JP2006240297A - Image processing device, image processing method, image processing program, recording medium, and printing device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To achieve an image recording of a high grade by making white stripes and unevenness in the density less conspicuous. <P>SOLUTION: This printing device is constituted by comprising a multiple value forming section 211, a block dividing section 213, and a pattern changing section 214. In this case, the multiple value coding section 211 relates dot diameters which can be formed by a nozzle 33 to each pixel of the inputting image data of a recording object image. The block dividing section 213 divides the pixels to which the dot diameters are related by the multiple value coding section 211 into blocks by each set of a plurality of the pixels. The pattern changing section 214 changes the combination pattern when the combination pattern for the dot diameters which are matched with respective pixels in the block is a specified combination pattern. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a technique for suppressing density unevenness during image recording.

2. Description of the Related Art Conventionally, there is a recording apparatus that includes a recording head that discharges ink and forms dots by printing ink on a medium such as paper, cloth, plastic, or OHP sheet (hereinafter also simply referred to as recording paper) to perform printing. Are known. In this type of recording apparatus, a plurality of nozzles are formed in the recording head, and ink is ejected from these nozzles.
By the way, in this type of recording apparatus, a plurality of nozzles are formed in the recording head, and ink is ejected from these nozzles. In such a recording apparatus, it is known that the dot diameter (dot area) formed by the ink droplet and the formation position vary for each nozzle. In such a case, depending on the image to be recorded, white stripes (so-called banding) and density unevenness may occur, and the quality of the recorded image may be deteriorated.

Therefore, conventionally, the direction (sub-scanning direction) perpendicular to the scanning direction (main scanning direction) of the recording head
For each dot group formed by a plurality of nozzles arranged in a large dot group, a dot group whose dot diameter is larger than the reference, a dot group whose small dot diameter is smaller than the reference, and a reference dot group whose dot diameter is the reference size There has been proposed a recording apparatus that performs recording so as to be irregularly arranged. According to this recording apparatus, there is no continuity of dot variation in the main scanning direction, and it is difficult to recognize the appearance of uneven stripes (see, for example, Patent Document 1).
JP-A-6-340094 (FIG. 17)

However, in the prior art, a large number of large dot groups may be formed continuously, or a large number of small dot groups may be formed continuously. In this case, density unevenness occurs. There's a problem.
In addition, when the large dot group, small dot group, small dot group, large dot group, etc. are arranged in the main scanning direction, they are sandwiched between large dot groups due to the density difference between the large dot group and the small dot group. There is a problem that a plurality of small dot groups appear as vertical stripes.

  The present invention has been made in view of the above-described circumstances, makes it difficult to notice white stripes and density unevenness, and achieves high-quality image recording, an image processing method, a program, a recording medium, And it aims at providing a recording device.

[Mode 1] In order to achieve the above object, an image processing apparatus according to mode 1 includes:
Extracting means for forming dots by ejecting droplets from a plurality of nozzles, and extracting pixels that can be formed by a printing apparatus that forms an image with the plurality of dots as a block of pixels, and each of the blocks in the block A determining unit that determines whether or not a combination of pixels is a predetermined combination, and a changing unit that changes the combination when the combination of pixels in the block is a predetermined combination as a result of the determination by the determining unit. It is characterized by comprising.

  According to this image processing apparatus, for example, when the combination pattern in the block is a predetermined pattern such as a combination in which white stripes and density unevenness are conspicuous, the combination pattern is changed. As a result, the combination pattern in the block can be changed to a combination pattern in which white stripes and density unevenness are inconspicuous, white stripes and density unevenness are less noticeable, and high-quality image recording can be achieved.

[Mode 2] An image processing apparatus according to mode 2
Extraction means for forming dots by ejecting droplets from a plurality of nozzles and extracting pixels associated with dot diameters that can be formed by a printing apparatus that forms an image with the plurality of dots as a block of pixels Determining means for determining whether or not a combination of dot diameters associated with each pixel in the block is a predetermined combination; and a combination of dot diameters associated with each pixel in the block And a changing means for changing the combination.

  According to this image processing apparatus, for example, when the dot diameter combination pattern in the block is a predetermined pattern such as a combination in which white stripes and density unevenness are conspicuous, the dot diameter combination pattern is changed. As a result, the dot diameter combination pattern in the block can be changed to a combination pattern in which white stripes and density unevenness are not conspicuous, and the gradation that can be expressed increases, so that higher-quality image recording can be performed. Particularly for streaks, the combination of dot diameters is changed (that is, it has been found that streaks can be mitigated by using a plurality of dot sizes), and therefore more effective.

[Mode 3] An image processing apparatus according to mode 3
The image processing apparatus according to the first or second aspect, wherein an abnormal nozzle extracting unit that extracts an abnormal nozzle from the plurality of nozzles and a division that blocks the pixels near the abnormal nozzle extracted by the abnormal nozzle extracting unit Means.
According to this configuration, for example, only the abnormal nozzle corresponding pixel and the pixels in the vicinity of the abnormal nozzle corresponding pixel are processed by being divided into blocks, so that the number of blocks can be reduced and the processing time can be shortened. Become.

[Mode 4] An image processing apparatus according to mode 4
In the image processing apparatus according to Aspect 3, when the combination of the dot diameters is a combination having a plurality of small dot diameters, the changing unit converts all or part of the small dot diameters into the small dots. It is characterized by changing to a combination in which the dot diameter is larger than the diameter.
According to this configuration, for example, small dot diameters in a block are combined and replaced with a large dot diameter. Therefore, since a large dot diameter is formed at a location where white stripes and density unevenness occur, these white stripes and density unevenness can be made inconspicuous.

[Mode 5] An image processing apparatus according to mode 5
In the image processing apparatus according to Aspect 3, when the combination of the dot diameters is a combination having a plurality of large dot diameters, the changing unit converts all or part of the large dot diameters into the large dots. It is characterized by changing to a combination in which the dot diameter is smaller than the diameter.
According to this configuration, for example, large dot diameters in a block are collected and replaced with small dot diameters. Accordingly, a small dot diameter is formed at a location where a dark streak occurs due to an adjacent dot approaching due to an abnormal discharge of the nozzle, so that this dark streak can be made inconspicuous.

[Mode 6] An image processing apparatus according to mode 6
The image processing apparatus according to Embodiment 3, further comprising an error diffusing unit that diffuses density errors before and after the change caused by changing the combination of dot diameters in the block to blocks not processed by the changing unit. It is characterized by providing.
According to this configuration, for example, even if the density in the block has changed due to a change in the dot diameter combination pattern in the block, the density of the change diffuses to other blocks as a density error. And compensated. As a result, high-quality image recording without losing area gradation is possible.

[Mode 7] An image processing apparatus according to mode 7
The image processing apparatus according to the third aspect, the abnormal nozzle corresponding pixel specifying unit that specifies an abnormal nozzle corresponding pixel corresponding to an abnormal nozzle that causes an abnormality in ink ejection among the pixels, and the pixel The abnormal nozzle corresponding pixel and a processing target pixel selecting unit that selects a pixel in the vicinity of the abnormal nozzle corresponding pixel, and the block dividing unit selects the pixel selected by the processing target pixel selecting unit for each of a plurality of pixels. It is characterized by dividing into blocks.
According to this configuration, for example, the abnormal nozzle comes to form a relatively large dot diameter, so that the deviation of the dot formation position becomes inconspicuous and white streaks and density unevenness can be suppressed.

[Embodiment 8] The image processing apparatus of Embodiment 8
The image processing apparatus according to claim 3, further comprising: an abnormal nozzle corresponding pixel specifying unit that specifies an abnormal nozzle corresponding pixel corresponding to an abnormal nozzle that causes an abnormality in ink ejection among the pixels, and the changing unit When the abnormal nozzle corresponding pixel is included in the block, the combination of the dot diameters in the block is an adjacent pixel adjacent to the abnormal nozzle corresponding pixel rather than the dot diameter of the abnormal nozzle corresponding pixel. A determination unit that determines whether or not the dot diameter is a larger combination, and as a result of the determination by the determination unit, when the dot diameter of adjacent pixels is a larger combination, It is characterized by changing to a combination in which the dot diameter is replaced between adjacent pixels.
According to this configuration, for example, the abnormal nozzle comes to form a relatively large dot diameter, so that the deviation of the dot formation position becomes inconspicuous and white streaks and density unevenness can be suppressed.

