JP2001177729A - Image coding method, image decoding method, and color facsimile apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image coding method, an image decoding method, and a color facsimile apparatus by which compression processing time of a color image can be shortened and addition of dummy data in the faxing can be suppressed. SOLUTION: The color facsimile apparatus is provided with a color image reader 27 to read a color image of an original, a controller 24 that applies compression coding to the read image data in compliance with the JPEG system, and a MODEM 23 or the like that faxes the compression-coded image data. When a setting size WT at faxing is larger than an original size WR in the reading of an original, the controller 24 adds a bank in a single color to the color image and composites image data, compresses the color image area in compliance with the JPEG system and compresses the blank area by a system other than that in compliance with the JPEG system.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to an image encoding method and an image decoding method for compressively encoding or decompressing color image data by the JPEG system. The present invention also relates to a color facsimile apparatus for transmitting color image data by compression encoding or decompression decoding by the JPEG method and transmitting the same.

[0002]

2. Description of the Related Art The JPEG system has been adopted as a color facsimile image compression system internationally standardized by the International Telecommunication Union (ITU).

When color image data is compressed or decompressed by the JPEG method, the entire area of the image data is usually processed. That is, at the time of compression, DCT (Discrete Cosine Transform) and division by a quantization matrix are performed on the entire area of the image data, and at the time of decompression, multiplication and inverse DCT (inverse discrete cosine transform) by the quantization matrix are performed. ) And the like are executed for the entire area of the image data.

[0004]

When a block of the same color is compressed by the JPEG system, the AC of the block is reduced.
Since the component becomes zero, the block data becomes only the DC component. As a result, for the same color block, the data compression rate becomes very high, and the communication time required for the transmission becomes shorter than the compression processing time. Therefore, in order to match the communication processing timing with the compression processing timing at the time of facsimile transmission, dummy data processing for adding dummy data to the compressed data and transmitting the data is required.

[0005] Unnecessary data transmission occurs due to such dummy data processing, and the utilization efficiency of the transmission network is reduced.

Further, when reading a document, blank portions and blank portions of the document are plain and should be processed as the same color data. May not be the same color data due to uneven distribution of the reading, sensitivity variation of the reading element, or the like. Therefore, even when the plain area is compressed by the JPEG method, the AC component of the block appears, and the same compression processing as that of the original image is performed.

A related prior art is disclosed in
No. 27538 describes a method of dividing a color image into blocks, classifying the pixels of each block into two or more approximate colors, separating one block into color information and resolution information, and performing an encoding process. ing.

Japanese Patent Application Laid-Open No. 11-75183 discloses that a plurality of code blocks are continuously generated by quantizing an image signal, and when a specific code is consecutive in a block, the specific code is replaced with a run-length code. A method for creating compressed image data is described.

SUMMARY OF THE INVENTION An object of the present invention is to provide an image encoding method capable of shortening the compression processing time of a color image and suppressing the addition of dummy data during transmission, an image decoding method corresponding to the method, and a color encoding method using these methods. A facsimile machine is provided.

[0010]

SUMMARY OF THE INVENTION The present invention is a method for encoding image data including a color image area and a single color margin area, wherein the color image area is compressed by the JPEG method and the margin area is compressed. This is an image encoding method characterized by performing compression by a method different from the JPEG method.

According to the present invention, when one image data includes a color image area and a blank area of a single color,
By compressing the color image area using the JPEG method, high-quality data compression equivalent to the international standard can be achieved, and the margin area is compressed using a method different from the JPEG method, so that it is faster and easier than the JPEG method. Since various compression processes can be applied, the compression processing time of the entire image can be reduced.

Further, according to the present invention, after the image data is divided into a plurality of blocks, if the brightness component and the color difference component of the pixels of the block are within a predetermined range, the block is determined to be a blank area and compressed. It is characterized by the following.

According to the present invention, when specifying the position of the blank area in the image data, after dividing the image data into a plurality of blocks, it is determined whether or not the brightness components and the color difference components of the pixels of the blocks are within predetermined ranges. By determining whether or not the blank area can be specified quickly and accurately.

