JPH10215380A - Image decoder and image decoding method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce increment of a memory capacity for an area discrimination signal. SOLUTION: Image data read by a scanner 1201 are A/D-converted, image processing such as gamma conversion is conducted, a character area is discriminated with a character area discrimination part 1204 to output a discrimination signal of every pixel. A gradation processing part 1205 conducts gradation processing by switching the processing from the image data and the discrimination signal. In the case of outputting a decoded image after compressing and storing the image data, the image data and an area discrimination signal are compressed and stored. Then the image storage part 1206 extends the image data and the area discrimination signal to output. In this case, a signal changeover part is connected to positions A, D, and the image data after extension are supplied to an image output part and a phase output part and the area discrimination signal after extension is supplied to the phase output part 1209. The phase output part 1209 outputs phase data of every pixel from the image data and the area discrimination information. The image output part 1210 switches a phase for every image and prints out the image data based on the phase data to output the image.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a digital copying machine having an image data storage unit for compressing and storing image data by block coding and an image filing system, and is used for image quality correction in an image output unit. The present invention also relates to a technique for embedding and storing an image area determination signal in a compressed signal.

[0002]

2. Description of the Related Art Image processing apparatuses that handle image data as digital signals, such as digital copying machines and image filing systems, have been widely used in offices and homes. FIG. 1 schematically shows the configuration of a digital copying machine among such image processing apparatuses. As shown in FIG. 1, the digital copying machine
Scanner 101, A / D conversion unit 102, image processing unit 10
3. An image output unit 104 is provided. The image data is read by the scanner 101, converted into a digital signal by the A / D conversion unit 102, and subjected to image processing such as gamma conversion and image quality correction by the image processing unit 103. The output unit 104 prints image data on paper for each pixel, and outputs an image.

FIG. 2 shows a configuration of the image output unit 104. As shown in FIG. 2, the image output unit 104
Then, a laser is output from the LD unit 202 in response to a signal from the image processing unit 201. This laser is reflected on a polygon mirror 204 through a cylinder lens 203, and the light reflected on the polygon mirror 204 is irradiated on a photoconductor 206 through an fθ lens 205 for optical path difference correction. Then, by rotating the polygon mirror 204 and scanning with the laser beam, the photosensitive member 2 is line by line.
Image data is written on the address 06.

FIGS. 3, 4 and 5 show a method for controlling the pixel density. Normally, the control of the pixel density is performed by changing the pulse width of a signal for controlling the width of the laser output with respect to the density value of each pixel as shown in FIG. By the way, in the method shown in FIG. 3, pixels are separated from each other at an edge portion of a thin line or a character perpendicular to the main scanning.
It will stand out as noise. As a method for reducing noise in such a case, as shown in FIG. 4, phase information is added to each pixel to change the position of the pixel. Since the phase information for noise reduction is used to change the control depending on the edge of the image, it is added in consideration of the values of the pixels (D-1) and D1 before and after the pixel D0 to which the phase information is added. . That is, as shown in FIG.
Pixels (D-1) before and after the pixel D0 to which the phase information is added,
From the value of D1, if (D-1) -D1> 64, the phase is the front side, if | (D-1) -D1 | ≤64, the phase is the center, (D
-1) If -D1 <-64, each phase information is added so that the phase is on the rear side.

In such a digital copying machine, a large number of gradations are shown with a small number of output gradations in a picture portion other than a character portion and a halftone dot portion. It is common to use a gradation process such as a method. Therefore, when the phase processing described with reference to FIGS. 4 and 5 is performed at the time of output, the image quality can be improved for lines and character image portions, but it can be improved for picture portions and halftone portions other than characters. If the phase processing is performed, the arrangement of the pixels due to the gradation processing is destroyed, which causes deterioration of the image quality. Therefore, it is better to fix the phase information. For this reason, the method of changing the phase based on the density information as shown in FIG. 5 is adopted in the line or character image portion, and the pulse width is simply fixed at a fixed phase in the picture portion or halftone portion where the gradation processing is performed. In other words, it is necessary to switch the method according to the content of the image to be output.

Therefore, it is necessary to determine the character area of the image, and the image processing unit 103 (FIG. 1) performs area determination. Switch processing. FIG. 6 is a block diagram illustrating a part for determining an area in the image processing unit 103. FIG. 7 exemplifies image data composed of characters, pictures, and halftone dots. As shown in FIG.
The image signal is sent to a character area determination unit 601 and a gradation processing unit 602.
Is input to The character area input unit 601 performs area determination on the input image signal using pattern matching or the like, and displays area determination information “1” in a character area 702 as shown in FIG. Region determination information “0” is added to the region including the region 701 for each pixel.
The area determination information for each pixel is input to the gradation processing unit 602 and the phase output unit 603, and the gradation processing unit 602 switches the gradation processing, and the phase output unit 603 switches the phase control. Based on the signal of the phase output unit 603, the image output unit 604 (104) switches the phase and outputs an image optimal for the image area.