[Mode 9] An image processing apparatus according to mode 9
In the image processing apparatus according to the eighth aspect, the change unit includes an edge determination unit that determines whether or not an edge portion of a recorded image is included, and when the edge portion is not included, Based on the combination of the dot diameters in the block, the dot diameter is changed between the abnormal nozzle corresponding pixel and the adjacent pixel.
According to this configuration, for example, when an edge portion is included in a block, the dot pattern of the block is not changed, so that the contour of the recorded image does not become unclear.

[Mode 10] An image processing apparatus according to mode 10 includes:
10. The image processing apparatus according to any one of forms 3 to 9, wherein a dot diameter that can be formed by the printing apparatus is associated with each pixel of image data of a recording target image and output to the block dividing unit. It further has a correspondence means.
According to this configuration, for example, the dot diameter correlating means associates the dot diameter that can be formed by the printing apparatus with each pixel of the image data. Efficient image processing can be performed because the labor of searching can be saved.

[Mode 11] An image processing method according to mode 11
An extraction step of ejecting droplets from a plurality of nozzles to form dots, and extracting pixels that can be formed by a printing apparatus that forms an image with the plurality of dots as a block of pixels, and each of the blocks in the block A determination step of determining whether or not a combination of pixels is a predetermined combination;
As a result of determination by the determination unit, when the combination of pixels in the block is a predetermined combination, a changing step of changing the combination;
It is characterized by comprising.
According to this configuration, the same effect as in the first aspect can be obtained.

[Mode 12] The image processing method according to mode 12
An extraction step of forming dots by ejecting droplets from a plurality of nozzles and extracting pixels associated with dot diameters that can be formed by a printing apparatus that forms an image with the plurality of dots as a block of pixels. A determination step of determining whether or not a combination of dot diameters associated with each pixel in the block is a predetermined combination; and a combination of dot diameters associated with each pixel in the block And a changing step for changing the combination.
According to this configuration, the same effect as in the second mode can be obtained.

[Mode 13] The image processing method according to mode 13
13. The image processing method according to claim 11 or 12, wherein an abnormal nozzle extraction step for extracting an abnormal nozzle from the plurality of nozzles, and a division for dividing a pixel in the vicinity of the abnormal nozzle extracted by the abnormal nozzle extraction step into blocks And a step.
According to this configuration, the same effect as in the third aspect is obtained.

[Mode 14] The image processing method according to mode 14
In the image processing method according to the thirteenth aspect, in the change step, when the combination of the dot diameters is a combination having a plurality of small dot diameters, all or a part of the small dot diameters are changed to the small dots. It is characterized by changing to a combination in which the dot diameter is larger than the diameter.
According to this configuration, the same effect as in the fourth aspect can be obtained.

[Mode 15] An image processing method according to mode 15
In the image processing method according to the thirteenth aspect, in the change step, when the combination of the dot diameters is a combination having a plurality of large dot diameters, all or a part of the large dot diameters are changed to the large dots. It is characterized by changing to a combination in which the dot diameter is smaller than the diameter.
According to this configuration, the same effect as in the fifth aspect can be obtained.

[Mode 16] The image processing method according to mode 16
The image processing apparatus according to the thirteenth aspect, further comprising an error diffusion step of diffusing density errors before and after the change caused by the change in the combination of dot diameters in the block to the blocks not processed by the change step. It is characterized by providing.
According to this configuration, the same effect as in the sixth aspect is obtained.

[Mode 17] An image processing method according to mode 17
The image processing apparatus according to the thirteenth aspect, the abnormal nozzle corresponding pixel specifying step for specifying an abnormal nozzle corresponding pixel corresponding to an abnormal nozzle that causes an abnormality in ink ejection among the pixels, and from among the pixels The abnormal nozzle corresponding pixel and a processing target pixel selecting step for selecting a pixel in the vicinity of the abnormal nozzle corresponding pixel, wherein the block dividing step selects the pixel selected by the processing target pixel selection step for each of a plurality of pixels. It is characterized by dividing into blocks.
According to this configuration, the same effect as in the seventh aspect can be obtained.

[Embodiment 18] The image processing method of Embodiment 18 is
The image processing method according to claim 13, further comprising: an abnormal nozzle corresponding pixel specifying step for specifying an abnormal nozzle corresponding pixel corresponding to an abnormal nozzle that causes an abnormality in ink ejection among the pixels, and the changing step When the abnormal nozzle corresponding pixel is included in the block, the combination of the dot diameters in the block is an adjacent pixel adjacent to the abnormal nozzle corresponding pixel rather than the dot diameter of the abnormal nozzle corresponding pixel. A determination step for determining whether or not the dot diameter is a larger combination, and as a result of the determination in the determination step, when the dot diameter of adjacent pixels is a larger combination, It is characterized by changing to a combination in which the dot diameter is replaced between adjacent pixels.
According to this configuration, the same effect as in the eighth aspect can be obtained.

[Mode 19] An image processing method according to mode 19 is
According to the image processing method of aspect 18, the changing step includes an edge determination step for determining whether or not an edge portion of a recorded image is included, and when the edge portion is not included, Based on the combination of the dot diameters in the block, the dot diameter is changed between the abnormal nozzle corresponding pixel and the adjacent pixel.
According to this configuration, the same effect as in the ninth aspect can be obtained.

[Mode 20] An image processing method according to mode 20
20. The image processing method according to any one of forms 13 to 19, wherein the dot diameter that can be formed by the printing apparatus is associated with each pixel of image data of a recording target image and output to the block dividing step. It further features a correspondence step.
According to this configuration, the same effect as in the tenth aspect can be obtained.

[Mode 21] The image processing program of mode 21 is
An extraction step of extracting, as a block of a plurality of pixels, a computer that forms a dot by discharging droplets from a plurality of nozzles to form a dot, and a printing apparatus that forms an image with the plurality of dots forms a block of the plurality of pixels A determination step of determining whether or not each pixel combination is a predetermined combination; and, as a result of determination by the determination means, if the combination of pixels in the block is a predetermined combination, the combination is changed An image processing program for functioning as a change step.
According to this configuration, the same effect as in the first aspect can be obtained.

[Mode 22] The image processing program of mode 22 is
A computer forms a dot by ejecting droplets from a plurality of nozzles, and a pixel that can be formed by a printing apparatus that forms an image using the plurality of dots is extracted as a block of pixels. An extraction step, a determination step of determining whether or not a combination of dot diameters associated with each pixel in the block is a predetermined combination, and a combination of dot diameters associated with each pixel in the block An image processing program for functioning as a change step for changing the combination when the combination is a predetermined combination.
According to this configuration, the same effect as in the second mode can be obtained.

[Form 23] The image processing program of form 23 is
23. The image processing program according to the form 21 or 22, wherein an abnormal nozzle extracting step for extracting an abnormal nozzle from the plurality of nozzles, and a dividing step for dividing a pixel in the vicinity of the abnormal nozzle extracted by the abnormal nozzle extracting unit. It is characterized by functioning as.
According to this configuration, the same effect as in the third aspect is obtained.

[Mode 24] The image processing program of mode 24 is
In the image processing program according to the twenty-third aspect, in the change step, when the combination of the dot diameters is a combination having a plurality of small dot diameters, all or a part of the small dot diameters are changed to the small dots. It is characterized by changing to a combination in which the dot diameter is larger than the diameter.
According to this configuration, the same effect as in the fourth aspect can be obtained.

[Mode 25] The image processing program of mode 25 is
In the image processing program according to the form 23, in the change step, when the combination of the dot diameters is a combination having a plurality of large dot diameters, all or a part of the large dot diameters are changed to the large dots. It is characterized by changing to a combination in which the dot diameter is smaller than the diameter.
According to this configuration, the same effect as in the fifth aspect can be obtained.

[Mode 26] The image processing program of mode 26 is
The image processing program according to claim 23, which functions as an error diffusion step for diffusing density errors before and after the change caused by changing the combination of dot diameters in the block to blocks not processed by the change step It is characterized by letting.
According to this configuration, the same effect as in the sixth aspect is obtained.

