi-valued image data according to claim 12, wherein the multi-valued encoding step comprises:
A multivalued image data encoding method comprising the multivalued image data encoding method described in 2, 3, 4, or 5. 14. When each line of multi-valued image data obtained by scanning an image and sampling in pixel units is used as an encoding line, the density level of each line is that of the immediately preceding pixel in the scanning order, and Means (4) for detecting the position of different pixels as a change point, and means for comparing the change point on the coding line with the change point on the reference line which is an already coded line to obtain a position difference Δa. (12) and a means (13) for obtaining the difference Δn between the density levels, and a predetermined two-dimensional displacement (Δa, Δn) corresponding to the obtained difference Δa between the positions and the difference Δn between the density levels. A multi-valued image data encoding device comprising: a means (15) for encoding a change point on the encoding line by obtaining a code V (Δa, Δn). 15. When each line of multi-valued image data obtained by scanning an image and sampling in pixel units is used as an encoding line, the density level of each line is that of the immediately preceding pixel in the scanning order, By detecting the position of a different pixel as a change point, a change point on the coding line is a0, a reference change point serving as a reference for defining another change point, and the reference change on the coding line. Seen in the scanning direction from the point a0 (hereinafter,
Means for detecting these first change points a1), the first change point a1 on the right of the change line a1 on the coded line, and a2, and the already encoded line. On the line, a change point on the right side of the corresponding position of the reference change point a0 and having a density level different from that of the change point a0 is b1, and the first change on the right side of the change point b1 on the reference line. The point is set as b2, a means for detecting these change points, a means for respectively obtaining the position difference Δa and the density level difference Δn on the respective lines of the change points a1 and b1, and the obtained position difference Δa. Means for determining whether or not the difference Δn between the concentration levels is within a predetermined range by using the two-dimensional displacement (Δa, Δn) as a displacement, and when the difference is within a predetermined range, the two-dimensional displacement Displacement ( Predetermined code V (Δ) corresponding to Δa, Δn)
a, Δn), means for encoding the change point a1, and then the encoded change point a1 as a new reference change point a0 and the change point a2 as a new change point a1.
A multi-valued image data encoding device comprising: means for repeating the above procedure. 16. When each line of multi-valued image data obtained by scanning an image and sampling in pixel units is used as an encoding line, the density level of each line is that of the immediately preceding pixel in the scanning order, By detecting the position of a different pixel as a change point, a change point on the coding line is a0, a reference change point serving as a reference for defining another change point, and the reference change on the coding line. Seen in the scanning direction from the point a0 (hereinafter,
Means for detecting these first change points a1), the first change point a1 on the right of the change line a1 on the coded line, and a2, and the already encoded line. On the line, a change point on the right side of the corresponding position of the reference change point a0 and having a density level different from that of the change point a0 is b1, and the first change on the right side of the change point b1 on the reference line. The point is defined as b2, and means for detecting these change points and the position of the change point b2 on the line are the change points a
A first determination means (10) for determining whether or not the position is on the left side of the position of 1 on the line, and if the result of the first determination is affirmative, that effect is encoded by a specific code P. And a means for subsequently selecting a pixel position on the coding line that is the same as the position of the change point b2 on the reference line as a new reference change point a0, and on each line of the change points a1 and b1. Means for obtaining the position difference Δa and the concentration level difference Δn, and the obtained position difference Δa and the concentration level difference Δn as a two-dimensional displacement (Δa, Δn), which is within a predetermined range. Second determination means (14) for determining whether or not
When the first determination result is negative and the second determination result is affirmative, a predetermined code V (Δa, Δn) corresponding to the two-dimensional displacement (Δa, Δn) is set. A means for encoding the change point a1 by obtaining, and subsequently, the encoded change point a1 as a new reference change point a0,
Means for repeating the above procedure with the change point a2 as a new change point a1 and a specific code H indicating that when the first determination result is negative and the second determination result is also negative. , A code R (Δa indicating the run length Δa0 from the change points a0 to a1
0) and the code L (Δn0) indicating the density difference Δn0 between the change points a0 and a1, the code R (Δa1) indicating the run length Δa1 from the change points a1 to a2, and the change point a.
A means for encoding the change points a1 and a2 with a code L (Δn1) indicating the density difference Δn1 between 1 and a2, and then the above procedure is repeated with the change point a2 as a new reference change point a0. A multivalued image data encoding device comprising: 17. The multi-valued image data encoding apparatus according to claim 15 or 16, wherein a two-dimensional displacement (Δa, Δ) between a position difference Δa between change points a1 and b1 and a density level difference Δn.
