JP2001086346A - Image-encoding device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain high compression efficiency, while maintaining image contrast using a simple configuration. SOLUTION: This image encoding device that reduces the amount of information of image data composed of a plurality of color components and performs processing, is provided with a group-dividing means 1 for dividing the image data composed, of the plurality of color components into image data of color components which belong to a 1st group and image data of color components belonging to a 2nd group, and an amount of information reducing means 2 for reducing the amount of information of the image data of the color components of the 1st and 2nd groups divided by the group dividing means. Then, the means 2 makes the polarity of distortion quantity caused by reducing the amount of information of the image data of the color components of the 1st group and the polarity of distortion quantity caused by reducing the amount of information of image data of the color components of the 2nd group reverse in polarity to each other.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image coding apparatus having a function of processing by reducing the information amount of image data composed of a plurality of color components.

[0002]

2. Description of the Related Art In recent years, with the progress of digital technology, opportunities for handling high-definition color images that appeal to human vision have increased. For this reason, a remarkable progress has been made in compression techniques for compressing and handling image data in order to reduce the amount of memory and the transmission time. For example, in the case of a digital color copying machine that creates four color plates of C (cyan), M (magenta), Y (yellow), and K (black) and superimposes them to form a full-color image, A large amount of memory for holding image data is used. In order to reduce the memory cost, an image coding technique for compressing data is used. The data compression processing techniques can be broadly classified into lossless compression and irreversible compression. Lossless compression is a method in which the same data as the original is obtained even after restoration after compression, and irreversible compression does not produce the same data as the original completely, but is restored with some distortion It is a method. However, in terms of the performance of the compression ratio, the irreversible compression method is generally superior. In an image forming apparatus such as a copying machine, a small amount of distortion is often allowed, and irreversible compression, which is excellent in compression rate performance, is often used to reduce the amount of memory. However, in the irreversible compression, since the image quality and the compression ratio have characteristics that are contradictory to each other, there has been conventionally devised how to improve the compression ratio without lowering the image quality. For example, Japanese Patent Application Laid-Open No. 5-153354 discloses a device that does not use the irreversible compression method for the K plate that is important in image quality. Also, Japanese Patent No. 269864
In Patent Document 1, the K signal is predicted from the CMY signal, so that the printing image data can be converted into a form having a lower correlation between signals, and the compression efficiency is increased.

[0003]

However, in the above-mentioned conventional example, Japanese Patent Laid-Open No. 5-153354, the K signal is processed independently of the CMY signal. When the reduced distortion occurs, there is a disadvantage that an image with reduced contrast is obtained. In addition, the above-mentioned conventional example of Japanese Patent No. 269864
According to Patent Document 1, although the compression efficiency can be increased with respect to the K signal, irreversible compression cannot be performed with respect to the CMY signal, and the compression efficiency as seen from all signals cannot be said to be high. Was. Therefore, the problem to be solved by the present invention is a simple configuration, while maintaining the contrast of an image,
It is an object of the present invention to provide an image encoding device capable of obtaining high compression efficiency.

[0004]

According to the first aspect of the present invention, there is provided an image encoding apparatus for processing by reducing the information amount of image data composed of a plurality of color components. Group classification means for classifying image data composed of a plurality of color components into image data of color components of a first group and image data of color components of a second group, and a first group classified by the group classification means And an information amount reducing means for reducing the information amount of the image data of the color components of the second group, wherein the information amount reducing means comprises a distortion caused by reducing the information amount of the image data of the color components of the first group. The polarity of the amount and the polarity of the amount of distortion generated by reducing the information amount of the image data of the color components of the second group are set to be opposite polarities.
Further, in the invention according to claim 2, in an image coding apparatus for processing by reducing the information amount of image data composed of a plurality of color components, the image data composed of a plurality of color components is Group classification means for classifying into image data of color components and image data of color components of a second group, and information amount reduction for reducing the information amount of image data of color components of the first group classified by the group classification means Means, a distortion amount measuring means for measuring an amount of distortion generated by the information amount reducing means, and a correction amount for the image data of the second group of color components based on the distortion amount measured by the distortion amount measuring means. The information amount reducing unit calculates the image data of the color component of the second group classified by the group classifying unit by the correction amount calculating unit. It is characterized in that also reduce the amount of information of image data obtained by calculating a positive amount.

