JP2012065088A - Image processing device, image processing method, image forming apparatus, program, and recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image processing device that performs reduction processing of the amount of coloring material to be used with a reduced operation amount without deteriorating image quality.SOLUTION: An AM dither processing part 106 compares an input value of a position of interest and a threshold of an AM dither matrix 109. If large dots are observed to be generated as a result of the comparison at a position immediately before and immediately above the point of interest, a dot rewrite processing part 110 rewrites the large dots into small dots in reference to a dot rewrite matrix 113, provided the rewriting is allowed at the position of interest.

Description

  The present invention relates to an image processing apparatus, an image processing method, an image forming apparatus, a program, and a recording medium that reduce the amount of color material used.

  Conventionally, as a method for reducing the amount of color material used, such as ink, a method of thinning out print data with a specific pattern to reduce the amount of color material actually used (see Patent Document 1) or input data On the other hand, there is a method (see Patent Document 2) of reducing the shadow side component having a large color material usage amount by reducing the gradation at a constant ratio.

  However, the above-described method is premised on the use as a color material usage reduction mode, and the image quality is lowered instead of the color material usage being reduced.

  For example, when thinning processing is performed, the image becomes rough due to a combination with the original image or halftone processing, a texture that does not exist in the original image is generated, and image quality degradation such as a decrease in image density occurs ( FIG. 1 (a)). When the gradation level is lowered, image quality deterioration due to the dot pattern does not occur, but the image density is lowered and the number of gradations that can be expressed is reduced (FIG. 1B).

  In addition, in BG / UCR processing, there is a method of increasing the amount of substitution with the Bk color material and reducing the use amount of the color color material, but there is no effect on CMYK single color data. The saturation of the image is reduced, and the image quality is deteriorated.

  Conventionally, the user's needs have been addressed by selectively using the “normal recording mode” with high image quality and the “color material usage reduction mode” with low image quality but low running cost. However, even in the normal recording mode, low cost and a reduction in the amount of color material used are required.

The present invention has been made in view of the above-described problems.
An object of the present invention is to provide an image processing apparatus, an image processing method, an image forming apparatus, a program, and a recording medium that execute a color material usage reduction process with a small amount of computation without degrading image quality.

  The present invention sequentially performs threshold processing on each pixel value of an input image using an AM dither matrix in which predetermined threshold values are arranged, thereby changing the pixel value of the pixel of interest to dot on / off with different dot sizes, respectively. And the threshold value processing means for converting the signal into the first pixel, and the dot-on size of the pixel of interest is the first size, the dot-on size at the already processed pixel position in the vicinity of the pixel of interest is the first size. A first determination unit that determines whether or not the pixel is a size; and when it is determined that the dot-on size in the vicinity of the pixel of interest is the first size, the first size of the pixel of interest is determined as follows: Second determination means for determining whether or not replacement with a second size smaller than the first size is permitted; and when the replacement is permitted, the first size of the pixel of interest is Above The most important feature that a change means for changing the second size.

  According to the present invention, in ink jet recording, the running cost is reduced by reducing the amount of ink that does not contribute to image quality. In other words, according to the present invention, by utilizing multi-value dot size modulation, by replacing a dot having a size larger than the recording resolution pitch with a locally smaller dot, Reduce excess ink. At this time, since the dot size is switched in consideration of covering with dots having a size larger than the recording resolution pitch, it is possible to avoid a decrease in density and a decrease in the number of gradations such as gradation shift.

It is a figure explaining deterioration of the picture quality by the conventional processing. The state of penetration of ink droplets into the paper and the relationship between the image density and the ink adhesion amount are shown. An example of multi-value processing by dot size is shown. The relationship between a gradation level and the ink adhesion amount is shown. It is a figure explaining the fundamental view of the present invention. An AM dither matrix is shown. An example of a switching dither matrix pattern based on the AM dither matrix pattern is shown. The structure of the Example of this invention is shown. The processing flowchart of the Example of this invention is shown. A dot replacement matrix is shown. The result of the replacement process of this invention is shown. Shows how to save the dot size flag. The example of a pattern which changed substitution density is shown.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 2 shows how ink droplets permeate in ink jet recording. (A) shows the penetration in the coated paper for inkjet, and (b) shows the penetration in the plain paper / office paper.