By the way, in a copying machine or the like that handles an image as a digital signal, it is possible to store the image in a memory. By storing the image data in the memory, the image once captured can be reused many times, or the input / output address can be changed, and processing and editing such as image rotation can be performed. However, the amount of information of the image is large, and if it is stored in the memory as it is, a large amount of memory is required. Since the unit price of the memory is high, the overall cost becomes high.

Therefore, if the image data is compressed and stored in the memory, the amount of memory can be reduced and the cost can be reduced. FIG. 8 to FIG. 11 show a block encoding system which is an image data compression system.
In the block coding method, as shown in FIG. 8, an image is decomposed into blocks and a 1-byte density value Lij in the block is divided.
Is compressed into an average value La (1 byte), a gradation width index La (1 byte), and a gradation quantization code φij (2 bits × 16) for each pixel by the algorithm shown in FIG. . Qj in FIG. 9 is a representative quantization value at the time of decoding, and as shown in FIG. 10, is a density value assigned to each code at the time of decoding. With this encoding method, as shown in FIG. 11, the data amount of 16 bytes of a 4 × 4 pixel block of 1 byte of pixels becomes 6 bytes, and the data amount can be compressed to ／.

[0009]

When image data is compressed in an image processing apparatus such as a digital copying machine or an image filing system that performs phase control when outputting an image, and the image is stored in a memory, the compression is performed. In addition to the obtained image data, an area for storing area determination information such as a character area is required. However, since the area determination information relating to the area such as a character is attached to each pixel, there is a problem that the amount of memory to be stored for storing the area determination information becomes very large. Was.

Therefore, the present invention has been made to solve the above-mentioned problems of the prior art, and an image decoding apparatus and an image decoding apparatus capable of reducing an increase in the amount of memory for an area determination signal. It is an object to provide a decoding method.

[0011]

