JP3728025B2 - Image processing method and apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
  The present inventionConvert input color space data to output color space dataThe present invention relates to an image processing method and apparatus.
[0002]
[Prior art]
Conventionally, an image processing method based on a color dot model is widely known as an image processing method for a color printer.
[0003]
FIG. 20 is a block diagram illustrating a configuration of an image processing unit in a conventional color printer. First, the RGB luminance signals input from the input terminal 101 are converted into CMY density signals by the density converter 102. Next, from the converted density signal, a black density signal K is generated by the black generation unit 103, and a halftone dot area signal in which the masking / UCR unit 104 removes the lower color and the crosstalk component of each density signal is compensated. It becomes. The output gamma correction unit 105 compensates for the linearity between the dot area signal and the output density due to dot gain and the like, and the binarization unit 106 binarizes each color component to form a dot pattern as an output terminal. From 107, the data is output to a printer engine (not shown).
[0004]
The density conversion unit 102 and the output γ correction unit 105 are configured by a normal lookup table (hereinafter referred to as “LUT”).
[0005]
[Problems to be solved by the invention]
However, in the above conventional example, since binarization processing is performed for each CMYK plane, the overlapping of CMYK dots is random, matching of color reproduction by masking, and limitation of the number of dots on dots However, it was very difficult.
[0006]
In addition, since each process of density conversion, black generation, masking / UCR, output γ correction, and binarization is performed independently, the processing takes time or the amount of hardware (calculation amount) becomes enormous. There was also a drawback.
[0007]
US Pat. Nos. 5,070,413 and USP 5,270,808 are known techniques for converting input color image data into output color image data within a three-dimensional color space. These technologies disclosed in USP obtain 1-bit output data for each of Y, M, C, and K from 8-bit input data for each of R, G, and B.
[0008]
In this method, input data represented by 8 bits each of R, G, and B in a three-dimensional color space is closer to which of 16 output colors represented by 1 bit of Y, M, C, and K. Therefore, 16 distances between the input data and the output color are obtained, and the one with the shortest distance is determined as the output color.
[0009]
In this case, there is a drawback that it takes time for the arithmetic processing, and high-speed processing and further image quality improvement processing have been desired.
[0010]
The present invention has been made to solve the above-described problems, and an object thereof is to provide an image processing method and apparatus capable of obtaining a high-quality color image by high-speed processing.
[0011]
Another object of the present invention is to convert each of a plurality of input color component data into data of a level closer to the input level, access a table with data having a reduced data amount, and generate a plurality of output color component data. Thus, an object of the present invention is to provide an image processing method and apparatus capable of easily and quickly obtaining a high-quality color image.
[0012]
A further object of the present invention is to obtain a high-quality color image with higher resolution than the input resolution easily and at high speed by generating a plurality of output color component dot patterns from a plurality of input color component data by table conversion. An object of the present invention is to provide an image processing method and apparatus capable of performing the above.
[0013]
A further object of the present invention is to generate an output dot pattern directly from input pixel data using an LUT in which an input color space is divided into a predetermined number and an output dot pattern is mapped for each divided space. By converting the output dot pattern into the input color space using an LUT that converts the color to be reproduced into the input color space, obtaining a difference (error) from the input pixel data, and diffusing the difference value to surrounding pixels, the color Reproduction and binarization processing are executed by searching for two LUTs and one error diffusion process, and an image output with good color reproduction can be easily obtained, and since CMYK dot patterns are mapped, CMYK An object of the present invention is to provide an image processing method and apparatus capable of strictly limiting the number of dot-on-dot mixed colors.
[0014]
A further object of the present invention is to execute error diffusion processing by density conversion and quantization in the RGB luminance space and color reproduction error diffusion processing in the output density space. In addition, since errors due to density conversion are corrected, image output with even better color reproduction can be obtained and error reproduction processing for color reproduction is performed in a quantized density space, reducing the amount of hardware. An object of the present invention is to provide an image processing method and apparatus.
[0015]
It is a further object of the present invention to perform scan conversion between error diffusion processing that occurs during density conversion and color space division and color reproduction error diffusion processing, with each error diffusion scan direction reversed. Therefore, an object of the present invention is to provide an image processing method and apparatus capable of improving phase distortion due to error diffusion.
[0016]
Another object of the present invention is to express one pixel by N dots (N is an integer equal to or greater than 2). Therefore, when enlarging to N times (area), enlargement processing is not necessary, and one color with N dots. Therefore, the influence of overlapping surrounding dots is smaller than that of a single dot, thereby improving the accuracy of reproduced color data and providing an image processing method and apparatus capable of improving color reproducibility. With the goal.
[0017]
A further object of the present invention is to provide a process for correcting the color shift due to the overlap of the boundary between the target pixel and the adjacent pixel, thereby improving the accuracy of the color reproduction error and further improving the color reproducibility. An object of the present invention is to provide an image processing method and apparatus.
[0020]
[Means for Solving the Problems]
  In order to achieve the above object, the present invention provides:An image processing method for converting input color space data to output color space data,Input color spaceInAn input process for inputting a plurality of color component data;A correction step for correcting a plurality of color component data input in the input step with a predetermined error signal, and a plurality of color components in the output color space that are predetermined to correspond to the values of the plurality of color components in the input color space. An output step for outputting dot patterns corresponding to values of a plurality of color components in the input color space corrected in the correction step from a dot pattern storage unit for storing dot patterns for each color component, and output in the output step A conversion step of converting the reproduced color of the target pixel into a plurality of color component values in the input color space from the dot pattern of the target pixel and the pixels around the target pixel, and the plurality of color components converted in the conversion step A generating step for generating the predetermined error signal based on a difference value between the value of the color component and the values of the plurality of color components corrected in the correcting step;It is characterized by having.
[0021]
  In order to achieve the above object, the present invention provides:An image processing device for converting input color space data to output color space data,Input color spaceInInput means for inputting a plurality of color component data;Correction means for correcting a plurality of color component data input by the input means with a predetermined error signal; and a plurality of color components in the output color space that are predetermined to correspond to values of the plurality of color components in the input color space. From dot pattern storage means for storing dot patterns for each color component, output means for outputting dot patterns corresponding to values of a plurality of color components in the input color space corrected by the correction means, and the dot pattern storage means A conversion unit that converts the output color of the target pixel into a plurality of color component values in the input color space from the output pixel pattern of the target pixel and the pixel adjacent to the target pixel; Generating means for generating the predetermined error signal based on a difference value between a color component value and a plurality of color component values corrected by the correcting means;It is characterized by having.
