KR101022777B1 - Image processing apparatus and image processing method - Google Patents

Abstract

An image processing apparatus for generating recording data used in an image forming apparatus for performing image formation by performing multiple recording scans for the same image area on a recording medium is divided into input image data into image data for each recording scan. On the basis of the allotment, the quantization unit for quantizing the image data for each of the recording scans based on the divided image data for each of the recording scans, and the image data for each of the quantized recording scans, A generation unit for generating record data, wherein the division unit divides the input image data into image data for each of the recording scans based on a division ratio that periodically varies in accordance with a spatial position of the image represented by the input image data. do.

Image processing apparatus, quantization, division, recording scanning, image data.

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 has been proposed as an example of an image forming apparatus which performs image formation by performing multiple recording scans of the same image area on a recording medium.

In an inkjet printer, an image is printed by ejecting ink droplets from the recording head and landing on the recording medium while the recording head is reciprocated in the main scanning direction and the recording medium is conveyed in the sub-scanning direction. In inkjet printers, variations occur in the direction and size of ink droplets, the impact position, and the like, depending on physical factors such as the characteristics of each nozzle, an error in the amount of paper conveyance, and a deviation in the recording head distance when printing an image. In the printing operation by one recording scan, this fluctuation becomes density unevenness and streaks on the printed image as it is, and causes a deterioration in image quality.

Thereby, a multi-pass recording method has been proposed as a countermeasure for suppressing the occurrence of such density spots and streaks. According to this technique, by combining the image processing and the printing control, it is possible to form the image at high speed while suppressing the deterioration of the image quality due to the density spots and streaks.

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

In Fig. 12, the recording head 5101 is composed of eight nozzles 5102 to simplify the description. Ink droplets 5103 are discharged from the nozzles 5102. Usually, when the main scan recording area in a given recording medium is completed in one recording scan, it is ideal that ink is ejected in a uniform direction with a uniform ejection amount as shown in FIG.

However, as described above, due to physical factors at the time of printing, variations in the direction and size of the ink droplets ejected from the respective nozzles occur. For this reason, a background part exists periodically with respect to the head main scanning direction, and the excessive dot overlaps with each other. In this state, the gathered dots are detected as density spots with respect to the arrangement direction of the nozzles. In addition, when a deviation occurs between recording scans, a portion following the recording scan is detected as a stripe.

In the above, in the multipath recording method, as shown in FIG. 13, the recording head 5201 performs a recording scan several times (in this example, three times). In this figure, the recording area is completed by performing two recording scans in units of four pixels, which are half of the eight pixels in the longitudinal direction. In this case, the eight nozzles 5202 in the recording head 5201 are divided into groups of four nozzles (upper nozzle group) and four nozzles (lower nozzle group) on the upper side. The dot in which one nozzle is recorded by one recording scan is obtained by sorting about half of the image data according to a certain predetermined image data arrangement. At the time of the second scan, dots corresponding to about half of the rest of the image data are embedded in the previously formed image, and the recording of the four pixel unit area is completed.

In the two-pass recording system, the first write scan and the second write scan complement each other according to a predetermined arrangement. As the image data array (selection mask pattern) used in this operation, in the usual case, the above-described arrangement in which a houndstooth check pattern is formed for each pixel in the longitudinal and horizontal directions as shown in Fig. 14 is used. Therefore, the unit recording area (four pixel units in this example) is completed by the first write scan for printing the Houndstooth check and the second write scan for printing the opposite Houndstooth check. The upper, middle, and lower ends of FIG. 14 show states of gradually completing recording in the same area using the Houndstooth check pattern and the Houndtooth check pattern. That is, first, as shown in the upper part of FIG. 14, in the first recording scan, the houndstooth check pattern (black circle) is recorded in a predetermined area of the recording medium using the following four nozzles. Next, as shown in the interruption of FIG. 14, in the second recording scan in the relevant area, paper feeding is performed for 4 pixels, and recording of the opposite Houndstooth check pattern (white circle) is performed using all eight nozzles. Do it. In addition, as shown in the lower part of FIG. 14, in the third recording scan in the relevant area, four pixels of paper are sent again, and the Houndstooth check pattern is recorded using the above four nozzles.

