JP2005203871A - Dither pattern generating apparatus, method, and program - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a dither pattern generating apparatus, a dither pattern generating method, and a dither pattern generating program capable of excellently reproducing an image. <P>SOLUTION: A flowchart indicating dither processing executed by an image processing system includes: steps S101 to S105 of printing a first measurement pattern including a plurality of density detection patterns, measuring the density, and detecting a region the change amount of the density of which is higher from the original density having been measured in advance; steps S107, S109 of generating a second measurement pattern wherein the number of measured patterns is increased for the region; a step S111 of measuring again the density by using the second measurement pattern; a step S113 of estimating a γ characteristic curve; and steps S115, S117 of generating a dither pattern wherein a linear γ characteristic is indicated on the basis of the estimated γ characteristic curve. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a dither pattern generation device, a dither pattern generation method, and a dither pattern generation program, and in particular, a dither pattern generation device, a dither pattern generation method, and a dither pattern generation that create a dither pattern that can reproduce an image satisfactorily. Regarding the program.

  2. Description of the Related Art Conventionally, in the technical field of image forming apparatuses such as laser printers, a technique for controlling the number of drawing dots corresponding to a density level using a dither method or the like to display a halftone image is known.

  Since the dither pattern used in the dither method is created in the initial state of the printer, as the printer is used, the photoconductor changes with time, and the following problems occur.

-Gradient banding (particularly in bright areas, a stepped pattern appears in the gradation that was smooth in the initial state)
・ Changes in γ characteristics ・ Failures such as blackout or overexposure Many methods have been proposed to correct changes in density due to deterioration of output devices over time when dithering is used to output binary images. ing. As a typical example, there is a technique in which a plurality of specific patterns are printed inside the output device, the density is measured by a sensor, and density correction (γ correction) is performed before dither processing.

  However, such a method has a problem that the gradation correction process causes a jump in gradation, resulting in a decrease in the number of output gradations.

  On the other hand, in the following Patent Document 1, a technique is disclosed in which a dither pattern is created by correcting the change in density of an output device so as to obtain a linear characteristic. The method is shown below.

  FIG. 21 is a diagram for explaining a conventional dither pattern creation method.

  Referring to the figure, the dither pattern is created as follows.

  (A) As pre-processing steps, the following (1) and (2) are performed.

  (1) Assign numbers 1 to M × N to each pixel in the M × N size dither matrix (see 1 in the figure).

  (2) The density values for all the patterns (1 to M × N) of the M × N size dither matrix are obtained in advance (see 2 in the figure).

  (B) Steps (3) to (5) below are performed as steps for actual density correction.

  (3) A plurality of measurement patterns are selected (see 3-a in the figure), and these measurement patterns are printed out. The density value of each measurement pattern is measured by a sensor, and interpolation processing is performed together with the density values of all the original patterns obtained in (2) (see 3-b in the figure), and the density values for all the current patterns Is estimated (see 3-c in the figure).

  (4) The pattern number corresponding to the output gradation level is selected (see 4-a in the figure) so that the change in density value is linear (equal intervals), and is stored in the pattern table (in the figure). 4-a).

  (5) A dither pattern is generated based on the dither matrix and the pattern table (see 5 in the figure).

  In this method, since the dither pattern is changed every time according to the density change, problems such as gradation skip are alleviated.

Patent Document 2 below discloses a technique for performing simple correction using simple correction with a small number of patterns and detailed correction with a large number of patterns, and determining whether or not to perform detailed correction based on a change state. ing.
JP 2001-111830 A JP 2001-309178 A

  In the method of Patent Document 1 described above, the density values of all current patterns are obtained (estimated) by interpolation using the density values of a plurality of measurement patterns and the original total density values.

However, since the density value for the measurement pattern may be affected by noise, there is a problem that the approximate density characteristic curve lacks accuracy. FIG. 22 shows the estimated density value of each pattern and the original density value. It is a figure which shows the relationship.

  Referring to the figure, it is assumed that the measurement data is different from the actual data because there is noise in the measurement value by the sensor in the portion surrounded by the dotted line.

