KR101009633B1 - Image processing apparatus and image processing method - Google Patents

Abstract

An image processing apparatus includes: a divider for dividing image data into pieces of print scan image data for a plurality of print scans, a quantizer for quantizing pieces of the print scan image data, and the quantized print scan image data And a generation section for generating fragments of print data for the plurality of print scans based on the fragments of. The quantization unit quantizes the fragments of the print scan image data so as to be mutually exclusive in the plurality of print scans when the density represented by the fragments of the print scan image data is low concentration.

Image processing apparatus, print scanning, image data, quantization unit, generation unit.

Description

Image processing apparatus and image processing method

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

An inkjet printer is known as an example of an image forming apparatus which forms an image by performing a plurality of print scans on the same image area on a print medium.

In an inkjet printer, an operation of discharging ink droplets from the print head to the print medium while reciprocating the print head in the main scanning direction and carrying out the operation of conveying the print medium in the sub-scanning direction are repeated to print an image on the print medium. In such an inkjet printer, variations in the direction, size, and impact position of ink droplets occur due to physical factors such as characteristic differences between nozzles during printing, errors in paper conveyance distance, and errors in printhead movement distance. . These fluctuations appear as density spots or streaks in the image printed by one print scan, and deteriorate the image quality.

As a method for suppressing the occurrence of such density spots and streaks, a multipass printing method is known. The multi-pass printing method is a combination of image processing and print control, and enables high-speed image formation while suppressing deterioration of image quality due to density spots and streaks.

Hereinafter, the multipath printing method will be described in detail with reference to FIG. 12.

Referring to FIG. 12, the print head 5101 is configured with a nozzle 5102. In order to simplify the description, the print head 5101 shall be composed of eight nozzles 5102. Ink droplets 5103 are discharged from the nozzles 5102. Usually, it is preferable that the same amount of ink is discharged from the nozzle 5102 in the direction as shown in Fig. 12 so as to complete printing in one print scan of the print area in a predetermined print medium.

However, as described above, when an image is printed by one print scan due to an error due to physical factors at the time of printing, the size and direction of the ink droplets ejected from a certain nozzle vary from nozzle to nozzle. For this reason, portions of the white paper are periodically present on the print medium or excessive dots overlap with each other in the head main scanning direction. In this state, the gathered dots are sensed on the print medium as density spots with respect to the arrangement direction of the nozzles. If a shift occurs between printed areas printed in the print scan, the boundary between these print areas is detected as stripes.

In the multi-pass printing method, as shown in FIG. 13, the print head 5201 is used to print several times (in this case, three times). Referring to Fig. 13, the printing of each print area consisting of four pixels (half of the longitudinal length in which eight pixels are arranged) is completed by two print scans. In this case, the eight nozzles 5202 provided in the print head 5201 are divided into a group of four nozzles (upper nozzle group) on the upper side and four nozzles (lower nozzle group) on the lower side. Dots printed by one nozzle in one print scan correspond to data obtained by sorting the image data about half along a predetermined image data array. In the second print scan, a dot corresponding to about half of the rest of the image data is embedded in the image formed by the one print scan, thereby completing printing of the four pixel unit area.

In the multipath printing method, for example, the two-pass printing method, the first print scan and the second print scan complement each other in accordance with a predetermined image data arrangement. As the predetermined image data array (selection mask pattern), a staggered arrangement is used for each pixel in the vertical and horizontal directions shown in FIG. Therefore, the unit print area (four pixel unit area in this case) is completed by the first print scan for printing the zigzag pattern and the second print scan for printing the opposite zigzag pattern. Fig. 14 shows a process of completing printing of the same area by using the zigzag pattern opposite to the zigzag pattern. That is, as shown in the upper part of FIG. 14, in the first print scan, the zigzag pattern (black circle) is printed on a predetermined area of the print medium using the following four nozzles. Next, as shown in the interruption of FIG. 14, in the second print scan, paper feeding is performed for four pixels, and printing of the zigzag pattern (white circle) opposite to the area of the print medium is carried out using all eight nozzles. Do it. Subsequently, as shown in the lower part of FIG. 14, in the third print scan, four pixels of paper are sent, and the zigzag pattern is printed again using the four nozzles.

Even in the case of using a multi-head having a variation as shown in Fig. 13, the multipath printing method can halve the influence on the print area due to the variation. In addition, even in the case where a shift occurs between the printed areas printed by the print scan, the influence of the shift can be halved in the multi-pass printing method. For this reason, density spots are reduced in the formed image. An example case in which printing of the unit area is completed by two print scans has been described. Increasing the number of print scans can further reduce the influence of the fluctuation and the misalignment. Accordingly, the density spot can be reduced in proportion to the number of print scans. In contrast, the print time increases in proportion to the number of print scans.

When the number of print scans is reduced to perform high-speed printing, it is difficult to average the fluctuation of ink droplets and the deviation between paths, so that density spots are more noticeable as compared with the case where the number of print scans is not reduced. Therefore, in order to improve the image quality in high-speed printing with a small number of print scans, a dot arrangement is required that has a strong (characteristic that image quality hardly decreases) against fluctuations in ink droplets and shifts between paths.