  Inkjet coated paper has a coating layer on the surface of the paper for fixing ink, and most of the adhered ink droplets can be reflected in the image quality. However, since the sheet itself is expensive and needs to be printed at a low recording speed, it is used when printing a small number of high-quality images.

  In contrast, since plain paper is not processed for inkjet recording or the like, the ink droplets that have landed on the paper penetrate into the paper more than spread on the paper. The permeated ink does not substantially contribute to the image quality, and only the ink remaining in the vicinity of the paper surface contributes to the image quality.

  For example, FIG. 2 (c) is a graph plotting the relationship between the ink adhesion amount and the density on plain paper, but there is room for ink to spread near the paper surface up to a certain amount of adhesion, and then the surface near the surface. The permeation area is filled, and after that, it only penetrates in the depth direction of the paper, and the density is saturated no matter how much it adheres. For plain paper used in large quantities in offices and the like, the amount of ink that penetrates into the paper without contributing to filling the paper surface increases directly the running cost.

  FIG. 3A shows a method for forming multi-value dots in ink jet recording. In ink jet recording, dots of different sizes can be formed by changing the size of the ejected droplets. In addition, although affected by the surface of the paper, the way of spreading the dots is almost uniform, and circular dots can be formed. Usually, a large dot for forming the vicinity of a solid gradation is set to a dot size equal to or larger than the dot pitch so that an unrecorded portion does not occur due to bending in the ejection direction or the like (FIG. 3B).

  However, with plain paper, as described above, an ink amount that penetrates into the paper and does not contribute to image quality is generated. When the gradation level and the ink adhesion amount are plotted on a graph, a non-linear relationship is obtained as shown in FIG. As can be seen from this graph, on the shadow side, after the coverage area is saturated, the droplet volume increases rapidly to obtain a constant gradation level (image density), and a very inefficient recording method is adopted. Will be.

  In consideration of this point, the present invention proposes an image processing method for reducing the amount of ink droplets that does not contribute to image quality improvement while ensuring image quality, that is, image density. Furthermore, when performing the image processing, if high-level arithmetic processing is required, the calculation speed decreases, the printing speed decreases, or an expensive system must be installed to ensure the calculation speed. Therefore, the present invention proposes a method that can be applied more simply.

  First, as means for securing the covering area, the amount of ink from the adjacent dot positions is used to reduce the ink size by reducing the dot size recorded at the target dot position.

  FIG. 5 is a diagram for explaining the basic concept of the present invention. As shown to (a), when the circumference | surroundings are enclosed by the large dot used by a solid filling, the substantial covering area improves by the protrusion part of a circumference | surroundings dot in the focused dot position located in the center. Therefore, as shown in (c), even if the target dot position is replaced with a dot that is one step or smaller than the dot used for solid filling, the covering ability does not decrease.

  In the case of a binary recording engine in which only two dots, “form” and “not form”, can be selected, dots are not formed at the target dot position, but in this case, the amount of protrusion from the surroundings is insufficient. Therefore, it is preferably applied to a multi-value recording engine that can form dots of a plurality of sizes (in the case of binary, the coverage and ink droplet amount can be adjusted by adjusting the size of large dots. Is possible to take).

  Further, as a means for determining whether or not to change the dot size, a method of performing pattern matching processing with reference to dot positions of m × n (m and n are integers of 1 or more) centered on the target dot position In this case, however, it is necessary to always retain dot information for the reference range, which increases the calculation cost for pattern matching.

  Therefore, in the present invention, as will be described later, by performing dot replacement using a matrix having the same phase and similarity as the basic pattern of the AM dither matrix, the memory cost is reduced, and the pattern matching calculation cost is unnecessary. .

  FIG. 6 shows an AM dither matrix. FIG. 6A shows a centralized AM dither matrix, and FIG. 6B shows a line dither matrix. In either case, the dots are solidly formed based on the basic tone defined by a fixed pitch from the highlight portion to the shadow portion, and gradation expression is performed (the input pixel value at the target pixel position and the matrix threshold value). Are converted into a dot-on signal when the input pixel value is equal to or greater than the threshold value, and converted into a dot-off signal when the input pixel value is less than the threshold value).