According to the present invention, block data is generated by decomposing each of the multi-gradation pixel data forming the image data into a predetermined number, and each pixel of the block data is generated. Is encoded into compressed data including a 2-bit gradation quantization code, average data, and a gradation width index, and it is determined whether or not the image data is a character image, and based on the determination result, A binary area determination signal is output for each pixel. If the area determination signal is a determination signal of a character area in the block data, 0 is set. If the block data includes a determination signal other than the character area in the block data, 1 is set. If the block data contains a determination signal other than the character area in the block data, it is inserted in the lower bit of the 2-bit gradation quantization code by inserting it into the least significant bit of either the average data of the compressed data or the gradation width index. An apparatus for decoding code data including area information of a character image generated by inserting an area determination signal for each character, comprising: Code identifying means for identifying lower bits and identifying whether or not the block data includes only data of a character area. When the code identifying means identifies that the data includes only a character area, an area determination signal is transmitted. If all are determined to be character area determination signals, and if it is determined that an area other than the character area is included, the lower bits of the 2-bit gradation quantization code are used as the area determination signal, and the lower bits are replaced with code data and area. A determination signal separating means, average data which is code data separated by the code data and area determination signal separating means, a gradation width index, and a 2-bit gradation quantization code for each pixel; Decoding means for decoding, it is provided in the image decoding apparatus to achieve the above objectives. According to the invention described in the claims, each of the multi-gradation pixel data forming the image data is decomposed into a predetermined number to generate block data, and the density data for each pixel of the block data is converted into 2-bit gradation quantum data. While encoding into compressed data consisting of an encoded code, average data, and a gradation width index, it is determined whether or not the image data is a character image, and a binary area determination signal for each pixel is determined based on the determination result. If the area determination signal includes a determination signal other than the character area in the block data, 0 is set, and if the block data includes a determination signal of only the character area in the block data, 1 is set. If the determination signal other than the character area is included in the block data, the area determination signal for each pixel is inserted into the lower bit of the 2-bit gradation quantization code. An apparatus for decoding code data including area information of a character image generated by performing the above-described processing, wherein the average data of the code data or the least significant bit in which the information is inserted with the gradation width index is identified. Code identification means for identifying whether or not data other than a character area is included in the block data, and when the code identification means identifies that the data area includes an area other than the character area, all the area determination signals are sent out of the character area. When it is determined that the signal includes a character area signal, the lower bits of the 2-bit gradation quantization code are used as an area determination signal, and the lower bits are code data to be replaced with 0, and area determination signal separation means. A decoding means for decoding the code data, the average data which is the code data separated by the area determination signal separating means, the gradation width index, and the 2-bit gradation quantization code into density data for each pixel. If, to achieve the object by comprising the image decoding apparatus. In the invention according to claim 3, each of the multi-gradation pixel data forming the image data is decomposed into a predetermined number to generate block data,
While the density data for each pixel of the block data is encoded into compressed data including a 2-bit gradation quantization code, average data, and a gradation width index, it is determined whether the image data is a character image, A binary area determination signal is output for each pixel based on this determination result. If the area determination signal is a determination signal for a character area in the block data, a 2-bit signal 00 is output. The 2-bit signal 01 is used for the determination signal other than the area, and the 2-bit signal 11 is used for the mixed data including the character area and the non-character area in the block data. One of the lower 2 bits, or
The bit is inserted into the least significant bit of both the average data and the gradation width index one bit at a time. An apparatus for decoding code data including area information of a character image generated by inserting an area determination signal for each character, and identifying an average data of the code data or a 2-bit signal included in a gradation width index. A code identifying means for identifying whether the block data includes only a character area, does not include a character area at all, or includes a character area and data other than a character area; When it is determined that all the area determination signals include the character area only, the area determination signal is determined to include only the character area. If it is determined that the character area and the other area are mixed, the lower bits of the 2-bit gradation quantization code are used as the area determination signal, and the lower bits are code data to be replaced with 0. Signal separating means, average data, which is code data separated by the code data and area determination signal separating means, and a gradation width index;
The object is achieved by providing a decoding means for decoding a bit gradation quantization code into density data for each pixel and an image decoding apparatus. According to the present invention, block data is generated by decomposing each of the multi-gradation pixel data forming the image data into a predetermined number, and the density data for each pixel of the block data is converted into 2-bit gradation data. While encoding into compressed data including the quantization code, the average data, and the gradation width index, it is determined whether or not the image data is a character image, and a binary area determination signal for each pixel is determined based on the determination result. Is output, and when the area determination signal is a determination signal of a character area in the block data, 0 is set, and when the block data includes a determination signal of a non-character area in the block data, 1 is set. Insert into the least significant bit of either indicator,
If the block data includes a determination signal other than a character region, code data including region information of a character image generated by inserting a region determination signal for each pixel into lower bits of a 2-bit gradation quantization code A method of decrypting
The average data of the code data or the least significant bit in which the information is inserted with the gradation width index is identified by the code identification means as to whether or not the block data includes data of only the character area, and the code identification means. If it is determined that only the character area is included, the code data and the area determination signal separating means use all the area determination signals as the determination signal of the character area. The lower bits of the tone quantization code are used as an area determination signal, and the lower bits are replaced with 0, and the code data, average data which is code data separated by the area determination signal separation means, a gradation width index, and a 2-bit scale are used. The above object is achieved by decoding the tone quantization code into density data for each pixel by a decoding means. According to the fifth aspect of the present invention, each of the multi-gradation pixel data forming the image data is decomposed into a predetermined number to generate block data, and the density data for each pixel of the block data is converted into 2-bit gradation data. While encoding into compressed data including the quantization code, the average data, and the gradation width index, it is determined whether or not the image data is a character image, and a binary area determination signal for each pixel is determined based on the determination result. Is output, and when the area determination signal includes a determination signal other than the character area in the block data, 0 is set. If the block width data is inserted into one of the least significant bits of the tone width index and the block data includes a determination signal other than the character area, the area determination signal for each pixel is inserted into the lower bit of the 2-bit tone quantization code. A method of decoding encoded data including the area information of the generated character image by,
The average data of the code data or the least significant bit in which the information is inserted by the gradation width index is used to identify whether or not the block data includes data other than the character area in the block data. If it is determined that the region includes a region other than the character region, the code data is determined by the region determination signal separating means as a determination signal other than the character region. The lower bits of the gradation quantization code are used as an area determination signal, and the lower bits are replaced with 0, and the code data, average data that is code data separated by the area determination signal separation means, a gradation width index, and 2 bits The above object is achieved by decoding the gradation quantization code of (1) into density data for each pixel by a decoding means. According to the sixth aspect of the present invention, each of the multi-gradation pixel data forming the image data is decomposed into a predetermined number to generate block data, and the density data for each pixel of the block data is converted into 2-bit gradation data. While encoding into compressed data including the quantization code, the average data, and the gradation width index, it is determined whether or not the image data is a character image, and a binary area determination signal for each pixel is determined based on the determination result. Is output. If the area determination signal is a determination signal for all character areas in the block data, a 2-bit signal 00 is output.
If the block data includes a character area and a determination signal other than the character area in the block data, the 2-bit signal 11 is set to the lower 2 bits of either the average data of the compressed data or the gradation width index.
If the bit or the least significant bit of both the average data and the gradation width index is inserted one bit at a time, and if the block data includes a character area and a judgment signal other than the character area, the gradation quantization code A method for decoding code data including region information of a character image generated by inserting a region determination signal for each pixel into lower bits, wherein the average data of the code data or two bits included in a gradation width index are included. Is identified by the code identification means, and all the character area only in the block data, or no character area is included, or character area and data other than the character area are identified.
When the code identifying means is identified as including only the character area only, the code data, the area determination signal separating means determines the area determination signal as the determination signal of only the character area, and is determined not to include the character area at all. When the area determination signal is determined to be a determination signal for only the area other than the character area, and when it is determined that the character area and the other area are mixed, the lower bits of the 2-bit gradation quantization code are defined as the area determination signal, The lower bits are replaced with 0, and the decoding means converts the above-mentioned code data, the average data which is the code data separated by the area determination signal separation means, the gradation width index, and the 2-bit gradation quantization code into density data for each pixel. The above purpose is achieved by decoding.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment in which an image decoding apparatus and an image decoding method according to the present invention are applied to a digital copying machine will be described below in detail with reference to FIGS. (1) Overview of Embodiment In this embodiment, the area determination signal is incorporated into the image compression data by the block coding method, and the data amount of the area determination signal is absorbed to reduce the amount of memory for storing the area determination information. It is to suppress the increase.