[0022]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments according to the present invention will be described in detail with reference to the drawings.
[0023]
[Embodiment 1]
FIG. 1 is a block diagram showing the configuration of the image processing unit in the first embodiment. In the figure, 10 is an input terminal, 11 is an adder, 12 is a limiter, 13 is a quantizer, 14 is a pattern table, 15 is a buffer, 16 is an output luminance table, 17 is an offset adder, 18 is a subtractor, 19 Is a limiter, 20 is a diffusion processing unit, and 21 is an output terminal.
[0024]
Here, the RGB luminance signals input from the input terminal 10 are each added with an error signal by a diffusion processing unit 20 (to be described later) in the adding unit 11 and input to the limiter 12 and the subtracting unit 18. The limiter 12 limits the output of the adder 11 to the existence range of the input RGB luminance signal, and outputs the result to the quantizer 13. The quantization unit 13 is for reducing the number of input bits to the pattern table 14, and for example, 9 bits of RGB are quantized to 3 bits of RGB.
[0025]
Next, a dot pattern with a limited number of mixed colors is mapped in advance in the pattern table 14. When a quantized RGB luminance signal is input, the CMYK dot pattern is stored in the buffer 15 and the output luminance table 16. At the same time, it is output from the output terminal 21 to a printer engine (not shown). For example, the maximum number of mixed colors (the maximum value of the number of colors that overlap with dots on) is “2”, the dot on is “1”, and the off is “0”.
[0026]
CMYK = (1100), (1010), (1001), (0110), (0101), (0011), (1000), (0100),
(0010), (0001), (0000)
11 colors are mapped in the quantized RGB space of the pattern table 14, and one of the 11 colors is selected and output according to the input RGB luminance signal.
[0027]
The buffer 15 outputs a dot pattern of a pixel spatially adjacent to the target pixel to the output luminance table 16. The output luminance table 16 stores in advance values obtained by converting the reproduction color of the pixel of interest in consideration of the influence of overlapping of adjacent pixels into RGB luminance signals, and the pixel of interest and its adjacent pixels are stored by the pattern table 14 and the buffer 15. When each dot pattern of the pixel is input, a converted value of the RGB luminance signal of the color reproduction color of the target pixel is output.
[0028]
Next, the offset adding unit 17 is for simplifying the configuration of the limiter 19 and the adding unit 11 to be described later. For example, the RGB input signals are 8 bits, and the error range to be diffused is [−128 to 128]. Then, by adding an offset of “128”, the output of the limiter 19 and the diffusion processing unit 20 becomes a positive value of “0 to 255”. The next subtracting unit 18 subtracts the output of the offset adding unit 17 from the output of the adding unit 11 and outputs the result to the limiter 19 as a color reproduction error. The limiter 19 limits the color reproduction error within a predetermined range and outputs the error to the diffusion processing unit 20. The diffusion processing unit 20 then diffuses the input color reproduction error to surrounding pixels according to a predetermined diffusion coefficient. The diffused error is accumulated for each pixel and output to the adder 11.
[0029]
For example, if the input signal is 8 bits for RGB (0 to 255), the error range to be diffused is [−128 to 128], and the offset is “128”, the output of the adder 12 is 9 bits of “0 to 512”. It becomes. Then, the limiter 12 limits the 9 bits of “0 to 512” to [128 to 383] (because the offset of “128” is added), which is the existence range of the input RGB signal. Next, in the case where the quantization unit 13 performs linear quantization, each of the upper 3 bits is removed by removing the second bit from the MSB of each of the limited RGB signals (to remove the “128” offset). Extract. Then, the pattern table 14 outputs 4 bits of dot patterns indicating ON / OFF of dots of each plane of CMYK stored in the address selected by the input 3 bits for each of RGB, 9 bits in total.
[0030]
In the pixel arrangement as shown in FIG. 7, if F is a target pixel, the buffer 15 outputs a dot pattern of B and E pixels indicated by bold lines to the output luminance table 16 (for pixels A and C in oblique directions). It is assumed that the influence on the target pixel F is small and is ignored here). The output luminance table 16 outputs the reproduction color of the target pixel from the above-described three-pixel dot pattern in RGB of 8 bits. The next offset adding unit 17 adds “128” to each of the RGB reproduction colors. That is, the MSB of each reproduction color of RGB is set as the MSB after addition, the 9th bit of RGB is output with the second bit from the MSB inverted as the MSB and the other bits as they are. The subtracting unit 18 subtracts 9 bits of each reproduction color added by offset from each 9 bits of RGB to which the error is added, and the result is an error range [0-255] after the offset addition by the limiter 19. It is limited to 8 bits and is output to the diffusion processing unit 20. Then, the diffusion processing unit 20 diffuses the input error by multiplying each of G, I, J, and K pixels indicated by broken lines in FIG. 7 by a predetermined diffusion coefficient. The total of the diffusion coefficients of the diffusion processing unit 20 does not exceed “1”, and the diffusion error output from the diffusion processing unit 20 is 8 bits of “0 to 255”.
[0031]
FIG. 8 is a diagram illustrating an example of pixels output from the buffer 15 during two-pass printing and pixels that diffuse errors. Here, it is assumed that BDEGJLOQ is printed in the first pass and ACFHIKPR is printed in the second pass. When J is the target pixel in the first pass, the reproduction color is determined from GEJ, and the error is diffused to the LOQ pixel. Next, when F is the target pixel in the second pass, a reproduction color is determined from BEFGJ indicated by a thick line, and an error is diffused to the HIK pixel indicated by a broken line. In this example, since the dot pattern of the upper, lower, left, and right pixels is fixed for the reproduced color in the second pass, the accuracy is very high.
[0032]
In FIG. 7 as well, the influence of the pixels G and J on the target pixel F can be compensated by the reproduced colors when the pixels G and J are determined. In the two-pass printing example of FIG. 8, the phase distortion in error diffusion can be apparently compensated by changing the scanning in the main scanning direction between the first pass and the second pass. That is, when G is the target pixel in the first pass (scanning from right to left), the error is diffused to the LJE pixel. Next, when F is the target pixel in the second pass (scanning is from left to right), the error is diffused to the HIK pixel indicated by the broken line.
