JP3666186B2 - Gradation processing method and apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a gradation processing method and apparatus suitable for use in an image forming apparatus such as a laser printer or an electronic copying machine, and more particularly to a gradation processing method and apparatus for generating a halftone image using a dither matrix. .
[0002]
[Prior art]
Conventionally, in an image forming apparatus such as a laser printer, gradation data developed in a dot matrix is compared with each threshold value of a threshold value matrix. For example, when each gradation value of gradation data is larger, “1” is set. When the values are the same or smaller, a halftone is generated by binarizing such as “0”.
[0003]
An example of a method for generating a halftone image using such a threshold matrix is shown in FIG.
[0004]
That is, in this example, the 4 × 4 threshold matrix 52 shown in FIG. 11B is introduced, and the density of the corresponding pixel of the gradation data 51 developed in a dot matrix form as shown in FIG. For example, when the density of the gradation data 51 is larger than the corresponding threshold value of the threshold value matrix 52, black “1” is given, and white “0” is given otherwise. ), Halftoned data 53 binarized is generated, and printing is performed in accordance with this, thereby generating a halftone image.
[0005]
On the other hand, in recent years, a technique for increasing the number of gradations by a factor of M by dividing one pixel (pixel) into M (M is an integer of M ≧ 2) dot areas and printing (hereinafter referred to as M double dense image technique). Has been proposed). A threshold matrix used in such a technique is shown in FIG. In the figure, a thick frame line represents one pixel.
[0006]
That is, for example, in a laser printer using a triple density image technology, a threshold value obtained by dividing one pixel (pixel) into three as shown in FIG. The matrix 55 is introduced, and first, the density of each pixel of the gradation data 54 developed in the dot matrix form shown in FIG. 12A is compared with each corresponding threshold value of the threshold value matrix 55 three times per pixel. As described above, when the density of the gradation data 54 is larger than the corresponding threshold values of the threshold value matrix 55, black “1” is assigned, and otherwise white “0” is assigned. As shown in c), binarized halftone data 56 is generated. Further, in the triple-density image technology, the number of “1” s in the three frames is counted. If “1” is 0, it is “00”, 1 is “01”, and 2 is “10”. If there are three, it is converted to a binary number such as “11”. Corresponding to each of these binary numbers, the pixel PC divided into three dot areas D1, D2, and D3 is divided into four tone levels of 0, 1, 2, and 3, as shown in FIG. Represented by P.
[0007]
[Problems to be solved by the invention]
The above-described M double-density image technology is a kind of resolution correction function. For example, in a laser printer or the like that employs the triple-density image technology, the gradation expression power is increased three times, and photographs with subtle shadows and gradations are displayed. Illustrations can be expressed beautifully and smoothly with gradation, which is very useful as an element technology for laser printers and the like.
[0008]
However, when, for example, the triple density image technology is employed, the size of the threshold matrix 55 in the row direction is 3 as the size of the normal threshold matrix 52 shown in FIG. 11B as shown in FIG. It will be doubled. When this is constituted by a circuit, it is necessary to store the threshold matrix 55 read by the CPU from the ROM or the like in the register, so that it directly affects the circuit scale and inevitably increases the circuit scale.
[0009]
In addition, as described above, it is necessary to compare and calculate the density of each pixel of the gradation data 54 and the corresponding threshold value of the threshold value matrix 55 three times per pixel. ”Is also converted into a binary numerical value as shown in FIG. 13, and the processing amount (time) of the gradation data increases accordingly.
[0010]
An object of the present invention is to generate a halftone image using a dither matrix having a size smaller than a threshold matrix for a conventional M double dense image while taking advantage of the M double dense image technology capable of smooth gradation expression. Another object is to provide a gradation processing method and apparatus capable of reducing the data processing amount (time).
[0011]
[Means for Solving the Problems]
To achieve the above object, in the gradation processing method and apparatus according to the present invention, the dither matrix is not divided into M (M ≧ 2) dot areas, and each dither value in the dither matrix is set to .. Grouping up to m-th (m ≧ 2), and for each group, the dither values of all pixels are serial numbers (0, 1, 2, 3,..., N) −M × N (M = A group obtained by adding the dither value to the density value of the gradation data for each pixel, defined by the number of dot regions, N = the total number of pixels belonging to the group preceding the group). Divided by the total number of pixels, and is limited to an integer value of 0, 1, 2, 3,..., M (M is an integer of M ≧ 2), and depending on each integer value It is characterized by expressing a tone P of M + 1 stages from 0 to M.