[Mode 27] The image processing program of mode 27 is
According to the image processing program according to aspect 23, an abnormal nozzle corresponding pixel specifying step for specifying an abnormal nozzle corresponding pixel corresponding to an abnormal nozzle that causes an abnormality in ink ejection among the pixels, and from among the pixels The abnormal nozzle corresponding pixel and a processing target pixel selecting step for selecting a pixel in the vicinity of the abnormal nozzle corresponding pixel, wherein the block dividing step selects the pixel selected by the processing target pixel selection step for each of a plurality of pixels. It is characterized by dividing into blocks.
According to this configuration, the same effect as in the seventh aspect can be obtained.

[Mode 28] The image processing program of mode 28 is
The image processing program according to claim 23, further comprising: an abnormal nozzle corresponding pixel specifying step for specifying an abnormal nozzle corresponding pixel corresponding to an abnormal nozzle that causes an ink ejection abnormality among the pixels, wherein the changing step includes: When the abnormal nozzle corresponding pixel is included in the block, the combination of the dot diameters in the block is a dot of an adjacent pixel adjacent to the abnormal nozzle corresponding pixel rather than the dot diameter of the abnormal nozzle corresponding pixel. A determination step for determining whether or not the diameter is a larger combination, and when the result of determination in the determination step is a combination in which the dot diameter of the adjacent pixel is larger, the adjacent to the abnormal nozzle corresponding pixel It is characterized by changing to a combination in which the dot diameter is replaced with the pixel.
According to this configuration, the same effect as in the eighth aspect can be obtained.

[Mode 29] The image processing program of mode 29 is
According to the image processing program of aspect 28, the changing step includes an edge determination step for determining whether or not an edge portion of a recorded image is included, and when the edge portion is not included, Based on the combination of the dot diameters in the block, the dot diameter is changed between the abnormal nozzle corresponding pixel and the adjacent pixel.
According to this configuration, the same effect as in the ninth aspect can be obtained.

[Mode 30] The image processing program of mode 30 is
The image processing program according to any one of forms 23 to 29, wherein the dot diameter that can be formed by the printing apparatus is associated with each pixel of image data of a recording target image and output to the block dividing step. It is characterized by functioning as a step with correspondence.
According to this configuration, the same effect as in the tenth aspect can be obtained.

[Mode 31] A recording medium according to mode 31 is a computer-readable recording medium on which the image processing program according to any one of modes 21 to 30 is recorded.
According to this configuration, the same effect as in the first aspect can be obtained.

[Mode 32] A printing apparatus according to mode 32 includes:
A recording head provided with a plurality of nozzles for ejecting ink to form dots, extraction means for extracting pixels that can be formed by the nozzles as a block of pixels, and a combination of each pixel in the block is predetermined. And a changing means for changing the combination of the pixels in the block when the combination of the pixels in the block is a predetermined combination as a result of the determination by the determining means. It is characterized by that.
According to this configuration, the same effect as in the first aspect can be obtained.

[Mode 33] A printing apparatus according to mode 33 is
A recording head provided with a plurality of nozzles for forming dots by ejecting ink; an extraction means for extracting pixels associated with dot diameters that can be formed by the nozzles as a block of pixels; A determination unit that determines whether or not each pixel combination is a predetermined combination, and a change that changes the combination when the combination of the dot diameters associated with the pixels in the block is a predetermined combination And means.
According to this configuration, the same effect as in the second mode can be obtained.

[Mode 34] A printing apparatus according to mode 34 includes:
34. The printing apparatus according to mode 32 or 33, wherein an abnormal nozzle extracting unit that extracts an abnormal nozzle from the plurality of nozzles, and a dividing unit that divides the pixels near the abnormal nozzle extracted by the abnormal nozzle extracting unit into blocks. It is characterized by comprising.
According to this configuration, the same effect as in the third aspect is obtained.

[Mode 35] A printing apparatus according to mode 35 is
In the printing apparatus according to Mode 34, when the combination of the dot diameters is a combination having a plurality of small dot diameters, the changing unit converts all or part of these small dot diameters into the small dot diameter. It is characterized by changing the combination to a larger dot diameter.
According to this configuration, the same effect as in the fourth aspect can be obtained.

[Mode 36] A printing apparatus according to mode 36 includes:
In the printing apparatus according to Form 34, in the case where the combination of the dot diameters is a combination having a plurality of large dot diameters, the changing unit converts all or part of these large dot diameters into the large dot diameter. It is characterized by changing to a combination with a smaller dot diameter.
According to this configuration, the same effect as in the fifth aspect can be obtained.

[Mode 37] A printing apparatus according to mode 37 includes:
The printing apparatus according to mode 34, further comprising error diffusion means for diffusing density errors before and after the change caused by changing the combination of dot diameters in the block to blocks not processed by the change means. It is characterized by that.
According to this configuration, the same effect as in the sixth aspect is obtained.

[Mode 38] A printing apparatus according to mode 38 includes:
In the printing apparatus according to the thirty-fourth aspect, an abnormal nozzle corresponding pixel specifying unit that specifies an abnormal nozzle corresponding pixel corresponding to an abnormal nozzle that causes an abnormality in ink ejection among the pixels, and from among the pixels, The abnormal nozzle corresponding pixel and a processing target pixel selecting unit that selects a pixel in the vicinity of the abnormal nozzle corresponding pixel, and the block dividing unit blocks the pixel selected by the processing target pixel selecting unit for each of a plurality of pixels. It is characterized by being divided into
According to this configuration, the same effect as in the seventh aspect can be obtained.

[Mode 39] A printing apparatus according to mode 39
35. The printing apparatus according to mode 34, further comprising: an abnormal nozzle corresponding pixel specifying unit that specifies an abnormal nozzle corresponding pixel corresponding to an abnormal nozzle that causes an abnormality in ink ejection among the pixels, and the changing unit includes When the abnormal nozzle corresponding pixel is included in the block, the combination of the dot diameters in the block is a dot of an adjacent pixel adjacent to the abnormal nozzle corresponding pixel rather than the dot diameter of the abnormal nozzle corresponding pixel. A determination unit configured to determine whether or not the diameter is a larger combination, and when the result of determination by the determination unit is a combination in which the dot diameter of the adjacent pixel is larger, the adjacent to the abnormal nozzle corresponding pixel It is characterized by changing to a combination in which the dot diameter is replaced with the pixel.
According to this configuration, the same effect as in the eighth aspect can be obtained.

[Form 40] A printing apparatus according to form 40 includes:
40. The printing apparatus according to claim 39, wherein the changing unit includes an edge determining unit that determines whether or not an edge portion of a recorded image is included, and the block is included when the edge portion is not included. Based on the combination of the dot diameters, the dot diameter is changed between the abnormal nozzle corresponding pixel and the adjacent pixel.
According to this configuration, the same effect as in the ninth aspect can be obtained.

[Form 41] A printing apparatus of form 41 includes:
41. The printing apparatus according to any one of forms 34 to 40, wherein the dot diameter that can be formed by the nozzle is associated with each pixel of the image data of the image to be recorded and output to the block dividing unit. The apparatus further comprises means.
According to this configuration, the same effect as in the tenth aspect can be obtained.

[First Embodiment]
The first embodiment of the present invention will be described below with reference to the drawings.
FIG. 1 is a schematic configuration diagram of a computer system 1 including a color inkjet printer (hereinafter simply referred to as “printer”) 2 which is one mode of a recording apparatus (image forming apparatus). As shown in this figure, the printer 2 includes a paper transport mechanism 20 that transports the recording paper 3, a head unit 21 that discharges ink toward the recording paper 3 to form dots, and ink that is produced by the head unit 21. A head drive circuit 22 (see FIG. 2) that controls ejection and dot formation, an operation panel 23, and a control circuit 24 that controls the exchange of signals with these paper transport mechanism 20, head unit 21, and operation panel 23 are provided. ing.

The paper transport mechanism 20 includes a paper feed motor 25 that is driven and controlled by a control circuit 24 and a paper feed roller 26 that is rotationally driven by the rotation of the paper feed motor 25. 3 is conveyed.
The head unit 21 includes an ink tank 27 and a line head 28.