Even when the multi-head with the fluctuation shown in FIG. 13 is used, when the multipath recording method is executed, the influence on the recording medium due to the fluctuation can be suppressed in half. In addition, when a deviation occurs between recording scans, the influence can be suppressed in half. For this reason, density | concentration spots are suppressed in the formed image. Here, the example which completed printing by performing two recording scans was demonstrated. In general, by increasing the number of recording scans, it is possible to suppress the influence of the fluctuation and the deviation. As a result, density spots can be suppressed in proportion to the number of recording scans. On the other hand, the printing time increases with the number of recording scans.

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

BACKGROUND ART There is known a technique of selecting from a print data and recording data corresponding to each recording scan by sorting with a regularity pattern having no regularity using random numbers or the like. For example, in the case where recording is performed by two recording scans, in the first recording scan, screening is performed in a random pattern using a random number, and in the second recording scan, the screening pattern is not regular. Sorting is performed with the inverted sorting pattern of to create record data. For this reason, there is no regularity in dot structure compared with the conventional recording by two recording scans, and image quality is improved. However, as described above, a variation occurs between the ink droplets and the recording scan. Since a complementary relationship is established by using a mask pattern between each recording scan to establish a complementary relationship, when a change in ink droplets and a deviation between recording scans occur, overlapping dots and periodic white background portions are formed, which are detected as density spots. Easy to be In particular, when the dot pattern interferes due to the deviation between recording scans, density spots and streaks appear as inappropriate patterns in the entire scan.

Therefore, for any dot pattern created from the print data of each recording scan, it is necessary to prevent the interference when a deviation occurs between the recording scans. However, it is difficult to obtain a mask pattern that prevents interference of dot patterns for any input image.

In view of the above, in order to solve the above problem, in the step of multi-value image data, a method of dividing each pixel value of the image data by a constant ratio or a method of dividing the pixel value by changing the ratio at random By this, a technique for distributing every recording scan is known. Furthermore, quantization is performed on multivalued data distributed respectively, and an image corresponding to recording scan with limited complementary relationship is generated. By these processes, the dependence of the change of the image density on the variation of ink droplets and the deviation between paths is reduced, and the image quality is improved.

However, when an image corresponding to each recording scan was generated by the above method, the arrangement of dots was unbalanced between the paths as shown in Fig. 15, and the dots sometimes overlapped. For this reason, streaks and unevenness may be detected in a printed image by dot arrangement between recording scans. In the case of distributing pixel values of multi-valued image data at a constant ratio, the dot pattern of each pass image interferes between recording scans depending on the arrangement of the resulting dots, and is easily detected as streaks and spots in the print image. On the other hand, when pixel values are distributed at random ratios, when variations occur between paths at the time of printing, concentration changes occur locally and are easily detected as unevenness. In order to further improve the image quality, there is a need for a method of suppressing the interference of the dot pattern and the change in density when a change in ink droplets, in particular, a deviation between passes occurs.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and the present invention provides an image processing apparatus and an image processing method for suppressing density unevenness of an image formed by a multipath recording method.

This invention has the following structures.

In one embodiment of the present invention, there is provided an image processing apparatus for generating recording data used in an image forming apparatus for performing image formation by performing a plurality of recording scans for the same image region on a recording medium. A division unit for dividing the input image data into image data for each of the recording scans according to a distribution ratio for dividing the image data for each recording scan to form image data, and based on the divided image data for each of the recording scans. And a quantization unit for quantizing the image data for each of the recording scans, and a generation unit for generating the recording data for each of the recording scans based on the quantized image data for each of the recording scans, wherein the distribution ratio is the image. It fluctuates periodically depending on the spatial position of the pixel value of the data.

Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings.

EMBODIMENT OF THE INVENTION Below, with reference to attached drawing, embodiment of this invention is described in detail. At this time, the configuration according to the embodiments described below is exemplified to the last, and the present invention is not limited to the configuration having the example.

In this embodiment, an example in which an inkjet printer is applied as a printer will be described. In addition, the case where printing by two recording scans is performed as a multipath system is demonstrated as an example.

1 is a block diagram showing a configuration example of a print system according to the first exemplary embodiment of the present invention. 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. The RAM 108 also provides a work area in which the CPU 105 temporarily stores various data during the control operation. The ROM 115 stores the boot program and various data nonvolatile. The host computer 101 also includes an input port 106, 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, the printer 102 is also connected to the output port 107. The printer 102 also has an input port 110 such as USB or LAN for receiving print data and control information, a control device 111 for performing internal control of the printer, print data and internal setting values. Memory 112 is provided. The printer 102 also includes a paper conveying apparatus 113 and a recording head 114 having a nozzle for ejecting ink onto the recording medium.

2 is a diagram showing a process according to the present embodiment. At this time, steps S21 to S25 represent processing in the host computer 101. In addition, steps S26 and S27 represent processing in the printer 102. At this time, the present embodiment is not limited to the above, and steps S21 to S27 also indicate processing in the printer 102. 5 is a figure explaining each processing part in the host computer 101 and the printer 102. As shown in FIG. In FIG. 5, the host computer 101 includes a color correction and color conversion unit 201 that performs color correction and color conversion on the input image, and a path generation unit 208 that generates a path image. The host computer also includes a dot separation method error diffusion processing unit 209 for quantizing each path and a print data conversion unit 203 for converting print data. Therefore, the printer 102 is provided with a dot forming unit 204 for performing dot forming so that each quantized path image corresponds to the dot, and a printing unit 205 for printing on a recording medium.

Hereinafter, the flow of a process according to the present embodiment will be described with reference to FIG. 2. First, an image to be printed on the host computer 101 is input using the input device 103 or the like (S21). Next, the input color or gray scale image is transmitted to the color correction and color conversion unit 201 of FIG. The color correction and 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 (S22). In general, each color component is processed separately, so that one color will be described.

The path generation unit 208 of FIG. 5 performs path generation on the image converted into the CMV component (S23). Here, path generation means generation of image data for each recording scan in the multipath system. Fig. 6 shows an input image 601 for generating paths, a distribution parameter 602 for determining the distribution ratio of pixel values to each path, a multiplier 603 and an adder 604. In addition, as the output, a first pass image 605 and a second pass image 606 exist. Path generation according to the present embodiment uses external parameters such as a distribution parameter 602 that determines a distribution ratio for distributing pixel values to each path. 7 is a flowchart explaining the path generation process in step S23 of FIG. Hereinafter, the path generation of FIG. 7 will be described in detail with reference to FIG. 6.

First, as an initial process, the pixel of the position (0,0) of the input image 601 is selected (S71). Next, among the pixels on the distribution parameter 602, a parameter (concentration value) at the same position as the selected pixel is obtained (S72). At this time, when the size of the distribution parameter 602 is smaller than the size of the input image 601, it is regarded as being arranged in a tile shape, and the distribution parameter is repeatedly used in the insufficient direction. Therefore, (x, y) is 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 the acquired parameter V (x, y) can be obtained as follows.

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

In this expression,

As shown in the following formula, when the parameter is acquired, the pixel value (input value) I (x, y) of the selected pixel is multiplied by the ratio of the maximum parameter Pmax of the parameter V (x, y) obtained in step S72. The first pass distribution pixel value D1 (x, y) distributed to the first pass image is calculated (S73, multiplier 603).

