JPH09163151A - Image data coder and coding method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize a spot color copying machine in which a specific color image is copied with the same memory capacity as that of a monochromatic copying machine. SOLUTION: A data separate section 2 uses a specific color flag signal to separate multi-gradation black and white/specific color mixture image data into black and white data and specific color data and they are fed to a black and white data coding section 5 and a specific color data coding section 6. They are coded separately, and code data La, Ld, ϕij are fed to a code data conversion section 7. Simultaneously a color mixture discrimination section 4 discriminates whether or not a color is mixed in the data. When the color is not mixed in the data based on the result of discrimination of the color mixture discrimination section 4, the code data conversion section 7 selects the code data fed from the black and white data coding section 5 or the specific color data coding section 6 and replaces the least significant bit of the code data Ld with a result of OR processing by the color mixture discrimination section 4. When any color is mixed, the high-order 4-bits of the code data La fed from the black and white data coding section 5 and the high-order 4-bits of the code data La fed from the specific color data coding section 6 are linked and the linked data are stored in a code memory 8 as new code data La.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image data coding apparatus and a coding method for compressing and storing image data by block coding.

[0002]

2. Description of the Related Art A digital copying machine that handles image data as a digital signal is known as one of image processing apparatuses. The structure of the digital copying machine of this means is briefly shown in FIG. That is, the scanner 31 reads the image data, the A / D conversion unit 32 converts it into a digital signal, the image processing unit 33 performs image processing such as gamma conversion and image quality correction, and the image output unit 34 outputs the image data on paper. The image is output by printing for each pixel.

In a copying machine that handles an image as a digital signal, the image can be stored in a memory. If the image data can be stored in the memory, the image once captured can be used many times, and the input and output addresses can be changed to perform processing and editing such as image rotation. However, the amount of information of an image is large, and if it is stored in the memory as it is, a large memory capacity is required (for example, an A4 size original is read with 256 gradations per pixel and a resolution of 4
Read at 00 dpi, it will be about 16 megabytes. ), Because the unit price of the memory is high, the overall cost becomes expensive. Therefore, a method is generally adopted in which the image data is not stored as it is, but is encoded once and the data amount is compressed and stored in a memory. That is, the data can be compressed and stored in the memory, and the required memory amount is reduced to reduce the cost.

In a block coding method in which image data is a compression method, an image is decomposed into blocks as shown in FIG. 4 and a 1-byte density value Lij in the block is averaged by La (1 Byte), gradation range index Ld
(1 byte), data is compressed into a code φij (2 bits × 16 pixels) for each pixel. By this encoding method, as shown in FIG. 6, the data amount of 16 bytes of a 4 × 4 pixel block of 1 byte of pixels becomes 6 bytes, and 3 /
It is possible to compress to the data amount of 8. Qj in FIG. 5 is a quantized representative value at the time of decoding and is a gradation value to which each code is assigned at the time of decoding as shown in FIG.

By the way, there is a recent digital copying machine which, when the image data includes a specific color such as red, discriminates the pixel of the specific color and outputs the specific color. For example, as shown in FIG. 8, when a copy is made of a document in which the area 41 is red and the other areas 42 are black and white,
The original in red is output as a copy. In such a copy, if the data of the red image is treated as multi-valued data similarly to the black-and-white image, the amount of information increases, so that it is possible to output by handling a specific color (often red or blue). For the sake of convenience, the copying machine configured as described above is referred to as a spot color copying machine in order to distinguish it from a full-color copying machine. The construction of such a spot color copying machine is shown in FIG. In this configuration, first, the scanner 51 uses R, G, B
Image sensor reads the R, G, B signals for each pixel, the A / D converter 52 converts the image data into an 8-bit digital signal, and the specific color signal determiner 53 converts the R, G, B for each pixel.
The color of the pixel is determined from the difference between the G and B signals, and if it is determined to be the specific color, the specific color flag signal 54 is turned on. If not determined, the specific color flag signal 54
Turn off. In response to the specific color flag signal 54, the image data switching unit 55 outputs the specific color gradation data converted from the R, G, B signals when the specific color flag signal 54 is on, and the R, G when it is off. , B signals converted from the black-and-white gradation data are switched pixel by pixel and sent to the image processing unit 56 together with the specific color flag signal data. After the image processing unit 56 performs image processing such as γ conversion, the image output unit 5
In step 7, an image consisting of a specific color and a black and white image is output from these data.