  The ink tank 27 is detachably provided with a cartridge 29A containing black (K) ink and a cartridge 29B containing color ink. As the color ink, for example, four color inks of cyan (C), magenta (M), and yellow (Y) are used. An ink supply path 30 is drawn from the ink tank 27 and connected to the line head 28, and ink is supplied from the ink tank 27 to the line head 28 via the ink supply path 30.

  As shown in FIG. 2, the line head 28 includes a holding frame 31 and a plurality of nozzle heads 32 that are fixed to the holding frame 31 side by side. Each nozzle head 32 is formed with a plurality of nozzles (ejection ports) 33 from which ink is ejected. These nozzles 33 are provided for each of black (K), cyan (C), magenta (M), and yellow (Y).

  Each nozzle 33 is provided with a piezo element (not shown) that is one of electrostrictive elements and has excellent responsiveness. These piezo elements are members that form ink passages that guide ink to the nozzle 33. It is arranged in contact. Piezo elements are those in which the crystal structure is distorted by the application of voltage, and electro-mechanical energy conversion is performed at a very high speed, and by applying a voltage of a predetermined time width between electrodes provided at both ends of the piezo element, The piezo element extends for a voltage application time and deforms one side wall of the ink passage. As a result, the volume of the ink passage contracts according to the expansion of the piezo element, and the ink corresponding to the contraction becomes ink droplets and is ejected from the tip of the nozzle 33 at high speed. The ink droplets soak into the recording paper 3 along the paper feed roller 26 to form dots and print an image.

  Further, by arranging a plurality of such nozzle heads 32 on the holding frame 31 along the width direction of the recording paper 3 (so-called main scanning direction), the nozzles 33 are arranged over the entire width of the recording paper 3, and the recording paper 3 The image is formed all at once over the entire width. An image is formed in the transport direction of the recording paper 3 by transporting the recording paper 3 in the transport direction (so-called sub-scanning direction) while forming an image in the width direction of the recording paper 3 by the head unit 21. .

  Here, each of the nozzles 33 is formed to have a substantially constant diameter. However, the printer 2 uses the nozzles 33 to make large dots (L), medium dots (M), and small dots. (S) and four types of dots without dots can be formed. Specifically, it is generally known that the dot diameter can be controlled by controlling the voltage waveform applied to the piezo element (particularly, the voltage waveform when a negative voltage is applied). Based on the relationship between the voltage waveform and the dot diameter, each voltage waveform for forming four types of dot diameters is prepared in advance, and by selecting these voltage waveforms as appropriate, four types of dots having different diameters can be obtained. It can be formed. A halftone is expressed by forming these four types of dots at an appropriate density.

  As shown in FIG. 1, the control circuit 24 of the printer 2 is connected to the computer 4 via a connector 40. The computer 4 is equipped with driver software for the printer 2, accepts user commands by operating a keyboard or mouse as an input device, and presents various information in the printer 2 on the screen display of the display device. Configure the user interface.

  FIG. 3 is a block diagram illustrating a configuration example of a main part of the printer 2 with the control circuit 24 at the center. As shown in this figure, the control circuit 24 includes a CPU (Central Processing Unit) 41, a programmable ROM (P-ROM (Read Only Memory)) 43, a RAM (Random Access Memory) 44, and a character generator (a dot matrix of characters). The arithmetic logic circuit includes a CG (Character Generator) 45 and an EEPROM (Electronically Erasable and Programmable ROM) 46.

The control circuit 24 further drives the head unit 21 connected to the I / F dedicated circuit 50 that is an interface (I / F (Interface)) with an external motor and the like, and the I / F dedicated circuit 50. A head drive circuit 22 that discharges ink and a motor drive circuit 54 that drives the paper feed motor 25 are provided.
The I / F dedicated circuit 50 has a built-in parallel interface circuit and can receive a print signal PS supplied from the computer 4 via the connector 40.

Next, the configuration of the computer 4 will be described with reference to FIG.
As shown in FIG. 4, the computer 4 includes a CPU 91, ROM 92, RAM 93, HDD (Hard Disk Drive) 94, video circuit 95, I / F 96, bus 97, display device 98, input device 99, and external storage device 100. ing.
The CPU 91 is a control unit that executes various arithmetic processes according to programs stored in the ROM 92 and the HDD 94 and controls each unit of the apparatus.

The ROM 92 is a memory that stores basic programs executed by the CPU 91 and data. The RAM 93 is a memory that temporarily stores programs being executed by the CPU 91 and data being calculated.
The HDD 94 reads data and programs recorded on a hard disk as a recording medium in response to a request from the CPU 91 and records data generated as a result of arithmetic processing of the CPU 91 on the hard disk.

The video circuit 95 is a circuit that executes a drawing process in accordance with a drawing command supplied from the CPU 91, converts the obtained image data into a video signal, and outputs the video signal to the display device 98.
The I / F 96 is a circuit that appropriately converts the expression format of signals output from the input device 99 and the external storage device 100 and outputs a print signal PS to the printer 2.
The bus 97 is a signal line that connects the CPU 91, the ROM 92, the RAM 93, the HDD 94, the video circuit 95, and the I / F 96 to each other and enables data exchange between them.

The display device 98 is configured by, for example, an LCD (Liquid Crystal Display) monitor or a CRT (Cathode Ray Tube) monitor, and displays an image according to the video signal output from the video circuit 95.
The input device 99 is configured by, for example, a keyboard and a mouse, and is a device that generates a signal corresponding to a user operation and supplies the signal to the I / F 96.

  The external storage device 100 includes, for example, a CD-ROM (Compact Disk-ROM) drive unit, an MO (MagnetoOptic) drive unit, and an FDD (Flexible DiskDrive) unit, and data recorded on a CD-ROM disc, an MO disc, and an FD. Or a program that reads out the program and supplies it to the CPU 91. In the case of the MO drive unit and the FDD unit, the data is supplied from the CPU 91 to the MO disk or FD.

  As described above, the printer driver software for the printer 2 is installed in the computer 4 in advance, and the printer driver is installed in the computer 4. The printer driver software incorporates an image processing program used for printing, and functions as the image processing apparatus 200 for the printer 2 when the computer 4 executes the image processing program.

FIG. 5 is a functional block diagram of the image processing apparatus 200 realized by the printer driver software for the printer 2 installed in the computer 4. As shown in this figure, the image processing apparatus 200 includes a color conversion unit 210, a multi-value conversion unit 211, a block division unit 213, a dot pattern change unit 214, and an error diffusion unit 215.
The color conversion unit 210 receives data expressed by an RGB (Red, Green, Blue) color system as input image data to be printed (recorded), and a CMYK (cyan, magenta, yellow, black) color system. Is converted to input image data expressed by the above, and output to the multi-value quantization unit 211. Here, the converted input image data defines the density value of each pixel constituting the image for each color system of CMYK.

  The multi-value conversion unit 211 changes the input density of each pixel of the input image data to any of the four types of dot diameters that can be formed by the printer 2 and outputs the change to the block division unit 213. In the present embodiment, as shown in FIG. 6, 256 gradations of 0 to 255 gradations are used as the gradation range of the input density, and the gradation range is divided into four gradation categories, No gradation, small dot (S), medium dot (M), and large dot (L) are assigned to the gradation classification in order from the lowest gradation. Therefore, the multi-value quantization unit 211 specifies to which gradation category the input density of the pixel of the input image data belongs, and associates the dot diameter corresponding to the gradation category, thereby adjusting the input density of each pixel. Convert to dot diameter. In this embodiment, the density (gradation) expressed by no dots, small dots (S), medium dots (M), and large dots (L) is set to 0, 95, 185, and 255, respectively. Has been.

  The block dividing unit 213 divides the input image data into blocks for each of a plurality of pixels, and outputs the input image data after the block division to the dot pattern changing unit 214. In the present embodiment, the block dividing unit 213 divides input image data into blocks every 2 × 2 pixels.

  The dot pattern changing unit 214 uses a dot diameter combination pattern (hereinafter simply referred to as a “dot pattern”) associated with each pixel of the input image data, and discharge characteristics (dot diameter and dot formation position of each nozzle). The pattern is changed to a dot pattern that can suppress white stripes and density unevenness due to variations in the characteristics), and the change result is output to the error diffusion unit 215. More specifically, the dot pattern change unit 214 includes a dot pattern change table 216 in which the dot patterns before and after the change are associated with each other. With reference to the dot pattern change table 216, the dot pattern of each block is changed. change.

