JP2021187100A - Image processing device and image processing method - Google Patents

Abstract

To output an image having a high resolution corresponding to a recording resolution of a recording device while achieving suppression of the granular feeling in a highlight region and the high optical density expression in a high density region.SOLUTION: An image processing device performs multi-pass recording on the basis of a quantization value generated by using a threshold matrix 500 and pass masks 601, 602 defining permission or non-permission of recording of dots in each recording scan. The frequency of the recording scan in which recording of dots is permitted for pixels set with a first threshold in the threshold matrix 500 is larger than the frequency of the recording scan in which recording of dots is permitted for pixels set with a second threshold that is smaller than the first threshold.SELECTED DRAWING: Figure 6

Description

The present invention relates to an image processing apparatus and an image processing method.

In an image recording device that records an image using the pseudo gradation method, it is possible to achieve both suppression of graininess in the highlight region (bright area) and expression of high optical density in the high density area (dark area). Desired.

In Patent Document 1, an inkjet capable of expressing high optical density by recording dots smaller than one pixel area in the highlight area to suppress graininess and recording a plurality of the dots in one pixel area in a high density area. The recording system is disclosed. According to Patent Document 1, a dot arrangement pattern that defines dot recording or non-recording for each pixel area of a recording medium and a mask pattern used for multipath recording are created in advance in association with each other. The above effects are obtained.

Japanese Unexamined Patent Publication No. 2005-280276

However, the dot arrangement pattern disclosed in Patent Document 1 records (1) or does not record (0) dots for each of the recording pixels in which several levels of quantization values possessed by each pixel are arranged at a higher resolution. It is for converting into a defined binary quantization value. Therefore, in the configuration of Patent Document 1, in order to obtain the above-mentioned several levels of quantization value, the quantization process is performed at a resolution lower than the recording resolution of the recording device, and the output image after recording is performed. In some cases, sufficient resolution could not be obtained.

The present invention has been made to solve the above problems. Therefore, the purpose is to output an image having high resolution corresponding to the recording resolution of the recording device while suppressing graininess in the highlight region and expressing high optical density in the high density region. Is to provide an image recording device capable of.

Therefore, the present invention records dots for each of the pixels arranged at a predetermined resolution by quantizing the multi-valued gradation values of the pixels arranged at a predetermined resolution using a threshold matrix. Alternatively, a quantization means that generates a quantization value indicating non-recording, a quantization value generated by the quantization means, and a path mask that determines whether or not to allow dot recording for each pixel in the recording scan of the recording head. Based on this, the recording head provided with a determination means for determining the pixels for recording dots in the recording scan and in which recording elements capable of recording dots are arranged is scanned by a recording medium in a predetermined direction. By alternately performing the recording scan and the transport operation of transporting the recording medium in a direction intersecting the predetermined direction, the image of the unit area of the recording medium is captured by the recording scan a plurality of times to have the predetermined resolution. The path mask is an image processing apparatus that performs image processing for recording in the above, and the path mask has the number of recording scans in which dots are allowed to be recorded for pixels in which the first threshold value is set in the threshold matrix. Dot recording allowance or non-permissibility for each pixel is greater than the number of recording scans allowed for dot recording for pixels with a second threshold smaller than the first threshold. It is characterized by being defined.

According to the present invention, it is possible to output an image having high resolution corresponding to the recording resolution of a recording device while suppressing graininess in a highlight region and expressing high optical density in a high density region. It becomes.

It is a block diagram of the inkjet recording apparatus. It is a figure which shows the arrangement state of the discharge port which becomes a recording element in a recording head. It is a block diagram for demonstrating the structure of control of a recording apparatus. It is a block diagram which shows the structure of the image processing function in an image processing unit. It is a figure which shows the threshold value matrix. It is a figure for demonstrating a path mask. It is a figure for demonstrating the two-pass multipath recording. It is a figure for demonstrating a path mask. It is a figure for demonstrating the multipath recording of 4 passes. It is a figure which shows the threshold value matrix. It is a figure for demonstrating a path mask. It is a figure which shows the recording or non-recording of a dot according to a quantization value and a mask value. It is a figure which compares the dispersibility of a dot by a different threshold matrix. It is a figure which shows the unit matrix and the 1st and 2nd path masks relative to each other. It is a figure for demonstrating how an image is recorded on a recording medium.

(First Embodiment)
<Configuration of image recording device>
FIG. 1 is a diagram for explaining a configuration of a recording device 1 that can be an image processing device of the present embodiment. The recording device 1 of the present embodiment is a serial type inkjet recording device.

The carriage 102 moves in the + X direction or the −X direction with the carriage motor 310 (see FIG. 3) as a drive source while being guided and supported by the guide shaft 103 extending in the X direction. The inkjet recording head 105 (hereinafter referred to as a recording head 105) mounted on the carriage 102 ejects ink according to the recording data in the process of moving the carriage 102. As a result, one band of images is recorded in the region of the recording medium P supported by the platen 104. In this recording scan, the moving speed of the carriage 102 is about 17.5 inches / sec.

When the recording scan for one band is performed, the spool 101 rotates by a predetermined amount using the transfer motor 311 (see FIG. 3) as a drive source, and the recording medium P intersects the recording scan by a distance corresponding to one band. Is conveyed in the + Y direction. By alternately performing such recording scanning for one band and the conveying operation, an image is formed stepwise on the recording medium P.