BACKGROUND ART A technique is known in which a screening pattern having no regularity using random numbers or the like is selected to generate print data used for each print scan. For example, assume that printing is performed by two print scans using this technique. In the first print scan, screening is performed using a random pattern or the like with a screening pattern without regularity. In the second print scan, screening is performed with a reverse screening pattern of the screening pattern without regularity, and each print data is selected. Write. In this case, since the dot structure is no longer regular as compared with the conventional printing by two print scans, the image quality is improved. However, as described previously, in printing, there occurs a variation between the ink droplets and the print scan. In each print scan, a mask pattern is used to form a complementary relationship between the print scans. Thus, when a change in the ink droplets and a shift between the print scans occur, overlapping dots and periodic white paper portions occur, which are detected as density spots. Easy to be In particular, when the dot pattern interferes due to the deviation between print scans, density spots and streaks appear as inappropriate patterns after the scan.

Therefore, for all the dot patterns created by the print scan, it is necessary to prevent the interference when the deviation between the print scans occurs. However, it is difficult to create a mask pattern that can prevent interference between dot patterns that can be used for any input image.

As a method of solving the above difficulties, each pixel value that is multi-value image data is distributed into pieces of multi-value image data used for each print scan, quantized pieces of these multi-value image data, and BACKGROUND OF THE INVENTION A method of generating a printed scan image with reduced complementary relationship using fragments is known. This method can reduce the influence of the change of the image density on the variation of the ink droplets or the deviation between the paths, and can improve the image quality.

However, in the case of generating a print scan image by the above method, quantization is performed in each print scan. Therefore, in this method, the relationship of the dot arrangement obtained by the print scan is not considered. For this reason, the small / mild part of the dot may be seen in the dot pattern produced by the print scan. These parts are detected as density spots on the printed image, and thus are a factor of the decrease in image quality. In the particularly low concentration portions on the printed image, the dots obtained in the path are close to each other, and blank portions appear. In this way, the small / mild portion of the dot tends to be noticeable. FIG. 15 is a diagram showing dot arrangement generated from an input image having a uniform density (low concentration) by the method described above. As is apparent from Fig. 15, the dots are arranged unevenly, and some of these dots overlap each other. Therefore, in order to improve image quality, it is necessary to consider further the dot arrangement of the low concentration part.

The present invention provides an image processing apparatus and an image processing method for suppressing density unevenness of an image formed by a multipath printing method.

An image processing apparatus is provided which generates print data for use in an image forming apparatus that performs image formation by performing a plurality of print scans on the same image area on a print medium. The image processing apparatus includes a divider for dividing image data into pieces of print scan image data for the plurality of print scans, a quantizer for quantizing pieces of the print scan image data, and the quantized print scan. And a generation section for generating pieces of print data for the plurality of print scans based on pieces of image data. The quantization unit quantizes the fragments of the print scan image data so as to be mutually exclusive in the plurality of print scans when the density represented by the fragments of the print scan image data is low concentration.

There is also provided an image processing method for generating print data for use in an image forming apparatus which performs image formation by performing a plurality of print scans on the same image area on a print medium. The image processing method includes dividing image data into pieces of print scan image data for the plurality of print scans, quantizing the pieces of print scan image data, and fragments of the quantized print scan image data. Generating fragments of print data for the plurality of print scans based on the plurality of print scans. When the density represented by the fragments of the print scan image data is low, the fragments of the print scan image data are quantized to be mutually exclusive in the plurality of print scans.

Also, a computer-readable storage medium having computer-executable instructions for controlling an image processing apparatus for generating print data for use in an image forming apparatus that performs a plurality of print scans on the same image region on a print medium to form an image. to provide. Here, the storage medium includes computer executable instructions for dividing image data into pieces of print scan image data for a plurality of print scans, computer executable instructions for quantizing the pieces of print scan image data, and the quantization Computer-executable instructions for generating fragments of print data for the plurality of print scans based on the fragments of the printed scan image data. When the density represented by the fragments of the print scan image data is low, the fragments of the print scan image data are quantized to be mutually exclusive in the plurality of print scans.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. In addition, the structure which concerns on each Example mentioned later is only an example, and this invention is not limited to the structure shown in drawing.

Hereinafter, a first embodiment of the present invention will be described with reference to the drawings. In this embodiment, the case where the inkjet printer performs two print scans using the multipass method will be described.

1 is a block diagram showing an example of the configuration of a print system according to the first embodiment. The print system of FIG. 1 includes a host computer 101, a printer 102, an input device 103, and an external storage device 104. In the host computer 101, the CPU 105 controls the operation of the entire host computer 101 in accordance with a program stored in the RAM 108 and the ROM 115. The RAM 108 is used as the main memory of the CPU 105, and a program executed by the CPU 105 is loaded into the RAM 108. This RAM 108 functions as a work area of the CPU 105, and the CPU 105 temporarily stores various data in the RAM 108 at the time of the control operation. The ROM 115 stores the boot program and various data nonvolatile. The host computer 101 also has an input port 106 such as a LAN or USB port, an output port 107 such as a LAN or USB port, a RAM 108, and an auxiliary storage device 109. In the host computer 101, an input device 103 such as a scanner or a digital camera and an external storage device 104 such as a CD-ROM drive or a memory card reader are connected to the input port 106. In the host computer 101, a printer 102 is connected to an output port 107. In addition, the printer 102 includes an input port 110 such as USB or LAN for receiving print data or control information, a control device 111 for controlling an operation performed inside the printer, print data and internal setting information. Memory 112, a paper conveying apparatus 113, and a print head 114 having a nozzle for ejecting ink onto a print medium.