When the determination result for determining whether or not n) is within a predetermined range is affirmative, the change point a1 is set to the two-dimensional displacement (Δa, Δ).
n), in the code V (Δa, Δn) to be encoded, Δa is any value in -3, -2, -1, 0, 1, 2, 3
A multivalued image data coding device, wherein a code when = 0 is matched with a code in a vertical mode of MR (Modified Read) code which is a standard coding method for binary black and white. 18. The multi-valued image data encoding device according to claim 15, 16 or 17, wherein, of all the lines to be encoded, the first line and the K-th line thereafter (where K is an integer). ), The columns of pixel positions detected as change points on the line are c0, c1, c2, c3, c4 ,, cN
(N is an arbitrary integer), these change point sequences c0, c
1, c2, c3, c4,, cN are code R (Δaj) indicating the run length Δaj from the change points cj to cj + 1 and L (j) indicating the density difference Δnj between the change points cj and cj + 1. Δnj) and (where j = 0 ,,, N-1), and adds the code EOL1 to the beginning of this code string to the beginning of this code string. apparatus. 19. Multi-valued image data obtained by scanning an image and sampling in pixel units is taken, and the minimum density level is white or the maximum density level is black depending on the density level of each pixel data. Means for binary quantization (60)
An output unit that takes in the multi-valued image data and outputs each pixel data without changing its density level; and, for the pixel data selected as a pixel of interest in the multi-valued image data, the pixel data and An image area discrimination means for discriminating whether or not the pixel data of interest belongs to a character / line drawing area based on respective density levels of the pixel data located around the pixel area and the pixel data located around the pixel area. If the result is affirmative, the output of the binary quantizing means is selected and passed, and if the result is negative, the selecting means (61) that selects and passes the output of the output means, and the output from the selecting means. When each line of a certain image data is used as a coded line, a density level of each line is different from that of the immediately preceding pixel in the scanning order, and a means for detecting a position of a different pixel as a change point, and a coded line The change point on the reference line, which is an already encoded line, to obtain the position difference Δa, the means to obtain the density level difference Δn, and the obtained position difference. The change point on the coding line is coded by obtaining the predetermined code V (Δa, Δn) corresponding to the difference Δn between Δa and the density level as a two-dimensional displacement (Δa, Δn). A multivalued image data encoding device comprising: a means (15); 20. The multi-valued image data obtained by scanning an image and sampling in pixel units is taken in, and the minimum density level is white or the maximum density level is black depending on the density level of each pixel data. Means for binary quantization (60)
An output unit that takes in the multi-valued image data and outputs each pixel data without changing its density level; and, for the pixel data selected as a pixel of interest in the multi-valued image data, the pixel data and An image area discrimination means for discriminating whether or not the pixel data of interest belongs to a character / line drawing area based on respective density levels of the pixel data located around the pixel area and the pixel data located around the pixel area. If the result is affirmative, the output of the binary quantizing means is selected and passed, and if the result is negative, the selecting means (61) that selects and passes the output of the output means, and the output from the selecting means. When each line of certain image data is an encoded line, the density level of each line is different from that of the immediately preceding pixel in the scanning order, and the position of a different pixel is detected as a change point. A change point on the No. of lines, the reference change point as a reference for defining the other change point a0, than the reference change point a0 on the coding line, as viewed in the scanning direction (hereinafter,
Means for detecting these first change points a1), the first change point a1 on the right of the change line a1 on the coded line, and a2, and the already encoded line. On the line, a change point on the right side of the corresponding position of the reference change point a0 and having a density level different from that of the change point a0 is b1, and the first change on the right side of the change point b1 on the reference line. The point is set as b2, a means for detecting these change points, a means for respectively obtaining the position difference Δa and the density level difference Δn on the respective lines of the change points a1 and b1, and the obtained position difference Δa. Means for determining whether or not the difference Δn between the concentration levels is within a predetermined range by using the two-dimensional displacement (Δa, Δn) as a displacement, and when the difference is within a predetermined range, the two-dimensional displacement Displacement ( Predetermined code V (Δ) corresponding to Δa, Δn)
a, Δn), means for encoding the change point a1, and then the encoded change point a1 as a new reference change point a0 and the change point a2 as a new change point a1.