  At this time, the estimated density value (approximate curve) is also affected by noise, so that there is a problem that a dither pattern faithful to the actual density change is not generated and a good image cannot be reproduced.

  The present invention has been made to solve the above-described problems, and provides a dither pattern generation device, a dither pattern generation method, and a dither pattern generation program that create a dither pattern that can reproduce an image satisfactorily. It is an object.

  In order to achieve the above object, according to one aspect of the present invention, a dither pattern generation device includes a first output unit that outputs a first measurement pattern composed of a first number of types of measurement patterns, and a first output unit. Measurement means for measuring the density value of the measurement pattern output by the calculation means, a calculation means for calculating the amount of change in density from the original density value based on the measurement result of the measurement means, and a calculation result of the calculation means A second measurement pattern creating means for creating a second measurement pattern composed of a second number of types of measurement patterns larger than the first number, in which more types of patterns are allocated to a region with a large amount of change; Second output means for outputting the second measurement pattern, and determination means for measuring the density value of the measurement pattern output by the second output means, and determining the current density characteristic based on the measured density value , Based on the current density characteristics determined by the determining means, and a dither pattern generating means for generating a dither pattern.

  Preferably, the determining means approximates the density characteristic curve based on the measured density value, and the dither pattern creating means selects a pattern whose density characteristic is linear from the approximated density characteristic curve.

  Preferably, the dither pattern creating means uses a basic dither pattern having the first number of gradations, each of the gradations having the second number of gradations lower than the first number of gradations, and the second corresponding to the gradation. The basic dither pattern is created by correcting the basic dither pattern based on a table in which one gradation is associated.

  Preferably, the second measurement pattern creation means divides the pattern type into a plurality of areas, and weights the number of patterns to be assigned to each area based on the calculation result of the calculation means, thereby obtaining an area with a large amount of change. The second measurement pattern is created so that more types of patterns are allocated.

  Preferably, the second measurement pattern creating means changes the weight of pattern distribution in accordance with each region.

  Preferably, a plurality of first measurement patterns are prepared, and any one pattern is selected and used.

  Preferably, in the selection of the first measurement pattern, a pattern having a larger number of patterns in a region having a large change amount of density value calculated at the time of the previous second measurement pattern creation is automatically selected.

  According to another aspect of the present invention, an image forming apparatus includes the dither pattern generation device described above.

  According to still another aspect of the present invention, the dither pattern creation method outputs the first measurement pattern including the first number of types of measurement patterns, and the first output step and the first output step. The measurement step for measuring the density value of the measurement pattern, the calculation step for calculating the amount of change in density from the original density value based on the measurement result of the measurement step, and the amount of change based on the calculation result of the calculation step A creation step for creating a second measurement pattern comprising a second number of types of measurement patterns greater than the first number, with more types of patterns distributed over a large area, and outputting a second measurement pattern The determination of determining the current density characteristic based on the measured density value by measuring the density value of the measurement pattern output by the second output step and the second output step And step, based on the current density characteristics determined by the determining step, and a creation step of creating a dither pattern.

  According to still another aspect of the present invention, the dither pattern creation program is output by the first output step for outputting the first measurement pattern composed of the first number of types of measurement patterns, and the first output step. The measurement step for measuring the density value of the measurement pattern, the calculation step for calculating the amount of change in density from the original density value based on the measurement result of the measurement step, and the amount of change based on the calculation result of the calculation step A creation step for creating a second measurement pattern comprising a second number of types of measurement patterns greater than the first number, with more types of patterns distributed over a large area, and outputting a second measurement pattern The density value of the measurement pattern output by the output step 2 and the second output step is measured, and the current density characteristic is determined based on the measured density value. And determining step, based on the current density characteristics determined by the determining step, to execute a generating step of generating a dither pattern to a computer.

  Hereinafter, an image processing system according to a preferred embodiment of the present invention will be described.

  The dither pattern generation method performed by the image processing system according to the present embodiment is for generating a dither pattern that is always desirable (linear in γ characteristics) regardless of the density change of the output device.