  FIG. 7 is a diagram schematically illustrating an example of the dot pattern change table 216. As shown in this figure, in the dot pattern change table 216, 12 types of change patterns are registered in advance as dot pattern change patterns. As these change patterns, a small dot (S) other than the largest dot (L), which is the largest dot, and some of the medium dots (M) are collected and the dot pattern is changed so as to make a larger dot. It has been. Also, the examples shown here are just a few, and there are actually more patterns.

Specifically, since the purpose of changing the dot is to use a large dot, S is 2 for M, S is 3 for L, and S and M are 1 for L. The dots are collected as
Specifically, first, the dot type after change is determined from the dot type before change. The dot type before the change and the dot type after the change are as follows.

S × 2 = M (means that there are two S before the change and one M after the change)
S × 3 = L
S × 4 = L + S
S + M = L
S + M × 2 = L + M (1 S and 2 M before change, 1 L and M after change)
S + M × 3 = L × 2 + S
S × 2 + M = L + S
S × 3 + M = L + M
M × 2 = L + S
M × 3 = L × 2 + M
M × 4 = L × 2 + M
In this way, the changed dot position is obtained from the density weight position, and is arranged from the largest dot closest to the density weight position.

When the distance to the density weight position is equal, the dots are arranged based on the dot arrangement before the change. Further, when the density weight position is the center, dots are arranged at the diagonal of the matrix (the order according to the size does not matter).
Here, the density weight position, when there is a density weight in the block, prevents the deterioration by arranging dots in a matrix with the density weight position.

Next, the principle of changing the dot pattern will be described.
FIG. 8 is a flowchart showing the basics of the change flow in the dot pattern table.
First, the number of dot types in the block is grasped (step S11), and the changed dot type is determined (step S12). Next, a density weight position is obtained (step S13), and it is determined whether or not the density weight position is in the center (step S14). If it is at the center, dots are arranged diagonally (step S15). If the density weight position is not at the center, a large dot is placed at the density weight position (step S16), and then it is determined whether there is a dot to be placed (step S17). If there is no dot to be arranged, the process ends (step S19). If there is no dot to be arranged, the dot is arranged closer to the density weight position (if the distance is equal, it may be arranged in either position) (step S18), and the process ends (step S19).

Next, with reference to FIG. 9, an example in the case of dot arrangement based on the principle flow of FIG. 8 will be specifically described.
First, as shown in FIG. 9A, four matrices are handled as coordinates, and as shown in FIG. 9B, (-1, 1), (1, 1), (-1, -1), respectively. ), (1, -1). Next, referring to the density values shown in FIG. 6, as shown in FIG. 9C, the weight positions of the dots are obtained, and normalization is performed so that the highest density in the figure becomes 1. . As a result, if values as shown in FIG. 9D are obtained, for example, calculations are performed in the order of I, II, III, and IV in FIG. The calculation formula is as follows.

X coordinate (0 × 1) + (95/185 × 1) + (95/185 × (−1) +
Y coordinate (0 × 1) + (95/185 × (−1)) + (95/185 × 1) +
As a result of the above calculation, the density weight position is the position of the mark x shown in FIG.
Therefore, in the dot arrangement after the change, the IV position has the highest priority. After the degree is placed in IV, it is II and III that are close to the x mark, but since they are the same distance and the dot arrangement before change is present in both II and III, the dot after change is arranged. Can be either.

In this way, as shown in FIG. 9 (f), the large L dot was placed in IV, and then the S dot was placed in II. The S dot may be III.
As a result of such a dot pattern change, the dot pattern of each block is changed to a dot pattern constituted by a relatively large dot diameter such as a large dot (L) and a medium dot (M). Therefore, since dots having a relatively large diameter are formed at the time of image recording, even if the dot diameter and the dot formation position vary for each nozzle 33, the deviation of the dot diameter and the dot formation position becomes inconspicuous.

The error diffusion unit 215 shown in FIG. 5 is an unprocessed pixel pattern that has not yet been subject to dot pattern change processing in order to compensate for a density error that occurs when the dot pattern change unit 214 changes the dot pattern of the block. A density error is diffused in a block.
Specifically, the density (gradation) expressed by the small dots (S), medium dots (M), and large dots (L) is 95, 185, and 255, respectively, and therefore the density of the block before the dot pattern change. The total value T1 and the density total value T2 of the block before the dot pattern change are respectively
(Total density value T1 before change, Total density value T2 after change) =
[Number of small dots (S) × 95 + number of medium dots (M) × 185 + number of large dots (L) × 255]. At this time, the density error G caused by the dot pattern change is
Density error G = Total density value before change T2−Total density value after change T1
Is required. Then, as shown in FIG. 10, the density error G is diffused at a predetermined diffusion ratio into several blocks whose dot patterns have not been changed.

  At this time, in this embodiment, among the blocks in which the dot pattern has not been changed, the block in which the density error G is generated in order to compensate the density error G in a block near the block in which the density error G has occurred. The density error G is diffused in each of at least two blocks adjacent to each other at a predetermined diffusion ratio. In addition, in the block where the density error G is diffused, the pixel closest to the block in which the density error G is generated among the pixels in the block absorbs the density error. In the pixel that has absorbed the density error, the dot diameter is changed according to the density error. Specifically, if the absorbed density error is G1, the dot diameter is reassigned again in accordance with the value of (already assigned dot diameter density) − (density error G1). For example, when a pixel to which a small dot (S) that has already been assigned (density “95”) is assigned absorbs a density error G1 of “−50”, the density of that pixel is 95 − (− 50). = 145 and belongs to the gradation classification to which the medium dot (M) is assigned (see FIG. 6), so the dot of the pixel is changed from the small dot (S) to the medium dot (M).

  The error diffusion unit 215 is provided in advance with a density error table 217 (FIG. 11) in which the dot pattern change pattern and the density error are associated with each other, and the error diffusion unit 215 receives the dot pattern from the dot pattern change unit 214. By receiving this change pattern, the density error G caused by the change of the dot pattern can be specified. Then, the error diffusion unit 215 converts the density error G to a density error G at a predetermined diffusion ratio in each of two blocks adjacent to the block in which the density error G is generated among the blocks whose dot patterns are not changed. The dot diameter is changed according to the density change of the pixel of the block that diffuses and absorbs the density error G, and the change result is output to the dot pattern change unit 214. On the other hand, when the dot pattern changing unit 214 changes the dot pattern of the block including the pixel that has absorbed the density error G, the dot pattern changing unit 214 sets the dot pattern of the block for the dot diameter that has been changed by absorbing the density error G. change.

  After the dot pattern adjustment unit 212 executes the dot pattern change and density error diffusion of the input image data as described above, the image processing apparatus 200 can process the printer 2 based on the output result of the dot pattern adjustment unit 212. A signal is generated and output to the printer 2 as a print signal PS.

Next, the operation of the present embodiment will be described.
For example, when a request for starting an application program is made by the user operating the input device 99 of the computer 4, the CPU 91 reads the corresponding application program from the HDD 94 and executes it. As a result, the application program is activated and image data can be generated or edited. When a request for printing the generated image is made via the input device 99 after the image is drawn or edited using such an application program, the CPU 91 stores the generated image data. Supply to printer driver software. At this time, the image data is data represented by the RGB color system. As the image data is supplied to the printer driver software, the computer 4 executes the image processing program and starts to function as the image processing apparatus 200 described above.

As shown in FIG. 12, in the image processing apparatus 200, when image data expressed in the RGB color system is input, the color conversion unit 210 converts the input image data into input image data in the CMYK color system. And output to the multi-value quantization unit 211 (step S1).
Next, the multi-value quantization unit 211 converts the input density of each pixel of the input image data into a dot diameter, associates the pixel and the dot diameter, and outputs them to the block division unit 213 (step S2).