2 is a diagram showing a process according to the present embodiment. The processing of steps S21 to S25 is performed by the host computer 101, and the processing of steps S26 and S27 is performed by the printer 102. However, the processing of steps S21 to S27 may be performed by the printer 102. FIG. 5 is a diagram for explaining processing units provided in the host computer 101 and the printer 102. Referring to FIG. 5, the host computer 101 includes a color correction / color conversion unit 201 that performs color correction and color conversion on an input image, a path generation unit 208 that generates a path image, and each of the input images. A dot separation method error diffusion processing unit 209 for quantizing path images and a print data conversion unit 203 for converting print data are provided. The printer 102 includes a dot forming unit 204 for forming a dot corresponding to each quantized path image, and a printing unit 205 for printing an image on a print medium.

The processing according to the present embodiment will be described below with reference to FIG. 2. First, the input device 103 inputs the image to be printed to the host computer 101 (step S21). The input color or gray scale image is transmitted to the color correction / color conversion unit 201 shown in FIG. The color correction / color conversion unit 201 performs color correction in accordance with the print settings, and converts the RGB component generally used for image data into a CM component suitable for printing in a printer (step S22). In general, these components are treated separately and one of these components will be described.

The path generation unit 208 of FIG. 5 performs path generation on the image converted into the CMV component (step S23). Path generation means generation of image data used for each print scan in the multipath system. 6 is a diagram for explaining path generation processing. In Fig. 6, there are an input image 601 that generates paths, a distribution parameter 602, a multiplier 603, and an adder 604 used to determine the distribution ratio of pixel values to each path. Also, as the output image, a first pass image 605 and a second pass image 606 are shown. In the path generation processing according to the present embodiment, external parameters such as a distribution parameter 602 for determining a distribution ratio for distributing pixel values in each path are used. FIG. 7 is a diagram for explaining in detail the path generation performed in step S23 of FIG. 2. Hereinafter, path generation will be described in detail with reference to FIGS. 6 and 7.

First, in step S71, the pixel at the position (0, 0) of the input image 601 is selected. In step S72, a parameter (concentration value) at the same position as the selected pixel is acquired for the pixel on the distribution parameter 602. In the case where the size of the distribution parameter 602 is smaller than the size of the input image 601, the distribution parameter 602 is used repeatedly in a short direction, that is, the distribution parameters 602 are arranged in a tile shape in the short direction. . Therefore, a parameter (concentration value) can be acquired using the following formula.

V (x, y) = P (x mod w, y mod h)

In this equation, (x, y) represents the position of the selected pixel on the image, w is the width of the parameter P, h is the height of the parameter P, and V (x, y) is the parameter (concentration value) to be obtained.

In step S73, the multiplier 603 multiplies the pixel value (input value) I (x, y) of the selected pixel by the ratio to the maximum parameter Pmax of the parameter V (x, y) obtained in step S72, A first pass distribution pixel value D1 (x, y) distributed to one pass image is calculated.

D1 (x, y) = I (x, y) * V (x, y) / Pmax

The first pass distribution pixel value D1 is stored in a first pass image buffer provided in the RAM shown in FIG. In step S74, the adder 604 subtracts the first pass distribution pixel value D1 from the input value of the selected pixel to calculate a second pass distribution pixel value D2. The second pass distribution pixel value D2 is stored in a second pass image buffer provided in the RAM 108 of FIG.

D2 (x, y) = I (x, y) -D1 (x, y)

In step S75, it is determined whether distribution processing has been performed for all the pixels included in the input image. If it is determined in step S75 that the distribution process has not yet been performed for the entire pixel, then in step S76 the next pixel is selected. The processes of S72 to S74 are repeated until the entire pixel is selected to obtain the first pass image 605 and the second pass image 606.

The path generation process will be described using specific numerical values. FIG. 8 is a diagram showing a path generation process shown in FIG. 6 using specific numerical values. In FIG. 8, there are an input image 801, a distribution parameter 802, a multiplier 803, an adder 804, a first pass image 805, and a second pass image 806. Each value represents a pixel value or a parameter. It is assumed that the pixel 807 is selected. For the pixel 807, the parameter 808 of the distribution parameter 802, which is at the same position as the pixel 807, is used. The maximum value of the parameter is 255. Therefore, the first pass distribution pixel value D1 is calculated by substituting I = 85, P = 100, and Pmax = 255 in the above equation, and D1 = 33 is obtained. In this case, although the fraction is omitted, the solution may be rounded off or to the nearest integer. The calculated first pass distribution pixel value D1 corresponds to the value of the pixel 809 of the first pass image 805. The second pass distribution pixel value D2 of the pixel 807 is subtracted from the density value of the pixel 807 by the first pass distribution pixel value D1, so that D2 (810) = 52 is obtained. All pixels included in the input image 801 are similarly processed to generate a first pass image and a second pass image. As previously described, when the distribution parameter 802 is smaller in size than the size of the input image 801, the distribution parameter 802 is repeatedly used in a direction in which the distribution parameter 802 is insufficient, that is, tiles in a direction in which the distribution parameter 802 is insufficient. Are listed by shape. Therefore, by using the above equation, it is determined which of the columns of the parameter 808 is used for the fifth column (part of the column 811 of the input image 801, the column of the coordinates (4, y)), and V (4, y) = P (4 mod 4, y mod 4) = P (0, y) (0 ≦ y ≦ 4) is obtained, and the first column of the distribution parameter 802, i.e., column 812, is used.