Next, a case will be described in which the image data is encoded and stored in the image data storage unit 58, the encoded data is decoded, and the image data is output.

The operations up to the scanner 51, the A / D conversion section 52, the specific color signal determination section 53, and the image data switching section 55 are the same as in the above case. The multi-gradation black-and-white / specific color mixed image sent from the image data switching unit 55 is coded by the block coding method described above, and the image data storage unit 5
8 and the specific color flag signal for each pixel is directly stored in the image data storage unit 58 as binary data. As a result, the data for one block to be stored is the block code 6 bytes plus the specific color flag signal 2 bytes (1 bit × 16 pixels) as shown in FIG. When reading from the image data storage unit 58, the accumulated code is decoded and returned to multi-tone black and white / specific color mixed data, and a specific color flag signal for each pixel is added to this, and the image processing unit 56 is added. The image output unit 57 outputs an image composed of a specific color and a monochrome image from these data.

[0008]

However, if such a system is adopted, it is necessary to accumulate not only the original image data but also the specific color flag signal for each pixel as binary data in the image data storage unit 58. Therefore, the required memory amount is increased and the cost for realizing the image memory unit is increased. Note that the amount of memory increase is A4 size and resolution is 400 dpi.
In case of the image, it becomes 2 megabytes. As described above, it is necessary to increase the memory amount for the red image signal, and if the memory amount is increased, the cost naturally rises.

The present invention has been made in view of the above points, and an object thereof is an image data coding apparatus capable of realizing a spot color copying machine capable of copying a specific color with the same memory capacity as a single color copying machine. And to provide a method.

[0010]

In order to achieve the above object, a first means is an image data encoding apparatus for encoding multi-gradation black-and-white and specific color mixed image data. A means for dividing the mixed image data into blocks each having a preset number of pixels, and all pixels in one block of the multi-tone black and white / specific color mixed image data are of a specific color, or black and white / specific colors are mixed. If a specific color and a black-and-white image are mixed in the block, the average gradation value for only the specific color and the black-and-white image only Means to determine the average gradation value of all, if all the pixels in the block is only a specific color or a monochrome image,
When a specific color and a black-and-white image are mixed in a block, a gradation dispersion index value indicating the variation of each pixel of the multi-tone black-and-white / specific-color mixed image data in each block is separately set for the specific color and the black-and-white image. If there is only a specific color or black-and-white image in the block, a means for obtaining the gradation dispersion index value for all of the multi-tone black-and-white / specific color mixed image data, and the specific color and black-and-white image When mixed, the multi-tone black and white / specific color mixed image data is quantized into two levels for each specific color and monochrome image,
When all the pixels in the block have only a specific color or a black and white image, a means for quantizing into four levels and a result determined by the determining means are set at a preset position of the gradation dispersion index value. And means for embedding,
In the block in which the specific color and the black and white image are mixed, the multi-tone black and white / specific color mixed image data is specified with the average gradation value of each of the specific color and the black and white image and the result determined by the determining unit. The gradation dispersion index value of each of the color and the black and white image and the two-level quantum value of the specific color and the black and white image obtained by the quantizing means are coded in block units, and only the specific color or the black and white image exists. In the block, the average gradation value, the gradation dispersion index value having the result determined by the determining unit, and the four-level quantized value obtained by the quantizing unit are coded in block units. It is characterized by doing.