[0005] According to the third aspect of the present invention, the first aspect is provided.
Or the plurality of color components of cyan, magenta, yellow, and black are included in the plurality of color components.
According to the fourth aspect of the present invention, the first, second or third aspect of the invention is provided.
In the image coding device described above, the color component of the image data of the second group is black. Further, according to the invention described in claim 5, according to claim 1,
4. The image encoding device according to 2 or 3, wherein the color component of the first group of image data is black. In the invention according to claim 6,
3. The image encoding apparatus according to claim 2, wherein the polarity of a change caused by a result of calculating a correction amount on the image data of the color component of the second group is a color of the first group measured by a distortion amount measuring unit. It is characterized in that the polarity is opposite to the polarity of the distortion amount of the image data of the component.

According to the first aspect of the present invention, when the information amount of the color component image data of the first group and the second group classified by the group classifying means is reduced by the information amount reducing means, The polarity of the amount of distortion caused by reducing the amount of information of the image data of the color components of the first group and the polarity of the amount of distortion caused by reducing the amount of information of the image data of the color components of the second group are reversed. Since it is designed to be polar, a part of the distortion generated in the first group is corrected in the second group, or a part of the distortion generated in the second group is corrected so that a visual effect can be obtained in the first group, The overall image quality can be prevented from deteriorating. According to a second aspect of the present invention, the image data of the first group and the second group of color components are classified by the group classification means, and the information amount of the color group image data of the first group is reduced by the information amount reduction means. The amount of distortion generated at that time is measured by the distortion amount measuring means, the correction amount calculating means calculates the correction amount for the image data of the second group based on the distortion amount, and the correction calculated by the correction amount calculating means. Since the amount is calculated by the image data of the second group, and the information amount reducing unit reduces the information amount of the image data of the color components of the second group after the calculation,
The correction based on the distortion amount generated in the first group can be applied to the image data of the color components of the second group.

According to a third aspect of the present invention, in addition to the invention of the image encoding apparatus configured as in the first or second aspect,
The plurality of color components are a plurality or all of the color components of cyan, magenta, yellow, and black, and thus can be handled as image data of color components whose correction conditions for producing a visual effect are well understood. According to a fourth aspect of the present invention, in addition to the invention of the image encoding apparatus configured as in the first, second, or third aspect, the color component of the second group of image data is black. Since only one color needs to be corrected, the configuration for performing the correction can be simplified. According to a fifth aspect of the present invention, in addition to the invention of the image encoding apparatus configured as in the first, second, or third aspect, since the color components of the first group of image data are black, the distortion is reduced. A configuration in which the correction of the amount is easily distributed to each color can be provided. According to a sixth aspect of the present invention, in addition to the image encoding apparatus of the second aspect, the polarity of the amount of distortion of the image data of the first group of color components and the color component of the second group are Since the polarity of the change generated as a result of calculating the correction amount for the image data is opposite to the polarity, it is possible to appropriately correct the color components of the entire image.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, embodiments of the present invention will be described in detail with reference to the accompanying drawings. FIG. 1 is a block diagram showing a main part of a color copying machine having a compression / decompression unit. In FIG. 1, an original is optically read using a line sensor, and R (red), G (green),
Gamma adjustment is performed by the gamma adjustment unit 11 on the B (blue) signal. Further, a filtering process by the filter unit 12, a CMY color conversion process by the CMY conversion unit 13, a background removal process and a black plate generation process by the background removal / K generation unit 14, a gradation process by the gradation processing unit 15, and the like are sequentially performed for each pixel. To form images of the respective colors. In the case of a color copying machine having only one writing means, four-color CMYK plates are formed in a plane-sequential manner. That is, after one color plate is formed, another color plate is formed, four color plates are sequentially formed, and these are combined to form one color image. In the case of a color copying machine having four writing means, CMYK
Can be formed almost simultaneously. However, since it is difficult to form the four-color plate completely at the same time due to the structure of the apparatus, the formation of the four-color plate is usually performed with a slight delay. The page memory unit 17 in FIG.
This is a memory portion for holding the K signal for one or more pages. In particular, if the number of scans is set to one for one original in a color copying machine having only one writing means, this can reduce power consumption, reduce noise, increase the reading speed, and vary the speed for each scan. This is necessary because it is effective for preventing the image quality from being degraded due to, for example. Also,
If the CMYK signals stored in the page memory unit 17 are read out with a slight delay, it is possible to shift the time for forming a four-color plate with a color copying machine having a plurality of writing means.