  Unlike the error diffusion process and randomly distributed dither, what size dots can be formed around the pattern of the AM dither matrix if the coordinates and input values of the dot formation position in the image data are known Is possible to guess.

  FIG. 7 shows a pattern example of the switching dither matrix based on the AM dither matrix pattern. FIG. 7A shows a line dither matrix for small dots, and FIG. 7B shows a line dither matrix for large dots. As shown in gradation levels 5 to 50, according to the input value and coordinates of the target pixel, the line-type dither matrix for small dots and large dots to be used is switched, and small dots and large dots corresponding to the gradation levels are switched. Is generated.

  FIG. 8 shows the configuration of an embodiment of the present invention. In FIG. 8, 101 is an image input unit, 102 is a CMM processing unit that converts RGB signals into CMY signals, 103 is a BG / UCR processing unit that generates black and removes undercolor, and 104 is the total amount of ink used. A total amount regulation processing unit that regulates tone characteristics, 105 a γ correction processing unit that corrects gradation characteristics, 106 an AM dither processing unit that performs halftone processing on an input image using an AM dither matrix, 107 a threshold processing unit, 108 is a first determination unit, 109 is a storage unit that stores an AM dither matrix (FIG. 7), 110 is a dot replacement processing unit that replaces a large dot dot-on signal with a small dot dot-on signal, and 111 is a second replacement unit. Determining unit, 112 is a size changing unit, 113 is a storage unit storing a dot replacement matrix (FIG. 10), and 114 is a bitmap data from halftone processed image data. Rendering processing unit for generating data, 115 is an output data.

  The input image data is, for example, 8-bit gradation (0 to 255), and the dot data after the threshold processing is converted into, for example, 2-bit (0 to 3) data. In other words, the dot-on signal for large dots is converted to “3”, and the dot-on signal for small dots is converted to “2”, which is one level lower.

FIG. 9 shows a process flowchart of the embodiment of the present invention.
The threshold processing unit 107 of the AM dither processing unit 106 acquires the target dot position coordinates (x, y) of the input image (steps 201 and 202), and the AM dither corresponding to the input value of the target dot position and the pixel position. The threshold value of the matrix 109 is compared (step 203). As a result of the comparison, if a large dot (the dot size flag is set to 1 and the others are set to 0) does not occur (No in step 204), the process proceeds to step 212, and the dot size (flag 0) corresponding to the comparison result is obtained. Keep it.

  As a result of the comparison, if a large dot is generated (Yes in Step 204), the first determination unit 108 acquires a dot size flag processed at the previous / immediately preceding dot position from the threshold processing unit 107 (Step 205). ). The dot position immediately before the target pixel (x, y) is (x-1, y), and the dot position immediately above is (x, y-1).

  The first determination unit 108 determines whether or not large dots are generated at both the immediately preceding / immediate positions (dot size flag is 1) (step 206), and large dots are detected at both the immediately preceding / immediate positions. If NO has occurred (No in step 206), the process proceeds to step 212, and the dot size (flag 1) at the target pixel position is held.

  When large dots are generated at both the immediately preceding / immediate positions (Yes at step 206), the second determination unit 111 of the dot replacement processing unit 110 refers to the dot replacement matrix 113 and refers to the dot position of interest. A replacement flag of (x, y) is acquired (step 207).

  FIG. 10A shows a dot replacement matrix stored in the storage unit 113. The size of the dot replacement matrix matches the size of the AM dither matrix (x and y coordinate positions match), and “1” is set at the position where dot size replacement is permitted in the x and y coordinates of the dot replacement matrix. “0” is set in a position where the dot size replacement is not permitted. When “1” is set, as shown in FIG. 10B, the large dot at that position is replaced with a small dot. When “1” is set, the large dot at that position is replaced with a small dot. Cannot be replaced.

  Further, the replacement position may be reflected in the AM dither matrix. FIGS. 10C and 10D respectively show a small-dot line dither matrix and a large-dot line dither matrix, as described above. FIGS. 10E and 10F show the AM dither matrix reflecting the replacement position. That is, “non: no” is set at the replacement position in FIG. 10 (f), and a large-dot line dither matrix for restricting the generation of large dots from the beginning is prepared. The dither matrices (e) and (f) may be simply switched instead of the dot replacement process as shown in FIG. That is, when the large dot dither matrix is referenced, replacement processing is also performed.