[0012]
As a result, it is possible to generate a halftone image using a smaller dither matrix compared to the conventional gradation processing method in which the threshold (dither) matrix is divided into M (M ≧ 2) dot areas. Become.
[0013]
That is, the invention according to claim 1 is a gradation processing method for converting gradation data into halftone data of M + 1 stages (M is an integer of M ≧ 2) per pixel using a dither matrix, A step of grouping each pixel from the first to mth (m ≧ 2) according to the position of each pixel in the dither matrix, and for each group, the dither values of all the pixels are assigned serial numbers (0, 1, 2, 3,..., N) −M × N (N is the total number of pixels belonging to the group preceding the group), and the density value of the gradation data is set for each pixel. One of 0, 1, 2, 3,..., M (M is an integer of M ≧ 2) after dividing the value obtained by adding the dither value by the total number of pixels in the group to which the dither value belongs. And limiting to an integer value of It is set to.
[0014]
In the conventional gradation processing method, the process of comparing and calculating the density of the input image and the corresponding threshold value of the threshold matrix M times per pixel, and the number of “1” s out of the M frames are counted 2 In contrast to the process of converting to a numerical value of a decimal number, the same number of gradations can be expressed by only one process.
[0015]
The invention according to claim 2 is characterized in that the dither matrix is of a dot concentration type.
[0016]
Furthermore, the invention according to claim 3 is characterized in that the dither matrix has dither values arranged in a spiral shape.
[0017]
Here, in the invention according to claim 4, grouping in the dither matrix in which the dither values are arranged in a spiral shape is performed for each pixel equidistant from the center point of the matrix, and the definition of the dither matrix is as follows: Dither values of all pixels are serial numbers (0, 1, 2, 3,..., N) −M × N (M = an integer of M ≧ 2 representing the number of the dot areas, N = the group concerned) The total number of pixels belonging to all groups at a short distance from the center point of the matrix.
[0018]
As a result, the density grows in a round shape (in a spiral shape), so that it is possible to generate a halftone image for making the contour look round.
[0019]
On the other hand, the invention according to claim 5 is characterized in that the dither matrix has dither values arranged in a line type.
[0020]
As a result, the density grows square (extends vertically), which is effective in generating a halftone image for making the outline appear square.
[0023]
On the other hand, the invention according to claim 6 is a gradation processing device that converts gradation data into 0 to M M + 1-stage (M is an integer of M ≧ 2) halftone data per pixel using a dither matrix. Grouping means for grouping each pixel from the first to mth (m ≧ 22) according to the position of each pixel in the dither matrix, and for each group, the dither values of all the pixels in the dither matrix , Serial number (0, 1, 2, 3,..., N) −M × N (N = the total number of pixels belonging to the group before the group), and the gradation for each pixel. The value obtained by adding the dither value to the density value of the data is divided by the total number of pixels in the group to which the dither value belongs, and then limited to an integer value of 0, 1, 2, 3,. An arithmetic means for performing an arithmetic operation Characterized in that it has a.
[0024]
Thereby, for example, even when the CPU has a circuit configuration in which the threshold matrix is stored in the register, it is possible to avoid an unnecessarily large circuit scale.
[0025]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the gradation processing method according to the first embodiment of the present invention will be described in detail with reference to the drawings.
[0026]
The present embodiment is applied to generation of a halftone image in a laser printer or the like using a triple density image technology. That is, in a laser printer or the like, the gradation data developed in a dot matrix is binarized using a dither matrix, and one pixel is divided into three dot areas and printed, so that 0 to 3 per pixel is printed. This is applied when expressing the four-stage tone P.
[0027]
First, the gradation processing apparatus used in this embodiment will be described with reference to FIGS.