Further, according to the present invention, the criterion for determining the margin area is:
It is set based on the ground color data of the document read by the document reading device, the blank reading data outside the document when the document reading device reads, or the input data by the data input device.

According to the present invention, the criterion of the margin area is set based on the document ground color data at the time of reading the document or the blank reading data outside the document, so that the criterion can be set by a simple operation. By providing a white back plate on the back of the document, the area outside the document becomes white data, so that the position of the document end can be easily specified by comparing it with the document ground color data. Further, the criterion of the margin area may be set interactively based on input data from a data input device such as a keyboard.

Further, according to the present invention, the compression method of the margin area is:
The DCT transform processing and the division rounding processing in the quantization table for the AC component obtained in the DCT transform processing are partially omitted in the calculation.

According to the present invention, the marginal region has less high spatial frequency components than the color image region, or is a noise component caused by dust or dirt even if high frequency components are present. Omission of the processing related to the AC component has little effect, and the compression processing time can be reduced by the omitted amount.

Further, according to the present invention, the compression method of the margin area is:
The AC component obtained by the DCT transform processing is set to zero.

According to the present invention, the blocks in the margin area are DCT-transformed and the AC component is set to zero, so that the margin block can be changed to a solid single color.
All of the processing relating to the C component can be omitted, the compression processing time can be shortened accordingly, and the transmission time can be shortened by reducing the data amount.

The present invention also relates to a method for decoding an image compressed by the JPEG method, wherein when the AC component of a block of compressed image data is zero, the block is subjected to JPE.
This is an image decoding method characterized in that decompression is performed by a method different from the G method.

According to the present invention, when the AC component of a block of compressed image data is zero, it is possible to decode the block in the JPEG format as it is, but it is determined that the block is a blank area, By performing decompression using a method different from the JPEG method, a faster and simpler decompression process can be applied than in the JPEG method, so that the decompression processing time of the entire image can be reduced.

Further, the present invention is characterized in that a block having zero AC component is calculated by partially omitting the multiplication process and the inverse DCT transform process in the quantization table relating to the AC component.

According to the present invention, a block having zero AC component is determined to be a blank area, and the omission of the processing related to the AC component has little effect, and the decompression processing time is reduced by the omitted amount. it can.

Also, the present invention provides a document reading unit for reading a color image of a document,
An image processing unit for compression-encoding in the G system; and a data transmission unit for facsimile transmission of the compression-encoded image data. If the set size WT for facsimile transmission is larger than the original size WR for original reading, image processing The unit is characterized in that after adding a blank portion of a single color to the color image and synthesizing the image data, the color image region is compressed by the JPEG method, and the blank region is compressed by a method different from the JPEG method. It is a color facsimile machine.

According to the present invention, when the set size WT at the time of facsimile transmission is larger than the document size WR at the time of document reading, a margin of a single color is added to the color image to synthesize the image data to thereby reduce the size. Discrepancies can be resolved. The single color of the margin can be set arbitrarily according to the user's preference by button operation or the like, and for example, image data such as a picture frame or a border of a photograph can be obtained. In addition, moving the position of the color image to the center results in image data in which the left and right are balanced.

Further, when one image data includes a color image area and a blank area of a single color, the color image area is compressed by the JPEG method, whereby high-quality data compression equivalent to the international standard can be performed. With
By compressing the blank area using a method different from the JPEG method, faster and simpler compression processing can be applied than in the JPEG method, so that the compression processing time of the entire image can be shortened. Shortening is also possible.

According to the present invention, there is provided a data receiving unit for receiving facsimile image data compressed by the JPEG system, an image processing unit for expanding and decoding the received image data by the JPEG system, and And a printing unit for printing the compressed image data when the AC component of the block of the compressed image data is zero.
This is a color facsimile apparatus characterized in that it is expanded by a method different from the G method.

According to the present invention, when the AC component of a block of compressed image data is zero, it is possible to decode the block in the JPEG format as it is, but it is determined that the block is a blank area, By performing decompression using a method different from the JPEG method, a faster and simpler decompression process can be applied than in the JPEG method, so that the decompression processing time of the entire image can be reduced.