[0033]
Further, the output luminance table 16 is obtained by conversion from actual measurement values. Therefore, not only density adjustment and color balance adjustment, but also color matching (correction of differences in reproduction color depending on the output medium) and the like can be handled by rewriting the output luminance table 16 (however, the pattern table 14 needs to be rewritten). In some cases).
[0034]
In the above description, the output luminance table 16 and the offset adding unit 17 are configured separately, but the offset adding unit 17 can be omitted by storing the value obtained by adding the offset in the output luminance table 16. Further, when the above-described processing is executed by a general-purpose processor such as a CPU or a DSP, a positive / negative value of 10 bits or more can be taken as data, so that an offset addition processing is not necessary.
[0035]
Further, although the pattern table 14 and the output luminance table 16 are configured by LUT, they may be configured by logic or calculation.
[0036]
As described above, according to the present embodiment, an output dot pattern is generated directly from input pixel data using an LUT in which an input color space is divided into a predetermined number and an output dot pattern is mapped for each divided space. The output dot pattern is converted into the input color space using the LUT that converts the color reproduced by the output dot pattern into the input color space, the difference (error) from the input pixel data is obtained, and the difference value is diffused to surrounding pixels. Thus, color reproduction and binarization processing are executed by searching for two LUTs and performing one error diffusion processing, and an image output with good color reproduction can be easily obtained. Also, since the CMYK dot pattern is mapped, the number of CMYK dot-on-dot color mixture can be strictly limited.
[0037]
[Embodiment 2]
Next, Embodiment 2 according to the present invention will be described in detail with reference to the drawings.
[0038]
FIG. 2 is a block diagram showing the configuration of the image processing unit in the second embodiment. In the figure, 22 is a density conversion unit, 23 is a pattern table, and 24 is an output density table. The other blocks are the same as in FIG.
[0039]
Here, the RGB luminance signals input from the input terminal 10 are converted into CMY density signals by the density converter 22. Hereinafter, the error diffusion process including the subtractor 18, the limiter 19, the diffusion processor 20, and the adder 11 is executed in the above-described CMY density space. Therefore, the output dot pattern of the pattern table 23 is mapped to the above-described CMY density space, and the output density table 24 converts the reproduction color of the pixel of interest into the CMY density signal in consideration of the influence of overlapping of adjacent pixels. Stores the value.
[0040]
According to the present embodiment, an image output with better color reproduction can be obtained by executing error reproduction processing for color reproduction in a density space that is linear with respect to vision.
[0041]
[Embodiment 3]
Next, Embodiment 3 according to the present invention will be described in detail with reference to the drawings.
[0042]
FIG. 3 is a block diagram showing the configuration of the image processing unit in the third embodiment. In the figure, 25 is an inverse quantization unit, 26 is a luminance conversion unit, 27 is a subtraction unit, 28 is a diffusion processing unit, 29 is an addition unit, 30 is a limiter, 31 is an inverse quantization unit, 32 is an addition / subtraction unit, and 33 is A quantization unit, 34 is an inverse quantization unit, and 35 is a subtraction unit. The other blocks are the same as in FIG.
[0043]
Here, the RGB luminance signals input from the input terminal 10 are added with an error signal accompanying density conversion and quantization from the diffusion processing unit 28 by the addition unit 11 for each RGB luminance signal, and the limiter 12 and the subtraction. Input to the unit 27. The limiter 12 limits the output of the adder 11 to the existence range of the input RGB luminance signal, and outputs the result to the density converter 22. The density conversion unit 22 converts the input RGB luminance signal into a CMY density signal and outputs it to the quantization unit 13. The quantization unit 13 is for reducing the number of input bits of the pattern table 23, and for example, 9 bits of CMY are quantized to 3 bits of CMY. The quantized CMY density signal is restored to the original RGB luminance signal through the inverse quantization unit 25 and the luminance conversion unit 26. The subtractor 27 calculates an error due to density conversion and quantization by subtracting the restored RGB luminance signal from the RGB output of the limiter 12. The calculated error is diffused to surrounding pixels by the diffusion processing unit 28, and the accumulated error is output to the adding unit 11.
[0044]
On the other hand, the quantized CMY density signal is also input to the adder 29, and an error signal associated with color reproduction is added for each CMY signal by the adder 29 and input to the limiter 30 and the inverse quantizer 31. . The limiter 30 limits the output of the adder 29 to the existence range of the quantized CMY signal and outputs the result to the pattern table 23. The inverse quantization unit 31 performs digit alignment with the CMY signal output from the offset addition unit 17 by converting the quantized CMY signal into a quantized representative value.
[0045]
The adder / subtractor 32 subtracts the CMY signal output from the offset adder 17 from the quantized representative value of the CMY signal output from the inverse quantizer 31, and at the same time performs the quantization by the quantizer 33 output from the subtractor 35. Add the error. The output of the adder / subtractor 32 is limited within a predetermined range by the limiter 19, and the result is diffused to surrounding pixels by the diffusion processor 20. The diffused error is accumulated for each pixel and output to the quantization unit 33 and the subtraction unit 35. The quantization unit 33 quantizes the error signal by the same method as the quantization unit 13. The quantized error signal is output to the adder 29 and the inverse quantizer 34. The inverse quantization unit 34 converts the quantized error signal into a quantized representative value, the subtraction unit 35 calculates a difference from the signal before quantization, and outputs the quantization error to the addition / subtraction unit 32. To do.
[0046]
The density conversion unit 22, the quantization unit 13, the inverse quantization unit 25, the luminance conversion unit 26, and the subtraction unit 27 can be configured by one LUT. In other words, a table for outputting quantization errors including quantization density signals and conversion errors may be generated for each RGB input signal. Similarly, the quantization unit 33, the inverse quantization unit 34, and the subtraction unit 35 can also be configured by one LUT.
[0047]
Thus, since the color reproduction error diffusion processing is performed in the quantized density space, the number of bits of the adder 29 and the limiter 30 and the memory capacity of the diffusion processing unit 20 (the line delay after quantizing the line delay). (When executed with data).
[0048]
According to the present embodiment, error diffusion processing by density conversion and quantization is executed in the RGB luminance space, and color reproduction error diffusion processing is executed in the output density space. In addition, since an error due to density conversion is also corrected, an image output with even better color reproduction can be obtained. In addition, since the color reproduction error diffusion process is performed in the quantized density space, the amount of hardware can be reduced.
[0049]
[Embodiment 4]
Next, a fourth embodiment according to the present invention will be described in detail with reference to the drawings.