A multi-valued image data encoding device comprising: means for repeating the above procedure. 21. Multi-valued image data obtained by scanning an image and sampling in pixel units is taken, and the minimum density level is white or the maximum density level is black depending on the density level of each pixel data. Means for binary quantization (60)
An output unit that takes in the multi-valued image data and outputs each pixel data without changing its density level; and, for the pixel data selected as a pixel of interest in the multi-valued image data, the pixel data and An image area discrimination means for discriminating whether or not the pixel data of interest belongs to a character / line drawing area based on respective density levels of the pixel data located around the pixel area and the pixel data located around the pixel area. If the result is affirmative, the output of the binary quantizing means is selected and passed, and if the result is negative, the selecting means (61) that selects and passes the output of the output means, and the output from the selecting means. When each line of certain image data is an encoded line, the density level of each line is different from that of the immediately preceding pixel in the scanning order, and the position of a different pixel is detected as a change point. A change point on the No. of lines, the reference change point as a reference for defining the other change point a0, than the reference change point a0 on the coding line, as viewed in the scanning direction (hereinafter,
Means for detecting these first change points a1), the first change point a1 on the right of the change line a1 on the coded line, and a2, and the already encoded line. On the line, a change point on the right side of the corresponding position of the reference change point a0 and having a density level different from that of the change point a0 is b1, and the first change on the right side of the change point b1 on the reference line. The point is defined as b2, and means for detecting these change points and the position of the change point b2 on the line are the change points a
A first determination means (10) for determining whether or not the position is on the left side of the position of 1 on the line, and if the result of the first determination is affirmative, that effect is encoded by a specific code P. And a means for subsequently selecting a pixel position on the coding line that is the same as the position of the change point b2 on the reference line as a new reference change point a0, and on each line of the change points a1 and b1. Means for obtaining the position difference Δa and the concentration level difference Δn, and the obtained position difference Δa and the concentration level difference Δn as a two-dimensional displacement (Δa, Δn), which is within a predetermined range. Second determination means (14) for determining whether or not
When the first determination result is negative and the second determination result is affirmative, a predetermined code V (Δa, Δn) corresponding to the two-dimensional displacement (Δa, Δn) is set. A means for encoding the change point a1 by obtaining, and subsequently, the encoded change point a1 as a new reference change point a0,
Means for repeating the above procedure with the change point a2 as a new change point a1 and a specific code H indicating that when the first determination result is negative and the second determination result is also negative. , A code R (Δa indicating the run length Δa0 from the change points a0 to a1
0) and the code L (Δn0) indicating the density difference Δn0 between the change points a0 and a1, the code R (Δa1) indicating the run length Δa1 from the change points a1 to a2, and the change point a.
A means for encoding the change points a1 and a2 with a code L (Δn1) indicating the density difference Δn1 between 1 and a2, and then the above procedure is repeated with the change point a2 as a new reference change point a0. A multivalued image data encoding device comprising: 22. The multi-valued image data obtained by scanning an image and sampling in pixel units is taken in, and for the pixel data selected as a pixel of interest therein, the pixel data and pixel data located in the periphery thereof, An image area discriminating means for discriminating whether the pixel data of interest belongs to a binary image area such as a character / line drawing or a multivalued image area such as a photograph based on the respective density levels of , The multi-valued image data obtained by scanning the image and sampling in pixel units is taken in, and the multi-valued image data taken in is taken in by using the result of the discrimination by the image area discrimination means. Image data belonging to the value image area is white, which is the minimum density level, and means for creating a first image data surface in which the image data belonging to the binary image area such as a character / line drawing is left unchanged; Using the discrimination result by the region discriminating means, the same multi-valued image data that has been captured is left in the same multi-valued image region such as a photograph, but remains in the binary image region such as a character or line drawing. Image data has a minimum density level of white, and means for creating a second image data surface, and image data belonging to the first image data surface is binary-quantized and encoded by the first encoding method. A first encoding means; a second encoding means for encoding the image data belonging to the second image data surface by a second encoding method different from the first encoding method; For the first image data surface and the second image data surface,
A multivalued image data encoding device, comprising: means for alternately transmitting encoded data from a head encoding line. 23. The multi-valued image data encoding device according to claim 22, wherein the second encoding means comprises:
A multivalued image data encoding device comprising the encoding means described in 4, 15, 16, 17, or 18. 24. The multi-valued image data encoding device according to claim 22 or 23, which identifies a coded data string by the first coding means and a coded data string by the second coding means. A multi-valued image data encoding device, wherein a code is added to the head of each encoded data string. 25. Multi-valued image data obtained by scanning an image and sampling in pixel units is taken in, and for the pixel data selected as a pixel of interest therein, the pixel data and pixel data located in the periphery thereof, Image area discrimination means for discriminating whether or not the pixel data of interest belongs to a character / line drawing area based on each density level of the pixel data, and if the discrimination result is affirmative, A binarization processing unit that binarizes the pixel data into white, which is the minimum density level, or black, which is the maximum density level, according to the density level; and an image data string binarized by the binarization processing unit. Is binary-coded by an MR coding system, and a multi-level coding unit that codes the pixel data string by a multi-level coding system when the determination result is negative, and the binary coding unit. Binarized by And a means for adding an identification code for identifying an encoding method to the head of each of the binary coded code string and the multi-valued coded string multi-valued coded by the multi-valued coding means. A multi-valued image data encoding device characterized. 26. The multi-valued image data encoding device according to claim 25, wherein the multi-valued encoding means comprises:
A multivalued image data encoding device comprising the multivalued image data encoding means described in 4, 15, 16, 17, or 18. 27. A multi-valued image data decoding step of decoding M-levels (where M is an integer) encoded multi-valued image data captured via a storage medium or a transmission medium, and the multi-valued image. The multi-valued image of M gradations decoded in the data decoding step is requantized into N gradations (where N is an integer, N ≦ M), and the quantization error at that time is quantized by the pixels around the target pixel. To match the average density levels before and after quantization.
A value error diffusion step, and when the gradation expression number n per pixel of the multivalued image display or printing means is n ≦ M, the requantization of the N value error diffusion step is performed corresponding to the gradation expression number n. A multi-valued image data restoration method, characterized in that the number of gradations for quantization is set to n, and the decoded multi-valued image of M gradations is re-quantized to n gradations. 28. A multi-valued image data decoding step for decoding M-levels (where M is an integer) encoded multi-valued image data captured via a storage medium or a transmission medium, and the multi-valued image. The multi-valued image of M gradations decoded in the data decoding step is requantized into N gradations (where N is an integer, N ≦ M), and the quantization error at that time is quantized by the pixels around the target pixel. To match the average density levels before and after quantization.
When the number of gradation representations per pixel nd of a display for displaying a multi-valued image and the number of gradation representations per pixel np of a printer for printing a multi-valued image are different and both are M or less. When reproducing a multi-valued image on a display, the number of gradations for requantization in the N-value error diffusion step is set to nd, and when reproducing a multi-valued image on a printer, requantization in the N-value error diffusion step is performed. A multi-valued image data restoration method, wherein the number of gradations for quantization is np, and the M-valued multi-valued image decoded in the multi-valued image data decoding step is requantized. 29. Multivalued image data decoding means (6) for decoding M gradation (where M is an integer) encoded multivalued image data taken in via a storage medium or a transmission medium.
8) and requantizing the multi-valued image of M gradations decoded by the multi-valued image data decoding means into N gradations (where N is an integer, N ≦ M), and a quantization error at that time To the pixels around the pixel of interest to match the average density levels before and after quantization N
Value error diffusion means (69), and when the gradation expression number n per pixel of the multivalued image display or printing means is n ≦ M, the N value error diffusion is performed corresponding to the gradation expression number n. A multivalued image data restoration device, wherein the number of requantization gradations of the means is set to n, and the decoded multivalued image of M gradations is requantized to n gradations. 30. A multi-valued image data decoding means (6) for decoding M-level (where M is an integer) encoded multi-valued image data fetched via a storage medium or a transmission medium.
8) and requantizing the multi-valued image of M gradations decoded by the multi-valued image data decoding means into N gradations (where N is an integer, N ≦ M), and a quantization error at that time To the pixels around the pixel of interest to match the average density levels before and after quantization N
A value error diffusion means (69), a display (70) for displaying a multi-valued image, and a printer (71) for printing the multi-valued image are provided, and the gradation representation number nd per pixel of the display and the When the number of gradation representations np per pixel of the printer is different and both are M or less, and when a multi-valued image is reproduced on the display, the number of gradations for requantization of the N-value error diffusion means is nd.
In the case of reproducing a multi-valued image with a printer, the number of requantization gradations of the N-value error diffusion means is set to np, and multi-valued M gradations decoded by the multi-valued image data decoding means, respectively. A multivalued image data restoration device characterized in that an image is requantized.