FIG. 2 is a diagram showing an arrangement state of discharge ports 201, which are recording elements in the recording head 105. 768 ejection ports 201 capable of ejecting the same type of ink are arranged in the Y direction at a density of N = 1200 per inch. Each ejection port 201 can eject about 4 (pl) of ink droplets at a frequency of 21 KHz. By recording scanning by the recording head 105 as described above, an image can be recorded on the recording medium P at a recording density of 1200 dpi in both the main scanning direction (X direction) and the sub scanning direction (Y direction). Hereinafter, for convenience, each of the 768 discharge ports will be referred to as n1 to n768 from the upstream side (−Y direction side) in the transport direction.

The method of ejecting ink from the ejection port 201 is not particularly limited, but in the present embodiment, a voltage is applied to the heat generating element to cause film boiling in the ink in contact with the heat generating element, and the generated bubble growth energy causes the ink to boil. Ink shall be ejected.

Although FIG. 2 shows an ink ejection port row for one color, a plurality of such ejection port rows may be prepared for each ink color. It is assumed that the recording head 105 of the present embodiment has discharge port rows for four colors of cyan, magenta, yellow, and black arranged in the X direction.

FIG. 3 is a block diagram for explaining a control configuration of the recording device 1. The CPU 300 controls the entire recording device 1 via the main bus line 305 while using the RAM 302 as a work area according to a program stored in the ROM 301.

The image input unit 303 receives a print job from a host device or the like connected to the outside. The CPU 300 expands the print job received by the image input unit 303 into the RAM 302, and causes the image processing unit 304 to perform image processing on the image data included in the print job. As a result, recording data that can be recorded by the recording head 105 is generated.

The head drive control circuit 307 drives the recording head 105 according to the recording data generated by the image processing unit 304. The carriage drive control circuit 308 drives the carriage motor 310 under the instruction of the CPU 300 and controls the movement of the carriage 102 in the ± X direction. The transfer control circuit 309 drives the transfer motor 311 under the instruction of the CPU 300 to transfer the recording medium in the Y direction. Under the instruction of the CPU 300, the operation unit 306 receives an instruction from the user and displays the information of the recording device 1 to the user.

<Image processing configuration>
FIG. 4 is a block diagram showing a configuration of an image processing function in the image processing unit 304. The color adjustment processing unit 401 performs color adjustment processing of the image data received by the image input unit 303. Specifically, RGB colors that can express 8-bit data of R (red), G (green), and B (blue) appearing in a standard color space such as S-RGB with the recording device 1. Map to space. In this embodiment, it is assumed that RGB 8-bit data having a resolution of 1200 dpi is generated.

The color conversion processing unit 402 uses the RGB 8-bit data output from the color adjustment processing unit 401 as the ink colors used in the recording device, C (cyan), M (magenta), Y (yellow), and K (black). It is converted into 12-bit data indicating each multi-valued gradation value.

The gamma correction processing unit 403 corrects the gradation value of each 12-bit data of CMYK generated by the color conversion processing unit 402. Specifically, the gradation value is corrected so that the gradation value represented by 12 bits and the optical density expressed on the recording medium have a linear relationship.

The quantization processing unit 404 performs quantization processing on each of the 12-bit data of CMYK. As a result, the gradation value of the 12-bit 4096 value is converted into the quantization value of the 1-bit 2-value. This 1-bit binary quantization value indicates dot recording (1) or non-recording (0) for each pixel region arranged at 1200 dpi on the recording medium.

The distribution processing unit 405 generates recorded data corresponding to each recording scan using a path mask described later based on the quantization value generated by the quantization processing unit 404. The recorded data is data that determines whether or not to record dots in each of the pixel regions for each recording scan. The recorded data generated by the distribution processing unit 405 is transferred to the head drive control circuit 307 by the CPU 300. The head drive control circuit 307 drives the recording head 105 in each recording scan according to the received recording data, and causes the ejection operation to be performed.

The recording device 1 of the present embodiment shall perform two-pass multipath recording. In the two-pass multi-pass recording, the recording scan using the 768 ejection ports 201 shown in FIG. 2 and the transfer operation of the recording medium for 384 pixels are alternately performed. In the unit area of the recording medium, an image is recorded by two recording scans by the recording head 105.

<Quantization processing unit>
FIG. 5 is a diagram showing a threshold matrix 500 used by the quantization processing unit 404 of FIG. 4. Such a threshold matrix 500 is stored in ROM 301 in advance. In the figure, each square corresponds to one pixel area, and the value attached to each pixel area indicates the threshold value used in the quantization process. The threshold matrix 500 of the present embodiment is configured by repeatedly arranging a unit matrix 501 having a 4 × 4 pixel region in the X direction and the Y direction. Each of the 16 pixels constituting the unit matrix 501 is set with any of 16 threshold values every 256 such as 256, 512 ... 4096.

The quantization processing unit 404 compares the gradation value obtained from the gamma correction processing unit 403 with the threshold value set for the corresponding pixel, and has a binary value indicating dot recording (1) or non-recording (0). Generate a quantized value. Here, assuming that the gradation value input from the gamma correction processing unit 403 is In, the threshold value of the corresponding pixel is Th, and the quantization value is Out.
When In ≧ Th, Out = 1
When In <Th, Out = 0
Will be.