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

The calculated first pass distribution pixel value is stored in the first pass image buffer of the RAM of FIG. 1. Further, a second pass distribution pixel value D2 distributed in the second pass image is calculated (S74, adder 604). As shown in the following equation, the first pass distribution pixel value is subtracted from the input value of the selected pixel, and the calculated second pass distribution pixel value D2 is the second pass image buffer of the RAM 108 of FIG. Is remembered.

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

Based on the condition of step S75, the selected pixel is advanced (S76), and the pixels are repeated S72 to S74 for the entire pixel to obtain the first pass image 605 and the second pass image 606. .

This process will now be described using specific numerical values. FIG. 8 shows the process of FIG. 6 using specific numerical values. 8 shows an example of 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. As an example, setting the pixel 807 as the selected pixel will be described. First, from the positional relationship, for the pixel 807, the parameter 808 of the distribution parameter 802 is used. Since the maximum value of the parameter is 255, the first pass distribution pixel value of the pixel 807 is D1 = 33 and the fraction is omitted based on I = 85, P = 100, and Pmax = 255. At this time, the fraction is omitted, but a fraction greater than 1/2 may be counted as 1, the rest may be discarded, or the fraction may be counted as 1. The calculated first pass distribution pixel value D1 corresponds to the pixel 809 of the first pass image 805. The second pass distribution pixel value of the pixel 807 is D2 810 = 52 obtained by subtracting D1 from the concentration of the pixel 807. All pixels included in the input image 801 are similarly processed to generate a first pass image and a second pass image, respectively. Further, with respect to the input image 801, the fifth column (part of the column 811 of the input image 801, the column of the coordinates 4 and y) not covered by the size of the distribution parameter 802 is arranged in a tile shape. , Is considered to be used repeatedly in a shortage direction, where V (4, y) = P (4 mod 4, y mod 4) = P (0, y) is established and the first column is used (where 0 ≦ y ≦ 4 is established). That is, column 812 of the parameter 802 is used.

At this time, the distribution parameter is set to distribute the pixel values, and spatial and periodic variations in the feeding direction and the carriage direction are added. As a method for such fluctuation, a fluctuation in either the feeding direction or the carriage direction may be used, or a fluctuation in the feeding direction and the carriage direction or a change in two or more directions may be used.

By distributing pixel values of the input image while adding spatial and periodic variations, periodic variations are revealed depending on the spatial position throughout the path. For this reason, with respect to the input to the dot separation system error diffusion processing unit 209 of FIG. 5 performed in a later process, the input values vary from one path to another (between recording scans). When images of the same input value are input between passes, the dot patterns obtained through error diffusion processing, print thermal data conversion, and dot formation may be similar to each other between the passes. If the dot patterns are similar to each other between the paths, the dot patterns may interfere with each other between the paths. As described above, when the input values are changed from each other between the paths, the dot patterns between the paths are not similar to each other, so that a similar dot pattern is generated between the paths, thereby suppressing interference of the dot patterns between the paths. In addition, there is an effect of suppressing a change in concentration caused when a deviation between paths occurs. Due to these synergistic effects, even when a variation in ink droplets during image formation occurs, in particular, a shift between paths occurs, interference of dot patterns is suppressed and image quality is less likely to deteriorate.

Each path image obtained by the path generation unit 208 in FIG. 5 is transmitted to the dot separation system error diffusion processing unit 209 corresponding to the quantization unit. At this time, the dot separation method error diffusion processing unit 209 described below is the same as the dot separation method error diffusion processing in step S24 of FIG. 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) which performs a process of preventing cyan and magenta dots from overlapping each other (for example, Japan Korean Patent Application Laid-Open No. 2003-116015). In the error diffusion processing method (dot separation method error diffusion) according to Japanese Patent Laid-Open No. 2003-116015, processing is performed so that dots between colors (magenta and cyan) do not overlap. In the present embodiment, the error diffusion processing method (dot separation method error diffusion) is applied not to color but to paths (between recording scans). In the present embodiment, the error diffusion processing method (dot separation method error diffusion) is not used between colors with different components, but the pixel values of the same component are distributed by the pass generation process, and the error is among the divided pixel values. It is characterized by the use of a diffusion treatment method.