Then, the block dividing unit 213 divides the input image data into a plurality of blocks every 2 × 2 pixels, and outputs the divided image data to the dot pattern changing unit 214 (step S3).
When the input image data divided into blocks is input from the block dividing unit 213, the dot pattern changing unit 214 executes a dot pattern changing process for changing the dot pattern of each block (step S4).

  In the dot pattern changing process, as shown in FIG. 13, the dot pattern changing unit 214 first takes out one unprocessed block and determines whether the dot pattern in the block is a dot pattern to be changed. The following processing is executed as much as possible. That is, the dot pattern changing unit 214 counts the number of small dots (S) in the block (step S40), and then counts the number of medium dots (M) in the block (step S41).

  Then, the dot pattern changing unit 214 determines whether or not there are two or more small dots (S) or medium dots (M) in the block (step S42), and small dots (S) or medium dots are determined. When there are two or more of any of (M) (step S42: TRUE), since these small dots (S) or medium dots (M) can be combined into larger dots, the dot pattern of the block is changed. Change is made (step S43), and the process is terminated. In detail about this step S42, the dot pattern change unit 214 refers to the dot pattern change table 216, identifies the change pattern corresponding to the current dot pattern, and based on the change pattern, the dot pattern in the block To change. Further, the change pattern at this time is output to the error diffusion unit 215.

  On the other hand, when there are not two or more small dots (S) or medium dots (M) in the block (step S42: FALSE), the dot pattern changing unit 214 includes small dots (S) and medium dots ( M) is present one by one (step S44). When there is one small dot (S) and one medium dot (M) (step S44: TRUE), these small dots (S) and medium dots (M) may be combined into a large dot (L). Since it is possible, the dot pattern changing unit 214 moves the processing procedure to step S43 described above, and changes the dot pattern of the block.

  Further, when there is not one small dot (S) and one medium dot (M) in the block (step S44: FALSE), the small dot (S) and the medium dot (M) cannot be combined. The dot pattern changing unit 214 ends the process without changing the dot pattern of the block.

  When the dot pattern change process is completed as described above, the image processing apparatus 200 determines whether there is an unprocessed block that has not been subjected to the dot pattern change process as shown in FIG. 12 (step S5). ). If there is an unprocessed block (step S5: TRUE), the error diffusion unit 215 executes an error diffusion process to diffuse the density error generated by the dot pattern change process in step S4 to the unprocessed block. (Step S6).

  In this error diffusion process, as shown in FIG. 14, the error diffusion unit 215 specifies a density error caused by the change pattern used in the dot pattern change process with reference to the density error table 217 (step S60). ), It is determined whether or not a density error has occurred (step S61). If no density error has occurred (step S61: FALSE), there is no density error to be diffused, and the error diffusion unit 215 ends the process. Even when the dot pattern of the block is not changed during the dot pattern changing process, there is no density error to be diffused, so the error diffusion unit 215 ends the process.

  On the other hand, if a density error has occurred (step S61: TRUE), the error diffusion unit 215 diffuses the density error to a block that has not yet been subjected to dot pattern change processing (step S63). As described above, in the present embodiment, the density error is diffused at a predetermined diffusion ratio to two blocks adjacent to the block in which the density error has occurred among the blocks that have not yet been subjected to the dot pattern change process. In the two blocks in which the density error is diffused, the density error is absorbed by the pixel closest to the block in which the density error has occurred.

  Then, the error diffusion unit 215 determines whether or not it is necessary to change the dot diameter of the pixel that has absorbed the density error, based on the density of the dot diameter of the pixel and the absorbed density error (step S63). . As a result of this determination, if the pixel density belongs to a larger or smaller dot diameter density range and it is necessary to change the dot diameter (step S63: TRUE), the error diffusion unit 215 Then, the dot diameter of the pixel is changed (step S64), and if it is not necessary to change the dot diameter (step S63: FALSE), the process is terminated.

When the error diffusion processing is completed as described above, the image processing apparatus 200 returns the processing procedure to step S4 in order to execute the dot pattern change processing for the unprocessed block as shown in FIG. Then, the dot pattern change process and the error diffusion process are sequentially performed one block at a time until there are no unprocessed blocks.
When there is no unprocessed block (step S5: FALSE), the image processing apparatus 200 generates a print signal PS based on the input image data on which the dot pattern change process and the error diffusion process have been performed, and sends it to the printer 2. Output (step S7).

  When the printer 2 receives the print signal PS, the CPU 41 drives the paper feed motor 25 to suck only one recording paper 3 and transfers it to the print start position. Then, when the print start position of the recording paper 3 moves to a position immediately below the line head 28, the CPU 41 supplies the print signal PS to the line head 28 via the head drive circuit 22 and starts printing. When printing is started, ink is ejected from each nozzle of the line head 28 to form a dot diameter defined by the print signal PS, and the recording paper 3 is intermittently conveyed in the conveyance direction. As a result, dots corresponding to the input image data generated by the computer 4 are formed on the recording paper 3.

  According to the embodiment described above, the dot pattern of the block is changed based on the dot pattern in the block. Specifically, when two or more small dot diameters such as a small dot (S) and a medium dot (M) exist in the block, they are combined and replaced with a large dot (L). Therefore, since a large dot diameter is formed at a location where white stripes and density unevenness occur, these white stripes and density unevenness can be made inconspicuous.

  Further, according to the present embodiment, the density error caused by the change of the dot pattern is diffused to the unprocessed block, so even if the density in the block has changed due to the change of the dot pattern, The density of the change is diffused to other blocks as a density error and compensated. As a result, high-quality image recording without losing area gradation is possible.

[Second Embodiment]
Next, a second embodiment of the present invention will be described.
In the first embodiment described above, the image processing apparatus 200 is configured to execute the block division process and the dot pattern change process on the entire pixels of the input image data. However, in the present embodiment, the image processing apparatus 200A. However, the configuration is such that processing is performed only on the periphery of a pixel where white stripes and density unevenness may occur. That is, as shown in FIG. 15, in addition to the image processing apparatus 200 of the first embodiment, the image processing apparatus 200A of the present embodiment further includes an abnormal nozzle specifying unit 250, an abnormal nozzle corresponding pixel specifying unit 251, and The configuration is different from that of the image processing apparatus 200 of the first embodiment in that the processing target pixel extraction unit 252 is provided.

  The abnormal nozzle specifying unit 250 specifies an abnormal nozzle 33M (see FIG. 16) that causes an ink ejection abnormality that causes white streaks and density unevenness among the plurality of nozzles 33 provided in the line head 28 (recording head). Are output to the abnormal nozzle corresponding pixel specifying unit 251.

  The abnormal nozzle corresponding pixel specifying unit 251 specifies the abnormal nozzle corresponding pixel A in which a dot is formed by the abnormal nozzle 33M from the pixels of the input image data, and outputs it to the processing target pixel extracting unit 252. Specifically, as shown in FIG. 16, the abnormal nozzle corresponding pixel A has a recording head in the direction in which dots are formed on the recording paper 3 by the abnormal nozzle 33M during image recording, that is, the recording head with respect to the recording paper 3. Are a series of pixels arranged in a relatively moving direction (hereinafter referred to as “recording direction”). Therefore, when the recording head is configured by the line head 28, the abnormal nozzle corresponding pixel specifying unit 251 specifies a series of pixels arranged along the conveyance direction of the recording paper 3 as the abnormal nozzle corresponding pixel A. In a recording apparatus (so-called multi-pass printer) in which a recording head is mounted on a carriage and performs recording while scanning in the width direction (main scanning direction) of the recording paper 3, the abnormal nozzle corresponding pixel specifying unit 251 includes the recording paper. A series of pixels arranged in the width direction (main scanning direction) 3 is specified as the abnormal nozzle corresponding pixel A.

Now, the processing target pixel extraction unit 252 shown in FIG. 15 extracts the abnormal nozzle corresponding pixel A and the pixels around the abnormal nozzle corresponding pixel A from the input image data, and outputs them to the block dividing unit 213. .
Therefore, in the present embodiment, the block dividing unit 213 divides the pixels extracted by the processing target pixel extracting unit 252 into blocks for each of a plurality of pixels and outputs the blocks to the dot pattern changing unit 214, and the dot patterns of those blocks Is changed by the dot pattern changing unit 254. Then, the image processing apparatus 200 generates the print signal PS based on the block in which the dot pattern is changed in this way and the input image data.