<Distribution processing unit>
6 (a) to 6 (c) are diagrams for explaining the path mask used by the distribution processing unit 405 of FIG. When performing 2-pass multipath recording, the 768 ejection ports shown in FIG. 2 are divided into two regions of 384 each, and different pass masks are used in each region. FIG. 6A shows the first pass mask 601 used in the discharge ports n1 to n384 (see FIG. 2) among the 768 discharge ports. Further, FIG. 6B shows a second pass mask 602 used at the discharge port n385-n768. Both path masks have a pixel area of 384 pixels in the Y direction and 256 pixels in the X direction.

In the figure, each square corresponds to a pixel area, the pixel shown in gray indicates a pixel that allows dot recording, and the pixel shown in white indicates a pixel that does not allow dot recording. The first pass mask 601 is configured by repeatedly arranging a unit mask 603 composed of a 4 × 4 pixel region in the X direction and the Y direction. Further, the second pass mask 602 is configured by repeatedly arranging a unit mask 604 composed of a 4 × 4 pixel region in the X direction and the Y direction. In the unit area of the recording medium, the recording scan according to the first pass mask 601 and the recording scan according to the second pass mask 602 are performed to complete the image.

<Multipath recording>
FIG. 7 is a diagram for explaining how an image is recorded on a recording medium in the two-pass multipath recording of the present embodiment. In the actual recording scan, the recording medium is conveyed to the recording head 105 in the + Y direction, but here, for convenience, the recording head 105 is shown in a form of moving in the −Y direction relative to the recording medium.

In the recording head 105, the discharge ports n1 to n384 perform recording according to the first pass mask 601 and the discharge ports n385 to n768 record according to the second pass mask 602. Here, focusing on the first unit area of the recording medium, in the first unit area, recording is performed according to the first pass mask 601 in the first recording scan, and after the transfer operation for 384 pixels, the second recording is performed. Recording is performed according to the second pass mask 602 by scanning. Further, in the second unit area, recording according to the first pass mask 601 is performed in the second recording scan, and after the transfer operation for 384 pixels, recording according to the second pass mask 602 is performed in the third recording scan. Will be done. As described above, in each of the unit regions arranged in the Y direction, the first recording scan according to the first pass mask 601 is performed, and then the second recording scan according to the second pass mask 602 is performed. The image is completed by being struck.

In the figure, the left side shows the positional relationship between the unit area of the recording medium and the unit matrix 501 (see FIG. 5). 96 (= 384/4) unit matrices 501 are associated with each unit region in the Y direction. The quantization processing unit 404 (see FIG. 4) compares the gradation value of each pixel with the corresponding threshold value in the unit matrix 501, and determines the recording (1) or non-recording (0) of dots for each pixel. .. The distribution processing unit 405 includes information indicating the recording (1) or non-recording (0) of the dots determined by the quantization processing unit 404, and information indicating the permissible (1) or non-permissible (0) of the recording indicated by the path mask. A logical product operation is performed between the two, and the recorded data of each recording scan is generated.

<Dot recording status>
FIG. 6 (c) shows the dots that are eventually recorded on the recording medium by the multipath recording of the present embodiment for the 8 × 8 pixel region in which the dot recording (1) is determined by the quantization processing unit 404. It is a figure which showed the number of each pixel. Two dots are recorded in a pixel in which dot recording is permitted in both the first pass mask 601 shown in FIG. 6 (a) and the second pass mask 602 shown in FIG. 6 (b). One dot is recorded in a pixel of either the first pass mask 601 or the second pass mask 602 in which dot recording is permitted. Then, for each pixel, recording of dots is permitted at least one of the first pass mask 601 and the second pass mask 602.

For example, in the upper left pixel, the first pass mask 601 allows the recording of dots, but the second pass mask 602 does not allow the recording of dots. Therefore, one dot is recorded in the area corresponding to the pixel by the first recording scan. Further, in the lower right pixel, dot recording is permitted by both the first pass mask 601 and the second pass mask 602. Therefore, in the area corresponding to the pixel, a total of two dots are recorded, one for each of the first and second recording scans.

The pixel in which the two dots are recorded in FIG. 6C corresponds to the pixel in which the four highest threshold values (3328, 3840, 3584, 4096) are set in the unit matrix 501 of FIG. In other words, for the pixels for which the four highest thresholds are set, the first and second pass masks 601 are allowed to be recorded by both the first pass mask 601 and the second pass mask 602. 602 is pre-created in association with the threshold matrix 500.

When two-pass multipath recording is performed using such a threshold matrix 500 and the first and second pass masks 601 and 602, a relatively small threshold value is obtained in the highlight region to the medium density region (0 to 3327). Dots will be recorded in order from the pixel for which is set. That is, in the highlight region to the medium density region, single dots with low visibility are gradually added as the gradation value increases, and the graininess of the entire image is suppressed.

On the other hand, in the high density region (3328 to 4096), dots are recorded one by one in the pixels in which low threshold values other than the above four threshold values are set, and then in the pixels in which the above four threshold values are set. Two dots are added at a time. That is, in the high density region, the ratio of the number of dots added to the increase in the gradation value is higher than in the highlight region to the medium density region, and the maximum optical density can be increased as compared with the conventional case.