[0050]
FIG. 4 is a block diagram showing the configuration of the image processing unit in the fourth embodiment. In the figure, reference numeral 36 denotes a scan conversion unit. Other blocks are the same as those in FIG.
[0051]
Here, the scan conversion unit 36 converts the scanning direction of the main scanning of the quantized density signal to the reverse direction. That is, when the RGB luminance signal input from the input terminal 10 is scanned from left to right, the scan conversion unit 36 changes the scan from right to left. Thereby, the diffusion coefficient in the main scanning direction of the error by the diffusion processing unit 28 and the diffusion coefficient in the main scanning direction of the error by the diffusion processing unit 20 are symmetric, and phase distortion due to error diffusion is improved.
[0052]
According to the present embodiment, scan conversion is performed between the diffusion process of errors that occur during density conversion and color space division, and the diffusion process of color reproduction errors, and the scan directions of the respective error diffusions are reversed. Therefore, phase distortion due to error diffusion is improved.
[0053]
[Embodiment 5]
Next, a fifth embodiment according to the present invention will be described in detail with reference to the drawings.
[0054]
FIG. 5 is a block diagram showing the configuration of the image processing unit in the fifth embodiment. In the figure, 37 is a correction value generation unit, and 38 is an addition / subtraction unit. The other blocks are the same as in FIG.
[0055]
Here, the buffer 15 outputs a dot pattern of a pixel spatially adjacent to the target pixel to the correction value generation unit 37. The correction value generation unit 37 receives the dot pattern of the target pixel and the dot pattern of the adjacent pixel, generates a correction value based on the overlap of the adjacent pixel with respect to the reproduction color of the target pixel output from the output density table 24, and performs addition / subtraction To the unit 38.
[0056]
FIG. 6 is a block diagram showing a specific configuration of the correction value generation unit 37 in the present embodiment. In the figure, 39 is a correction value table, and 40 is an adder.
[0057]
The correction value generation unit 37 includes a correction value table 39 corresponding to the number of pixels spatially adjacent to the target pixel output from the buffer 15, and an addition unit 40 that tabulates the correction values in each correction value table 39. Composed. In each correction value table 39, the dot pattern of the pixel of interest and the dot pattern of one adjacent pixel are input, and the correction value resulting from the overlapping of the two pixel dot patterns is output to the adder 40. The adder 40 totals the correction values in each correction value table 39 and outputs the result to the adder / subtractor 38.
[0058]
For example, in the case of the pixel arrangement shown in FIG. 7, the number of correction value tables 39 is 2. If F is the target pixel, the dot patterns of BF and EF are input to each correction value table 39, respectively. Further, since the influence of overlap is determined by the combination of two pixels, it is only necessary to correct one of them. That is, the influence of the overlap with G and J may be corrected with the reproduced colors of G and J.
[0059]
Note that in order to correct the influence of overlapping of the three pixels BEF and BFG in order to obtain a stricter correction value, a correction value table for the combination of the three pixels may be added. In this case, since the dot pattern of the pixel G must be fixed, the reproduction color error output from the limiter 19 is diffused after the pixel H, for example, a HIJK pixel.
[0060]
According to the present embodiment, since the process of correcting the color shift due to the overlap of dots between the target pixel and the adjacent pixel is provided, the output density table 24 does not need to consider the influence of the overlap of adjacent pixels, and the input Becomes only the dot pattern of the target pixel, and the capacity of the table becomes very small. Further, the capacity of the correction value table 39 may be a combination of dot patterns of two upper and lower pixels.
[0061]
[Embodiment 6]
Next, Embodiment 6 according to the present invention will be described in detail with reference to the drawings.
[0062]
FIG. 9 is a block diagram showing the configuration of the image processing unit in the sixth embodiment. In the figure, 41 is a representative color conversion unit, 42 is an output pattern generation unit, and 43 is an output density table. The other blocks are the same as in FIG.
[0063]
Here, the representative color conversion unit 41 selects a representative color corresponding to the quantized CMY density signal, and outputs an ID code for identifying the representative color to the output pattern generation unit 42 and the output density table 43. The output pattern generation unit 42 generates a CMYK dot pattern from the ID code for identifying the representative color and outputs it to the printer engine (not shown) from the output terminal 21.
[0064]
The output density table 43 generates a value obtained by converting the reproduced color of the representative color into a CMY density signal from the ID code for identifying the representative color, and outputs the value to the offset adding unit 17.
[0065]
This embodiment is a configuration example in the case where one pixel of image data input from the input terminal 10 is expressed by a plurality of dots. For example, if one pixel of the input image data is composed of 4 dots of FGJK as in the shaded portion shown in FIG. 12, assuming that 8 colors of CMYKRGBW can be expressed with 1 dot, 4 dots include the difference in overlap. 666 colors can be expressed (when 1 color is 11 dots, it is 2046). Of the above-mentioned 666 colors, when 512 colors having a uniform color reproducibility range as much as possible in the uniform perceptual color space such as Lab and Luv are selected as representative colors, the ID code becomes 9 bits, and the quantization unit 13 , The representative color conversion unit 41, the output pattern generation unit 42, and the output density table 43 can be configured by 2048 × 9, 512 × 16, and 512 × 24 LUTs, respectively.
[0066]
According to the present embodiment, since one pixel is expressed by N dots (N is an integer of 2 or more), enlargement processing is not necessary when enlarging N times (area). In addition, since one color is expressed by N dots, the influence due to the overlap of surrounding dots is considerably smaller than the case of one dot (the effect is smaller as N is larger). For this reason, the accuracy of the reproduced color data is improved, and the color reproducibility is improved. The output density table 43 can be easily configured by outputting patches of representative colors from a printer and measuring them. Therefore, color matching can be easily realized by actually measuring the patch and updating the output density table 43.
[0067]
[Embodiment 7]
Next, a seventh embodiment according to the present invention will be described in detail with reference to the drawings.
[0068]
FIG. 10 is a block diagram showing the configuration of the image processing unit in the seventh embodiment. In the figure, 44 is an output density table. The other blocks are the same as those in FIG.
[0069]
Here, the output density table 44 of the present embodiment generates a value obtained by converting the reproduced color of the representative color into the CMY density signal from the quantized CMY density signal, and outputs the value to the offset adding unit 17. The following is the same as in the sixth embodiment.