[0029]

FIG. 1 is a block diagram showing an electrical configuration of an embodiment of the present invention. The color facsimile apparatus includes a network control device 22, a modem 23, a control device 24, a color image storage device 25, and a color printing device 2.
6, a color image reading device 27, a storage device 28, an input keyboard 210, a handset 211, a display device 212, and the like.

The modem 23 modulates the digital signal into an analog signal suitable for the telephone network 21,
The analog signal from 1 is demodulated into a digital signal. A network controller 22 is interposed between the modem 23 and the telephone network 21. The network controller 22 monitors the status of the telephone network 21 and switches between the handset 211 and the modem 23.

Here, the facsimile transmission using the telephone network 21 will be described. However, facsimile transmission via a communication path such as a serial cable, a parallel cable, or a LAN (Local Area Network) cable may be used.

The color image reading device 27 has a function of optically reading an original and converting it into an electric signal. For example, three color light sources such as LEDs and fluorescent lamps are sequentially turned on for each line read, and one color is read. A method of receiving light with a CCD line sensor, equipped with color filters for three colors using a white light source.
For example, a method of receiving light by a CCD line sensor for each color is used. When a read signal is supplied to the color printing device 26, a copy operation is performed, and when a read signal is supplied to the modem 23, a facsimile transmission operation is performed.

The color printing device 26 has a function of printing image data received via the telephone network 21 and the modem 23 or image data read by the color image reading device 27 on a recording medium. , A color electrophotographic system, a color electrostatic recording system, a color thermal transfer system, a color photographic exposure system, and the like. As a color printing method, a method in which three primary colors of each pixel show multi-step gradation, such as a silver halide film of a photograph or a sublimation thermal transfer method, and a second floor, in which each color has a dot, as in a normal ink jet method. There is a method capable of expressing only a tone, and when expressing a halftone by the latter method, a pseudo halftone expression such as a dither method or an error diffusion method is used. For example, when the dot resolution of the color printing device 26 is higher than the dot resolution of the received image, the received image is interpolated so as to match the resolution of the color printing device 26 with respect to each printing dot by three primary colors (C, M) of each color. , Y), and then determine the presence or absence of printing for each dot defining the resolution of the color printing device 26 for each primary color using a pseudo halftone technique.

The color printing device 26 includes a medium sensor for detecting the presence or absence of a recording medium to be printed, a jam sensor for detecting the occurrence of a jam in which the recording medium is jammed in the transport path, and various recording methods such as an ink ribbon, toner, and ink. The control device 24 can determine whether the color printing device 26 is printable or unprintable based on the output of the sensor.

The color image storage device 25 has a function of storing received image data or read image data, and is constituted by, for example, a memory or a hard disk.
By providing the color image storage device 25, many complicated functions such as temporary storage, transfer, broadcast transmission, substitute reception, and memory transmission of received image data become possible.

The storage device 28 is composed of a ROM or a RAM, and functions as a storage area for programs and data and a work area.

The input keyboard 210 has a function of inputting a user's instruction, and is provided with a plurality of buttons such as a reception start button, a transmission button, and dial buttons corresponding to "0 to 9, *, #". Can be

The display 212 displays various information for the user,
For example, it has a function of displaying operation guidance, an operation state, a warning, and the like. For example, an LCD (liquid crystal panel) displaying several lines
Etc.

The control unit 24 is a CPU (central processing unit).
And operates in accordance with a program stored in the storage device 28 to manage control of the entire facsimile apparatus and perform data processing such as compression, decompression, encoding, and decoding of image data. For example, MH (Modified Huffman) method or MR (Modif
iED READ) compression and decompression of a single color image, etc., and JPEG compression and decompression according to the ITU-T recommendation for color images.

Further, the control device 24 performs a mutual conversion of the color specification system, for example, a color image expressed by R, G, B systems which are three primary colors used when reading an image, and three subtractive primary colors used in color printing. And a color image expressed in C, M, and Y systems, and L *, a used for transmission and reception.
*, B * It has a function of mutually converting color images represented by color space coordinates.