As a result, according to the present embodiment, the range of expression of the optical density in the entire density range (0 to 4096) can be expanded as compared with the conventional case. Specifically, assuming that the recording duty in which dots are recorded one by one in each pixel is 100%, gradation expression is conventionally performed with a recording duty of 0% to 100%, but in the present embodiment. Then, gradation expression is performed with a recording duty of 0% to 125%. Then, in the present embodiment, the quantization processing unit 404 (see FIG. 4) performs the quantization processing under a resolution of 1200 dpi, which is equal to the recording resolution of the recording device 1. From the above, according to the present embodiment, it is possible to output an image having high resolution corresponding to the recording resolution of the recording device while suppressing graininess and expressing high optical density. ..

In the above, two dots are recorded for the pixel in which the highest four thresholds are set, but the number of thresholds for recording the two dots may be increased or decreased. .. For example, if two dots are recorded for a pixel in which the highest eight threshold values are set, the entire density area (0 to 4096) can be expressed in gradation with a recording duty of 0% to 150%. become.

Further, in the above, the threshold matrix 500 is a unit matrix 501 in which the threshold arrangement is fixedly arranged repeatedly in the X direction and the Y direction. However, the threshold matrix 500 is a plurality of unit matrices in which the threshold arrangements are different from each other. May be arranged and configured. In any case, in the pixel in which the threshold value equal to or higher than the predetermined value is set in the threshold matrix 500, dot recording is permitted in both of the two pass masks, and in the other pixels, dot recording is permitted in one of the two pass masks. If this is done, the effect of this embodiment can be obtained.

(Second embodiment)
Also in this embodiment, the recording device 1 described with reference to FIGS. 1 to 4 is used. Further, the quantization process is performed using the threshold matrix 500 described with reference to FIG. However, in the first embodiment, 2-pass multipath recording is performed, but in this embodiment, 4-pass multipath recording is performed. In the case of 4-pass multi-pass recording, an image is recorded in the unit area of the recording medium by four recording scans by the recording head 105.

8 (a) to 8 (e) are diagrams showing a path mask used by the distribution processing unit 405 of the present embodiment. In the case of 4-pass multi-pass recording, the 768 ejection ports shown in FIG. 2 are divided into four regions of 192 each, and different pass masks are used for each region. In this embodiment, FIG. 8A shows a first pass mask 801 used in the discharge ports n1 to n192. FIG. 6B shows the second pass mask 802 used in the discharge ports n193 to n384. FIG. 6 (c) shows a third pass mask 803 used in the discharge ports n385-n576. FIG. 6D shows a fourth pass mask 804 used in the discharge ports n577 to n768. Each pass mask has a pixel area of 192 pixels in the Y direction and 256 pixels in the X direction. Further, each pass mask is configured by repeatedly arranging unit masks composed of 4 × 4 pixel regions in the X direction and the Y direction, as in the first embodiment.

FIG. 9 is a diagram for explaining how an image is recorded on a recording medium in the 4-pass multipath recording of the present embodiment in the same manner as in FIG. 7. In the recording head 105, the discharge ports n1 to n192 record according to the first pass mask 801 and the discharge ports n193 to n384 record according to the second pass mask 802. Further, the discharge ports n385 to n576 record according to the third pass mask 803, and the discharge ports n577 to n768 record according to the fourth pass mask 804. Then, between each recording scan, the recording medium is conveyed by 192 pixels in the Y direction. As a result, in any unit area on the recording medium, an image is recorded by four recording scans by different ejection port areas of the recording head 105.

FIG. 8 (e) shows the number of dots eventually recorded on the recording medium for each pixel in the 8 × 8 image area in which the dot recording (1) is determined by the quantization processing unit 404. It is a figure. Of the first to fourth pass masks 801 to 804 shown in FIGS. 8A to 8D, four dots are recorded in the pixels in which dot recording is permitted in all the pass masks. Of the first to fourth pass masks 801 to 804, three dots are recorded in the pixels in which dot recording is permitted in the three pass masks, and the pixels in which dot recording is permitted in the two pass masks are recorded. Two dots are recorded. Of the first to fourth pass masks 801 to 804, one dot is recorded in a pixel for which dot recording is permitted with only one pass mask. In any of the pixels, at least one of the first to fourth pass masks 801 to 804 is allowed to record dots.

Here, the pixel in which the four dots are recorded in FIG. 8 (e) corresponds to the pixel in which the four highest threshold values (3328, 3840, 3584, 4096) are set in the unit matrix 501 of FIG. do. Further, the pixel in which the three dots are recorded corresponds to the pixel in which the next highest four threshold values (2304, 2560, 2816, 3072) are set in the unit matrix 501 of FIG. Further, the pixel in which the two dots are recorded corresponds to the pixel in which the next highest four threshold values (1280, 1530, 1792, 2048) are set in the unit matrix 501 of FIG. Further, the pixel in which one dot is recorded corresponds to the pixel in which the four lowest threshold values (256, 512, 768, 1024) are set in the unit matrix 501 of FIG.