[0028]
As shown in FIG. 1, the gradation processing device 1 includes a dither matrix 2, grouping data 3 in which each dither value in the dither matrix 2 is grouped up to the first to mth (m ≧ 2), For each pixel, a value obtained by adding each dither value in the dither matrix 2 to the density value of the multitone image data developed in a dot matrix form is divided by the total number of pixels in the group to which the dither value belongs according to the grouping data 3. The arithmetic unit 4 that performs an operation to limit the integer value to any one of 0, 1, 2, and 3 and the 0, 1, 2, and 3 integer values obtained by the arithmetic unit 4 in four stages of 0 to 3 Are provided with a triple density data conversion unit 5 for converting the data into each of the tones P. Note that the arithmetic unit 4 can be configured by a CPU of a printer controller or the like (not shown) such as a laser printer and its register group. Further, the dither matrix 2 and the grouping data 3 can be stored in a ROM or the like in the printer controller by a lookup table method. The triple density data conversion unit 5 can be constituted by, for example, a CPU and a RAM in the printer controller. Bitmap data output as triple density data by the triple density data conversion unit 5 is a laser. A halftone having four levels of tone P of 0 to 3 per pixel by being sent to a print engine 6 of a printer or the like (not shown) and printed in a form in which one pixel is divided into three dot areas. An image is generated.
[0029]
Next, the definition method of the dither matrix 2 and the grouping method in the grouping data 3 will be described with reference to FIGS.
[0030]
The dither matrix 2 has a 4 × 4 matrix size as shown in FIG. 2, and hereinafter, the positions of pixels (pixels) in the dither matrix 2 are set to 0 to 0 as shown in FIG. Shown by numbers up to 15. These numbers are not related to the dither value or the like and are merely for convenience of explanation.
[0031]
The dither matrix 2 is used for a 3 × dense image, but is not divided into three dot areas. The grouping in the grouping data 3 is such that each pixel (pixel) in the dither matrix 2 is first, second, second for each of the equidistant from the center point of the matrix 2 as shown in FIG. Up to 3 groups are grouped. The first, second, and third groups include 4, 8, and 4 pixels, respectively, as shown in FIG. On the other hand, according to the grouping data 3, the dither matrix 2 is defined by assigning the dither values of all the pixels in the dither matrix 2 to the serial numbers (0, 1, 2, 3,..., N) -M for each group. × N (M = M in an M double dense image, that is, 3 in the present embodiment, N = the total number of pixels belonging to a group before the group).
[0032]
That is, as shown in FIG. 2 (c), four pixels at positions 5, 6, 10, and 9 shown in FIG. 2 (a) that are closest to the first group, that is, the center point of the dither matrix 2. Are assigned dither values of 0, 1, 2, and 3, respectively. Further, in the second group, that is, at the second distance from the center point of the dither matrix 2, eight pixels at positions 4, 1, 2, 7, 11, 14, 13, 8 shown in FIG. Are assigned dither values of 0-4M, 1-4M, 2-4M, 3-4M, 4-4M, 5-4M, 6-4M, and 7-4M, respectively. Further, the four pixels at the positions 0, 3, 15 and 12 shown in FIG. 4A which are the farthest from the center point of the third group, that is, the dither matrix 2, are respectively 0-12M, 1− Dither values of 12M, 2-12M, and 3-12M are assigned. Here, M represents triple density.
[0033]
When the gradation expression method using the dither matrix 2 is employed, gradation expression in which the halftone density grows in a spiral shape as shown in FIG. 3 becomes possible. That is, the halftone pattern generation method of this embodiment generates a so-called area gradation pattern, and each pixel takes a value of 0 to 3, and the larger the value, the larger the black area. To do. First, as described above, all the pixels are first divided into three groups for each pixel that is equidistant from the center point of the dither matrix 2. First, the first group, that is, 5 shown in FIG. , 6, 10, and 9 alternately increase the values of the four pixels by one. If all four pixels have the value of M, then the second group, that is, eight pixels at positions 4, 1, 2, 7, 11, 14, 13, 8 shown in FIG. Increase the value by 1 alternately. When all of the eight pixels have reached 3, finally, the values of the four pixels in the third group, that is, the positions 0, 3, 15, and 12 shown in FIG. As described above, since the black area increases as the value of 0 to 3 of each pixel increases, n indicates the density of the image, and gradation expression from n = 0 to n = 48 is possible. . As a result, the same gradation number n = 0 to 48 can be expressed using the dither matrix 2 having a smaller size than the conventional threshold matrix 55 [see FIG. It becomes. In addition, as is clear from FIG. 3, in this embodiment, the dark portion from n = 0 to n = 48 grows in a round shape (in a spiral shape), so a half for making the contour appear round. This is particularly effective as a tone pattern. As described above, since the halftone pattern is defined, 12 numbers such as 4M in the second group or 12M in the third group are set to 3 before the number of pixels increases. It represents the number of pixels that have been reached.