FIG. 2 is a flowchart showing a typical example of the operation of compression-encoding a color image by the JPEG system.
Since there are many combinations of options in the processing procedure of a color image, the most standard procedure will be described here.

First, starting from step s31, in step s32, the color image reading device 27 reads a color image of a document and, for example, 200 dpi (d)
The image data is converted into 8-bit image data of each RGB color at a resolution of (otper inch) × vertical 200 dpi and stored in the color image storage device 25.

Next, in step s33, the control device 24 extracts the RGB system image data stored in the color image storage device 25 and converts it into L * a * b * color coordinates. Next, in step s34, the L * component indicating the lightness is held at the same resolution, and the a * b * component indicating the color difference is subjected to data compression to reduce the resolution in the main scanning direction and the sub scanning direction to half by data thinning or the like. .

Next, in step s35, the control unit 24 sets the main scanning 8 dots * for each of the lightness component L * and color difference components a * and b *
The image data is cut out in blocks composed of 8 dots in the sub-scanning direction, and the image data is divided into a plurality of blocks. Next, step s36
Performs a DCT transform (discrete cosine transform) for each block to convert the data into a two-dimensional frequency distribution matrix expression.

Next, at step s37, the control device 24
The lightness matrix and the color difference matrix that have been subjected to the CT conversion are divided by a predetermined quantization table, and rounding is performed by converting the quotient to an integer. At this time, the compression ratio and quality of the image change depending on the value of the quantization table. As the numerical value of the quantization table increases, the compression ratio of the image increases and the speed of transmission increases, but the image quality tends to deteriorate. .

Next, in step s38, the control device 24 encodes each matrix, which has been subjected to the division and rounding processing in the quantization table, by a predetermined Huffman table, and performs data compression. Next, in step s39, the control device 24 supplies the encoded image data to the modem 23 together with the used quantization table and Huffman table, and transmits the data to the reception destination.

The color facsimile apparatus on the receiving side is also shown in FIG.
The received image data is decompressed and decoded according to a procedure reverse to that of FIG. That is, the received Huffman table is used to decode the received image data, and then the received quantization table is multiplied to calculate a brightness matrix and a chrominance matrix.
Performs a transform (inverse discrete cosine transform) to obtain a lightness component L
*, CMYK expanded to block data consisting of color difference components a * and b *, and further added with a CMY-based or black component
After conversion into each component of the system, color printing is performed.

FIG. 3 is an explanatory diagram showing the relationship between the original size at the time of original reading and the set size at the time of facsimile transmission. The size of the image to be transmitted is specified in several standard sizes such as A4 size and B4 size according to the ITU-T standard. On the other hand, the document size at the time of reading the document is not particularly limited as long as the document can be read by the color image reading device 27, and is arbitrary from a small size such as a postcard to a large size such as a newspaper. The set size WT at the time of facsimile transmission is automatically selected so as to include the original size at the time of original reading, unless otherwise specified.

For example, when a postcard-size original is conveyed in the longitudinal direction and transmitted in A4 size, as shown in FIG.
Since the image reading position 12 indicating the boundary of the document area (hatched portion) is included in the transmission image position 11 indicating the boundary of the transmission area, the leading margin 13 and the trailing margin 1
4, margins such as a right margin 15 and a left margin 16 are generated. These margins need to be supplemented with some data at the time of transmission, and generally single color data such as white is added to the periphery of the document image data.

As a method of detecting the image reading position 12, a method of detecting the leading end position and the trailing end position of the document by a combination of a lever and a photocoupler, and a position of the document guide are detected to estimate the left end position and the right end position of the document. A method, a method of detecting the positions of the front, rear, left, and right edges of the document by image analysis of the read data can be applied.

In the present invention, when the set size WT at the time of facsimile transmission is larger than the document size WR at the time of document reading, a single color margin is added to the color image to synthesize the image data, and then the color image area is JPEG. The margin area is compressed by a method different from the JPEG method.