As described above, in the present embodiment, the first to fourth pass masks 801 to 804 are associated with the threshold matrix 500 in advance so that the higher the threshold is set, the more dots can be recorded. Has been created. As a result, according to the present embodiment, the gradation is expressed in the entire density area (0 to 4096) with a recording duty of 0% to 250%, and the expression range of the optical density is further expanded as compared with the first embodiment. It will be possible to expand.

(Third embodiment)
Also in this embodiment, the recording device 1 described with reference to FIGS. 1 to 4 is used. Further, as in the second embodiment, 4-pass multipath recording shall be performed. However, the quantization processing unit 404 of the present embodiment converts the gradation value of the 12-bit 4096 value into the quantization value of the 2-bit 3-value. This 2-bit, 3-value quantized value indicates dot recording (01), (10), or non-recording (00) for each pixel region arranged at 1200 dpi on a recording medium.

10 (a) and 10 (b) are diagrams showing a threshold matrix used by the quantization processing unit 404 of the present embodiment. The quantization processing unit 404 of the present embodiment performs quantization processing using two threshold matrices, a first threshold matrix 1001 shown in FIG. 10A and a second threshold matrix 1002 shown in FIG. 10B. I do.

In the first and second threshold matrices 1001 and 1002, each square corresponds to one pixel area, and the value shown in each pixel indicates the threshold used in the quantization process. Here, in the first threshold matrix 1001 shown in FIG. 10A, a threshold value included in the range of 0 to 2048 is set. On the other hand, in the second threshold value matrix 1002 shown in FIG. 10B, a threshold value included in the range of 2049 to 4096 is set. Similar to the threshold matrix 500 described in the first embodiment, each of the threshold matrices is configured by repeatedly arranging the unit matrices 1003 and 1004 composed of 4 pixels × 4 pixel regions in the X direction and the Y direction, respectively. Will be done. Such a threshold matrix 500 is stored in ROM 301 in advance.

The quantization processing unit 404 of the present embodiment performs quantization processing using the first threshold matrix 1001 for pixels having gradation values of 0 to 2048, and records (01) or does not record (00) dots. ) Is determined. Further, for pixels having gradation values of 2049 to 4096, a quantization process is performed using the second threshold matrix 1002 to determine dot recording (10) or non-recording (00). As a result, all the gradation values from 0 to 4096 are converted into any of (01), (10) or (00). FIGS. 11 (a) to 11 (f) show the distribution processing unit of the present embodiment. It is a figure for demonstrating the path mask used by 405. FIG. 11A shows a first pass mask used in the discharge ports n1 to n192. FIG. 11B shows a second pass mask used at the discharge ports n193 to n384. FIG. 11 (c) shows a third pass mask used at the discharge ports n385-n576. FIG. 11D shows a fourth pass mask used at the discharge ports n577 to n768. Both have a pixel area of 192 pixels in the Y direction and 256 pixels in the X direction.

In the path mask of the present embodiment, any mask value of "00", "01", or "10" is set for each pixel. Here, the mask value "01" indicates that dots are recorded when the quantization value is "10". Further, the mask value "10" indicates that dots are recorded when the quantization value is "01" or "10". Further, the mask value "00" indicates that the dots are not recorded. FIG. 12 shows the contents of dot recording (1) or non-recording (0) determined according to the combination of the quantized value (00, 01, 10) and the mask value (00, 01, 10). ..

In the present embodiment, the mask value "10" is set so as to have a complementary relationship with the first to fourth pass masks. In other words, the first to fourth pass masks are created so that the mask value is "10" in any one of the first to fourth pass masks for each pixel. On the other hand, regarding the mask value "01", in the pixel in which four high threshold values are set, the first to first pass masks have a mask value of "01" in two of the first to fourth pass masks. The path mask of 4 is created. Further, in the pixels in which the remaining threshold values are set, the first to fourth pass masks are created so that the mask value becomes "01" in any one pass mask.

In this embodiment, 4-pass multipath recording is performed using the threshold matrix and path mask described above. The state in which the image is recorded on the recording medium is the same as in FIG. 9 described in the second embodiment. That is, in each unit region, the recording scans according to the first to fourth pass masks are sequentially performed with the transfer operation for 192 pixels intervening, and the image is completed.

FIG. 11 (e) shows recording on a recording medium when multipath recording of the present embodiment is performed on an 8 × 8 pixel region whose quantization value is determined to be “01” by the quantization processing unit 404. It is a figure which showed the number of dots to be formed for each pixel. In this case, in each recording scan, dots are recorded only in the pixels whose mask value is "10", and as a result, one dot is recorded in all the pixels.

On the other hand, FIG. 11 (f) shows a recording medium when multipath recording of the present embodiment is performed on an 8 × 8 pixel region whose quantization value is determined to be “10” by the quantization processing unit 404. It is a figure which showed the number of dots recorded in 1 for each pixel. In this case, in each recording scan, dots are recorded in the pixel whose mask value is "01" and the pixel whose mask value is "10". As a result, as shown in FIG. 11 (f), three dots are recorded in the pixel in which the four highest threshold values are set in FIG. 10 (b), and two dots are recorded in the other pixels. It will be recorded.