  Specifically, the density value is first measured using the first measurement pattern, and an area where the amount of change from the original density value measured in advance is large is detected. Then, the density value is measured again using the second measurement pattern in which the number of measurement patterns is increased for the region, and the γ characteristic curve is estimated. Finally, a dither pattern that makes the γ characteristic linear is generated based on the estimated γ characteristic curve.

  With the above operation, it is possible to measure the density value again by increasing the number of measurement patterns for areas where the density change is large, so it is possible to determine whether the density change is due to noise or is actually changing. In addition, the density characteristic curve of the dither pattern can be estimated with high accuracy.

  As a result, it is possible to provide an image processing system capable of reducing the influence of noise and the like and reproducing a good image.

  FIG. 1 is a diagram showing a configuration of an image processing system in one embodiment of the present invention.

  Referring to the figure, the image processing system includes an image input device 100 typified by a scanner, an image processing device 101 constituted by a computer, and an image output device 102 typified by a printer.

  The image data read by the image input apparatus 100 is sent to the image processing apparatus 101, where appropriate processing is performed on the image data, and then sent to the image output apparatus 102 to be output to a print medium such as paper. Is done.

  In addition to the scanner, the image input device 100 may be a recording medium such as a digital camera or a storage device, a communication line, or the like.

  FIG. 2 is a block diagram showing the configuration of the system of FIG. 1 in more detail.

  Referring to the figure, image input device 100 includes an image input unit 201.

  The image processing apparatus 101 includes an image processing unit 202, a dither processing unit 203, a basic dither pattern storage unit 204, a measurement dither pattern creation unit 205, a first measurement pattern table storage unit 206, and a second measurement use. A pattern table calculation unit 207, an output dither pattern creation unit 208, an output pattern table correction unit 209, and an output pattern table storage unit 210 are provided.

  The image output apparatus 102 includes a printer engine 211 and a density measuring unit (density sensor) 212.

  The image data input from the image input unit 201 is sent to the image processing unit 202, subjected to appropriate image processing, and then converted into multivalued CMYK data.

  The converted CMYK data is sent to the dither processing unit 203, subjected to binarization processing by the dither pattern created by the measurement dither pattern creation unit 205 or the output dither pattern creation unit 208, and binary CMYK data Converted to data.

  The CMYK data is sent to the printer engine 211 and printed out.

  The basic dither pattern storage unit 204 stores a basic dither pattern that can reproduce the number of gradations b (where b ≧ a) that is greater than or equal to the number of gradations a that the image processing apparatus 101 reproduces.

  The output pattern table storage unit 210 stores an output pattern table that is a table for associating each reproduced gradation a with one of the b gradations that can be expressed by the basic dither pattern.

  The output pattern table correction unit 209 corrects the output pattern table based on the density change measured by the density measurement unit 212.

  The first measurement pattern table storage unit 206 stores a first measurement pattern table that is a table for measuring density values using m measurement patterns. The second measurement pattern table calculation unit 207 is configured to check the density change in more detail for a density region having a large change amount from the original density value based on the density value measured by the first measurement pattern table. A second measurement pattern table, which is a table for measuring density values using a measurement pattern of (n> m), is created.

  The measurement dither pattern creation unit 205 creates a measurement dither pattern (first measurement pattern, second measurement pattern) based on the first measurement pattern table or the second measurement pattern table.

  FIG. 3 is a block diagram illustrating a hardware configuration of the image processing apparatus 101 in FIG.

  Referring to the figure, an image processing apparatus 101 includes a CPU 601 that controls the entire apparatus, a display 605, and a LAN (local area network) card 607 (or a modem card) for connecting to a network or communicating with the outside. An input device 609 including a keyboard and a mouse, a flexible disk drive 611, a CD-ROM drive 613, a hard disk drive 615, a RAM 617, and a ROM 619.

  A program for driving the CPU (computer) 601 can be recorded on a recording medium such as the flexible disk F or the CD-ROM 613a. This program is sent from a recording medium to a RAM or other recording medium and recorded. The program may be recorded on a recording medium such as a hard disk, ROM, RAM, or memory card and provided to the user. Further, such a program may be downloaded and executed from an external site via the Internet.