FIG. 4 is a flowchart showing the procedure of the image encoding process according to the present invention. This procedure shows a process for one block corresponding to steps s36 to s38 in FIG.

First, starting from step s41, in step s42, the control device 24 verifies the color difference, brightness value and variation between pixels in one block of 8 dots × 8 dots, and in step s43, the brightness component If the chrominance component is within a predetermined range, that is, if the variance of the chrominance and lightness values is equal to or less than a predetermined value, the block can be determined to be a margin area, and step s44 is performed.
Shifts to simplification processing.

The criteria for determining the margin area can be set based on the ground color data of the document read by the document reading device, the blank reading data outside the document when the document reading device reads, or the input data by the data input device. it can. Note that there is a possibility that there is a block in which the brightness and the color difference are small in the original color image area. Therefore, the margin area determination routine may be applied only to the peripheral area of the document.

On the other hand, if there is a large variation in the values of the color difference and the brightness, the block can be determined to be a color image area, and the process proceeds to the normal compression processing in step s45, and in step s47, steps s36 to s36 in FIG. After processing with the same contents as in s38, in step s410 each matrix is coded with a predetermined Huffman table to perform data compression, and in step s411, the process proceeds to the next block processing.

In the simplification processing of the margin, the compression processing time is reduced by partially omitting the DCT transform processing and the division rounding processing in the quantization table for the AC component obtained in the DCT transform processing. It is shortened.

That is, in step s46, only the DC component of the DCT conversion is calculated by calculating the average value of the color difference and brightness in the block, and the DCT conversion processing for the AC component is omitted. Next, the DC component calculated in step s48 is divided by the DC component of the quantization table to perform a rounding process. Next, in step s49, zero is substituted for the AC component of the brightness matrix and the color difference matrix. In this way, only the process related to the DC component is executed, and the process related to the AC component is omitted. Finally, a brightness matrix and a color difference matrix including only the DC component are created.

Next, at step s410, the control device 24
Each matrix is encoded using a predetermined Huffman table to perform data compression, and the process proceeds to the next block processing in step s411.

The data coded by the normal compression processing and the data coded by the simplification processing are combined as one piece of image data, and transmitted to the destination according to step s39 in FIG. As the transmission method, a) a method of transmitting coded data collectively in page units, b) a method of executing the encoding process and the transmission process in block units in parallel, and the like are possible. And the storage capacity of the color image storage device 25 and the like on the transmitting side or the receiving side. In this case, if the encoding process takes more time than the transmission process, it becomes necessary to add dummy data to the transmission data. However, the encoding process speed is reduced by applying the above-described simplification process. It is possible to avoid unnecessary processing such as adding dummy data.

A normal color decoding process can be applied to the color facsimile machine on the receiving side. That is, the received image data is decoded using the received Huffman table, and then a multiplication process is performed on the received quantization table to calculate a lightness matrix and a color difference matrix, and then an inverse DCT transform (inverse discrete cosine transform) is executed. And the lightness component L *,
After decomposing into block data composed of the color difference components a * and b *, and converting the data into CMY-based components or CMYK-based components to which a black component is added, color printing is performed.

In such a decompression decoding process, a simplification process in which the process related to the AC component is omitted can be applied. In other words, after decoding the received image data using the Huffman table, the A
When all the C components are zero, the multiplication process and the inverse DCT transform process of the quantization table execute only the process related to the DC component. As a result, the decompression processing time corresponding to the margin processing at the time of transmission can be reduced.

In the above description, a color facsimile apparatus has been described as an example of an apparatus that performs JPEG encoding or decoding. However, the present invention can be applied to any communication apparatus using a network such as the Internet.

[0063]

As described in detail above, according to the present invention, 1
When one image data includes a color image area and a single-color margin area, the color image area is compressed by the JPEG method, so that high-quality data compression equivalent to the international standard can be performed. Is JPEG
By compressing in a different format, JPEG
Since a faster and simpler compression processing can be applied than the method, the compression processing time of the entire image can be reduced.