As described above, in the present embodiment, the first and second threshold matrices 1001 and 1002 and the first to fourth threshold matrices 1001 and 1002 are allowed so that the higher the threshold value is set, the more dots can be recorded. It is created in association with the path mask of. As a result, in the present embodiment, the gradation expression is performed in the entire density range (0 to 4096) with a recording duty of 0% to 225%, and the expression range of the optical density is further expanded as compared with the first embodiment. Can be done.

(Fourth Embodiment)
Also in this embodiment, the recording device 1 described with reference to FIGS. 1 to 4 is used. Further, as in the first embodiment, 2-pass multipath recording is performed. However, the threshold matrix of the present embodiment is not a unit matrix of 4 × 4 pixels but a unit matrix of 128 × 128 pixels. Each of the 128 × 128 pixels (16384 pixels) is set with four threshold values of 1 to 4096 in a highly dispersible state. As the unit matrix of the present embodiment, a threshold matrix in which low frequency components having blue noise characteristics are suppressed can be used.

13 (a) and 13 (b) show the dispersibility of dots recorded on a recording medium depending on whether a threshold matrix with suppressed low frequency components is used or a threshold matrix in which thresholds are randomly set is used. It is a figure which compares. Here, the case where the image data in which the gradation value of each pixel is uniformly 512 is input is shown. When the gradation value is 512, the dots are recorded in the pixels in which the threshold values of 1 to 512 are set, and the dots are not recorded in the pixels in which the threshold values of 513 to 4096 are set. Comparing FIGS. 13 (a) and 13 (b), although the same number of dots are recorded in both of them, the dispersibility of the dots is higher in FIG. 13 (a) using the threshold matrix in which the low frequency component is suppressed. It can be seen that the graininess is high and the graininess is suppressed.

In the present embodiment, a first pass mask and a second pass mask as described in the first embodiment are prepared while using such a threshold matrix having excellent dispersibility. Specifically, in the pixel in which the threshold value of 1-3584 is set in the threshold matrix, dot recording is permitted by one pass mask, and in the pixel in which the threshold value of 3585-4096 is set, dot recording is permitted by both pass masks. Prepare two path masks like this. Similar to the threshold matrix, these two path masks have a pixel area of 128 × 128 as a unit mask.

Then, after using the threshold matrix and the first and second pass masks, 2-pass multipath recording is performed. Although the size of the unit matrix is different, the state in which the image is recorded on the recording medium is the same as in FIG. 7 described in the first embodiment. In each unit area of the recording medium, the recording scan according to the first pass mask and the recording scan according to the second pass mask are performed in sequence, and the gradation expression can be performed with a recording duty of 0% to 125%. It will be possible. Of course, also in the present embodiment, as in the first embodiment, the range of the optical density for performing gradation expression can be further expanded by further expanding the range of the threshold value in which the two dots are recorded. ..

As described above, according to the present embodiment, an image having a high resolution corresponding to the recording resolution of the recording device while expressing a high optical density while further suppressing the graininess as compared with the first embodiment. It becomes possible to output.

In the above, the case of recording an image generated by using a threshold matrix with suppressed low frequency components by 2-pass multipath recording has been described, but of course, the same image can also be recorded by 4-pass multipath recording. can. In this case, the first to fourth pass masks having a pixel area of 128 × 128 may be prepared. Then, the position of the recording allowable pixel of the first to fourth pass masks is set in the second embodiment so that the number of pass masks on which dot recording is permitted increases as the pixel has a larger threshold value set in the threshold matrix. It may be adjusted in the same manner as above.

(Fifth Embodiment)
Also in this embodiment, the recording device 1 described with reference to FIGS. 1 to 4 is used. Further, as in the first embodiment, 2-pass multipath recording is performed. However, in the present embodiment, a threshold matrix composed of a unit matrix having a pixel region larger in the Y direction than the transfer amount (384 pixels) between each recording scan in 2-pass multi-pass recording is used. ..

FIG. 14 is a diagram showing relative sizes and positions of the unit matrix 1400 used in the present embodiment, the first pass mask 1401 and the second pass mask 1402. In the present embodiment, the unit matrix 1400, the first pass mask 1401 and the second pass mask 1402 have 768 pixels corresponding to twice the transport amount (384 pixels) in the Y direction (transport direction) and 512 pixels in the X direction. Has an area. As for the unit matrix 1400, it is assumed that the low frequency component is suppressed as in the fourth embodiment.

The recordable pixels of the first pass mask 1401 and the second pass mask 1402 are set based on the unit matrix 1400 in the same manner as in the fourth embodiment. That is, in the pixels in which the threshold values of 1 to 3584 are set in the unit matrix 1400, dot recording is permitted on one of the first pass mask 1401 and the second pass mask 1402. Further, in the pixel in which the threshold value of 3585 to 4096 is set in the unit matrix 1400, dot recording is permitted by both the first pass mask 1401 and the second pass mask 1402.