(2) Details of Embodiment (a) First Embodiment This embodiment relates to decoding, but for convenience of explanation, an encoding method for generating encoded data to be decoded will first be described. explain. FIG. 12 shows the configuration of a digital copying apparatus using blocks. First, a case in which an image is output without being stored in the image storage unit 1206 will be described. First, image data is read by a scanner 1201, converted into a digital signal by an A / D converter 1202, subjected to image processing such as gamma conversion by an image processor 1203, and supplied to a character area / area determiner 1204 and a gradation processor 1205. I do. The character area determination unit 1204 determines a character area from the supplied image data, and supplies a determination signal for each pixel to the gradation processing unit 1205, the image storage unit 1206, and the signal switching unit 1208.
The gradation processing unit 1205 performs gradation processing by switching gradation processing based on the supplied image data after image processing and the determination signal, and performs image processing unit 1206 and signal switching unit 1
270. Since the image storage unit 1206 does not store an image, the storage processing of the supplied image data and the determination signal is not particularly performed.

Here, since no image is stored in the image storage unit 1206, the signal switching unit 1207 is switched to B,
The signal switching unit 1208 is connected to the C side. Thereby, the image output unit 1210 and the phase output unit 1209 have:
Image data is supplied from the gradation processing unit 1205. The phase output unit 1209 is directly supplied with an area determination signal for identifying the character area obtained by the area determination unit 1204, and creates phase data for each pixel based on the area determination information and the image data, and outputs the phase data. It is supplied to the image output unit 1210. The phase data is created from the pixels (D-1) and D1 before and after the target pixel D0, for example, by the method described with reference to FIG. In the image output unit 1210, the gradation processing unit 12
Image data supplied from the phase output unit 1209
The printing is performed by switching the phase for each image based on the phase data supplied from the printer, and the image is output.

Next, a case where image data is compressed and stored in the image storage unit 1206, decoded, and an image is output will be described. In this case, the operation when the image data read by the scanner 1201 is first output from the image output unit is:
This is performed in the same manner as when no image data is stored. That is, the signal switching units 1207 and 1208 are connected to the B and C sides, perform printing based on the image data from the gradation processing unit 125, and output an image. In parallel with this process,
In the image storage unit 1206, the image data supplied from the gradation processing unit 1205 and the area determination signal supplied from the character area determination unit 1204 are compressed and stored by a method described later. When the information of one page is stored, the image storage unit 1206 outputs the image data and the area determination signal after being expanded.

At this time, the signal switching units 127 and 128 are connected to the A and D sides, and the image data expanded by the image storage unit 1206 is transmitted to the image output unit 1210 and the phase output unit 1209 via the signal switching unit 1207. The supplied and expanded region determination signal is supplied to the phase output unit 1209 via the signal switching unit 128. The phase output unit 1209 creates phase data for each pixel from the image data and the area determination information supplied from the image storage unit 1206, and supplies the phase data to the output image output unit 1210. Image output unit 1
In 210, the image data supplied from the image storage unit 1206 is printed by switching the phase for each image based on the phase data supplied from the phase output unit 1209.
Output an image.

Next, a characteristic part of the present embodiment in which the code data and the area determination signal are combined in the image storage unit 1206 will be described in detail with reference to FIG. As shown in FIG. 13, in the image storage unit 1206, the gradation processing unit 1
The image data supplied from 205 is a 4-line FIFO
After the data for four lines is stored once in 1301, the data is encoded for each 4 × 4 pixel block in the encoding unit 1302, and the data of La, Ld, and φij are output and supplied to the area determination signal combining unit 1304. Is done. On the other hand, the area determination signal supplied from the character area determination unit 1204 is stored in the binary 4-line FIFO 1303 for four lines, and then is input to the area determination signal synthesis unit 1304 by the area determination signal for each 4 × 4 pixel block. Is supplied to the area determination signal combining unit 1304.

In the area determination signal synthesis unit 1304, 4 × 4
The area determination signal for each block is combined with the image data supplied from the encoding unit 1302 for each block. The synthesis of the area determination signal and the image data is performed for each block of 4 × 4 pixels, and the method is as shown in FIG.
In FIG. 15, the area signal of the character area is set to 1 and the area signal of the other areas is set to 0 as the area determination signal in the square of FIG.
In the case of a block of 4 × 4 pixels and all character regions as in (A), the region information bit b0 in the block is set to 0. In this case, the 2-bit gradation quantization code φij for each pixel is directly stored in the memory. Is stored. Further, as shown in FIG. 15B, in the case of a block of 4 × 4 pixels and the area signal in the block includes a non-character area, the area information bit b0 in the block =
The lower one bit of the 2-bit gradation quantization code φij for each pixel is replaced with the area determination signal at the corresponding position. The intra-block area information bit b0 is stored in the least significant bit of one byte of La or Ld as shown in FIG. By inserting the area determination signal in this manner, the area signal can be combined with the code data and stored in the memory 1305 without increasing the data amount.