Further, the distribution parameter sets each parameter such that the distribution of each pixel value produces a spatial and periodic change in the feeding direction and the carriage direction. The distribution of each pixel value may be a change in either the feeding direction or the carriage direction, or may generate spatial and periodic changes in two or more directions such as the feeding direction and the carriage direction.

Since the distribution performs distribution of each pixel value so as to generate spatial and periodic changes, periodic changes appear depending on the spatial position of the path image. Therefore, as will be described later, path (print scan) images having different input values are input to the dot separation method error diffusion processing unit 209 shown in FIG. When a path image of the same input value is input to the dot separation method error diffusion processing unit 209, the dot pattern obtained by performing error diffusion processing, print data conversion, and dot formation, which will be described later, on the path image may be similar to each other. do. If the dot patterns obtained from the path images are similar to each other, these dot patterns may interfere with each other. Accordingly, by generating different input values of the path image input to the dot separation method error diffusion processing unit 209, it is possible to prevent the occurrence of similar dot patterns from the path image. This can suppress the interference of the dot pattern with respect to the printed image. In addition, it is possible to suppress the concentration change due to the deviation between the paths. Even if fluctuations in ink droplets and shifts between paths occur, such a synergistic effect suppresses interference of dot patterns and deterioration of image quality.

Each path image obtained by the path generation unit 208 shown in FIG. 5 is transmitted to the dot separation system error diffusion processing unit 209 corresponding to the quantization unit. The dot separation method error diffusion processing performed by the dot separation method error diffusion processing unit 209 in step S24 shown in FIG. 2 will be described. In the dot separation method error diffusion performed by the dot separation method error diffusion processing unit 209, an error diffusion processing method (dot separation method error diffusion method) in which cyan and magenta dots do not overlap with each other (for example, Japanese Patent Application Laid-Open No. 2003-116015). The error diffusion processing method (dot separation method error diffusion method) in Japanese Laid-Open Patent Publication No. 2003-116015 is to prevent dots of different colors (magenta and cyan) from overlapping each other. In this embodiment, the error diffusion processing method (dot separation method error diffusion method) is performed on the values of the pixels of the same component distributed in the path generation processing, without using the processing performed on the dots of different color components. Used for processing.

The dot separation method error diffusion unit 209 performs an error diffusion process on the low concentration portions of the path image so that the dots are mutually exclusive, thereby generating a quantized path image. For this reason, dots are arranged exclusively in the low concentration part of a path image. In addition, the pixel value used in this embodiment is a density value.

FIG. 16 is a diagram illustrating an example of a dot pattern obtained by performing a dot separation method error diffusion process on a two-pass image in the dot separation method error diffusion unit 209. In this embodiment, two path images are generated from the input images. From these two path images, a dot pattern similar to that obtained by error diffusion processing a single image can be formed. Since individual dots are appropriately provided for the passes, generation of small / mild portions of the dots is suppressed. Accordingly, even when ink droplets fluctuate during printing or deviations between paths occur, density spots may be difficult to be detected. Such a method of providing a dot to a path is very difficult to implement when using a method of providing a dot to a path and a method of independently performing quantization between paths, as in the prior art.

FIG. 9 is a diagram for explaining in detail the dot separation method error diffusion processing performed in step S24 of FIG. 2. 10 is a diagram showing an example of a lookup table used to determine an output value from an input value in a dot separation error spreading process. In this embodiment, the input value including the propagated error has a value from -63 to 319, and the output quantization level has a value from 0 to 2. In each of the separated areas, the value in parentheses is the output. The level of the input value and the quantization is not limited to the above values and levels, but may be other values and levels.

First, in step S91, pixels at positions (0, 0) are selected in each of two path images. In step S92, the pixel value (hereinafter referred to as an input value) of the selected pixel of each path image is obtained. In step S93, an output value is determined using the lookup table shown in FIG. 10 from the two input values obtained above. For example, when the input value of the selection pixel of the first pass image is P1 = 40 and the input value of the selection pixel of the second pass image is P2 = 120, the first pass output value is 0 and the second pass output value is 1. to be. In step S94, an error between the first pass output value and the threshold value and an error between the second pass output value and the threshold value is calculated on the first pass and the second pass image, respectively, and the calculation is performed on the peripheral pixels on the first pass and the second pass image. Propagated error. This process is repeated for all the pixels (steps S95 and S96).