Next, a two-pass multipath recording using the unit matrix 1400, the first pass mask 1401 and the second pass mask 1402 generated as described above will be described. In the case of two-pass multi-pass recording, each of the unit matrix 1400, the first pass mask 1401 and the second pass mask 1402 can be considered by being divided into two regions in the Y direction. Here, for convenience, the region of 384 pixels on the + Y direction side of the unit matrix 1400 is referred to as a threshold matrix D1, and the region of 384 pixels on the −Y direction side is referred to as a threshold matrix D2. Further, the region of 384 pixels on the + Y direction side of the first pass mask 1401 is called a pass mask A1, and the region of 384 pixels on the −Y direction side is called a pass mask A2. Further, the region of 384 pixels on the + Y direction side of the second pass mask 1402 is called a pass mask B1, and the region of 384 pixels on the −Y direction side is called a pass mask B2. The pixel region corresponding to the threshold matrix D1 is subjected to gradation expression with a recording duty of 0 to 125% by a recording scan according to the pass mask A1 and a recording scan according to the pass mask B1. The pixel region corresponding to the threshold matrix D2 is gradation-represented with a recording duty of 0 to 125% by a recording scan according to the pass mask A2 and a recording scan according to the pass mask B2.

FIG. 15 is a diagram for explaining how an image is recorded on a recording medium in the two-pass multipath recording of the present embodiment. In the case of the present embodiment, the recording head 105 switches the path mask used for each recording scan. This will be described in detail below.

In the first recording scan, the discharge ports n1 to n384 of the recording head 105 perform recording according to the path mask A1. In the second recording scan, the discharge ports n1 to n384 of the recording head 105 record according to the pass mask A2, and the discharge ports n385-n768 record according to the pass mask B1. In the third recording scan, the discharge ports n1 to n384 of the recording head 105 record according to the pass mask A1, and the discharge ports n385-n768 record according to the pass mask B2. In the fourth recording scan, the discharge ports n1 to n384 of the recording head 105 record according to the pass mask A2, and the discharge ports n385-n768 record according to the pass mask B1. After that, in the same manner, in the odd-numbered recording scan, the discharge ports n1 to n384 of the recording head 105 record according to the pass mask A1, and the discharge ports n385-n768 record according to the pass mask B2. Further, in the even-numbered recording scan, the discharge ports n1 to n384 of the recording head 105 record according to the pass mask A2, and the discharge ports n385-n768 record according to the pass mask B1.

Here, focusing on the first unit region corresponding to the threshold matrix D1, the image is recorded in the first unit region by the recording scan according to the pass mask A1 and the recording scan according to the pass mask B1. On the other hand, in the second unit region corresponding to the threshold matrix D2, an image is recorded by a recording scan according to the pass mask A2 and a recording scan according to the pass mask B2. Hereinafter, similarly, the odd-numbered unit area is subjected to the recording scan according to the pass mask A1 and the pass mask B1, and the even-numbered unit area is subjected to the recording scan according to the pass mask A2 and the pass mask B2. In any unit area, the threshold matrix and the path mask are created in advance in association with each other so that dots can be recorded in two recording scans for pixels for which a high threshold is set. ..

From the above, also in the present embodiment, it is possible to output an image having high resolution corresponding to the recording resolution of the recording device while suppressing the graininess and expressing high density.

In the above, the case of using the unit matrix 1400 having twice the size of the transport amount (384 pixels) in the Y direction has been described, but in the present embodiment, the size of the unit matrix is the transport amount (384 pixels). It can be made even larger under the condition of an integral multiple. It is also possible to record the same image with 4 or more multipaths.

In any case, a unit matrix having a size that is an integral multiple of the amount of transportation for multipath recording and a plurality of pass masks based on the contents of the unit matrix may be prepared. Then, by performing the recording scan a plurality of times for the unit region while switching the appropriate path mask in each recording scan, a high optical density is expressed while suppressing the graininess as in the above embodiment, and the recording resolution of the recording device is obtained. It is possible to output an image having a correspondingly high resolution.

(Other embodiments)
In the above embodiment, an image recording apparatus using four color inks of cyan, magenta, yellow, and black has been described as an example. However, the image processing of the present invention as described above does not have to be applied to all ink colors. For example, black may be subjected to image processing as described above, and other colors may be subjected to the same image processing as before to express gradation under a recording duty of 0% to 100%. Further, a pass mask for multi-pass recording may be prepared individually for each ink color, and the recording duty of the maximum density may be different for each ink color.

Further, the types of ink used are not limited to the above four colors. For example, a monochrome printer using only black ink may be used, or an ink having a low content concentration of a coloring material such as light cyan or light magenta, or a special color ink such as red, blue, or green may be used.

Further, the number of multipaths is not limited to 2 passes or 4 passes as described in the above embodiment. The above embodiment can be applied to a form of performing multipath recording in which recording scanning is performed M times (M is an integer of 2 or more) with respect to a unit area. For example, in the case of 3-pass multipath recording, it is possible to record up to 3 dots in one pixel, and in the case of 8-pass multipath recording, it is possible to record up to 8 dots in one pixel. Will be. In any case, the number of recording scans that are allowed to record dots for pixels for which a threshold value greater than or equal to a predetermined value is set in the threshold matrix is the number of dot recordings for pixels for which other threshold values are set. It suffices to prepare a path mask such that the number of recording scans is greater than the number of recording scans allowed.

Further, in the above embodiment, the recording device 1 provided with the recording head 105 has been described as the image processing device of the present invention. However, the image processing device of the present invention can also be an image processing device connected to the outside of the recording device and for generating recorded data used in the recording device.