A second means is an image data encoding device for encoding multi-tone black and white and specific color mixed image data,
Among the means for dividing the multi-tone black-and-white and specific color mixed image data into blocks composed of a preset number of pixels, and the block-divided multi-tone black-and-white and specific color mixed image data,
A pixel value for which a flag signal indicating a multi-tone specific color pixel is raised is compared with a preset threshold value, and if the pixel value is higher than the threshold value, the pixel value is changed to a white image pixel value,
When the pixel value is lower than the threshold value, means for changing the specific color pixel for lowering the flag signal of the pixel, and average within one block of multi-tone black and white / specific color mixed image data processed by the changing means The means for obtaining the gradation value and the flag signal processed by the means for changing are examined to find out how much the gradation value for each pixel varies within one block of the multi-gradation monochrome / specific color mixed image data. By examining the flag signal processed by the means for obtaining the gradation dispersion index value and the changing means, it is determined whether or not a specific color exists in one block of multi-tone monochrome / specific color mixed image data. And a specific color exists in the block, the multi-tone black-and-white / specific color mixed image data in the block is quantized into two levels by using the average gradation value and the gradation dispersion index value. When the color does not exist in the block, it is provided with means for quantizing into four levels, and means for embedding the result judged by the judging means in a preset position of the gradation dispersion index value. Tone / monochrome / specific color mixed image data is encoded on a block-by-block basis into the average gradation value and the gradation dispersion index value having the result determined by the determining means, and the quantization is performed in a block in which a specific color exists. The two-level quantized value and the flag signal obtained by the means for encoding and the four-level quantized value obtained by the means for quantizing in a block in which no specific color exists are encoded in block units. To do.

A third means is an image data coding method for coding multi-tone black and white and specific color mixed image data,
The multi-tone black-and-white / specific color mixed image data is divided into blocks each having a preset number of pixels, and all the pixels in one block of the multi-tone black-and-white / specific color mixed image data are of a specific color or black-and-white. Whether the specific color is mixed or only the black and white pixel is determined, and when the specific color and the black and white image are mixed in the block according to the determination result, the average gradation value of only the specific color and the black and white image of only the specific color are determined. Average gradation values are calculated respectively. If all the pixels in the block have only a specific color or a black and white image, the average gradation values of all the blocks are calculated, and the specific color and the black and white image are mixed in the block. In this case, a gradation dispersion index value indicating the variation of each pixel in one block of the multi-tone black-and-white / specific color mixed image data is obtained separately for the specific color and the black-and-white image, When only a specific color or a black and white image exists, the gradation dispersion index value is obtained for all of the multi-tone black and white / specific color mixed image data, and when the specific color and the black and white image are mixed, the multi-level Tone monochrome / specific color mixed image data 2 for each specific color and monochrome image
If all pixels in the block are of a specific color or a black and white image, the quantization result is quantized into four levels, and the determination result is embedded in a preset position of the gradation dispersion index value, In the block in which the specific color and the black and white image are mixed, the average gradation value of each of the specific color and the black and white image, and the specific color having the result determined by the determining unit are used. The gradation dispersion index value of each black-and-white image, the specific color obtained by the quantizing means, and the two-level quantum value of each black-and-white image are coded in block units. , The average gradation value, the gradation dispersion index value having the result judged by the judging means, and the four levels obtained by the quantizing means. Characterized by coding in block units and Le quantized value.

A fourth means is an image data coding method for coding multi-tone black and white and specific color mixed image data,
Multi-tone black-and-white and specific color mixed image data is divided into blocks of a preset number of pixels, and the multi-tone black and white and specific color mixed image data is divided into multi-tone specific color pixels. The pixel value for which the flag signal is set is compared with a preset threshold value, if the pixel value is higher than the threshold value, it is changed to the pixel value of the white image, and if the pixel value is lower than the threshold value, the pixel The flag signal is lowered, the average gradation value in one block of the multi-gradation black-and-white / specific color mixed image data processed in this way is obtained, and the flag signal processed by the changing means is examined,
Multi-tone black-and-white / specific color A gray-scale dispersion index value indicating how much the gray-scale value of each pixel varies in one block of mixed image data, and the flag signal is checked to check the multi-tone black-and-white / specific color. It is determined whether or not a specific color exists in one block of the mixed image data, and if the specific color exists in the block, the average gradation value and the gradation dispersion index value are used to determine the multi-level in the block. Quantize mixed tone black and white / specific color image data into 2 levels, and 4 if no specific color exists in the block.
Quantize to a level, embed the judgment result in a preset position of the gradation dispersion index value, and have the multi-gradation black-and-white / specific color mixed image data with an average gradation value within a block and the judgment result. The gradation dispersion index value within the block is coded in block units, and the block having a specific color has the 2-level quantized value and the flag signal, and the block having no specific color has the 4-level quantized value. It is characterized by encoding in units.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings.