A case where the code generated in this way is decoded in the image storage unit 1206 will be described with reference to FIG. As shown in FIG. 16, when decoding, the code data for each block including the information of the area determination signal is read from the memory 1605 (1305), and the area determination signal separation unit 1604 separates the code data and the area determination signal. I do. FIG. 17 is a flowchart showing the operation of the area determination signal separation processing in area determination signal separation section 1604. As shown in FIG. 17, first, the area determination signal separation unit 1604 reads the code data from the memory 1605 in units of 6 bytes (step 1701). Next, the in-block area information bit b0 stored in the least significant bit of La or Ld is referred to (step 170).
2) If b0 = 1 (step 1702; yes),
The lower bits of φij are separated as an area determination signal (step 1703), and then 0 is inserted into the lower bits of φij (step 1704). On the other hand, if the intra-block area information bit b0 stored in the least significant bit of La or Ld is b
When 0 = 0 (step 1702; no), φij is left as it is, and the area determination signal in the block is set to 1 indicating that all the areas are character areas (step 1705).

In this manner, the area determination signal separating section 160
In 4, after separating the code data and the area determination signal,
The code data is decoded into image data for each block by a decoding unit 1602, and stored in a 4-line FIFO 1601.
Image data is arranged in units of four lines of main scanning. The area determination signal separated by the area determination signal separation unit 1604 is 2
The value is stored once in the 4-line FIFO 1603 and output in correspondence with the image data.

As described above, according to the first embodiment,
A good image can be obtained by decoding the code data obtained by synthesizing the area determination signal and performing image processing through each area with reference to the area determination signal. Further, since the area determination signal is stored in the least significant bit of La or Ld of the code data, there is almost no effect on the decoded image. However, according to this method, when the area signal in the block is a 4 × 4 pixel block and includes a non-character area, the gradation quantization code φij has only 1-bit information, so that the image quality of a part other than the character is slightly degraded. This is a method that gives priority to the image quality of characters.

(B) Second Embodiment The second embodiment relates to a method of giving priority to image quality other than characters. First, the encoding method differs from the first embodiment in which the image quality of characters is prioritized only in the processing of the area determination signal combining unit 1304, and therefore only that part will be described. As shown in FIG. 18, in the area determination signal synthesis unit 1304, the area determination signal and the image data are combined as shown in FIG. Is set to 0, and in the case of a block of 4 × 4 pixels and all non-character areas as shown in FIG. 18A, the area information bit b0 in the block is set to b0 = 0. Key quantization code φ
ij is stored in the memory as it is. FIG.
When the area signal in the block includes a character area in a block of 4 × 4 pixels as in (B), the area information bit b0 in the block is set to 1 and the lower order of the 2-bit gradation quantization code φij for each pixel is set. One bit is replaced with the area determination signal at the corresponding position. The intra-block area information bit b0 is
It is stored in the least significant bit of one byte of La or Ld as shown in FIG. By inserting the area determination signal in this manner, the area signal can be combined with the code data without increasing the data amount.

The case where the code thus generated is decoded in the image storage unit 1206 will be described. In the decoding processing according to the second embodiment, the only difference from the first embodiment that prioritizes the image quality of characters is the area determination signal separation unit 1604 shown in FIG. The processing will be described. FIG.
9 is a flowchart illustrating the operation of the area determination signal separation processing in the area determination signal separation unit 1604. First, the area determination signal separation unit 1604 reads the code data from the memory 1605 in units of 6 bytes (step 19).
01). Next, the in-block area information bit b0 stored in the least significant bit of La or Ld is referred to (step 1902). If b0 = 1 (step 1902; yes)
s), the lower bits of φij are separated as an area determination signal (step 1903), and then 0 is inserted into the lower bits of φij (step 1904). On the other hand, when b0 = 0 (step 1902; no), φij is left as it is, and the area determination signals in the block are all set to 0 indicating that they are non-character areas (step 1905).

Thus, according to the second embodiment,
A good image can be obtained by decoding the code data obtained by synthesizing the area determination signal and performing image processing suitable for each area with reference to the area determination signal. However, according to this method,
If the area signal in the block is a × 4 pixel block and includes a character area, the gradation quantization code φij has only 1-bit information, so the image quality of the character area may be slightly degraded. It can be said that this method gives priority to the image quality of the picture area and the halftone dot area.