Further, although the inkjet recording device that ejects ink as droplets has been described above as an example, the image recording method is not limited to the inkjet method. Any image recording device may be used as long as it is an image recording device that applies a color material to a recording medium to form dots and expresses pseudo gradation.

In any case, in a configuration in which the quantization process using the threshold matrix is performed at a resolution equal to the recording resolution of the recording device 1, if the path mask used for multipath recording can be prepared in association with the threshold matrix, the present invention. Can work effectively.

The present invention supplies a program that realizes one or more functions of the above-described embodiment to a system or device via a network or storage medium, and one or more processors in the computer of the system or device reads and executes the program. It can also be realized by the processing to be performed. It can also be realized by a circuit (for example, ASIC) that realizes one or more functions.

1 Recording device (image processing device)
105 Recording head 201 Discharge port (recording element)
404 Quantization processing unit 405 Distribution processing unit 500 Threshold matrix 601 First pass mask 602 Second pass mask P Recording medium

Claims (12)

By quantizing the multi-valued gradation values of each of the pixels arranged at a predetermined resolution using a threshold matrix, a quantum indicating recording or non-recording of dots for each of the pixels arranged at a predetermined resolution. Quantization means to generate the conversion value and
A determination to determine the pixel to record a dot in the recording scan based on the quantization value generated by the quantization means and a path mask that determines the permissible or non-permissible of dot recording for each pixel in the recording scan of the recording head. Equipped with means,
The recording scan in which the recording head in which the recording elements capable of recording dots are arranged is scanned in a predetermined direction with respect to the recording medium, and the transfer in which the recording medium is conveyed in a direction intersecting the predetermined direction. An image processing device that performs image processing for recording an image in a unit area of the recording medium at the predetermined resolution by performing the recording scan a plurality of times by alternately performing operations.
In the path mask, a second threshold value is set in which the number of recording scans in which dots are allowed to be recorded for pixels for which the first threshold value is set in the threshold value matrix is smaller than the first threshold value. An image processing apparatus characterized in that the permissible or non-permissible dot recording for each pixel is defined so that the number of recording scans permissible for dot recording for a pixel is greater than the number of recording scans allowed. The quantization means generates the binary quantization value indicating recording or non-recording of dots by comparing the gradation value with the threshold value stored in association with each pixel in the threshold matrix. The image processing apparatus according to claim 1, wherein the image processing apparatus is characterized by the above. The quantization means is characterized in that the quantized value of three values is generated by comparing the gradation value with the threshold value stored in association with each pixel in the threshold matrix. The image processing apparatus according to. The image of the unit area is recorded by the recording scan of the recording head twice.
In the path mask, the pixel in which the first threshold value is set is allowed to record dots in the two recording scans, and the pixel in which the second threshold value is set is allowed to record dots. The claim is characterized in that the permissibility or non-permissibility of dot recording for each pixel is defined so that dot recording is permitted in one of the two recording scans. The image processing apparatus according to any one of 1 to 3. The image of the unit area is recorded by the recording scan of the recording head M times (M is an integer of 2 or more).
The path mask is applied to each pixel so that the larger the threshold value set in the threshold matrix, the larger the number of the recording scans in which dot recording is allowed in the M times of the recording scans. The image processing apparatus according to any one of claims 1 to 3, wherein the permissible or non-permissible of dot recording is defined. The image processing apparatus according to any one of claims 1 to 5, wherein the threshold matrix is configured by repeatedly arranging a unit matrix in which a fixed arrangement of thresholds set for each pixel is repeatedly arranged. The image processing apparatus according to claim 6, wherein the unit matrix is a threshold matrix in which low frequency components are suppressed. The image processing apparatus according to claim 6 or 7, wherein the unit matrix has a pixel region that is an integral multiple of the transport amount of the recording medium in the transport direction. The image processing apparatus according to any one of claims 1 to 8, wherein the recording head records black dots. The image processing apparatus according to any one of claims 1 to 9, further comprising a recording means for causing the recording head to perform the recording scan based on the determination of the determination means. The image processing apparatus according to any one of claims 1 to 10, wherein the recording head is an inkjet recording head that ejects ink from an ejection port and records dots on the recording medium. By quantizing the multi-valued gradation values of each of the pixels arranged at a predetermined resolution using a threshold matrix, a quantum indicating recording or non-recording of dots for each of the pixels arranged at a predetermined resolution. The quantization process to generate the conversion value and
A pixel for recording a dot in the recording scan is determined based on the quantization value generated by the quantization step and a path mask that determines the permissibility or non-permissibility of dot recording for each pixel in the recording scan of the recording head. Has a decision process and
The recording scan in which the recording head in which the recording elements capable of recording dots are arranged is scanned in a predetermined direction with respect to the recording medium, and the transfer in which the recording medium is conveyed in a direction intersecting the predetermined direction. It is an image processing method for performing image processing for recording an image of a unit area of the recording medium at the predetermined resolution by performing the recording scan a plurality of times by alternately performing operations.
In the path mask, a second threshold value is set in which the number of recording scans in which dots are allowed to be recorded for pixels for which the first threshold value is set in the threshold value matrix is smaller than the first threshold value. An image processing method characterized in that the permissible or non-permissible dot recording for each pixel is defined so that the number of recording scans permissible for dot recording for a pixel is greater than the number of recording scans allowed.

Images