The lookup table of FIG. 10 includes an area 1001 (high concentration area) in which the path image is independently quantized and an area 1002 (low concentration area) in which the path image is quantized exclusively. As is clear from the table, the output value is determined without being affected by the input value of the path image in the area 1001 in which the path image is independently quantized, but the influence of the input value of the path image in the area 1002 in which the path image is exclusively quantized The output value is determined under In this way, in the low concentration region (area 1002), a plurality of path images are processed as one path image, and dots are exclusively arranged in the path images. As a result, in the low concentration region of the path image, the dots are mutually exclusive, so that an image with reduced density unevenness can be formed. The propagation error fluctuates, and the area where the path picture is independently quantized and the area where the path picture is exclusively quantized are used alternately. Accordingly, no deterioration in image quality occurs at the boundary between these two areas. In order to further improve image quality, noise used to vary the threshold required for quantization may be added.

Subsequently, in step S25, the path image obtained by the dot separation method error diffusion processing unit 209 is input to the print data conversion unit 203 and converted into print data.

The converted print data is transmitted from the host computer 101 to the printer 102. The printer 102 receives the print data and stores the print data in a print buffer provided in the memory 112.

In step S26, the dot forming unit 204 converts the print data stored in the print buffer into two-value print data indicating whether or not the dot is ejected (ON or OFF). By allocating a 2 × 2 area to the print data received by the printer 102, that is, one pixel of the image before dot formation, the quantization level can be maintained even in the data obtained after dot formation. 11 is a diagram illustrating exemplary dot formation performed based on a relationship between a quantization level and any dot arrangement in which the quantization level is converted. Dots are arranged based on this relationship. In addition, when it is not necessary to convert the print data into two values indicating ON or OFF of each dot, for example, the diameter of each dot for which the two-value data is obtained or discharged in the quantization process may be changed to two or more. In this case, the dot formation need not be performed.

After determining the dot arrangement, in step S27, print data is sent to the printing unit 205, and printing is started. FIG. 3 is a diagram schematically showing a state in which a second scan is performed using a multipass printing method. The print head C01 discharges ink while reciprocating in the main scanning direction to form an image on the print medium P01. The front part in the sub-scan direction of the print head C01 is called the print head front part C02, and the rear part of the print head C01 opposite to the print head front part C02 is called the print head rear part C03.

First, a first scan is performed. In this embodiment, since two-pass scanning is performed, the first scan prints in an area of 1/2 of the print head length, and after the second scan, prints in an area of the print head length. Data for the print scan of the first pass image is transmitted to the rear part C03 of 1/2 of the length of the print head C01. The print head C01 performs a first pass image print scan in the main scanning direction to print an image in the first scanned image formation range A01. After the first scan is finished, the paper conveying apparatus conveys the print paper in the sub-scanning direction by 1/2 of the length of the print head C01, and the first scanned image forming range A01 moves to the position A01 '.

Subsequently, a second scan is performed. In the print head C01, data on the print scan of the second pass image is transmitted to the entire print head. The print head C01 again performs a print scan in the main scanning direction and prints data on the print scan of the second pass image in the second scan image formation range A02. After the second scan is finished, the paper conveying apparatus again conveys the printing paper in the sub-scanning direction by 1/2 of the length of the print head C01. In the third scan, data for the print scan of the first pass image is transmitted to the entire print head C01. After the third scan, data for the first pass image print scan and data for the second pass image print scan are alternately sent to the print head, and the same print scan as the second scan is repeatedly performed. For this reason, a printed image is formed.

Fig. 4 is a diagram showing a printing state on a sheet of paper of the first and second scanned image forming ranges A03. In this illustrated printing state, a second scan is performed and the print head is at about the middle of the sheet. The image formation completion range A07 is a range formed after completing two print scans. The image formation completion range A07 is a range obtained by superimposing the first scan image formation range A01 'and the second scan image formation range A04, that is, a range obtained after completing the printing of the two-pass image.

According to this embodiment, in the dot separation method error diffusion processing, dots are exclusively arranged in the low concentration portion of the path image. Since the dots are arranged exclusively, generation of small / mild portions of the dots can be prevented. When dot arrangement is performed by the conventional method, dots are randomly and sparsely arranged as shown in FIG. On the other hand, when dot arrangement is performed using the method according to the present embodiment, the arrangement of exclusive and balanced dots is made as shown in FIG.

This embodiment can be accomplished using a general purpose computer without using a dedicated architecture or a special processing device.

The method for causing the dot separation method error diffusion processing unit 209 to perform the three-value quantization method has been described. However, the dot separation method error diffusion processing unit 209 may perform a quantization method of two or more values.

As described previously, the dot forming process is not necessarily performed. When dot formation processing is performed, a different dot arrangement method may be used for each pass. For example, there is a method of arranging dots in a first pass using the dot arrangement shown in Fig. 11 and exclusively arranging dots in a second pass at a position different from those of the dots arranged in the first pass. . When printing data is generated by applying the method according to the present embodiment, it is possible to perform dot forming processing independently for each path, unlike the exclusive mask method. Accordingly, different dot arrangements can be performed for each pass, so that more flexible dot arrangements can be performed. By properly arranging the dots, the image quality can be improved.

In this embodiment, the processing is performed for each image. However, if the amount of data written to / read from the buffer needs to be reduced to reduce memory consumption or processing time, processing may be performed in raster image units.