  As described above, according to the present embodiment, since the above-described deblock division processing and block dot pattern change processing are executed only for the abnormal nozzle corresponding pixel A and the surrounding pixels, the above-described first In addition to the effects of the first embodiment, the number of blocks that are subject to dot pattern change processing can be reduced, and the processing time can be shortened.

[Third Embodiment]
Next, a third embodiment of the present invention will be described.
In the first and second embodiments described above, the dot pattern changing unit 213 of the image processing apparatus 200 is configured to change the dot pattern by collecting the dots in the block into larger dots. In the embodiment, when the dot pattern changing unit 213 changes the dot pattern, the arrangement of the dots in the block is changed so that white stripes and density unevenness are not noticeable.

  FIG. 17 is a block diagram showing a functional configuration of the image processing apparatus 200B according to the present embodiment. As shown in this figure, the image processing apparatus 200B according to the present embodiment is similar to the second embodiment in addition to the configuration of the image processing apparatus 200 of the first embodiment, and includes an abnormal nozzle specifying unit 250 and an abnormal nozzle correspondence. Although the pixel specifying unit 251 and the processing target pixel extracting unit 252A are provided, the functions of the processing target pixel extracting unit 252A and the dot pattern changing unit 214A are different.

  Specifically, the processing target pixel extraction unit 252A extracts the abnormal nozzle corresponding pixel A and one column of adjacent pixels B (see FIG. 16) adjacent to the abnormal nozzle corresponding pixel A from the input image data. Two pixel columns of the abnormal nozzle corresponding pixel A and the adjacent pixel B are output to the block dividing unit 213. As a result, the two pixel columns are divided into blocks of 2 × 2 pixels by the block dividing unit 213 and output to the dot pattern changing unit 214A.

Based on the dot pattern of the block, the dot pattern changing unit 214A changes the dot pattern in the block by changing the arrangement of dots in the block so that white stripes and density unevenness are not noticeable.
Next, a dot pattern replacement flow will be described with reference to FIGS.

  FIG. 18 is a flowchart showing a dot pattern replacement method. In the following description, “vertical” indicates the pixel column direction assigned to each nozzle, the sub-scanning direction in the case of a line head, and the main scanning direction in the case of serial.

  First, after grasping the abnormal nozzle, the nozzle information of the abnormal nozzle is acquired (step S71). Next, the number of dot types in the block is grasped (step S72), and it is determined whether or not the number of dots in the block is 3 or more (step S73). If the number of dots is not three or more, the process ends as it is (step S81). If the number of dots is 3 or more, it is determined whether or not L is 2 (step S74). If there are two Ls, it is determined whether or not L dots are arranged vertically in adjacent pixels of the abnormal nozzle (step S75). If they are aligned vertically, the dot pattern is replaced (step S81), and the process ends (step S82). In step S74, if L is not two, it is determined whether there are two M and the rest is S (step S76). As a result, when there are two M and the remaining is S, it is determined whether or not M dots are arranged vertically in the adjacent pixels of the abnormal nozzle (step S77). If they are aligned vertically, they are replaced (step S80) and the process is terminated (step S81). In step S76, if there are two M and the remaining is not S, it is determined whether there is one each for M and L (step S78). If not one by one, the process ends as it is (step S81). In the case of one by one, it is determined whether or not M and L are arranged vertically in adjacent pixels of different nozzles (step S79). If they are aligned vertically, they are replaced (step S80) and the process is terminated (step S81). If they are not aligned vertically, the process ends as it is (step S81).

As described above, replacement is performed when the conditions are met. However, when the conditions are met, the pattern is as shown in FIG. In the case of these patterns, the upper left and lower right are interchanged. As a result, since a relatively large dot diameter is formed, the deviation of the dot formation position becomes inconspicuous, and white stripes and density unevenness are suppressed.
Here, as shown in FIG. 20, when there are at least two pixels without dots in the block, the dot pattern changing unit 214A may include an edge (edge) portion in the recorded image. Determine and do not change the dot pattern for that block.

  Further, as shown in FIG. 21, the total density value of each adjacent pixel B in the block (255 × 2 = 510 in the illustrated example) and the total density value of each abnormal nozzle corresponding pixel A (95 × in the illustrated example). 2 = 190), the dot pattern changing unit 214A also determines that the block may include an edge portion in the recorded image even if the difference is equal to or greater than a predetermined value (for example, 300). Do not change the dot pattern.

As described above, when the dot pattern changing unit 214A determines whether the edge portion of the recorded image is included in the block, and determines that the edge portion is included, the dot pattern changing unit 214A sets the dot pattern for the block. Since no change is made, the contour of the recorded image does not become unclear.
In this embodiment, since the dot pattern is changed by replacing the dot diameter in the block, a density error does not occur due to the dot pattern change, and the above-described error diffusion unit 215 is not required.

[Modification]
Each of the above-described embodiments is merely an aspect of the present invention, and can be arbitrarily modified without departing from the spirit of the present invention.
For example, in each of the above-described embodiments, the case where the image processing apparatus 200 divides the input image data into blocks of 2 × 2 pixels is illustrated. However, the present invention is not limited to this, and i × j (i, j May be configured to divide the block into pixels each having an integer of 2 or more. However, if the resolution is relatively low and the number of pixels included in the input image data is small, if the dot pattern change process is executed by dividing into large blocks, block noise may occur, so depending on the resolution of the input image data It is desirable to use a block of a different size.

  Further, for example, in each of the above-described embodiments, the image processing apparatus 200 is configured to execute the dot pattern change process only once for all the blocks. However, the present invention is not limited to this. In other words, the image processing apparatus 200 may be configured to shift the input image data into blocks by shifting the pixels to be divided into blocks by several pixels, and to execute the dot pattern change process on each block again.

According to this configuration, since the dot diameter of each pixel of the input image data is further replaced with a large dot (L), white stripes and density unevenness can be made less noticeable.
Further, in each of the above-described embodiments, when the image processing apparatus 200 is a pattern in which the combination pattern of the dot diameters of the blocks has a plurality of small dot diameters, all or a part of these small dot diameters is reduced to the small Although the configuration for changing to a pattern replaced with a dot diameter larger than the dot diameter has been described, not limited to this, in the case of a pattern having a plurality of large dot diameters, all or part of these large dot diameters The pattern may be changed to a pattern in which the dot diameter is smaller than the larger dot diameter.

According to this configuration, large dot diameters in a block are collected and replaced with small dot diameters. Accordingly, a small dot diameter is formed at a location where a dark streak occurs due to an adjacent dot approaching due to an abnormal discharge of the nozzle, so that this dark streak can be made inconspicuous.
Further, for example, in each of the above-described embodiments, the recording head is configured to eject ink using a piezo element. However, a recording head that ejects ink by other methods may be used. For example, a recording head that energizes a heater disposed in the ink passage and ejects ink by bubbles generated in the ink passage may be used.

  For example, in each of the above-described embodiments, an example in which the present invention is applied to the printer 2 that includes the line head 28 as a recording head and performs printing only by transporting the recording paper 3 in the transport direction without scanning the recording head. Although explained, it is not limited to this. That is, the present invention is also applied to a printer in which a recording head is mounted on a carriage and printing is performed by ejecting ink from the nozzles of the recording head while moving the recording head in the width direction of the recording paper 3 (so-called main scanning direction). It is possible to apply.

  Further, for example, in each of the above-described embodiments, the computer 4 functions as the image processing apparatus 200 (200A, 200B) by incorporating an image processing program into the printer driver software installed in the computer 4. However, the present invention is not limited to this. Instead, the image processing program may be executed by the control circuit 24 of the printer 2 so that the control circuit 24 functions as the image processing apparatus 200 (200A, 200B). In this configuration, the image processing program is stored in advance in the P-ROM 43 of the control circuit 24, for example. Alternatively, the image processing program may be stored in a semiconductor chip or the like, and the semiconductor chip may function as the image processing apparatus 200 (200A, 200B).

  The image processing program described above can be stored in advance in the semiconductor ROM of the computer 4 or the printer 2 and incorporated in the product, or can be distributed via a network such as the Internet. Further, as shown in FIG. 22, it can be easily provided to a desired user through a computer-readable recording medium 300 such as a CD-ROM, DVD-ROM, or FD.