The page memory unit 17 has, for example, a resolution of 600 dpi and a gradation of 32 bits / pix.
el, paper size A3, the memory capacity is 280
MB. Therefore, the compressed data is stored in the page memory unit 17, and the data is restored to the original data or almost original data by applying the data decompression technique by the compression / decompression unit 16 at the write timing. To the gradation processing unit 15. As described above, by applying the data compression and data decompression technology by the compression / decompression unit 16, the memory capacity of the page memory unit 17 can be reduced. In addition, to reduce the memory capacity by this data compression technology, irreversible compression, in which data that is closer to the original form is obtained with some distortion, is more effective than lossless compression, in which data is restored and completely the same as the original data is obtained. In general, the reduction effect is larger. It is also well known that if the amount of distortion is large at the time of restoration, the image quality is reduced accordingly.

FIGS. 2 and 3 are block diagrams showing a main part of an image coding apparatus according to the present invention. In FIG.
A CMYK signal input to a compression encoding unit 2 serving as an information amount reducing unit that performs irreversible compression is once input to a group classification unit 1 serving as a group classification unit, and the image data of the color component of the first group is added to the CMYK signal. The image data is classified into image data of color components of the second group. Here, the group classification unit 1 uses CMY as the image data of the color components of the first group.
The image data is classified into image data based on signals and image data based on K signals as image data of color components of the second group. Each image data grouped by group,
The signal is input to a predetermined input terminal of the compression encoder 2. Further, the first group compression encoding circuit 2a of the compression encoding unit 2 performs a compression encoding process on the input first group CMY signals. Further, the distortion amount determination unit 2b determines the polarity of the distortion amount of the first group generated by the compression encoding process of the first group compression encoding circuit 2a, and the second group compression encoding circuit 2c determines the polarity of the second group. The polarity of the amount of distortion generated by performing the compression encoding process on the K signal is made to be opposite to the polarity of the amount of distortion of the first group. Here, the manner of operation of the distortion amount determination unit 2b that reverses the polarity of the distortion amount of the first group and the distortion amount of the second group is, for example, based on the determination of the polarity of the distortion amount of the first group. The second group compression encoding circuit 2 is arranged so that the distortion amount of the second group is opposite in polarity.
c, or the K signal processed by the second group compression encoding circuit 2c may be operated.

FIG. 3 shows that the group classification unit 1 uses the K-signal image data as the first group color component image data and the C-signal image data as the second group color component image data.
The image data is classified into image data based on the MY signal. Each image data classified by group is input to a predetermined input terminal of the compression encoding unit 2. In the first group compression encoding circuit 2a of the compression encoding section 2, the input first group K
The signal is subjected to a compression encoding process. Further, the distortion amount determination unit 2b determines the polarity of the distortion amount of the first group generated by the compression encoding process of the first group compression encoding circuit 2a, and the second group compression encoding circuit 2c determines the polarity of the second group. The polarity of the amount of distortion generated by performing the compression encoding process on the CMY signal is made to be opposite to the polarity of the amount of distortion of the first group. FIG. 4 is an example of a block diagram showing the image encoding apparatus based on FIG. 2 in more detail. In the figure, a group classification unit 1 classifies image data based on a CMY signal of a first group and image data based on a K signal of a second group. Each of the classified image data is input to a predetermined input terminal of the compression encoder 2. Also, each compression encoding circuit of the compression encoding unit 2 converts, for example, image data to 8 ×
DCT (Discrete Cosine Tr) in block units of 8 pixels
The DCT circuit performs an ansform process, a quantization circuit that quantizes the transform coefficient generated by the DCT circuit, an entropy encoding circuit that entropy encodes the quantization result, and the like. First, the C signal of the first group is compression-encoded by the DCT circuit 2C1, the quantization circuit 2C2, and the entropy encoding circuit 2C3, and is stored in the page memory unit 17.