An inkjet printer is used as an example of the image forming apparatus according to this embodiment. However, any device capable of forming an image by a plurality of print scans, for example, a laser printer, may be used.

According to this embodiment, density irregularity of an image formed by the multipass printing method can be suppressed.

Hereinafter, a second embodiment of the present invention will be described. In the first embodiment, the printing of the two-pass image has been described. However, the number of two or more pass images may be printed. As an example, a case of performing three-pass image printing will be described. In the path generation unit 208 shown in the first embodiment, a separate distribution parameter having a waveform that is in phase out of phase with the waveform of the distribution parameter for the path generation unit 208 is prepared by using two distribution parameters. The pixel value is divided into three parts. Fig. 17 shows an example of the data flow when creating a three-pass image at the time of path division. The path generation unit 208 inputs an input image 1801, a first pass distribution parameter 1802, and a third pass distribution parameter 1806. Based on the following equation, the distribution pixel value for each pixel of each pass image is calculated, and the 1st pass image 1807, the 2nd pass image 1808, and the 3rd pass image 1809 are created.

The input value of the selected pixel is called I (x, y), the first pass distribution parameter is called P1 (x, y), the third pass distribution parameter is called P3 (x, y), and the maximum parameter is It is called Pmax. The first pass distribution pixel value D1 (x, y), the second pass distribution pixel value D2 (x, y) and the third pass distribution pixel value D3 (x, y) are calculated as follows:

D1 (x, y) = I (x, y) ＊ P1 (x, y) / Pmax

D3 (x, y) = I (x, y) ＊ P3 (x, y) / Pmax

D2 (x, y) = I (x, y) -D1 (x, y) -D3 (x, y).

In the dot separation method error diffusion processing unit 209 shown in FIG. 5, an output value is determined from input values of three path images using a table in which the two-dimensional lookup table shown in FIG. 10 is expanded in three dimensions. After the dot separation method error diffusion processing, the processing of steps S203 to S205 is performed for each pass.

By processing as described above, printing of a three-pass image can be achieved. Therefore, not only two-pass images but also multi-pass printing of a plurality of pass images such as three-pass images or four-pass images may be performed.

That is, not only a few pass images but also a plurality of pass images may be printed.

Hereinafter, a third embodiment of the present invention will be described.

In the first embodiment, the same processing was performed for each color. However, it is also possible to perform different processing for each color. For example, when printing by C, M, Y, and white, the method according to the first embodiment is applied to printing in a relatively noticeable color such as C, M, and Y colors, and Y colors As described above, another conventional method may be applied to printing in a relatively inconspicuous color.

As described above, for example, when high-speed image processing is required, the method according to the first embodiment is applied to printing with visible colors, and printing with colors other than visible colors is conventional. Apply the method. On the other hand, when high quality printing is required, the method according to the first embodiment is applied to printing in all colors. Thus, embodiments of the present invention can be flexibly selected and performed.

Hereinafter, a fourth embodiment of the present invention will be described. The path generation unit 208 according to the first embodiment does not need to use distribution parameters, and may distribute pixel values by using a formula. For example, when path generation is performed in an environment in which it is difficult to secure a buffer of distribution parameters, it is preferable that the pixel values are distributed using a formula. For example, when a mathematical expression is used to print a two-pass image, the distribution ratio may be changed periodically using a trigonometric function as in the following equation.

These equations show the case of changing only in the carriage direction.

D1 (x, y) = I (x, y) ＊ P ＊ (1 + sia (2π x / T)) / 2

D2 (x, y) = I (x, y) -D1 (x, y)

In these formulas, I (x, y) denotes an input value of a selected pixel, P denotes an amplitude, T denotes a period, D1 denotes a first pass distribution pixel value, and D2 denotes a second pass distribution pixel value.

The spatial change may be generated in either the carriage direction or the paper feed direction, or in the inclination direction. Alternatively, the spatial change may be generated to be circularly symmetric as shown in FIG. 18. As a method of generating such a change, not only a method of generating a change periodically, but also a method of changing the period depending on the position, or a method of combining a plurality of periodic changes may be used.

Hereinafter, a fifth embodiment of the present invention will be described. In the first embodiment, the dot separation method error diffusion processing unit 209 shown in FIG. 5 is configured to input the input pixel values (first pass image and second pass image input) obtained before distributing each pixel value to a pass image. If the sum of values) is a low concentration value, a table employing an exclusive dot arrangement is used. However, the dot separation method error diffusion processing unit 209 may use a table that adopts exclusive arrangement of dots when the pixel value after distributing each pixel value in the path image is a low concentration value. In this case, the parameters of the table used in the dot separation method error diffusion processing unit 209 are changed (for example, as shown in FIG. 19), and are exclusively used for the area 2901 which independently performs the error diffusion processing on the path image. The area 2902 which performs the error diffusion process is changed.

Hereinafter, a sixth embodiment of the present invention will be described.