[0070]
As described above, according to the present embodiment, the CMY density value of the reproduced color is generated directly from the quantized CMY density signal, so that the output density is equivalent to the processing of the representative color conversion unit 41 compared to the sixth embodiment. The processing of the table 44 becomes faster. Further, when the number of bits of the ID code for identifying the representative color is larger than the number of bits of the quantized CMY density signal, the capacity of the output density table 44 can be reduced.
[0071]
[Embodiment 8]
Next, an eighth embodiment according to the present invention will be described in detail with reference to the drawings.
[0072]
FIG. 11 is a block diagram showing the configuration of the image processing unit in the eighth embodiment. In the figure, reference numeral 46 denotes a boundary extraction unit, 47 denotes a correction value generation unit, and 48 denotes an addition / subtraction unit. The other blocks are the same as those in FIG.
[0073]
Here, the boundary extraction unit 46 outputs the dot pattern at the boundary between the target pixel and the adjacent pixel to the correction value generation unit 47. On the other hand, the correction value generation unit 47 generates a correction value due to the overlap of the boundary portion from the dot pattern of the boundary portion between the target pixel and the adjacent pixel, and outputs the correction value to the addition / subtraction unit 48 to correct the influence of the boundary portion. The configuration of the correction value generation unit 47 is the same as that of FIG.
[0074]
For example, when one pixel of the input image data is composed of 4 dots of FGJK as in the shaded portion shown in FIG. 12, the boundary portion extraction unit 46 extracts 7 pixels of BCEFGIJ. The correction value generation unit 47 inputs four sets of dot patterns of BF, CG, EF, and IJ to each correction value table, sums the correction values in each correction value table, and adds them to the addition / subtraction unit 48 as correction values for the boundary portion. Output.
[0075]
According to the present embodiment, since the process of correcting the color misregistration due to the overlap of the boundary between the target pixel and the adjacent pixel is provided, the accuracy of the color reproduction error is improved and the color reproducibility is further improved.
[0076]
In the present embodiment, the upper and left boundary portions are corrected. However, the present invention is not limited to this. For example, only the left boundary portion may be used for buffer saving.
[0077]
[Embodiment 9]
Next, a ninth embodiment according to the present invention will be described in detail with reference to the drawings.
[0078]
FIG. 13 is a block diagram showing the configuration of the image processing unit in the ninth embodiment. In the figure, reference numeral 49 denotes a color reproduction range out-of-color determination unit, and 50 denotes a limiter. The other blocks are the same as those in FIG.
[0079]
Here, the out-of-color-reproduction-range determination unit 49 determines whether the above-described representative color is a color at the boundary of the color reproduction range. The direction error is set to “0”.
[0080]
When colors outside the color reproduction range of the representative colors are continuously input, the input color cannot be reproduced, and errors accumulate, resulting in deterioration of color reproducibility. In the present embodiment, the limiter 50 sets the error in the direction outside the color reproduction range to “0”, so that the error is not accumulated, and deterioration of the color reproducibility of the input color within the color reproduction range can be prevented. In this case, the output image is an image in which the input color outside the color reproduction range is limited to the closest representative color.
[0081]
In the present embodiment, the out-of-color reproduction range determination is executed by the ID code for identifying the representative color. However, the present invention is not limited to this. For example, the input of the out-of-color reproduction range determination unit 49 is quantized. It is also good. In this case, one bit of the output of the representative color conversion unit 41 may be added and the added bit may be connected to the limiter 50.
[0082]
Further, the accumulation of errors due to the input color outside the color reproduction range of the representative color is obtained by replacing a part of the reproduction color stored in the output density table 43 (the color that is the outermost outline of the color reproduction range) with the color reproduction range of the input color space. It can also be prevented by setting to include. In this case, the out-of-color reproduction range determination unit 49 is not necessary. Further, the output image is an image in which the input color outside the color reproduction range is compressed within the color reproduction range (color reproducibility near the boundary of the color reproduction range is not compensated).
[0083]
[Embodiment 10]
14 and 15 are block diagrams showing an image processing unit in the tenth embodiment. In the figure, 60 is an input terminal, 61 is a density converter, 62 is an adder, 63 is a diffusion processor, 64 is a subtractor, 65 is a limiter, 66 is a quantizer, 67 is an output density table, and 68 is a code table. 69 and 70 are interface units, 71 is an HV conversion unit, 72 is a pattern table, 73 is a rearrangement unit, and 74 is a head control unit.
[0084]
In the tenth embodiment, it is assumed that an output of 300 dpi (ppi: Pixel Per Inch) is output at 1200 dpi (dpi: Dot Per Inch). Further, the processing from the input terminal 60 to the interface unit 69 is the host side (printer driver) processing, and the processing from the interface unit 70 to the head control unit 74 is the processing on the printer side.
[0085]
The R, G, and B signals input from the input terminal 60 are converted into CMY density signals by the density converter 61. The converted CMY density signals are each added with an error signal from a diffusion processing unit 63 (described later) by the adding unit 62 and input to the limit 65 and the calculation unit 64. The limiter 65 limits the output of the adder 62 to the CMY signal existence range and outputs the result to the quantizer 66. The quantization unit 66 is for reducing the number of input bits of the code table 68, and for example, 9 bits of CMY are quantized to 4 bits of CMY.
[0086]
In the code table 68, codes corresponding to representative colors described later are mapped in advance, and when a quantized CMY signal is input, a representative color code corresponding to the input CMY signal is output. The representative color code is input to the HV conversion unit 71 via the host side interface unit 69, the transmission path 201 (usually a printer cable), and the printer side interface unit 70. The HV conversion unit 71 changes the reading order of the representative color code in accordance with the dots of the print head. The pattern table 72 converts the input representative color code into an output dot pattern. The rearrangement unit 73 rearranges the converted dot patterns in the order of transmission to the head control unit 74. The head controller 74 prints the input dot data. The conversion to the output dot pattern by the pattern table 72 and the rearrangement to the head transfer data by the rearrangement unit 73 are performed in synchronization with the head control (print engine). Further, since the CMYK heads are usually arranged away from each other, the HV conversion unit 71 and the subsequent processes are performed independently for each color. Therefore, the pattern table 72 is actually separated for each color, and any one of CMYK dot patterns is output for the input code.
[0087]
On the other hand, the output density table 67 stores data corresponding to the density observed when the dot pattern corresponding to the representative color code is printed, that is, the reproduction color of the printer. Difference, that is, an output density error, is calculated, and the error is diffused to surrounding pixels by the diffusion processing unit 20 by a known error diffusion method.