(C) Third Embodiment Next, a third embodiment will be described. In the third embodiment, the image quality of a character or non-character area is not prioritized.
The area determination signal is synthesized equally in the non-character area. Also in the third embodiment, the encoding method differs from the first embodiment in which the image quality of characters is prioritized only in the processing of the area determination signal combining unit 1304, and therefore only that part will be described. As shown in FIG. 21, the area determination signal and the image data are synthesized by the area determination signal synthesis unit 1304. As shown in FIG. Is set to 0, and as shown in FIG. 21A, in the case of a block of 4 × 4 pixels and all of the character area, the area information bits b1 = 0 and b0 = 0 in the block are set to 2 bits. The 2-bit gradation quantization code φij is stored in the memory as it is. In the case of a block of 4 × 4 pixels and all non-character areas as shown in FIG. 21B, the area information bits b1 = 0 and b0 = 1 in the block are set to 2 bits. Is stored in the memory as it is. Further, as shown in FIG.
In the case of a × 4 pixel block, if a region signal in a block includes both a character region and a non-character region, the two-bit region information bits b1 = 1 and b0 = 1 in the block, and a 2-bit gradation for each pixel The lower one bit of the quantization code φij is replaced with the area determination signal at the corresponding position. As shown in FIG. 20, the in-block area information bits b1 and b0
It is stored in the least significant two bits of one byte of a or Ld, or divided into the least significant one bit of both La and Ld. By inserting the area determination signal in this manner, the area signal can be combined with the code data without increasing the data amount.

A case where the code generated in this way is decoded in the image storage unit 1206 will be described. In the decoding process according to the third embodiment, the only difference from the first embodiment in which the image quality of characters is prioritized is the region determination signal separation unit 1604 shown in FIG. The processing will be described. FIG.
2 is a flowchart showing the operation of the area determination signal separation processing in the area determination signal separation unit 1604. First, the area determination signal separating unit 1604 reads the code data from the memory 1605 in units of 6 bytes (step 21).
01). Next, the in-block area information bits b0 and b1 stored in the lower two bits of La or Ld are referred to (steps 2102 and 2103). When b0 = 0 (step 2102; no), φij is left as it is. , The area determination signals in the block are all set to 1 indicating that they are character areas (step 2104). On the other hand, b1 =
0 (step 2102; yes, step 210)
3; no), φij is left as it is, and the area determination signals in the block are all set to 0 indicating that the area is a non-character area (step 2105). If b1 = 1 (step 2102; yes, step 2103; no), φij
Are separated as an area determination signal (step 2).
106) Then, 0 is inserted into the lower bits of φij (step 2107). Thus, according to the third embodiment, a good image can be obtained by decoding the code data in which the area determination signal is synthesized, and performing image processing that passes through each area with reference to the area determination signal. Can be

In this method, as shown in FIG.
In a part where a character area and a non-character area coexist, the gradation quantization code φij has only 1-bit information. In such an area, the image quality is slightly degraded. Less, deterioration is not so noticeable. Further, since 2 bits of the information of La and Ld are used as the in-block area information bits, the image data at the time of decoding is affected, but the image quality is hardly noticeable.

[0028]

According to the first and fourth aspects of the present invention, since it is not necessary to separately store and transmit the compressed data and the area determination signal, the total data amount increases. Therefore, the size of the memory for storing the compressed data can be reduced, and the transmission time of the compressed data can be reduced. Compare the code information of the area other than the character area with the character area,
Since it is often used for embedding an area determination signal, it is more effective when obtaining image quality with priority on a character area. According to the second and fifth aspects of the present invention, since it is not necessary to separately store and transmit the compressed data and the area determination signal, the total data amount does not increase and the compressed data and the area determination signal do not increase. Has the effect of contributing to downsizing of the memory for storing the data and shortening of the transmission time of the compressed data. Since the code information of the character area is used more frequently for embedding the area determination signal than the area other than the character area, it is more effective when obtaining the image quality with priority on the area other than the character area. According to the third and sixth aspects of the present invention, since it is not necessary to separately store and transmit the compressed data and the area determination signal, the total data amount does not increase, and the compressed data and the area determination signal do not increase. Has the effect of contributing to downsizing of the memory for storing the data and shortening of the transmission time of the compressed data. Since the code information of the character region and the code information of the region other than the character region are equally used for embedding the region determination signal, it is effective when the image quality of the character region and the region other than the character region is not particularly given priority. .

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a digital copying machine to which an image decoding device is applied.

FIG. 2 is a configuration diagram of an image output unit of the digital copying machine;

FIG. 3 is an explanatory diagram of a pixel density control by changing a pulse width of a signal for controlling a laser output width with respect to a density value of each pixel;

FIG. 4 is an explanatory diagram of a case where noise is reduced by adding phase information for each pixel and changing the position of the pixel.

FIG. 5 is an explanatory diagram showing a calculation formula for determining phase information.

FIG. 6 is a block diagram of a part for determining an area in the image processing unit.

FIG. 7 is an explanatory diagram illustrating an example of image data including characters, pictures, and halftone dots;

FIG. 8 is an explanatory diagram of the same as the above, for a block coding method.