In the first embodiment, the dot separation method error diffusion processing unit 209 uses a table. However, in environments where it is difficult to obtain a table buffer, you may use a formula instead of a table. For example, Japanese Patent Laid-Open No. 2000-354172 discloses a method of comparing input values of cyan and magenta with each other and determining output values of cyan and magenta based on the comparison result. For example, by applying this method to the processing performed on the path image, the expression can be used to determine the output values. In the following equations and inequalities, P1 represents the input value of the first pass, P2 represents the input value of the second pass, T1, T2, S1, S2 represents the threshold, O1 represents the first pass output, and O2 represents the second pass output. . The following equations and inequalities are examples used to determine the output values according to the first embodiment to the last, where the equations and inequalities differ from the input values and output values of the following equations and inequality equations. It should be noticed that

When P1 + P2≤T1

(O1, O2) = (0,0).

When T1 <P1 + P2≤T2

If P2≤P1, (O1, O2) = (1,0),

If P2 ≦ P1, (O1, O2) = (0,1).

When T2 <P1 + P2

For each input P (= P1, P2),

If P≤S1, P = 0,

If S1 <P≤S2, then P = 1,

If S2 <P, then P = 2.

The following are exemplary formulas and inequalities that apply specific thresholds.

When P1 + P2≤124

(O1, O2) = (0,0).

When 124 <P1 + P2≤251,

If P2≤P1, (O1, O2) = (1,0),

If P2≤P1, (O1, O2) = (0,1),

When 251 <P1 + P2

For each input P (= P1, P2),

If P≤64, P = 0,

If 64 <P≤191, then P = 1,

If 191 <P, then P = 2.

The thresholds used for the inequality are examples in the present embodiment to the last. For example, thresholds different from the above-described thresholds may be used, and the thresholds may be changed during the error diffusion process.

Hereinafter, a seventh embodiment of the present invention will be described. In the fifth embodiment, the dot separation method error diffusion processing unit 209 shown in FIG. 5 uses a table. However, in environments where it is difficult to obtain a table buffer, you may use a formula instead of a table. For example, the following equation and inequality are used to determine the output value. In the following equations and inequalities, P1 represents an input value of the first pass, P2 represents an input value of the second pass, T1, T2, and S1 represents a threshold value, O1 represents a first pass output value, and O2 represents a second pass output value. The following equations and inequalities are examples used to determine the output values according to the first embodiment, and the equations and inequalities are changed when the possible input values and the possible output values are different from the input values and output values of the following equations and inequality equations. You should know that For each input P (= P1, P2), it is assumed that P ≦ T1.

When P1 + P2≤S1

(O1, O2) = (0,0).

When S1 <P1 + P2

If P2≤P1, (O1, O2) = (1,0),

If P2≤P1, (O1, O2) = (0,1),

If T1 <P≤T2, then P = 1,

If T2 <P, then P = 2.

The following are exemplary formulas and inequalities that apply specific thresholds. For each input P (= P1, P2), it is assumed that P≤192.

When P1 + P2≤124

(O1, O2) = (0,0).

When 124 <P1 + P2

If P2≤P1, (O1, O2) = (1,0),

If P2≤P1, (O1, O2) = (0,1),

If 192 <P≤255, P = 1,

If 255 <P ≦ 319, P = 2.

The thresholds used for the inequality are only examples in this embodiment. For example, of course, it is possible to employ modified thresholds of the above equation, and it is also possible to employ a method of varying the thresholds during the error diffusion process.

Hereinafter, an eighth embodiment of the present invention will be described. In the first embodiment, the dot separation error diffusion processing unit 209 in FIG. 5 performs the dot separation error diffusion processing. However, the dot separation method error diffusion processing unit 209 may perform a dot separation method error diffusion processing of another form different from that described in the first embodiment. For example, the dot separation system error diffusion processing unit 209 may use different error diffusion processing parameters for each pass. Examples of such error diffusion processing parameters include parameters for determining a threshold of quantization for error diffusion processing and parameters for changing the threshold.

For example, an error diffusion method using different error diffusion thresholds for each pass will be described. A high threshold T == 170 is used for the first pass and a low threshold T == 85 for the second pass. Using these thresholds, error diffusion processing is performed. In the low concentration portion, the threshold value is replaced for each error diffusion process in the predetermined region.

When print data is generated using the method according to the present embodiment, quantization processing is performed on these path images after generating the path images. Accordingly, in the quantization process, different parameters can be used for each pass image, and more flexible parameters can be set as compared with the conventional method. In other words, a more optimal quantization parameter can be applied, which makes it possible to improve the print quality. In the case where the same parameter is used for each pass in the quantization process and an input having similar variation for the pass is provided, a similar dot pattern in the pass is generated as a result of quantization. Dot patterns generated in the path easily interfere with each other. This causes the deterioration of image quality. By using different parameters for each pass in the quantization process, different quantization results can be obtained in that pass even when an input with similar variation for the pass is provided. This can prevent the interference of the dot pattern generated in the path and the image quality is improved.

The present invention provides a computer-readable storage medium storing program codes of software for realizing the functions of the above-described embodiments, to a system or an apparatus, and the computer (or CPU or MBP) of the system or apparatus is programmed from the storage medium. It may be achieved to read and execute the code. In this case, the program code itself read out from the storage medium realizes the functions of the above-described embodiments. That is, the present invention includes a storage medium storing the program code.