  Returning to FIG. 9, if the acquired flag is “0” (No in Step 208), the second determination unit 111 determines that the large dot at that position cannot be replaced with the small dot, and proceeds to Step 212. move on.

  If the acquired flag is “1” (Yes in Step 208), the second determination unit 111 determines that the large dot at that position is replaced with the small dot. The size changing unit 112 replaces the large dot at that position with a small dot (step 209), and updates the dot size flag according to the result of the target dot position (step 210).

  If the pixel position is not the final dot position of the image (No in step 211), the threshold processing unit 107 updates the target dot position to the next position (x + 1, y) (step 213), and thereafter performs the same processing. .

  In the present invention, as described above, conversion data of the dot position processed immediately before is held (for example, stored in the AM dither processing unit 106 as flag data of 1 for large dots and 0 for the other), and immediately above and immediately above. Only when a large dot is formed at the dot position processed in step 1, the dot replacement determination is performed.

  This is because when the focused dot position is at the edge of the image, the dot quality is reduced by simply applying replacement without referring to the dot size immediately before and immediately above, thereby reducing the edge quality. (The line becomes thin and rattling occurs) (FIG. 11A). Therefore, in the present invention, the dot replacement determination process is performed only when a large dot is formed at the dot position processed immediately before and immediately above (FIG. 11B). In the present invention, it is possible to perform replacement processing with higher image quality than simply processing the entire image with a uniform replacement pattern.

  Further, in the present invention, the dot size is replaced by using a dither matrix used for halftone processing and a substantially similar matrix having the same basic tone period, thereby generating moiré due to interference with halftone processing and appearance. Pattern changes can be avoided.

  In the present invention, as shown in FIG. 12, the dot size flag data is updated for each process, so that the flag holding line buffer is only one line buffer, so that the memory cost can be minimized. .

  That is, in the one-line buffer of the threshold processing unit 107, conversion data of already processed dot size (large dot is 1 and other than that) is used as the flag (flag 1) of the previous dot position (x-1, y). 0) is held, the already processed dot size conversion data (large dot: 1 or 0) is held as the flag (flag 2) of the dot position (x, y-1) directly above, and the dot position of interest ( As a flag (x, y) (flag 3), conversion data of a dot size (large dot: 1) as a result of threshold processing is held.

  As described above, in the determination process of step 206, referring to the flag 1 of the immediately preceding dot position (x-1, y) and the flag 2 of the immediately above dot position (x-1, y), both are large dots, When the large dot is replaced with the small dot by the determination process in step 208 and the size change process in step 209, the flag 3 “1” at the target dot position (x, y) is updated to “0”. At the same time, the flag 2 at the dot position (x−1, y) immediately above is also updated to “0” (according to the flag at the target dot position (x, y)). Thereafter, the target dot position is shifted to the next position (x + 1, y) and the same processing is executed.

  In the present invention, by referring to the dot size replacement by the dot replacement matrix having the same period / substantially similar to the dither matrix and the output dot information of the pixel processed immediately before, advanced pattern matching processing is not required. It is possible to form an image without damaging the image edge.

  Furthermore, in the present invention, the effect of reducing the ink consumption can be adjusted by the density of the pattern for dot replacement. For example, FIGS. 13A and 13B show examples of dot replacement matrix patterns. Pattern example 2 has a larger replacement amount than pattern example 1, that is, a pattern that can further reduce ink consumption.

  The above-described patterns 1 and 2 may be automatically switched to patterns having different densities by the dot replacement processing unit 110 in accordance with the user's judgment and the characteristics of the paper. In particular, for paper with a large amount of blur, the decrease in image density is small even if the amount of replacement is increased. Conversely, for a paper with a small amount of blur, the amount of replacement needs to be small. For paper that can manage brands, register a switching pattern that matches the characteristics of the paper, and if the user selects it, or if barcode processing or identification processing is applied on the paper side, read it to switch May be.