On the other hand, the DCT circuit 2C1 and the quantization circuit 2
A part of the signal compressed by C2 is returned to the restoration unit 5, and restored by the inverse quantization circuit 5C2 and the inverse DCT circuit 5C1 so as to be close to the original C signal. Input to the measuring unit 3. In the distortion amount measurement unit 3,
From the C signal before being processed by the compression encoding unit 2 and the C signal restored by the restoration unit 5, the distortion amount measurement circuit 3C1
Thus, the magnitude and polarity of the distortion amount are measured in pixel units. The measured result is transmitted to a correction amount calculation unit 4 which is a correction amount calculation unit. The above processing is performed for the C signal, the M signal, and the Y signal, and the magnitude and polarity of the measured distortion amount of each signal are transmitted to the correction amount calculation unit 4. Further, the correction amount calculation unit 4 first checks the polarity of the distortion amount of the CMY signal. When all the polarities of the distortion amounts of the three signals are positive or negative, the minimum value of the absolute values of the distortion amounts of the three signals is selected and output. For example, if the distortion amount of the C signal is ΔC = 6, the distortion amount of the M signal is ΔM = 2, and the distortion amount of the Y signal is ΔY = 5, the output Δcorrection of the correction amount calculation unit 4 becomes 2, and ΔC = −3. , ΔM = −5 and ΔY = −4, the output Δcorrection of the correction amount calculation unit 4 becomes −3. The correction value obtained here is subtracted from the K signal by the K signal correction amount calculation unit 6. An example showing this state is shown in FIG.
That is, in FIG. 6, the amount of distortion generated when the C signal is subjected to the compression encoding process is set to ΔC = −3, the amount of distortion generated when the M signal is subjected to the compression encoding process is set to ΔM = −5, and the Y signal When the amount of distortion generated when the compression encoding process is performed is ΔY = −4, the correction amount to be corrected to the K signal before the compression encoding process is:
The distortion amount ΔC of the C signal which is the minimum value of the absolute value of the distortion amount of the three signals
= −3, and the process of subtracting from the K signal is performed. This is the same as adding a value in which the polarity of the correction amount is reversed to the K signal.

As described above, a part of the distortion generated when the CMY signal is subjected to the compression encoding process is replaced with the K signal to perform a correction for obtaining a visual effect. Further, in the correction amount calculation unit 4 of the present invention, when the polarity of the distortion amount of the three signals is mixed with positive and negative, the output Δ correction of the correction amount calculation unit 4 = 0.
And Further, the above ΔC = −3, ΔM = −5, Δ
If the CMY signals tend to decrease as a whole, as in the case of Y = -4, an image with reduced contrast will result. However, the image quality is degraded by increasing the K signal by 3 and performing compression coding. Can be reduced. When the CMY signals tend to increase as a whole, an image having enhanced contrast is obtained. However, the K signal is reduced by a predetermined value and compression encoding is performed to enhance the contrast. It becomes possible to suppress. Further, the K signal from which the correction value has been subtracted by the K signal correction amount calculating unit 6 is also converted into the DCT circuit 2K1 and the quantization circuit 2K.
Since the compression encoding process is performed by the K2 and the entropy encoding circuit 2K3, a new distortion also occurs in the K signal.
However, since the K signal to be compression-encoded is shifted from the original data by an amount corresponding to the amount of distortion of the CMY signal,
It goes without saying that the contrast is surely corrected. The method of calculating the correction amount by the correction amount calculation unit 4 is not limited to the method described above. It is also possible to use the maximum and average absolute values of the distortion amount ΔC of the C signal, the distortion amount ΔM of the M signal, and the distortion amount ΔY of the Y signal. ΔC, Δ
A value obtained by multiplying the maximum value or the average value of the absolute values of M and ΔY by a predetermined value may be output. Further, the predetermined value to be multiplied may be changed.