  FIG. 4 is a diagram showing a schematic configuration of the printer engine 211 of FIG.

  Referring to the figure, printer engine 211 forms an image on intermediate transfer member 502 by the developing unit. When correcting the output pattern table, a density detection pattern is formed on the intermediate transfer member 502. By using the sensor 501, the density measuring unit 212 measures the actual density of the density detection pattern.

  5 and 6 are diagrams illustrating specific examples of the basic dither pattern. FIG. 5 and FIG. 6 are connected at a portion (A) in the drawing.

  The basic dither pattern is composed of a horizontal 48 × vertical 24 pixel size. Further, in the figure, for easy understanding, the basic dither pattern is divided into blocks of horizontal 12 × vertical 3 pixel size by a solid line (this one block is referred to as “basic pattern”). Note that the “basic patterns” in contact with each other in the vertical direction are shifted horizontally. As a result, for example, the basic pattern located on the left and right of the second column from the top has a pixel size of 6 × 3 pixels, but the two patterns are considered to be connected horizontally, and other basic patterns Similarly, it is assumed that a basic pattern of one horizontal 12 × vertical 3 pixel size is formed. There are four basic patterns and four horizontal patterns.

  Each of the horizontal 48 × vertical 24 pixels of the basic dither pattern is assigned a value (number) from 1 to 1152. This value indicates the order of dots to be lit. If the dot is not turned on when 0 and the basic dither pattern is turned on when the gradation is 1152, then a total of 1153 gradations can be expressed.

  FIG. 7 is a diagram showing the density characteristics of the basic dither pattern shown in FIGS.

  Referring to the figure, the vertical axis indicates the density value when the pattern is printed from gradation 1 (this pattern is called the pattern No. 1 pattern). The vertical axis is normalized with the density value at 1 at the gradation 1152 (this pattern is referred to as pattern No. 1152). As shown in the figure, normally, the rise of the density is steep at the portion where the gradation is low, but when it exceeds a certain level, it tends to be saturated and the increase in density becomes small.

  8 to 10 are diagrams showing specific examples of pattern tables recorded in the output pattern table storage unit 210. FIG.

  Here, an image with 256 gradations is processed, and each gradation of 256 gradations is recorded in association with which of the 1153 gradations of the basic dither pattern.

  FIG. 11 is a diagram illustrating the relationship between the output of the sensor 501 and the image density.

  Referring to the figure, since the output value (A0, A1) and density (C0, C1) of sensor 501 correspond one-to-one, the density of the image formed from the sensor output value can be known.

  FIG. 12 is a diagram showing the contents of the first measurement pattern table.

  Referring to Fig. 12, the first measurement pattern table is a table for printing a total of eight types of patterns 1 to 8 (note that no pattern printing is performed, pattern No. 0 is here) Not included in the pattern type). Here, as the dither pattern for measurement, the pattern number of the basic dither pattern. Eight patterns corresponding to each central position after dividing (number) into eight equal parts are used (when the total number of pattern numbers of the basic dither pattern is 1152, the pattern numbers are 72, 216 , 360, 504, 648, 792, 936, 1080).

  However, the number of patterns included in the first measurement pattern table is not particularly limited as long as it is smaller than the number of patterns in the second measurement pattern table.

  FIG. 13 is a diagram showing the contents of the second measurement pattern table.

  The second measurement pattern table is a pattern table for examining in detail the portion in which the density change is large as a result of the measurement in the first measurement pattern table, and is held more than the number of patterns in the first measurement pattern table. There are many patterns. Here, 32 types of patterns 1 to 32 are used, but the number of patterns is not particularly limited as long as the number of patterns is larger than the number of patterns in the first measurement pattern table.

  The second measurement pattern table is created based on the measurement result of the concentration measurement unit 212, and detailed processing thereof will be described later.

  FIG. 14 is a flowchart showing dither processing executed by the image processing system according to the present embodiment.

  In step S101, first, a first measurement dither pattern is output based on the first measurement dither pattern table, and a density value is measured using a sensor 501 incorporated in the printer. In step S103, this is compared with a reference density value measured in advance, and it is detected whether or not there is a region with a large change.