[0034]
FIG. 4 shows a flow for defining the dither matrix 2.
[0035]
Now, the gradation processing method of the present embodiment will be described with reference to FIGS.
[0036]
In the gradation processing method of the present embodiment, the density value of multitone image data (see FIG. 1) [for example, the density values of 0 to 48 shown in FIG. The value obtained by adding the corresponding dither value of the dither matrix 2 shown in FIG. 4 is divided by the total number of pixels (pixels) in the group to which the dither value in the grouping data 3 belongs, and is any one of 0, 1, 2, 3 It is limited to an integer value, and four tones P (see FIG. 13) of 0 to 3 in a 3 × dense image are expressed according to each integer value.
[0037]
That is, as shown in FIGS. 1 and 5, first, the density value of one pixel [for example, the density value 32 shown in FIG. 12A] is fetched from the multitone image data (see FIG. 1) (step 101). . The dither value (2-4M) corresponding to the dither matrix 2 is added to this value (32) (step 102). As a result, a value of 32 + 2−4 × 3 = 22 is obtained. This value (22) is divided by the number of pixels 8 [see FIG. 2 (b)] in the group [second group [see FIG. 2 (b)]] to which the pixel belongs in the grouping data 3 (step 103). As a result, the calculation result d = 22 ÷ 8 = 2.75 is obtained (step 104). The value of the calculation result d is limited to the range of 0 to 3 (steps 105 to 108), and the decimal part is not obtained (step 109). Thereby, the calculated values 0, 1, 2, or 3 of the pixel are obtained (steps 110 to 112, steps 106 and 108), and the above is performed for all the pixels (steps 113 and 114). FIG. 6A shows halftone area gradation data 12 obtained by the above calculation.
[0038]
As shown in FIG. 6A, the area gradation data 12 has a value of binary number / pixel (00, 01, 10, 11) in which each pixel takes one of 0, 1, 2, and 3. ) Is converted into triple dense data, such as 00 → 000, 01 → 001or100, 10 → 011or110, 11 → 111, and sent to the print engine 6 by the triple dense data converter 5 shown in FIG. By printing in a form in which one pixel is divided into three dot regions, a halftone image having four levels of tone P of 0 to 3 per pixel is generated.
[0039]
Here, when the tone P is 1 and 2 as in 01 → 001or100 and 10 → 011or110, there are two possible dot patterns (see FIG. 13), but the tone processing method of this embodiment uses them. In the triple density image, black (= 1) is changed to the left or the right by looking at the value of the adjacent pixels on the left and right sides, and control is performed so that black is connected. That is, the left and right adjacent pixel values are compared, and if left ≤ right, black is shifted to the right (01 → 001, 10 → 011), while if left> right, black is shifted to the left (01 → 100, 10 → 110). To control.
[0040]
FIG. 6B shows a halftone image printed as described above.
[0041]
As can be seen from the halftone image of FIG. 6B, the same half-tone image as that of the conventional three-fold density can be obtained.
[0042]
A gradation processing method according to the second embodiment of the present invention will be described with reference to FIGS.
[0043]
This second embodiment also relates to the generation of a halftone image when using the triple density image technique. In the present embodiment, as shown in FIG. 7A, the grouping data 3 ' Is a group of four pixels in the second column as a first group, eight pixels in the first and third columns as a second group, and four pixels in the fourth column as a third group. is there.
[0044]
In the present embodiment, the dither matrix is defined by assigning the dither values of all pixels in the dither matrix to serial numbers (0, 1, 2, 3,..., For each group according to the grouping data 3 ′. n) −M × N (M = M in an M double-density image, that is, in the present embodiment, 3, N = the total number of pixels belonging to a group preceding the group).
[0045]
As a result, a dither matrix 2 ′ shown in FIG. 7B is obtained.
[0046]
The gradation processing method of the present embodiment is the same as that of the first embodiment described above except that the above grouping data 3 ′ and dither matrix 2 ′ are used.
[0047]
That is, the corresponding dither value of the dither matrix 2 ′ shown in FIG. 7B is added to the density value of the multitone image data (see FIG. 1) [for example, the density values of 0 to 48 shown in FIG. 12A]. The obtained value is divided by the total number of pixels (pixels) in the group to which the dither value belongs in the grouping data 3 ′, and is limited to an integer value of 0, 1, 2, 3 Correspondingly, 0 to 3 levels of tone P (see FIG. 13) in the 3 × dense image are expressed.