FIG. 9 is an explanatory diagram showing an algorithm in the block coding method.

FIG. 10 is an explanatory diagram of a density value assigned to each code at the time of decoding.

FIG. 11 is an explanatory diagram showing the degree of compression of the data amount by the encoding method.

FIG. 12 is a block diagram of a digital copying apparatus to which the image decoding apparatus according to the embodiment of the present invention is applied.

FIG. 13 is a block diagram of a portion that combines code data and an area determination signal in the image storage section of the digital copying machine.

FIG. 14 is an explanatory diagram showing a storage location of an in-block area information bit b0 in the digital copying machine.

FIG. 15 is an explanatory diagram of combining an area determination signal and image data in the digital copying machine.

FIG. 16 is a block diagram of a decoding part in an image storage unit of the digital copying machine.

FIG. 17 is a flowchart showing the operation of the area judgment signal separation processing in the area judgment signal separation section of the digital copying machine.

FIG. 18 is an explanatory diagram of a combination of an area determination signal and image data in the digital copying machine according to the second embodiment.

FIG. 19 is a flowchart illustrating the operation of the area determination signal separation process in the area determination signal separation unit according to the second embodiment.

FIG. 20 is an explanatory diagram showing storage locations of intra-block area information bits b1 and b0 in the digital copying machine according to the second embodiment.

FIG. 21 is an explanatory diagram of a combination of an area determination signal and image data in the digital copying machine according to the third embodiment.

FIG. 22 is a flowchart illustrating the operation of the area determination signal separation processing in the area determination signal separation unit according to the third embodiment.

[Explanation of symbols]

 1201 scanner 1202 A / D converter 1203 image processing unit 1204 character area determination unit 1205 gradation processing unit 1206 image storage unit 1207 signal switching unit 1208 signal switching unit 1209 phase output unit 1210 image output unit 1301, 1601 4-line FIFO 1302 code Combining sections 1303, 1603 Binary 4-line FIFO 1304 Area judgment signal synthesis section 1305 (1605) Memory 1602 Composite section 1604 Area judgment signal separation section

Claims (6)