  FIG. 15 is a diagram illustrating a specific example of the relationship between the reference density value and the measured density value.

  This is a pattern number of the basic dither pattern as the measurement dither pattern. 8 patterns (eight patterns 1 to 8 in FIG. 12) corresponding to the respective central positions obtained by dividing the pattern into eight are used.

  In FIG. 15, the amount of change between the reference density value and the measured density value is calculated. Here, the difference between the density values is simply set as the amount of change. Then, it is determined whether the change amount exceeds a preset threshold value. If the amount of change for any measurement dither pattern is equal to or less than the threshold value, it is assumed that no density change has occurred, and density correction processing is not performed (NO in step S105 in FIG. 14). Then, a default output pattern table is read (step S121 in FIG. 14).

  On the other hand, if the amount of change exceeds the threshold value in one or more patterns (YES in step S105 in FIG. 14), a second measurement pattern table is created in which the number of measurement patterns is increased or decreased according to the amount of change (FIG. 14). Step S107).

  Here, a description will be given based on the example of FIG.

  FIG. 16 is a diagram illustrating a specific example of the amount of change between the reference density value and the measured density value.

  First, it is assumed that the reference density value and the change amount of the measured density value corresponding to each of the eight measurement patterns are calculated as shown in FIG.

  Referring to FIGS. 15 and 16, the density change is particularly large in the portions (1) and (2) (pattern Nos. 72 and 216) and exceeds the threshold, and the portion (5) (pattern No. 648)), it is assumed that no change has been detected.

  Here, consider a case where 32 patterns are used as the second measurement dither pattern.

  FIG. 17 is a first diagram for explaining a method of creating the second measurement pattern table.

  First, 16 half of the 32 patterns are divided equally into 8 and are equally allocated to 8 regions ((1) to (8)) ("distribution 1" in the figure).

  Next, the remaining 16 pieces are weighted according to the rate of change in each area and distributed ("distribution 2" in the figure). Then, the sum of the two distribution numbers is used as the final measurement pattern distribution number ("total" in the figure).

  By the processing of FIG. No. 8 from the area of No. 1 to 144, 6 out of 145-288, No. Three measurement patterns are selected from 1009 to 1152. The selection method at this time is as follows. Is simply divided equally, and the pattern No. of the portion at the divided position is divided. Shall be obtained. That is, when a pattern is selected from the example of FIG. Is as shown in FIG.

  That is, in the area (1), the pattern No. Eight patterns of 18, 36, 54, 72, 90, 108, 126, and 144 are selected from 1 to 144. Similarly, the patterns having the number of patterns obtained from FIG. 17 are selected in the other areas.

  Then, based on the second measurement pattern table, the second measurement dither pattern is output (step S109 in FIG. 14). The density value corresponding thereto is measured again (step S111 in FIG. 14), and a density characteristic curve indicating the current density is estimated (step S113 in FIG. 14). The density characteristic curve is estimated by approximating the curve with a multi-order curve such as a fifth order using a least square approximation method or the like.

  FIG. 19 is a diagram illustrating a method of estimating a density characteristic curve.

  In the figure, the measured values are indicated by square points, and the estimated curve is indicated by a solid line.

  Based on the estimated density characteristic curve, 256 pattern Nos. Whose density changes are linear are shown. The output pattern table is corrected (changed) by selecting (step S115 in FIG. 14). Then, an output dither pattern is created by using the basic dither pattern and the output pattern table (step S117 in FIG. 14).

  The output dither pattern is used, the image is dithered, and printing is performed (step S119 in FIG. 14).

  FIG. It is a figure for demonstrating the selection method of.

  In this example, the density values are selected at equal intervals so that the density change is constant, and the pattern is selected. May be selected.

  In the above-described embodiment, all the pattern Nos. Of the basic dither pattern are used as the first measurement dither pattern. However, the present invention is not limited to this. For example, when it is known in advance that the change in the density characteristics of the highlight area is large, the number of patterns in the highlight area may be increased. Also, the number is not limited to eight, and any number such as 16, 32 may be selected.