[0048]
FIG. 8A shows the halftone area gradation data 14 obtained by the above calculation, and FIG. 8B shows the halftone image.
[0049]
As can be seen from FIGS. 8A and 8B, according to the second embodiment, the concentration grows squarely (extends vertically) from n = 0 to n = 48. It is effective as a halftone pattern for making the outline look square.
[0050]
A gradation processing method according to the third embodiment of the present invention will be described with reference to FIGS.
[0051]
In the third embodiment, the dither matrix 2 ″ is composed of a 6 × 6 matrix as shown in FIG. 9C. For convenience of explanation, the positions of the pixels in the dither matrix 2 ″ are indicated by numbers from 0 to 35 as shown in FIG. Further, as can be seen from FIGS. 9A to 9C, the dither matrix 2 ″ has the dither values arranged in a spiral shape in the same manner as the dither matrix 2 of the first embodiment described above.
[0052]
In the present embodiment, as shown in FIGS. 9B and 9C, the grouping in the grouping data 3 ″ indicates each pixel (pixel) in the dither matrix 2 ″ as shown in FIG. 9B. In this way, the first, second, third, fourth, fifth, and sixth groups are grouped for each one that is equidistant from the center point of the matrix 2 ″. The first, second, third, fourth, fifth, and sixth groups are respectively 4, 8, 8, 8, 8, and 4 pixels as shown in FIG. (Pixel) is included. On the other hand, the definition method of the dither matrix 2 ″ is that the dither values of all the pixels in the dither matrix 2 ″ are assigned serial numbers (0, 1, 2, 3,. 7) −M × N (M = M in an M double dense image, N = the total number of pixels belonging to a group preceding the group).
[0053]
FIG. 10 shows a flow for defining the dither matrix 2 ″.
[0054]
As mentioned above, although this invention was described about specific embodiment, this invention is not limited to these, It is applied also about other embodiment within the range of the invention described in the claim.
[0055]
For example, the dither matrix 2 and the grouping data 3 and the like may be defined on software (program).
[0056]
In the above-described embodiment, 4 × 4 and 6 × 6 halftone (dither) matrices are used. However, a matrix of 8 × 8 or 16 × 16 may be used. This can be selected in view of the performance of the engine.
[0057]
Furthermore, although the above-described embodiment has been described with respect to halftone pattern generation when using the 3 × dense image technology, more pixels are used, such as a 7 × dense image, a 15 × dense image, and a 31 × dense image. Of course, it can be applied to fine control. In such a case, the difference between the conventional method and the method of the present invention becomes larger.
[0058]
【The invention's effect】
As described above, according to the gradation processing apparatus and method according to the present invention, compared to the conventional gradation processing method in which the dither (threshold) matrix is divided into M (M ≧ 2) dot areas. A halftone can be defined using a smaller matrix.
[0059]
Therefore, for example, even when the CPU has a circuit configuration in which the dither matrix is stored in the register, it is possible to prevent the circuit scale from becoming unnecessarily large.
[0060]
In the conventional gradation processing method, the density data density and the threshold value corresponding to the threshold matrix are compared and calculated M times per pixel, and the number of “1” s in the M frames is determined. While the process of counting and converting to a binary number is necessary, the same number of gradations can be expressed by only one series of processes.
[0061]
Therefore, the processing amount (time) of the gradation data can be reduced by that amount, so that the throughput when applied to a laser printer or the like is improved.
[0062]
As described above, a gradation processing method capable of generating a halftone image with a simpler hardware configuration and reducing the data processing amount (time) while utilizing the advantages of the M double dense image technology capable of smooth gradation expression. And an apparatus can be provided.
[Brief description of the drawings]
FIG. 1 is a functional block diagram showing a configuration of a gradation processing apparatus used in an embodiment of the present invention.
FIGS. 2A and 2B are diagrams for explaining a gradation processing method according to the first embodiment of the present invention, and FIG. 2A shows the positions of pixels in the dither matrix 2 for convenience of explanation; FIG. 4B is a diagram showing a grouping method for grouping data 3, and FIG. 4C is a diagram showing a configuration of the dither matrix 2.