[First Embodiment] Since the configuration of this embodiment is the same as that shown in FIG. 9, the same reference numerals are allotted to the same parts as in the above-described conventional example in the following description. The overlapping description will be appropriately omitted.

The feature of the present invention resides in the internal structure of the image data storage unit 58 in FIG. 9, the details of which are shown in FIG.
In FIG. 1, of the multi-tone black and white / specific color mixed image data and the multi-tone black / white / specific color mixed image data of the pixel-specific color flag signals, four lines of data are stored once by the 4-line FIFO 1. To the data separation unit 2 in the form of a 4 × 4 pixel block. At this time, at the same time, the specific color flag signal 54 is sent to the data separation section 2 and the color mixture determination section 4 through the 4-line FIFO memory 3. The data separation unit 2 uses the specific color flag signal 54 to perform multi-tone black and white
The specific color mixed image data is divided into black and white data and specific color data and sent to the black and white data encoding unit 5 and the specific color data encoding unit 6, respectively. These are separately coded by the block coding method described above, and the code data of La, Ld, and φij are sent to the code data conversion unit 7. At the same time, the color mixture determination unit 4 checks whether all the specific color flag signals 54 in one block are on, all are off, or whether on-off is mixed. This can be realized by taking the logical product and the logical sum of all the specific color flag signals 54 of each pixel in the block. When all the specific color flag signals 54 in one block are turned on, both the logical product and the logical sum are turned on. When all the specific color flag signals 54 in one block are off, both the logical product and the logical sum are off. When the specific color flag signals 54 in one block are mixed on and off, the logical product is off but the logical sum is on. In this way, the 2-bit determination result of the logical product and the logical sum is sent to the code data conversion unit 7. In the code data conversion unit 7, the specific color flag signal 5 in one block is based on the determination result of the color mixture determination unit 4.
If all 4 are turned on or all are turned off, the coded data sent from the black-and-white data coding unit 5 or the specific color data coding unit 6 is selected according to the value, and Ld The least significant bit is replaced with the logical sum result of the color mixture determination unit 4. When the specific color flag signals 54 in one block are mixed on and off, that is, when the values of the logical product and the logical sum of the determination results of the color mixing determination unit 4 are different, they are sent from the monochrome data encoding unit 5. The upper 4 bits of the code data La and the upper 4 bits of the code data La sent from the specific color data encoding unit 6 are connected,
It is stored in the code memory 7 as a new La. Similarly, the code data L sent from the monochrome data coding unit 5
The upper 4 bits of d and the upper 4 bits of the code data Ld sent from the specific color data encoding unit 6 are concatenated to make a new Ld, and the least significant bit of Ld is the logic of the color mixture determination unit 4. The sum result is replaced and stored in the code memory 7.

For φ data, the upper 1 bit of the code data φij sent from the monochrome data coding unit 5 and the upper 1 bit of the code data φij sent from the specific color data coding unit 6 are combined. As a result, new φij data is stored in the code memory 7.

In the code data stored by such processing, when the specific color flag signals 54 in one block are all on or all are off, the least significant bit of Ld is simply judged as a color mixture. Since only one bit of the logical sum result of the unit 4 is replaced, the code amount is the same as in the case of performing normal block coding. Even when the specific color flag signals in one block are mixed on and off, as described above, La and Ld are 4 bits (the least significant bit of a part of Ld is the logical sum result of the color mixture determination unit 904). Since it is replaced by bits, it is reduced to 3 bits.) The reduced one is concatenated and accumulated, and φij is also concatenated by reducing 1 bit at a time. And the code amount is the same.