  In the above-described embodiment, the first dither pattern for measurement is used in advance. However, the present invention is not limited to this. For example, a plurality of measurement dither patterns such as those with a larger number of patterns in the highlight area and those with a larger number of patterns in the shadow area are prepared for use by the user. May be selectable.

  Alternatively, when the second dither pattern for measurement is created, which region has the largest change amount is calculated, and the number of patterns in that region is increased to obtain the first measurement of the next density correction processing. It may be automatically used as a dither pattern.

  In the above-described embodiment, the change amount between the reference density value and the measured density value is simply calculated based on the difference, but the present invention is not limited to this. For example, if it is known in advance that the influence of noise is large in the shadow area, the weight of the shadow area may be reduced, that is, the change amount may be multiplied by a coefficient α (<1).

  In the above-described embodiment, the second number of dither patterns for measurement is set to 32. However, the present invention is not limited to this. That is, any number may be used as long as it is greater than or equal to the first measurement dither pattern.

  Furthermore, in the above-described embodiment, 16 half of the second number of dither patterns for measurement are equally distributed to 8 regions and the remaining 16 are weighted and distributed, but this is not restrictive. All of the number of dither patterns (32 in the above embodiment) may be weighted and distributed. Or, if you want to improve the accuracy of the highlight area in advance, distribute the first 16 as 3, 3, 2, 2, 2, 1, 1, 1, 1, and weight the remaining 16 You may make it do. That is, any method may be employed as long as the distribution of the second measurement pattern is changed according to the amount of change in the density value of the first measurement pattern.

  In the above embodiment, when determining the second measurement dither pattern, the number of patterns is divided into eight regions corresponding to the number of measurement patterns. Any number of divisions such as 16 may be used. Further, the actual pattern No. is determined from the number of patterns allocated to each area. However, the present invention is not limited to this. In other words, any method may be employed as long as it is a method for selecting the number obtained by a predetermined calculation from each divided area.

  Further, the system of FIG. 1 (or a part thereof) may be incorporated in one MFP (multi function peripheral), facsimile apparatus, printer apparatus, and copying machine.

  As described above, according to the present embodiment, the density characteristic curve can be accurately estimated regardless of the presence of noise or the like, so that a dither pattern that always maintains appropriate linear characteristics can be created. effective.

  The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is shown not by the above description of the embodiments but by the scope of claims for patent, and is intended to include meanings equivalent to the scope of claims for patent and all modifications within the scope.

1 is a diagram illustrating a configuration of an image processing system according to one embodiment of the present invention. FIG. 2 is a block diagram showing the configuration of the system of FIG. 1 in more detail. It is a block diagram which shows the hardware constitutions of the image processing apparatus 101 of FIG. FIG. 3 is a diagram illustrating a schematic configuration of a printer engine 211 in FIG. 2. It is a figure which shows the specific example of a basic dither pattern. It is a figure following FIG. It is the figure which showed the density | concentration characteristic of the basic dither pattern shown in FIG. 5 and FIG. It is a figure which shows the specific example of the pattern table recorded on the pattern table storage part 210 for output. It is a figure following FIG. It is a figure following FIG. It is a figure which shows the relationship between the output of a sensor, and the density of an image. It is a figure which shows the content of the pattern table for 1st measurement. It is a figure which shows the content of the pattern table for 2nd measurement. It is a flowchart which shows the dither process which the image processing system in this Embodiment performs. It is a figure which shows the specific example of the relationship between a reference | standard density value and a measured density value. It is a figure which shows the specific example of the variation | change_quantity of a reference | standard density value and a measured density value. It is the 1st figure for demonstrating the preparation method of the pattern table for 2nd measurement. It is a 2nd figure for demonstrating the production method of the 2nd measurement pattern table. It is a figure which shows the estimation method of a density | concentration characteristic curve. Pattern No. It is a figure for demonstrating the selection method of. It is a figure for demonstrating the conventional dither pattern creation method. It is a figure which shows the relationship between the density value of each estimated pattern, and the original density value.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 100 Image input device, 101 Image processing apparatus, 102 Image output device, 201 Image input part, 202 Image processing part, 203 Dither processing part, 204 Basic dither pattern storage part, 205 Measurement dither pattern creation part, 206 For 1st measurement Pattern table storage unit, 207 Second measurement pattern table calculation unit, 208 Output dither pattern creation unit, 209 Output pattern table correction unit, 210 Output pattern table storage unit, 211 Printer engine, 212 Density measurement unit, 501 sensor 502 Intermediate transfer member.