[Claims] 1. A multi-tone pixel data forming image data is decomposed into a predetermined number to generate block data.
While the density data for each pixel of the block data is encoded into compressed data including a 2-bit gradation quantization code, average data, and a gradation width index, it is determined whether the image data is a character image, Based on this determination result, a binary area determination signal is output for each pixel, and 0 if this area determination signal is a determination signal of a character area in the block data,
When the block data includes a determination signal other than the character area, 1 is inserted into the least significant bit of either the average data of the compressed data or the gradation width index, and the block data includes the determination signal other than the character area. Is a device that decodes code data including region information of a character image generated by inserting a region determination signal for each pixel into lower bits of a 2-bit gradation quantization code, Data or code identification means for identifying the least significant bit in which the information is inserted with the gradation width index, and identifying whether or not the block data includes data of only a character area; When it is determined that only the area is included, the area determination signal is used as the determination signal for the entire character area. The bits are used as an area determination signal, and the lower bits are code data to be replaced with 0, area determination signal separation means, and the code data, average data which is code data separated by the area determination signal separation means, a gradation width index, and 2 bits. Decoding means for decoding a bit gradation quantization code into density data for each pixel. 2. Generating block data by decomposing each of multi-gradation pixel data forming image data into a predetermined number,
While the density data for each pixel of the block data is encoded into compressed data including a 2-bit gradation quantization code, average data, and a gradation width index, it is determined whether the image data is a character image, A binary area determination signal is output for each pixel based on the determination result, and 0 when this area determination signal includes a determination signal other than the character area in the block data.
Is inserted into the least significant bit of one of the average data of the compressed data and the gradation width index when the block data includes the determination signal of only the character area, and the determination signal of the block data other than the character area is included in the block data. Is included, a device that decodes code data including region information of a character image generated by inserting a region determination signal for each pixel into lower bits of a 2-bit gradation quantization code, Code identification means for identifying the average data of the data or the least significant bit in which the information is inserted by the gradation width index, and identifying whether or not data other than the character area is included in the block data; If it is determined by the means that an area other than the character area is included, all area determination signals are determined to be signals other than the character area. The lower bits of the child code are used as an area determination signal, and the lower bits are code data to be replaced with 0, area determination signal separation means, and the code data, average data being code data separated by the area determination signal separation means. Decoding means for decoding the gradation width index and the 2-bit gradation quantization code into density data for each pixel. 3. A block data is generated by decomposing each of the multi-gradation pixel data forming the image data into a predetermined number,
While the density data for each pixel of the block data is encoded into compressed data including a 2-bit gradation quantization code, average data, and a gradation width index, it is determined whether the image data is a character image, A binary area determination signal is output for each pixel based on this determination result. If the area determination signal is a determination signal for a character area in the block data, a 2-bit signal 00 is output. The 2-bit signal 01 is used for the determination signal other than the area, and the 2-bit signal 11 is used for the mixed data including the character area and the non-character area in the block data. One of the lower 2 bits, or
The bit is inserted into the least significant bit of both the average data and the gradation width index one bit at a time. An apparatus for decoding code data including region information of a character image generated by inserting a region determination signal for each code, comprising identifying an average data of the code data or a 2-bit signal included in a gradation width index. A code identification unit for identifying whether the block data includes only a character region, does not include a character region at all, or includes a character region and data other than a character region; and the code identification unit includes only a character region. When it is determined that the region determination signal is included, all the region determination signals are determined to be only the character region. And Mino judgment signal, when a character area and other areas has been identified as being mixed,
The lower bits of the 2-bit gradation quantization code are used as an area determination signal, and the lower bits are code data to be replaced with 0.
Area determination signal separation means; decoding means for decoding the code data, average data, code data separated by the area determination signal separation means, a gradation width index, and a 2-bit gradation quantization code into density data for each pixel An image decoding device comprising: 4. A block data is generated by decomposing each of multi-gradation pixel data forming image data into a predetermined number.
While the density data for each pixel of the block data is encoded into compressed data including a 2-bit gradation quantization code, average data, and a gradation width index, it is determined whether the image data is a character image, Based on this determination result, a binary area determination signal is output for each pixel, and 0 if this area determination signal is a determination signal of a character area in the block data,
When the block data includes a determination signal other than the character area, 1 is inserted into the least significant bit of either the average data of the compressed data or the gradation width index, and the block data includes the determination signal other than the character area. Is a method for decoding code data including region information of a character image generated by inserting a region determination signal for each pixel into lower bits of a 2-bit gradation quantization code. The data or the least significant bit in which the information is inserted by the gradation width index is identified by the code identification means as to whether or not the block data includes data of only the character area, and the code identification means includes only the character area. If it is determined that all the area determination signals are character area determination signals by the code data and area determination signal separation means, and if it is determined that an area other than the character area is included, two bits are used. And lower bits of the gradation quantization code and area identification signal, said lower bits, 0
And the decoding means decodes the code data, the average data which is the code data separated by the area determination signal separation means, the gradation width index, and the 2-bit gradation quantization code into density data for each pixel. An image decoding method, characterized in that: 5. A block data is generated by decomposing each of multi-gradation pixel data forming image data into a predetermined number.
While the density data for each pixel of the block data is encoded into compressed data including a 2-bit gradation quantization code, average data, and a gradation width index, it is determined whether the image data is a character image, A binary area determination signal is output for each pixel based on the determination result, and 0 when this area determination signal includes a determination signal other than the character area in the block data.
Is inserted into the least significant bit of either the average data of the compressed data or the gradation width index when the block data includes the determination signal of only the character area, and the determination signal of the block data other than the character area is included in the block data. Is included, a method of decoding code data including region information of a character image generated by inserting a region determination signal for each pixel into lower bits of a 2-bit gradation quantization code, The average data of the data or the least significant bit in which the information is inserted with the gradation width index is identified by the code identification means as to whether data other than the character area is included in the block data. When it is determined that the area includes a region other than the character region, the code data and the region determination signal separating unit determine that all the region determination signals are the determination signals other than the character region, and that the region determination signal includes the character region signal. In this case, the lower bits of the 2-bit gradation quantization code are used as an area determination signal, and the lower bits are replaced with 0. A plane image decoding method, wherein a tone width index and a 2-bit gradation quantization code are decoded into density data for each pixel by a decoding means. 6. A block data is generated by decomposing each of multi-gradation pixel data forming image data into a predetermined number, and density data for each pixel of the block data is converted into a 2-bit gradation quantization code. While encoding into compressed data including the average data and the gradation width index, it is determined whether or not the image data is a character image.
A value determination signal is output. If the determination signal is a determination signal for all character areas in the block data, a 2-bit signal 00 is output. In the case where the character area and the judgment signal other than the character area are mixed in the block data, the signal 01 of the above-mentioned is converted into the 2-bit signal 11 by the lower 2 bits of either the average data of the compressed data or the gradation width index, or Insert one bit at a time into the least significant bits of both the data and the tone width index. If the block data includes a character area and a determination signal other than the character area, the lower bits of the tone quantization code are assigned to each pixel. A method of decoding code data including region information of a character image generated by inserting a region determination signal of The two-bit signal included in the block data is identified by the code identifying means, and whether the block data includes only a character area, does not include any character area, or includes both a character area and data other than a character area, When the code identifying means is identified as including only the character area only, the code data, the area determination signal separating means determines the area determination signal as the determination signal of only the character area, and is determined not to include the character area at all. When the area determination signal is determined to be a determination signal for only the area other than the character area, and when it is determined that the character area and the other area are mixed, the lower bits of the 2-bit gradation quantization code are defined as the area determination signal, The lower bits are replaced with 0, and the decoding means decodes the code data, the average data which is the code data separated by the area determination signal separation means, the gradation width index, and the 2-bit gradation quantization code. Image decoding method is characterized in that so as to decode each of the density data.