Second Embodiment Since the configuration of this embodiment is the same as the configuration shown in FIG. 9, the same reference numerals will be given to the same parts as in the above-mentioned conventional example in the following description. The overlapping description will be appropriately omitted.

The feature of the present invention resides in the internal configuration of the image data storage unit 705 in FIG. 9, the details of which are shown in FIG. In FIG. 2, among the multi-tone black and white / specific color mixed image data and the specific color flag signal for each pixel,
The specific color mixed image data is stored in the 4-line FIFO 21 once for 4 lines and then sent to the specific color pixel changing unit 22 in the form of a 4 × 4 pixel block. At this time, the specific color flag signal 54 is simultaneously sent to the 4-line FIFO memory 23.
Through the specific color pixel changing unit 22.

The specific color pixel changing section 22 uses the specific color flag signal 54 to compare the multi-tone monochrome / specific color mixed image data with the preset value of the threshold value register 24 for only the specific color data. If the pixel value is higher than the threshold value, the specific color data is changed to the pixel value of the white image, and if the pixel value is lower than the threshold value, the specific color flag signal 54 of the pixel is turned off.

Next, the image data passing through the specific color pixel changing unit 22 is sent to the encoding unit 25 and encoded by the block encoding method described above, and the encoded data of La, Ld and φij are converted into the encoded data converting unit. Sent to 26. At the same time, the specific color flag signal is sent to the color mixing determination unit 27, and it is determined whether all the specific color flag signals 54 in one block are off or not off. This can be realized by taking the logical sum of all the specific color flag signals 54 of each pixel in the block. When the specific color flag signals 54 in one block are all off, the logical sum is also off. When all the specific color flag signals 54 in one block are on, and when both on and off are mixed, the logical sum is on. In this way, the 1-bit result of the logical sum is sent to the code data conversion unit 26.

In the code data conversion unit 26, when all the specific color flag signals 54 in one block are turned off based on the judgment result of the color mixture judgment unit 27, it is sent from the coding unit 25. The least significant bit of Ld is replaced with the logical sum result of the color mixture determination unit 27. If all of the specific color flags in one block are on or there is a mixture of on and off, the least significant bit of Ld is the color mixture determination unit 27.
At the same time, the lower 1 bit of each pixel in the code data of φij is replaced with the specific color flag signal 54. The code data thus converted is stored in the code memory 28.

[0024]

As described above, according to the present invention, the following effects can be obtained.

According to the first and third aspects of the present invention, when the specific color exists in each block of the image data to be encoded, the processing content of the block encoding is switched to the normal encoding method. By encoding and including the specific color flag signal in the encoded block code, it is not necessary to store the block code data separately from the block code data, thereby reducing the memory for the specific color flag signal. Can be realized with the same memory capacity as a monochromatic copying machine. At this time, by separating the data into the black-and-white image and the specific color image in one block and encoding them separately, it is possible to suppress the encoding deterioration in the block in which the monochrome image and the specific color image are mixed.

According to the invention described in claims 2 and 4, when the specific color exists in each block of the image data to be encoded, the processing content of the block encoding is switched to the normal encoding method. By encoding and including the specific color flag signal in the encoded block code, it is not necessary to store the block code data separately from the block code data, thereby reducing the memory for the specific color flag signal. Can be implemented with the same amount of memory as a monochromatic copying machine. At that time, if the gradation of the specific color is not important, the specific color can be binarized and stored in the memory, and the influence on the encoding of the monochrome image can be reduced. Further, this makes it possible to switch the processing contents as appropriate according to the importance of gradation.

[Brief description of the drawings]

FIG. 1 is a diagram showing an internal configuration of an image data storage unit and a processing procedure according to a first embodiment of the present invention.

FIG. 2 is a diagram showing an internal configuration of an image data storage unit and a procedure of processing according to a second embodiment of the present invention.