[0088]
To express a 1200 dpi CMYK dot pattern at 300 ppi, 4 × 4 × 4 = 64 bits are required. Here, if the representative color code is 8 bits, data compression of 8/64 = 1/8 is possible. Of the 2 ^ 64 output patterns, the number of colors that can be identified is quite small, and an appropriate representative color should be selected in consideration of variations in output dot position accuracy, dot diameter, dot density (shading), etc. For example, even if the number of representative colors is considerably narrowed, the output image hardly changes. On the other hand, since the number of data transmitted through the transmission path 201 can be reduced by considerably reducing the number of representative colors, not only the transmission time can be reduced, but also the buffer capacity required for the HV converter 71. This greatly reduces the cost of the printer. Note that colors other than the representative colors are represented by combinations of representative colors by the error diffusion method at 300 ppi.
[0089]
FIG. 16 is a diagram illustrating the concept of the code table 68 of the present embodiment.
[0090]
Since the input CMY color space is quantized to 4 bits for each color by the quantization unit 66, a representative code corresponding to the lattice point in FIG. 16 is mapped. This configuration is similar to the three-dimensional LUT color conversion method, but in the three-dimensional LUT color conversion method, the color data of all the lattice points of the corresponding small cube is output, and the lower-order bits truncated at the time of quantization are used. Although linear interpolation is performed, in this configuration, a representative color code of one corresponding grid point is output, converted to a reproduction color of the printer by the output density table 67, and the difference from the input data before quantization by the subtraction unit 64 Is corrected as an error to the surrounding pixels to correct the quantization error. That is, the two errors of the quantization error and the printer output density error are corrected by one error diffusion. Therefore, the color processing and binarization processing conventionally performed are integrated into the above-described simple configuration, and data compression by reducing representative colors is simultaneously performed. Also, resolution conversion can be performed simultaneously by changing the size of the output dot pattern in the pattern table 72 (in this embodiment, the main scanning and sub-scanning are 4 × 4 because it is 4 times). As a result, the number of pixels to be processed is greatly reduced, and the processing can be executed at a very high speed, including the effect of simplification of the above processing.
[0091]
Next, a method for generating the table will be described.
[0092]
FIG. 19 is a diagram showing a specific example of the pattern table 72 of the present embodiment.
[0093]
First, a dot pattern of each CMYK color as shown in FIG. 19 is set, and a representative color is determined.
[0094]
The following methods can be considered as the representative color determination method.
(1) A patch with all output patterns is output from a printer, the color of the patch is measured, and gradation is uniform in a specific color space (input CMY space, L * a * b * space, etc.) Select 256 patterns.
(2) The relationship between the dot pattern and the reproduction color is modeled, and the reproduction color for all output patterns is obtained by calculation, and is selected so as to be uniform in a specific color space as in (1).
[0095]
However, since there are 2 ^ 64 total output patterns as described above, it is not practical to search for all output patterns. Therefore, the number of target patterns is reduced by excluding the number of mixed colors, rotation, and pattern matching by mirror image, and after narrowing down to the number of patterns that can be measured by modeling in (2), for example, 1000 patterns, Perform the operation. At this time, a pattern having a large measurement variation is deleted as an unstable pattern, or 256 representative colors are determined in consideration of a reduction prohibition of a single dot pattern or the like in order to reduce a granular feeling in a highlight portion. In other words, by modeling in (2), narrow down to 1000 patterns out of 2 ^ 64, print a batch of 1000 patterns, measure the color, and create 256 patterns with uniform gradation from the 1000 patterns. Select.
[0096]
FIG. 18 is a specific example of the output density table 67 of this embodiment.
[0097]
When the representative color dot pattern is determined by the above operation, an output density table 67 is created.
[0098]
First, a patch based on all output patterns of representative colors is output from a printer, and the color of the patch is measured. In order to reduce printer variations and measurement errors, a plurality of measurements are performed by changing the position of the patch, and an average value is obtained.
[0099]
Next, the obtained average colorimetric values (X, Y, Z) are converted into the input color space (C, M, Y) according to the following procedure.
(1) X, Y, Z → NTSC → RGB
R = (1.910X−0.532Y−0.288Z) / 100
G = (− 0.985X + 1.999Y−0.028Z) / 100
B = (0.058X−0.118Y−0.898Z) / 100
(2) NTSC-RGB → Density (Dr, Dg, Db)
Dr = -log10 (R)
Dg = -log10 (G)
Db = -log10 (B)
(3) Normalization (Dmax: maximum density, Dmin: minimum density)
C = (Dr−Dmin) × 255 / (Dmax−Dmin)
M = (Dg−Dmin) × 255 / (Dmax−Dmin)
Y = (Db−Dmin) × 255 / (Dmax−Dmin)
The converted colorimetric value is stored as reproduced color data at an address indicated by the representative color code in the output density table 67.
[0100]
In the conversion method to the input color space, the log function is used for the conversion to the RGB density. However, the conversion is not limited to this, and the conversion may be performed using the LUT. Further, when it is desired to shift the output color of the printer from the input color as in gamut compression, it can be realized by reversely correcting the values stored in the output density table 67. For example, when gamut compression is performed, the value of the reproduction color data is gradually shifted toward the outside of the color reproduction range of the printer so that the reproduction color data includes the color reproduction range of the input color space. Note that the white (blank) reproduction colors CMY are all zero.
[0101]
FIG. 17 is a specific example of the code table 68 of the present embodiment.
[0102]
The mapping of the representative color code to the code table 68 is performed based on the distance from the converted colorimetric value. That is, if the color data (quantized representative value) of the grid points is C ′, M ′, Y ′ and the converted colorimetric values are C, M, Y, the square of the distance r 2 is
r ^ 2 = (C-C ') ^ 2+ (M-M') ^ 2+ (Y-Y ') ^ 2
It becomes. The representative color code that minimizes the distance is stored in the corresponding address of the code table 68. Here, in order to minimize the quantization error, instead of the value obtained by combining the bit weights of the color data of the lattice points, the quantization representative value (specifically, the bit weight of the output of the quantization unit 66). And the quantization step / 2). This is because the quantization unit 66 cuts out the upper bits (that is, cuts out the lower bits). When rounding (rounding off) instead of rounding down the lower bits, a value with all the lower bits set to 0 may be used.
[0103]
As an evaluation value for the mapping, not only the square of the distance but also an absolute value of a difference may be used, for example.
[0104]
Further, the quantized representative value is not limited to the median value of the quantized value, and may be shifted entirely or partially.