FIG. 5 is an example of a block diagram showing the image encoding apparatus based on FIG. 3 in more detail. In the figure, a group classification unit 1 classifies image data based on a first group of K signals and image data based on a second group of CMY signals. Each of the classified image data is input to a predetermined input terminal of the compression encoder 2. Also, each compression encoding circuit of the compression encoding unit 2 converts, for example, image data to 8 ×
DCT (Discrete Cosine Tr) in block units of 8 pixels
4 includes a DCT circuit for performing an ansform) process, a quantization circuit for quantizing a transform coefficient generated by the DCT circuit, and an entropy coding circuit for entropy coding the quantization result. Is the same as Further, in this case, the first group K
The signal is compression-encoded by the DCT circuit 2K1, the quantization circuit 2K2, and the entropy encoding circuit 2K3, and is stored in the page memory unit 17. DCT circuit 2
Part of the signal processed by the K1 and the quantization circuit 2K2 is returned to the restoration unit 5, and the inverse quantization circuit 5K2 and the inverse DC
The signal is restored to a shape close to the original K signal by the T circuit 5K1 and input to the distortion amount measurement unit 3. The distortion amount measurement unit 3 measures the magnitude and polarity of the distortion amount on a pixel-by-pixel basis by the distortion amount measurement circuit 3K1 from the K signal before processing and the K signal restored by the restoration unit 5. The measured result is transmitted to the correction amount calculation unit 4.

If the next signal to be compression-coded is a C signal, the correction amount calculating section 4 corrects the magnitude and polarity of the distortion amount obtained by the distortion amount measuring circuit 3K1 to the C signal correction amount calculating section 7. Output as a value. The C signal correction amount calculation unit 7 subtracts the obtained correction value from the C signal. The C signal subjected to the correction processing in this way is subjected to compression encoding processing by the DCT circuit 2C1, the quantization circuit 2C2, and the entropy encoding circuit 2C3 of the compression encoding unit 2, and is stored in the page memory unit 17. You. Similarly, the M signal and the Y signal corrected by the M signal correction amount calculation unit 8 and the Y signal correction amount calculation unit 9 are subjected to compression coding processing by the compression coding unit 2, and are sequentially stored in the page memory. Stored in the unit 17. Here, the output of the correction amount calculation unit 4 may output the magnitude and polarity of the distortion amount obtained by the distortion amount measurement circuit 3K1 as a correction value as described above, or may output the value multiplied by a predetermined value. You may. 4 and 5, the compression encoding process of the compression encoding unit 2 is performed in units of blocks by DCT (Discrete Coding).
sine Transform) processing, but DC
The processing is not limited to the T processing, and other orthogonal transformation such as Hadamard transformation, subband transformation, wavered transformation, BTC (Block Truncation Coding), or the like may be used. Entropy coding is also effective for improving the compression ratio, but is not necessary when performing fixed-length compression. In some cases, the compression-encoding process is not performed on the corrected signal. In the description of the embodiment, the compression encoding unit 2 that performs irreversible compression as information amount reduction means
As described above, a simple pixel unit quantization such as truncation of n bits on the LSB side or reduction of the number of bits using a table may be used. Also, truncation quantization for the CMY signal,
The K signal may be configured to perform round-up quantization or vice versa.

[0016]

As described above, according to the first aspect of the present invention,
Perform the compression encoding process so that the polarity of the distortion amount of the first group and the polarity of the distortion amount of the second group are mutually opposite polarities, in the second group based on the distortion amount generated in the first group, or Since the first group is corrected based on the amount of distortion generated in the second group so that a visual effect can be obtained, it is possible to provide an image encoding device that can obtain high compression efficiency while maintaining the contrast of the entire image. It became so. According to the second aspect of the present invention, the correction for obtaining the visual effect based on the distortion amount generated in the first group can be adapted to the image data of the color components of the second group.
It has become possible to provide an image encoding device that can obtain high compression efficiency while maintaining the contrast of the entire image. According to the invention of claim 3, in addition to the invention of the image encoding apparatus of claim 1 or 2, image data of cyan, magenta, yellow, and black color components whose correction conditions are well understood are handled. Therefore, it is possible to provide an image coding apparatus in which color components can be easily corrected and image deterioration is small. According to the fourth aspect of the present invention, in addition to the image encoding apparatus of the first, second or third aspect, an image encoding apparatus in which the configuration for performing the correction is simplified and appropriate correction is performed. Now available. According to the fifth aspect of the invention, in addition to the invention of the image encoding apparatus of the first, second or third aspect, the color component of the first group of image data is black, so that the distortion amount of the black component can be corrected. It is now possible to provide an image encoding device that can achieve high compression efficiency while performing fine correction of image contrast because it can be dispersed into each color component other than black. According to the invention of claim 6, in addition to the invention of the image encoding apparatus of claim 2, the polarity of the amount of distortion of the image data of the first group of color components and the image data of the second group of color components are corrected. The polarity of the change caused by the result of the calculation of the amount is opposite to the polarity, so that it is possible to provide an image encoding device capable of appropriately correcting the color components of the entire image.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a main part of a color copying machine having a compression / decompression unit.