FIG. 3 is a block diagram showing a schematic configuration of a digital copying machine according to an embodiment and a conventional example.

FIG. 4 is an explanatory diagram showing an image data compression method of a block coding method.

FIG. 5 is an explanatory diagram showing an algorithm of an image data compression method of a block coding method.

FIG. 6 is an explanatory diagram showing a state when image data is compressed by a block coding method.

FIG. 7 is an explanatory diagram showing density values at the time of decoding.

FIG. 8 is a diagram showing a document having red and black images.

FIG. 9 is a block diagram showing a schematic configuration of a copying machine capable of two-color output having a function of compressing and storing an image in a memory.

FIG. 10 is an explanatory diagram showing a storage state of image data for one block.

[Explanation of symbols]

 1,3,21,23 4 line FIFO 2 data separation unit 4 color mixture determination unit 5 black and white data coding unit 6 specific color data coding unit 7,26 code data conversion unit 8,28 code memory 22 specific color pixel changing unit 24 threshold register 25 encoding unit 27 color mixture determination unit 51 scanner 52 A / D conversion unit 53 specific color determination unit 54 specific color flag signal 55 image data switching unit 56 image processing unit 57 image output unit 58 image data storage unit

Claims (4)

[Claims] 1. An image data encoding device for encoding multi-tone black-and-white and specific color mixed image data, and means for dividing the multi-tone black-and-white and specific color mixed image data into blocks each having a preset number of pixels. Means for determining whether all pixels in one block of multi-tone black and white / specific color mixed image data have a specific color, whether black / white / specific colors are mixed, or only black and white pixels, and the determining means According to the determination result, when the specific color and the monochrome image are mixed in the block, the average gradation value only for the specific color and the average gradation value only for the monochrome image are obtained respectively, and all the pixels in the block are In the case of only specific colors or black and white images, a means for obtaining the average gradation value of all in the block, and in the case of mixing specific colors and black and white images in the block, the multi-tone black and white / specific color The gradation dispersion index value that indicates the variation of each pixel in one block of the existing image data is obtained separately for the specific color and the black and white image, and if only the specific color or the black and white image exists in the block, the gradation A means for obtaining the dispersion index value for all of the multi-tone black and white / specific color mixed image data, and the multi-tone black / white /
A unit for quantizing the specific color mixed image data into two levels for each of the specific color and the black and white image, and for quantizing into four levels when all the pixels in the block are only the specific color or the monochrome image, and the determining unit. Means for embedding the result determined by the above into the preset position of the gradation dispersion index value, the multi-gradation black and white / specific color mixed image data, in a block in which a specific color and a black and white image are mixed, The average gradation value of each of the specific color and the black-and-white image, the gradation dispersion index value of each of the specific color and the black-and-white image having the result judged by the judging means, and the specification obtained by the quantizing means. The two-level quantum values of the color and the black and white image are coded in block units, and in the block in which only a specific color or a black and white image exists, the average gradation value and the Image data encoding apparatus, wherein the gradation dispersion index value having the result determined by the determining unit and the 4-level quantized value obtained by the quantizing unit are encoded in block units. . 2. An image data encoding apparatus for encoding multi-tone black-and-white and specific color mixed image data, and means for dividing the multi-tone black-and-white and specific color mixed image data into blocks each having a preset number of pixels. , Of the block-divided multi-tone black and white / specific color mixed image data, a pixel value for which a flag signal indicating a multi-tone specific color pixel is set is compared with a preset threshold value, and When the pixel value is high, it is changed to the pixel value of the white image, and when the pixel value is lower than the threshold value, a unit for changing the specific color pixel that lowers the flag signal of the pixel and a unit for changing the specific color processed by the changing unit. Means for obtaining an average gradation value within one block of gradation black and white / specific color mixed image data, and the flag signal processed by the changing means are examined, and multi gradation black and white / specific color mixed images A means for obtaining a gradation dispersion index value indicating how much the gradation value varies for each pixel in one block of data, and a flag signal processed by the changing means is checked to determine multi-tone black / white / specification. Means for determining whether or not a specific color exists in one block of color-mixed image data, and a block using the average gradation value and the gradation dispersion index value when the specific color exists in the block Multi-tone black and white