As a storage medium for supplying the program code, for example, a flexible disk, hard disk, optical disk, magneto-optical disk, CD-ROM, CD-R, magnetic tape, nonvolatile memory card, ROM, or DVD is used. You may also

By the computer executing the read program code, the functions of the above-described embodiments are realized. In addition, OS (Operation System) running on a computer under the instruction of the program code may perform part or all of the actual processing to realize the functions of the above-described embodiments.

The program code read from the storage medium may also be recorded in a memory provided in a function expansion board inserted into a computer or a function expansion unit connected to a computer. Subsequently, under the instruction of the program code, a CPU or the like provided in the function expansion board or the function expansion unit may perform part or all of the actual processing to realize the functions of the above-described embodiments.

Although the invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the exemplary embodiments disclosed above. The following claims are to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.

1 is a block diagram showing a configuration example of a print system according to a first embodiment of the present invention.

2 is a diagram showing a process according to the first embodiment.

3 is a diagram schematically showing a state in which a second scan is performed using a multipass printing method.

4 is a diagram showing a printing state of the first and second scanned image forming ranges A03 on the print medium.

FIG. 5 is a diagram for explaining processing units provided in the host computer and the printer. FIG.

6 is a diagram for explaining path generation processing.

7 is a diagram for explaining the path generation processing in detail.

8 is a diagram for specifically describing path generation processing.

9 is a diagram illustrating the dot separation system error diffusion processing in detail.

10 is a view showing a lookup table used in the dot separation method error diffusion processing.

11 is a table illustrating a relationship between quantization level and dot arrangement used to determine the arrangement of dots.

FIG. 12 is a diagram showing a state in which the same amount of ink is discharged in the same direction by using the multi-pass printing method.

Fig. 13 shows a plurality of (3) main scans performed by the print head, and the printing of the print scanning unit area including four pixels (half of the length in the longitudinal direction in which eight pixels are arranged) is performed two print scans (2 Is a diagram showing a processing performed by two passes).

FIG. 14 is a diagram showing a process of completing printing of the same area by using a zigzag pattern and an opposite zigzag pattern.

FIG. 15 is a diagram illustrating an example of dot arrangement of low concentration portions obtained after independently performing error diffusion processing on two path images. FIG.

FIG. 16 is a diagram showing an example of dot arrangement of low concentration portions obtained after performing dot separation error diffusion processing on two path images. FIG.

17 is a diagram showing an example process of creating three path images using distribution parameters.

18 is a diagram illustrating an example of a distribution parameter of circular symmetry.

FIG. 19 is a diagram illustrating an exemplary lookup table used to determine whether a pixel value obtained after distribution of each pixel value to a path is a low concentration value.

Claims (15)

An image processing apparatus for generating print data for use in an image forming apparatus that performs image formation by performing a plurality of print scans on the same image region on a print medium, A divider for dividing image data into pieces of print scan image data for the plurality of print scans; A quantization unit for quantizing fragments of the print scan image data; A generation unit for generating pieces of print data for the plurality of print scans based on the pieces of the quantized print scan image data, And the quantization unit quantizes pieces of the print scan image data so as to be mutually exclusive in the plurality of print scans when the density represented by the pieces of print scan image data is less than a threshold. The method of claim 1, And the quantization unit quantizes the pieces of the print scan image data so as to be independent of the plurality of print scans when the density represented by the pieces of the print scan image data is greater than or equal to a threshold. The method of claim 1, The quantization unit performs quantization by performing error diffusion processing. The method of claim 3, wherein And the quantization unit performs quantization by performing dot separation scheme error diffusion processing. The method of claim 1, And the quantization unit quantizes a part of color components of the image data. The method of claim 1, The quantization unit performs quantization on all of the color components of the image data. An image processing method for generating print data for use in an image forming apparatus that performs image formation by performing a plurality of print scans on the same image area on a print medium, Dividing image data into pieces of print scan image data for the plurality of print scans; Quantizing the fragments of the print scan image data; Generating fragments of print data for the plurality of print scans based on the quantized fragments of the print scan image data, And when the density represented by the pieces of the print scan image data is less than a threshold, the pieces of the print scan image data are quantized to be mutually exclusive in the plurality of print scans. The method of claim 7, wherein And when the density represented by the pieces of print scan image data is equal to or greater than a threshold, the pieces of print scan image data are quantized to be independent of each other in the plurality of print scans. The method of claim 7, wherein And quantization by performing error diffusion processing. The method of claim 9, An image processing method characterized in that quantization is performed by performing a dot separation method error diffusion processing. The method of claim 7, wherein And quantizing a part of color components of the image data. The method of claim 7, wherein And quantization of all of the color components of the image data. A computer-readable storage medium having computer-executable instructions for controlling an image processing apparatus for generating print data for use in an image forming apparatus that performs a plurality of print scans on the same image area on a print medium to form an image, Computer executable instructions for dividing the image data into pieces of print scan image data for a plurality of print scans; Computer executable instructions for quantizing fragments of the print scanned image data; Has computer executable instructions for generating pieces of print data for the plurality of print scans based on the quantized pieces of print scan image data, And when the density represented by the pieces of print scan image data is less than a threshold, the pieces of print scan image data are quantized to be mutually exclusive in the plurality of print scans. The method according to claim 1 or 2, And said threshold value is varied. 9. The method according to claim 7 or 8, And the threshold is varied.

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