FIG. 2 is a block diagram illustrating a main part of an image encoding apparatus according to the present invention in which image data of color components of a first group is used as CMY signals.

FIG. 3 is a block diagram illustrating a main part of an image encoding apparatus according to the present invention in which image data of a first group of color components is a K signal.

FIG. 4 is a block diagram showing the image encoding apparatus according to the embodiment of the present invention shown in FIG. 2 in more detail;

FIG. 5 is a block diagram showing the image encoding apparatus according to the embodiment of the present invention shown in FIG. 3 in more detail;

FIG. 6 is an explanatory diagram showing a state of correcting a K signal of a second group based on a distortion amount due to a CMY signal of a first group.

[Explanation of symbols]

REFERENCE SIGNS LIST 1 group classification unit (group classification unit) 2 compression encoding unit (information amount reduction unit) 2a first group compression encoding circuit 2b distortion amount determination unit 2c second group compression encoding circuit 2C1, 2M1, 2Y1, 2K1 DCT circuit 2C2, 2M2, 2Y2, 2K2 Quantization circuit 2C3, 2M3, 2Y3, 2K3 Entropy coding circuit 3 Distortion amount measurement unit (distortion amount measurement unit) 3C1, 3M1, 3Y1, 3K1 Distortion amount measurement circuit 4 Correction amount calculation unit (correction) 5 Reconstruction unit 5C1, 5M1, 5Y1, 5K1 Inverse DCT circuit 5C2, 5M2, 5Y2, 5K2 Inverse quantization circuit 6 K signal correction amount calculation unit 7 C signal correction amount calculation unit 8 M signal correction amount calculation unit 9 Y signal correction amount calculation unit 11 Gamma adjustment unit 12 Filter unit 13 CMY conversion unit 14 Background removal / K generation unit 15 Tone processing unit 16 Contraction / expansion unit 17 page memory section

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 5C057 AA07 DC01 EA01 EL01 EM09 EM16 FE03 GG01 5C078 AA09 DA00 DA01 DB00

Claims (6)

[Claims] An image coding apparatus for processing by reducing the amount of information of image data composed of a plurality of color components, wherein the image data composed of a plurality of color components is converted to image data of a first group of color components. Group classification means for classifying image data of color components of the first group and the second group, and information amount reduction means for reducing the information amount of image data of color components of the first and second groups classified by the group classification means The information amount reducing means reduces the polarity of the amount of distortion caused by reducing the amount of information of the image data of the color components of the first group and the amount of information of the image data of the color components of the second group. An image encoding apparatus, wherein the polarity of a distortion amount caused by the above is reversed. 2. An image encoding apparatus for processing by reducing the amount of information of image data composed of a plurality of color components, wherein the image data composed of a plurality of color components is converted to image data of a first group of color components. A group classification unit that classifies the image data of the color components of the first group and an image data of the color components of the second group; an information amount reduction unit that reduces the information amount of the image data of the color components of the first group classified by the group classification unit; Distortion amount measuring means for measuring the amount of distortion caused by the amount reducing means, and correction amount calculating means for calculating a correction amount for the image data of the color component of the second group based on the amount of distortion measured by the distortion amount measuring means The information amount reducing unit causes the image data of the color components of the second group classified by the group classification unit to calculate the correction amount calculated by the correction amount calculation unit. Image coding apparatus characterized by reducing also the amount of information of the image data. 3. The image encoding apparatus according to claim 1, wherein the plurality of color components are a plurality of or all color components of cyan, magenta, yellow, and black. . 4. The image encoding apparatus according to claim 1, wherein the color component of the image data of the second group is black. 5. The image encoding device according to claim 1, wherein the color component of the image data of the first group is black. 6. The image encoding apparatus according to claim 2, wherein a polarity of a change caused by a result of calculating a correction amount on the image data of the color component of the second group is measured by a distortion amount measuring unit. An image coding apparatus, wherein the polarity of the distortion amount of the image data of one group of color components is opposite to the polarity of the distortion amount.