FIG. 3 is a diagram showing a pattern in which the halftone density grows when the gradation expression method according to the first embodiment of the present invention is employed;
FIG. 4 is a flowchart showing a method for defining a dither matrix 2;
FIG. 5 is a flowchart for explaining an arithmetic method used in the gradation processing method according to the first embodiment of the present invention;
6A is a diagram showing halftone area gradation data obtained by the calculation of FIG. 5, and FIG. 6B is a diagram showing a printed halftone image.
7A and 7B are diagrams for explaining a gradation processing method according to a second embodiment of the present invention, where FIG. 7A is a diagram showing a grouping method of grouping data 3 ′, and FIG. 7B is a dither matrix; It is a figure which shows the structure of 2 '.
FIG. 8A is a diagram showing halftone area gradation data obtained according to the second embodiment of the present invention, and FIG. 8B is a diagram showing the printed halftone image.
FIG. 9 is a diagram for explaining a gradation processing method according to a third embodiment of the present invention, where FIG. 9A is a diagram for explaining the position of a pixel in the dither matrix 2 ″; (B) is a diagram showing a grouping method of grouping data 3 ″, and (c) is a diagram showing a configuration of a dither matrix 2 ″.
FIG. 10 is a flowchart showing a method for defining a dither matrix 2 ″.
11A and 11B are diagrams for explaining a conventional general gradation processing method (without using an M double density image technique), in which FIG. 11A is gradation data developed in a dot matrix, and FIG. Is a diagram showing the configuration of a threshold matrix, and (c) is a diagram showing halftone gradation data obtained.
FIGS. 12A and 12B are diagrams for explaining a gradation processing method using a conventional triple density image technique, where FIG. 12A is gradation data developed in a dot matrix, and FIG. 12B is a threshold matrix configuration; FIG. 6C is a diagram showing halftone gradation data obtained.
FIG. 13 is a diagram for explaining a gradation processing method using a conventional triple density image technique.
[Explanation of symbols]
1 Gradation processing device
2 Dither matrix
2 'dither matrix
2 ″ dither matrix
3 Grouping data
3 'grouping data
3 ″ grouping data
4 Calculation unit
5 3x dense data converter
6 Print engine
12 Area gradation data
51 gradation data
52 threshold matrix
53 Halftone data
54 gradation data
55 Threshold Matrix
56 Halftone data

Claims (6)

(In M, an integer of M ≧ 2) gradation data M + 1 step per pixel using the dither matrix to a gradation processing method for converting halftone data,
Grouping the pixels from the first to the mth (m ≧ 2) according to the position of each pixel in the dither matrix;
For each group, the dither values of all the pixels are assigned serial numbers (0, 1, 2, 3,
..., n)-M x N (N = the total number of pixels belonging to the group preceding the group),
For each pixel, the value obtained by adding the dither value to the density value of the gradation data is divided by the total number of pixels in the group to which the dither value belongs, and then 0, 1, 2, 3,. gradation processing method characterized by chromatic steps to limit any integer value, a.   2. The gradation processing method according to claim 1, wherein the dither matrix is of a dot concentration type.   3. The gradation processing method according to claim 1, wherein the dither matrix has dither values arranged in a spiral shape. 4. The gradation processing method according to claim 3, wherein the grouping is performed for each pixel equidistant from a center point of the matrix, and the dither matrix is defined by assigning dither values of all pixels to serial numbers (0, 1, 2, 3,..., N) -M.times.N ( M.gtoreq.2 integer, N = total number of pixels belonging to all groups closer to the center of the matrix than the group). The gradation processing method characterized by the above-mentioned.   3. The gradation processing method according to claim 1, wherein the dither matrix has dither values arranged in a line type. (The M integer of M ≧ 2) M + 1 stage gradation data 0~M per pixel using the dither matrix to a grayscale processor for converting the halftone data,
Grouping means for grouping each pixel from the first to mth (m ≧ 22) according to the position of each pixel in the dither matrix;
For each group, the dither values of all pixels in the dither matrix are assigned serial numbers (0, 1, 2, 3,..., N) −M × N (N = all the groups belonging to the previous group). Means defined by the number of pixels),
For each pixel, the value obtained by adding the dither value to the density value of the gradation data is divided by the total number of pixels in the group to which the dither value belongs, and then 0, 1, 2, 3,. gradation processing apparatus characterized by having a calculating means for performing an operation that limits any integer value.

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