A unit for quantizing the specific color mixed image data into two levels, and a unit for quantizing the specific color into four levels when the specific color does not exist in the block; and a preset result of the gradation dispersion index value, which is determined by the determining unit. And a unit for embedding the multi-tone black-and-white / specific color mixed image data into the average tone value and the tone dispersion index value having a result determined by the determining unit. In the block in which the specific color exists, the two-level quantization value and the flag signal obtained by the quantizing means, and in the block in which the specific color does not exist, the four-level quantum obtained by the quantizing means. An image data encoding device characterized by encoding in block units into encoded values. 3. An image data encoding method for encoding multi-tone black-and-white and specific color mixed image data, wherein the multi-tone black-and-white and specific color mixed image data is divided into blocks each having a preset number of pixels, It is judged whether all the pixels in one block of gradation black-and-white / specific color mixed image data have a specific color, whether black-and-white / specific color are mixed, or only black-and-white pixels. When a specific color and a black-and-white image are mixed with each other, an average gradation value for only the specific color and an average gradation value for only the black-and-white image are obtained, and all the pixels in the block have only the specific color or only the black-and-white image. In this case, the average gradation values of all the blocks are calculated, and if the specific color and the black and white image are mixed in the block, the image in one block of the multi-tone black and white / specific color mixed image data is obtained. The gradation dispersion index value for displaying each variation is obtained separately for the specific color and the black-and-white image, and when only the specific color or the black-and-white image exists in the block, the gradation dispersion index value is set to the multi-tone black and white. When all the specific color mixed image data are obtained, and when the specific color and the black and white image are mixed, the multi-gradation monochrome / specific color mixed image data is quantized into two levels for each of the specific color and the black and white image, If all the pixels of the particular color or only the monochrome image are quantized into four levels, the determination result is embedded in the preset position of the gradation dispersion index value, and the multi-tone monochrome / specific color mixture In a block in which image data is mixed with a specific color and a black and white image, the average gradation value of each of the specific color and the black and white image and the result determined by the determination unit are specified. The gradation dispersion index value of each of the constant color and the black-and-white image and the two-level quantum value of each of the specific color and the black-and-white image obtained by the quantizing means are coded in block units, and only the specific color or the black-and-white image exists. In the non-block, the average gradation value, the gradation dispersion index value having the result judged by the judging means, and the four-level quantized value obtained by the quantizing means are coded in block units. An image data encoding method characterized by encoding. 4. An image data encoding method for encoding multi-tone black-and-white and specific color mixed image data, wherein the multi-tone black-and-white and specific color mixed image data is divided into blocks each having a preset number of pixels. Of the divided multi-tone black-and-white / specific color mixed image data, the pixel value for which a flag signal indicating a multi-tone specific color pixel is set is compared with a preset threshold value, and a pixel higher than the threshold value is compared. If the value is a value, the pixel value of the white image is changed, and if the pixel value is lower than the threshold value, the flag signal of the pixel is lowered. The average gradation value in a block is obtained, the flag signal processed by the changing unit is checked, and the gradation value for each pixel in one block of multi-gradation monochrome / specific color mixed image data is determined. A gradation distribution index value indicating whether the specified color is present is checked, the flag signal is checked, and it is determined whether or not a specific color exists in one block of multi-gradation monochrome / specific color mixed image data. , The average gradation value and the gradation distribution index value
The specific color mixed image data is quantized into 2 levels, and when the specific color does not exist in the block, it is quantized into 4 levels, and the determination result is embedded in a preset position of the gradation dispersion index value, Tonal black and white / specific color mixed image data is encoded on a block-by-block basis into an in-block average gradation value and the in-block gradation dispersion index value having the determination result. A method for encoding image data, characterized in that a block having no specific value and the flag signal and a specific color is encoded into the four-level quantized value in block units.