[0105]
In the above embodiment, the input of the output density table 67 is a representative color code, but it may be a CMY signal after quantization. In this case, the code table 68 and the output density table 67 are integrated, and the representative color code and the output density value (reproduced color) can be obtained by a single LUT search. In particular, if the representative color code is 8 bits, the output density value is 24 bits (8 × 3 = 24), so the output is a 32-bit (8 + 24 = 32) table, and matching is performed when the host is a 32-bit process. Good. Further, by correcting and storing values so that color reproduction errors do not accumulate for input outside the printer color reproduction range, color misregistration outside the printer color reproduction range can be prevented.
[0106]
The present invention may be applied to a system composed of a plurality of devices such as a host computer, an interface, and a printer, or to an apparatus composed of a single device such as a copying machine. Needless to say, the present invention can also be applied to a case where the present invention is achieved by supplying a program stored in a storage medium to a system or apparatus.
[0107]
【The invention's effect】
  As explained above, according to the present invention,By correcting the color misregistration caused by overlapping with the surrounding pixels of the target pixel, the accuracy of the color reproduction error is improved and the color reproducibility is further improved.be able to.
[0108]
[Brief description of the drawings]
FIG. 1 is a block diagram illustrating a configuration of an image processing unit according to a first embodiment.
FIG. 2 is a block diagram illustrating a configuration of an image processing unit according to a second embodiment.
FIG. 3 is a block diagram illustrating a configuration of an image processing unit according to a third embodiment.
FIG. 4 is a block diagram illustrating a configuration of an image processing unit according to a fourth embodiment.
FIG. 5 is a block diagram illustrating a configuration of an image processing unit according to a fifth embodiment.
FIG. 6 is a block diagram illustrating a configuration of a correction value generation unit according to a fifth embodiment.
7 is a diagram illustrating a spatial position of each pixel in Embodiment 5. FIG.
8 is a diagram illustrating a spatial position of each pixel when the target pixel of the correction value generation unit is 4. FIG.
FIG. 9 is a block diagram illustrating a configuration of an image processing unit according to a sixth embodiment.
FIG. 10 is a block diagram illustrating a configuration of an image processing unit according to a seventh embodiment.
FIG. 11 is a block diagram illustrating a configuration of an image processing unit according to an eighth embodiment.
12 is a diagram illustrating a spatial position of each pixel in Embodiment 8. FIG.
FIG. 13 is a block diagram illustrating a configuration of an image processing unit according to the ninth embodiment.
FIG. 14 is a block diagram illustrating a configuration of an image processing unit according to a tenth embodiment.
FIG. 15 is a block diagram illustrating a configuration of an image processing unit according to a tenth embodiment.
FIG. 16 is a diagram illustrating a concept of a code table according to the tenth embodiment.
FIG. 17 is a specific example of a code table.
FIG. 18 is a specific example of an output density table.
FIG. 19 is a specific example of a pattern table.
FIG. 20 is a block diagram showing a configuration of a conventional example.

Claims (20)

An image processing method for converting input color space data to output color space data,
An input process for inputting a plurality of color component data in the input color space;
A correction step of correcting a plurality of color component data input in the input step with a predetermined error signal;
An input color corrected in the correction step from a dot pattern storage unit that stores a dot pattern for each of the plurality of color components in the output color space, which is predetermined to correspond to the values of the plurality of color components in the input color space An output step of outputting a dot pattern corresponding to a plurality of color component values in space;
A conversion step of converting the reproduced color of the target pixel into values of a plurality of color components in the input color space from the dot pattern of the target pixel output in the output step and pixels around the target pixel;
A generation step of generating the predetermined error signal based on a difference value between a plurality of color component values converted in the conversion step and a plurality of color component values corrected in the correction step;
An image processing method comprising: And a quantization step of quantizing each of the plurality of color component data corrected in the correction step into data of a level lower than the input level,
The dot pattern stored in the dot pattern storage unit is predetermined to correspond to a plurality of color component values at a level quantized in the quantization step. Image processing method. An image processing method for converting input color space data to output color space data,
An input process for inputting a plurality of color component data in the input color space;
A color space conversion step of converting a plurality of color component data input in the input step into a plurality of color component data in an output color space;
A correction step of correcting a plurality of color component data converted in the color space conversion step with a predetermined error signal;
From a dot pattern storage unit that stores a dot pattern for each of a plurality of color components in the output color space, which is predetermined to correspond to the values of the plurality of color components in the output color space, a plurality of corrected in the correction step An output process for outputting a dot pattern corresponding to the value of the color component;
A conversion step of converting the reproduced color of the target pixel into values of a plurality of color components in the output color space from the dot pattern of the target pixel output in the output step and pixels around the target pixel;
A generation step of generating the predetermined error signal based on a difference value between a plurality of color component values converted in the conversion step and a plurality of color component values corrected in the correction step;
An image processing method comprising: And a quantization step of quantizing each of the plurality of color component data corrected in the correction step into data of a level lower than the input level,
The dot pattern stored in the dot pattern storage unit is predetermined to correspond to a plurality of color component values at a level quantized in the quantization step. Image processing method. Further, a correction value generation for generating a correction value for correcting a shift in reproduction color due to the overlap of the dot between the target pixel and the surrounding pixels from the dot pattern of the target pixel output in the output step and the surrounding pixels of the target pixel. Process,
The image processing method according to claim 3, further comprising: Further, a quantization step of quantizing each of the plurality of color component data corrected in the correction step into data having a level lower than the input level;
An arbitrary ID code is output by inputting the data quantized in the quantization step to a table in which ID codes of a predetermined number of representative colors that can be expressed by a plurality of output dot patterns are mapped to the output color space. ID code output process,
The image processing method according to claim 3, wherein the output step outputs a dot pattern for each of a plurality of color components in an output color space in accordance with the ID code. An image processing method for converting input color space data to output color space data,
An input process for inputting a plurality of color component data in the input color space;
A color space conversion step of converting a plurality of color component data input in the input step into a plurality of color component data in an output color space;
A correction step of correcting a plurality of color component data converted in the color space conversion step with a predetermined error signal;
A quantization step of quantizing each of the plurality of color component data corrected in the correction step into data of a level lower than an input level;
A representative color conversion step of selecting a representative color corresponding to a plurality of color component data in the output color space quantized in the quantization step and outputting an identification code for identifying the representative color;
From the identification code output from the representative color conversion step, a dot pattern generation step of generating a dot pattern for each of a plurality of color components in the output color space;
Based on a plurality of color component data in the output color space quantized in the quantization step, a conversion step for converting to a plurality of color component data in the output color space, which corresponds to a reproduced color,
A generation step of generating the predetermined error signal based on a difference value between a plurality of color component values converted in the conversion step and a plurality of color component values corrected in the correction step;
An image processing method comprising:   The conversion step includes an output color space corresponding to a reproduction color of the representative color according to an identification code for identifying a representative color corresponding to a plurality of color component data in the output color space quantized in the quantization step. The image processing method according to claim 7, wherein the data is converted into a plurality of color component data. Further, an extraction step of extracting a dot pattern at the boundary between the target pixel and the surrounding pixels from the dot pattern of the target pixel and the surrounding pixels generated in the dot pattern generation step;
From the dot pattern extracted in the extraction step, a correction value generation step for generating a correction value for correcting a shift in reproduction color due to dot overlap between the target pixel and surrounding pixels;
The image processing method according to claim 7, further comprising: And a step of determining whether the representative color selected in the representative color conversion step is a boundary color of a predetermined color reproduction range or not.