When specifying the position of the blank area in the image data, after dividing the image data into a plurality of blocks, it is determined whether or not the lightness component and the color difference component of the pixels of the block are within a predetermined range. Thus, the blank area can be specified quickly and accurately.

The compression method of the blank area is omitted by partially omitting and calculating the DCT transform processing and the division and rounding processing in the quantization table for the AC component obtained by the DCT transform processing. The compression processing time can be shortened by the minute.

According to the present invention, when the AC component of the block of the received compressed image data is zero, it is possible to decode the block as it is by the JPEG method, but it is determined that the block is a blank area. Then, by performing decompression using a method different from the JPEG method, a faster and simpler decompression process can be applied than in the JPEG method, so that the decompression processing time of the entire image can be reduced.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an electrical configuration of an embodiment of the present invention.

FIG. 2 is a flowchart illustrating a typical example of an operation of compression-encoding a color image by the JPEG method.

FIG. 3 is an explanatory diagram showing a relationship between a document size at the time of document reading and a set size at the time of facsimile transmission.

FIG. 4 is a flowchart illustrating a procedure of an image encoding process according to the present invention.

[Explanation of symbols]

 Reference Signs List 22 network control device 23 modem 24 control device 25 color image storage device 26 color printing device 27 color image reading device 28 storage device 210 input keyboard 211 handset 212 display device

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H04N 11/04 H04N 7/133 Z F term (Reference) 5C057 AA06 AA07 EA01 EA02 EA07 ED06 EL01 EM09 EM16 FE01 FE03 GH05 5C059 KK11 MA00 MA23 MC11 MC32 MC34 ME02 PP01 PP15 PP16 PP23 SS06 SS15 SS28 TA16 TB08 TC02 TC04 TD12 UA02 UA05 5C078 AA09 BA21 BA23 BA57 CA36 DA01 DA02 5J064 AA03 BA09 BA16 BC01 BD06

Claims (9)

[Claims] 1. A method for encoding image data including a color image area and a single color margin area, wherein the color image area is compressed by a JPEG method and the margin area is compressed by a method different from the JPEG method. Image encoding method. 2. After the image data is divided into a plurality of blocks, if the lightness component and the color difference component of the pixels of the block are within a predetermined range, the block is determined to be a margin area and compressed. 2. The image encoding method according to claim 1, wherein: 3. A criterion for determining a margin area is set based on ground color data of a document read by a document reading device, blank reading data outside a document when the document reading device reads, or input data by a data input device. 2. The image encoding method according to claim 1, wherein: 4. A method for compressing a margin area is performed by partially omitting a DCT transform process and a division rounding process in a quantization table for an AC component obtained by the DCT transform process. The image encoding method according to claim 2. 5. The image encoding method according to claim 4, wherein in the compression method of the blank area, the AC component obtained by the DCT transform processing is set to zero. 6. A method for decoding an image compressed by the JPEG method, wherein when the AC component of a block of the compressed image data is zero, the block is expanded by a method different from the JPEG method. Image decoding method. 7. A block whose AC component is zero is an AC component.
Multiplication and inverse DC in quantization table for components
7. The image decoding method according to claim 6, wherein the calculation is performed by partially omitting the T conversion processing. 8. A document reading unit for reading a color image of a document, an image processing unit for compressing and encoding the read image data in a JPEG format, and a data transmitting unit for facsimile transmitting the compressed and encoded image data. When the set size WT at the time of facsimile transmission is larger than the document size WR at the time of document reading, the image processing unit adds a single color margin to the color image, synthesizes the image data, and then converts the color image area into a JPEG image. A color facsimile apparatus, wherein the compression is performed by a method and the margin area is compressed by a method different from the JPEG method. 9. A data receiving unit for receiving facsimile image data compressed by the JPEG system, an image processing unit for expanding and decoding the received image data by the JPEG system, and printing the expanded and decoded image data on paper. A color facsimile apparatus, comprising: a printing unit; and, when the AC component of the block of the compressed image data is zero, the image processing unit expands the block by a method different from the JPEG method.