  In addition, even for a paper whose brand is unknown, the degree of ink bleeding may be measured, and a paper switching pattern having characteristics close to the registered data may be applied.

  The dot replacement process described above can be applied as a program or an image processing circuit such as an ASIC. When applied as a program, the same function can be realized by storing the program in a recording medium or reading and executing the program by an image processing system via a network.

DESCRIPTION OF SYMBOLS 101 Image input part 102 CMM process part 103 BG / UCR process part 104 Total amount regulation process part 105 γ correction process part 106 AM dither process part 107 Threshold process part 108 First determination part 109 AM dither matrix memory part 110 Dot replacement process part 111 Second determination unit 112 Size change unit 113 Dot replacement matrix storage unit 114 Rendering processing unit 115 Output data

JP 2006-270927 A JP-A-9-216419

Claims (12)

  Each pixel value of the input image is sequentially thresholded using an AM dither matrix in which predetermined threshold values are arranged, thereby converting the pixel value of the pixel of interest into dot on / off signals of different dot sizes, respectively. And when the dot-on size of the pixel of interest is the first size, is the dot-on size at the already processed pixel position in the vicinity of the pixel of interest the first size? First determination means for determining whether or not the dot-on size in the vicinity of the target pixel is the first size, the first size of the target pixel is determined as the first size; Second determination means for determining whether or not replacement with a second size smaller than the size is permitted; and when the replacement is permitted, the first size of the pixel of interest is set to the second size Rhino The image processing apparatus characterized by comprising a changing means for changing to.   The second determination means includes a replacement table in which a permission flag for permitting replacement is set at a predetermined position of each pixel of a matrix having the same shape as the AM dither matrix when determining permission for replacement. The image processing apparatus according to claim 1, wherein the image processing apparatus is referred to.   The AM dither matrix includes a first size dither matrix and a second size dither matrix, and a permission flag for permitting the replacement is set at a predetermined position of the first size AM dither matrix. The image processing apparatus according to claim 2, wherein:   The image processing apparatus according to claim 2, wherein the second determination unit refers to a plurality of replacement tables having different numbers of permission flags depending on a color material usage amount.   5. The image processing apparatus according to claim 4, wherein the second determination unit refers to any one of the plurality of replacement tables according to a type of recording paper or according to a user designation.   The pixels in the vicinity of the pixel of interest are the pixel immediately before the pixel of interest and the pixel immediately above, and the threshold processing means sets the first size of the dot on of the pixel immediately before the pixel of interest as the first flag. And the first dot-on size of the pixel immediately above the target pixel is stored as a second flag, and the first dot-on size of the target pixel is stored as a third flag. A buffer, wherein the first determination unit refers to the first and second flags during the first determination process of the target pixel, and the change unit determines from the first size of the target pixel. The image processing apparatus according to claim 1, wherein the second and third flags are updated in accordance with the change to the second size.   The threshold processing means switches between a dither matrix for a first size and a dither matrix for a second size of the AM dither matrix according to a pixel value and a pixel position of the pixel of interest. Item 6. The image processing apparatus according to Item 1.   The image processing apparatus according to claim 1, wherein the first size is a dot size that can be filled, and the second size is one or more steps smaller than the first size.   Each pixel value of the input image is sequentially thresholded using an AM dither matrix in which predetermined threshold values are arranged, thereby converting the pixel value of the pixel of interest into dot on / off signals of different dot sizes, respectively. And when the dot-on size of the pixel of interest is the first size, is the dot-on size at the already processed pixel position in the vicinity of the pixel of interest the first size? A first determination step of determining whether or not and a dot-on size in the vicinity of the target pixel is determined to be the first size, the first size of the target pixel is determined as the first size A second determination step for determining whether or not replacement with a second size smaller than the size is permitted; and when the replacement is permitted, the first size of the pixel of interest is set to the second size Rhino An image processing method characterized by comprising a changing step of changing to.   9. The image processing apparatus according to claim 1, and an image forming unit that forms an image on a recording medium by ejecting droplets of different sizes based on image data from the image processing apparatus. An image forming apparatus comprising:   A program for causing a computer to implement the image processing method according to claim 9.   A computer-readable recording medium on which a program for causing a computer to implement the image processing method according to claim 9 is recorded.