The determination step outside the color reproduction range is characterized in that, when it is determined that the color is a boundary color of the color reproduction range, a value for not accumulating errors in the direction outside the color reproduction range is output to the generation step. The image processing method according to claim 7. An image processing device for converting input color space data to output color space data,
Input means for inputting a plurality of color component data in the input color space;
Correction means for correcting a plurality of color component data input by the input means with a predetermined error signal;
Dot pattern storage means for storing a dot pattern for each of the plurality of color components in the output color space, which is predetermined to correspond to the values of the plurality of color components in the input color space;
Output means for outputting a dot pattern corresponding to the values of a plurality of color components in the input color space corrected by the correction means;
Conversion means for converting the output color at the target pixel from the dot pattern of the target pixel output from the dot pattern storage means and the pixel adjacent to the target pixel into values of a plurality of color components in the input color space;
Generating means for generating the predetermined error signal based on a difference value between a plurality of color component values converted by the converting means and a plurality of color component values corrected by the correcting means;
An image processing apparatus comprising: Furthermore, it has quantization means for quantizing each of the plurality of color component data corrected by the correction means into data of a level lower than the input level,
Dot patterns stored in said dot pattern storage unit according to claim 11, characterized in that predetermined so as to correspond to the value of the plurality of color components in quantized levels in the quantized means Image processing apparatus. An image processing device for converting input color space data to output color space data,
Input means for inputting a plurality of color component data in the input color space;
Color space conversion means for converting a plurality of color component data input by the input means into a plurality of color component data in an output color space;
Correction means for correcting a plurality of color component data converted by the color space conversion means with a predetermined error signal;
From a dot pattern storage unit that stores dot patterns for each of a plurality of color components in the output color space, which are predetermined to correspond to values of the plurality of color components in the output color space, a plurality of corrections corrected by the correction unit Output means for outputting a dot pattern corresponding to the value of the color component;
Conversion means for converting a reproduced color of the target pixel into values of a plurality of color components in an output color space from a dot pattern of the target pixel output by the output unit and pixels around the target pixel;
Generating means for generating the predetermined error signal based on a difference value between a plurality of color component values converted by the converting means and a plurality of color component values corrected by the correcting means;
An image processing apparatus comprising: Furthermore, it has quantization means for quantizing each of the plurality of color component data corrected by the correction means into data of a level lower than the input level,
14. The dot pattern stored in the dot pattern storage unit is predetermined to correspond to a plurality of color component values at a level quantized by the quantization means. Image processing apparatus. Further, a correction value generation for generating a correction value for correcting a shift in reproduction color due to overlapping of dots between the target pixel and the surrounding pixels from the dot pattern of the target pixel output by the output unit and the pixels around the target pixel. Means,
The image processing apparatus according to claim 13, further comprising: Further, a quantization means for quantizing each of the plurality of color component data corrected by the correction means into data having a level lower than the input level;
An arbitrary ID code is output by inputting the data quantized by the quantization means to a table in which an ID code of a predetermined number of representative colors that can be expressed by a plurality of output dot patterns is mapped to an output color space. ID code output means,
The image processing apparatus according to claim 13, wherein the output unit outputs a dot pattern for each of a plurality of color components in an output color space in accordance with the ID code. An image processing device for converting input color space data to output color space data,
Input means for inputting a plurality of color component data in the input color space;
Color space conversion means for converting a plurality of color component data input by the input means into a plurality of color component data in an output color space;
Correction means for correcting a plurality of color component data converted by the color space conversion means with a predetermined error signal;
Quantization means for quantizing each of the plurality of color component data corrected by the correction means into data of a level lower than the input level;
Representative color conversion means for selecting a representative color corresponding to a plurality of color component data in the output color space quantized by the quantization means and outputting an identification code for identifying the representative color;
Dot pattern generation means for generating a dot pattern for each of a plurality of color components in an output color space from the identification code output from the representative color conversion means;
Conversion means for converting to a plurality of color component data in the output color space, corresponding to the reproduced color, based on the plurality of color component data in the output color space quantized by the quantization means;
Generating means for generating the predetermined error signal based on a difference value between a plurality of color component values converted by the converting means and a plurality of color component values corrected by the correcting means;
An image processing apparatus comprising:   The conversion means outputs an output color space corresponding to a reproduction color of the representative color according to an identification code for identifying a representative color corresponding to a plurality of color component data in the output color space quantized by the quantization means The image processing apparatus according to claim 17, wherein the image processing apparatus is converted into a plurality of color component data. Furthermore, an extraction unit that extracts a dot pattern of a boundary portion between the target pixel and the surrounding pixels from the dot pattern of the target pixel and the surrounding pixels generated by the dot pattern generation unit;
Correction value generation means for generating a correction value for correcting a shift in reproduction color due to dot overlap between the target pixel and surrounding pixels from the dot pattern extracted by the extraction means;
The image processing apparatus according to claim 17, further comprising: Furthermore, it has a color reproduction range out-of-range determination unit for determining whether the representative color selected by the representative color conversion unit is a boundary color of a predetermined color reproduction range,
The out-of-color-reproduction-range determining unit, when determining that it is a boundary color of the color reproduction range, outputs to the generation unit a value for not accumulating errors in a direction outside the color reproduction range. The image processing apparatus according to claim 17.

Images