Claims (10)

First output means for outputting a first measurement pattern comprising a first number of types of measurement patterns;
Measuring means for measuring the density value of the measurement pattern output by the first output means;
Calculation means for calculating the amount of change in density from the original density value based on the measurement result of the measurement means;
Based on the calculation result of the calculation means, a second measurement pattern consisting of a second number of types of measurement patterns larger than the first number, in which more types of patterns are allocated to a region with a large amount of change. A second measurement pattern creating means for creating;
Second output means for outputting the second measurement pattern;
Determination means for measuring a density value of the measurement pattern output by the second output means, and determining a current density characteristic based on the measured density value;
A dither pattern generation apparatus comprising: a dither pattern generation unit that generates a dither pattern based on a current density characteristic determined by the determination unit. The determination means approximates a density characteristic curve based on the measured density value,
The dither pattern generation device according to claim 1, wherein the dither pattern creating unit selects a pattern having a density characteristic linear from the approximate density characteristic curve.   The dither pattern creating means uses a basic dither pattern having a first number of gradations, each of gradations having a second number of gradations lower than the first number of gradations, and a second corresponding to the gradation. The dither pattern generation apparatus according to claim 1, wherein the basic dither pattern is generated by correcting the basic dither pattern based on a table in which one gradation is associated.   The second measurement pattern creation means divides the pattern type into a plurality of areas, and weights the number of patterns to be assigned to each area based on the calculation result of the calculation means. The dither pattern generation device according to claim 1, wherein the second measurement pattern is created so that more types of patterns are distributed.   The dither pattern generation apparatus according to any one of claims 1 to 4, wherein the second measurement pattern creation unit changes the weight of pattern distribution according to each region.   The dither pattern generation apparatus according to claim 1, wherein a plurality of the first measurement patterns are prepared, and any one pattern is selected and used.   In the selection of the first measurement pattern, a pattern in which the number of patterns in a region having a large amount of change in density value calculated at the time of creating the second measurement pattern is increased is automatically selected. Item 7. The dither pattern generation device according to Item 6.   An image forming apparatus comprising the dither pattern generation device according to claim 1. A first output step of outputting a first measurement pattern comprising a first number of types of measurement patterns;
A measurement step of measuring a density value of the measurement pattern output by the first output step;
A calculation step for calculating the amount of change in density from the original density value based on the measurement result of the measurement step;
Based on the calculation result of the calculation step, a second measurement pattern composed of a second number of types of measurement patterns larger than the first number, in which more types of patterns are allocated to a region with a large amount of change. A second measurement pattern creation step to be created;
A second output step of outputting the second measurement pattern;
A determination step of measuring a density value of the measurement pattern output by the second output step, and determining a current density characteristic based on the measured density value;
A dither pattern generation method comprising: a dither pattern generation step of generating a dither pattern based on the current density characteristic determined in the determination step. A first output step of outputting a first measurement pattern comprising a first number of types of measurement patterns;
A measurement step of measuring a density value of the measurement pattern output by the first output step;
A calculation step for calculating the amount of change in density from the original density value based on the measurement result of the measurement step;
Based on the calculation result of the calculation step, a second measurement pattern composed of a second number of types of measurement patterns larger than the first number, in which more types of patterns are allocated to a region with a large amount of change. A second measurement pattern creation step to be created;
A second output step of outputting the second measurement pattern;
A determination step of measuring a density value of the measurement pattern output by the second output step, and determining a current density characteristic based on the measured density value;
A dither pattern generation program for causing a computer to execute a dither pattern creation step for creating a dither pattern based on the current density characteristic determined in the determination step.

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