  Further, in each of the above-described embodiments, the first embodiment describes an apparatus called “recording apparatus”, “image forming apparatus”, and “printer”, and the second embodiment describes an apparatus called “image processing apparatus”. However, these devices and the range of printing devices are defined as follows.

  "Recording device" is a device that performs actual recording on a medium. A device having a printing function as one of recording means is a "printing device", and "printing device" and "printer" are synonymous. An image processing apparatus forms an image used exclusively for a recording apparatus. The term “image processing apparatus” refers to an apparatus that does not have at least recording means (such as printing). On the other hand, “image forming apparatus” is almost synonymous with “recording apparatus”, but “image forming apparatus” is an apparatus that forms an image. This includes the case of recording a signal as well as an image, such as an apparatus. Further, when the term “image” is used in the description of “recording apparatus”, it is synonymous with “image forming apparatus”.

It is a figure which shows the computer system for printing of 1st Embodiment of this invention. It is a figure which shows the structure of a head unit. It is a figure which shows the functional structure of the control circuit of a printer. It is a figure which shows the functional structure of a computer. It is a figure which shows the functional structure of the image processing apparatus which concerns on 1st Embodiment. It is a figure for demonstrating multi-valued input image data. It is a figure which shows typically an example of the dot pattern change table 216. FIG. It is a flowchart which shows the basics of the change flow in a dot pattern table. FIG. 9 is a diagram for specifically explaining an example when dots are arranged based on the flow of FIG. 8. (A) is four matrices, (b) is coordinates, (c) is a weight position of dots, (d) is a weighting value, (e) is a density weight position, and (f) is a diagram showing an arrangement result. . It is a figure for demonstrating the spreading | diffusion of the density | concentration error accompanying a dot pattern change. It is a figure which shows a density | concentration error table. It is a flowchart which shows the image processing which concerns on 1st Embodiment. It is a flowchart of the dot pattern change process of 1st Embodiment. It is a flowchart which shows the error diffusion process of 1st Embodiment. It is a figure which shows the functional structure of the image processing apparatus which concerns on 2nd Embodiment. It is a figure which shows an abnormal nozzle and an abnormal nozzle corresponding | compatible pixel. It is a figure which shows the functional structure of the image processing apparatus which concerns on 3rd Embodiment. It is a flowchart which shows the replacement method of a dot pattern. It is a figure which shows the result processed according to the flow of FIG. It is a figure for demonstrating judgment of an edge. It is a figure for demonstrating judgment of an edge. It is a figure which shows the recording medium with which the image processing program of this invention was recorded.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 2 ... Printer, 3 ... Recording paper (media), 4 ... Computer, 24 ... Control circuit, 28 ... Line head, 33 ... Nozzle, 33M ... Abnormal nozzle, 200, 200A, 200B ... Image processing apparatus, 210 ... Color conversion part , 211, multi-value conversion unit, 213, block division unit, 214, 214 A, dot pattern change unit, 215, error diffusion unit, 216, dot pattern change table, 217, density error table, 250, abnormal nozzle specifying unit, 251 ... Abnormal nozzle corresponding pixel specifying unit, 252 and 252A ... Processing target pixel extracting unit, 300 ... Recording medium, A ... Abnormal nozzle corresponding pixel, B ... Adjacent pixel

Claims (14)

An extraction means for forming dots by discharging droplets from a plurality of nozzles, and extracting pixels that can be formed by a printing apparatus that forms an image with the plurality of dots as a block of pixels;
Determining means for determining whether or not the combination of each pixel in the block is a predetermined combination;
As a result of determination by the determination means, when the combination of pixels in the block is a predetermined combination, a change means for changing the combination;
An image processing apparatus comprising: Extraction means for forming dots by ejecting droplets from a plurality of nozzles and extracting pixels associated with dot diameters that can be formed by a printing apparatus that forms an image with the plurality of dots as a block of pixels When,
Determining means for determining whether or not a combination of dot diameters associated with each pixel in the block is a predetermined combination;
When the combination of dot diameters associated with each pixel in the block is a predetermined combination, changing means for changing the combination;
An image processing apparatus comprising:   2. The apparatus according to claim 1, further comprising: an abnormal nozzle extracting unit that extracts an abnormal nozzle from the plurality of nozzles; and a dividing unit that divides the pixels in the vicinity of the abnormal nozzle extracted by the abnormal nozzle extracting unit. Or the image processing apparatus of 2.   In the case where the combination of the dot diameters is a combination having a plurality of small dot diameters, the changing means is a combination in which all or part of the small dot diameters are replaced with dot diameters larger than the small dot diameters. The image processing apparatus according to claim 3, wherein the image processing apparatus is changed. The changing means is
When the combination of the dot diameters is a combination having a plurality of large dot diameters, the whole or a part of these large dot diameters is changed to a combination in which the dot diameter is smaller than the large dot diameter. The image processing apparatus according to claim 3.   4. The apparatus according to claim 3, further comprising error diffusion means for diffusing density errors before and after the change caused by changing the combination of dot diameters in the block to blocks not processed by the change means. Image processing apparatus. An abnormal nozzle corresponding pixel specifying means for specifying an abnormal nozzle corresponding pixel corresponding to an abnormal nozzle that causes an abnormality in ink ejection among the pixels;
Among the pixels, the abnormal nozzle corresponding pixel, and a processing target pixel selection means for selecting a pixel in the vicinity of the abnormal nozzle corresponding pixel,
The image processing apparatus according to claim 3, wherein the block dividing unit divides the pixel selected by the processing target pixel selecting unit into blocks for each of a plurality of pixels. An abnormal nozzle corresponding pixel specifying means for specifying an abnormal nozzle corresponding pixel corresponding to an abnormal nozzle that causes an abnormality in ink ejection among the pixels;
When the abnormal nozzle corresponding pixel is included in the block, the changing means is such that the combination of dot diameters in the block is adjacent to the abnormal nozzle corresponding pixel rather than the dot diameter of the abnormal nozzle corresponding pixel. A determination unit configured to determine whether or not a dot diameter of an adjacent pixel is a larger combination; and as a result of determination by the determination unit, when the dot diameter of an adjacent pixel is a larger combination, the abnormal nozzle The image processing apparatus according to claim 3, wherein the combination is changed to a combination in which the dot diameter is replaced between the corresponding pixel and the adjacent pixel.   The changing unit includes an edge determination unit that determines whether or not an edge portion of a recorded image is included, and when the edge portion is not included, based on a combination of dot diameters in the block, The image processing apparatus according to claim 8, wherein the image processing apparatus is changed to a combination in which a dot diameter is replaced between the abnormal nozzle corresponding pixel and an adjacent pixel.   10. The apparatus according to claim 3, further comprising: a dot diameter association unit that associates a dot diameter that can be formed by the printing apparatus with each pixel of image data of an image to be recorded and outputs the image to the block dividing unit. The image processing apparatus according to any one of the above. An extraction step of ejecting droplets from a plurality of nozzles to form dots, and extracting pixels that can be formed by a printing apparatus that forms an image with the plurality of dots as a block of pixels;
A determination step of determining whether or not a combination of each pixel in the block is a predetermined combination;
As a result of determination by the determination unit, when the combination of pixels in the block is a predetermined combination, a changing step of changing the combination;
An image processing method comprising: Computer
An extraction step of forming dots by discharging droplets from a plurality of nozzles, and extracting pixels that can be formed by a printing apparatus that forms an image with the plurality of dots as a block of pixels;
A determination step of determining whether or not a combination of each pixel in the block is a predetermined combination; and, as a result of determination by the determination means, if the combination of pixels in the block is a predetermined combination, the combination Change step to change,
Image processing program to function as   A computer-readable recording medium on which the image processing program according to claim 12 is recorded. A recording head provided with a plurality of nozzles for discharging ink to form dots;
Extraction means for extracting pixels that can be formed by the nozzle as a block of a plurality of pixels;
Determining means for determining whether or not the combination of each pixel in the block is a predetermined combination;
And a changing unit configured to change the combination when the combination of the pixels in the block is a predetermined combination as a result of the determination by the determining unit.

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