For this reason, in the dot separation method error diffusion section 209, the image portions corresponding to low concentrations perform an error diffusion process so that the dots are mutually exclusive, thereby generating a quantized path image. In this process, dots are exclusively arranged between paths in the image portion corresponding to the low concentration. At this time, the pixel value used according to the present embodiment is a density value.

FIG. 14 is an example of the result of dot arrangement of the image for two passes by the dot separation method error diffusion unit 209 by the error diffusion processing of the dot separation method. In this embodiment, two path images are generated from the input image, but dot patterns equivalent to those obtained when the single image is error-diffused can be formed. Furthermore, each dot is appropriately classified into each path, and the phenomenon that the degree of density of dots is sparse between the paths is suppressed. Thus, even when ink droplets are enlarged or deviations between paths occur during printing, the above state is difficult to be detected as density spots. Such a method of decomposing a dot into a path is very difficult to realize in the case of using a method of decomposing a path into a fixed path by a pixel position as in the prior art, or performing quantization independently between paths.

FIG. 9 is a flowchart for explaining in detail the dot separation method error diffusion processing performed in step S24 of FIG. 2. 10 is 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 regions of the lookup table, the value in parentheses is the output. At this time, the input value and the level of quantization are not limited to the above examples, and other input values or quantization levels may be used.

First, the pixel at the position (0, 0) is selected in each of the two path images (S91). Then, a pixel value (hereinafter referred to as an input value) of the selected pixel of each path image is obtained (S92). From the two input values obtained above, an output value is determined using the lookup table shown in FIG. 10 (S93). 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. The error generated on the basis of the determination of the output value on each path image and the error are propagated to the peripheral pixels as in the conventional error diffusion (S94). This process is repeated for all the pixels (S95 and S96).

In the lookup table of FIG. 10, there is an area 1001 (high concentration area) independently quantized between paths and an area 1002 (low concentration area) exclusively quantized between paths. As can be seen from this table, the output value is determined without being influenced by the input value between the paths in the area 1001 to be independently quantized, but the output value is changed according to the input value in the area 1002 which is exclusively quantized between the paths. In the area (region 1001) corresponding to the low concentration in this manner, the plurality of path images are processed as if a plurality of path images are regarded as one image, and dots are mutually exclusive to generate a path image. As a result, in the low concentration region, the dots are mutually exclusive, so that an image with reduced density unevenness can be formed. In addition, the propagated error fluctuates, and quantized regions are alternately used independently of quantized regions exclusively between passes. For this reason, deterioration of image quality does not occur at the boundary between these two areas. At this time, in order to further improve image quality, noise or the like may be added to vary the threshold used for performing quantization.

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

Thereafter, the converted print data is transmitted to the inkjet printer 102 connected to the host computer 101. In the inkjet printer 102, when print data is received, the print data is stored in a print buffer in the memory 112.

The dot forming unit 204 converts the image data stored in the print buffer into two-value data between ON and OFF indicating whether or not the dot is ejected (S26). By allocating an area of 2x2 to one pixel of the print image data received by the printer 102, that is, one pixel of the image before dot formation, the quantization level is also maintained in the data after dot formation. 11 shows an example of dot formation indicating what kind of dot arrangement converts each quantization level, and the arrangement of the dots is determined based on this correspondence relationship. In this case, when it is not necessary to convert the image data to ON or OFF in the above cases, for example, the image data is converted into binary data in the quantization process, or the diameters of the dots to be discharged are at least two forms. In the case where it can be changed to, the dot forming process need not be performed.

After determining the dot arrangement, print data is sent to the printing unit 205, and actual printing is started (S27). Fig. 3 is a schematic diagram of a printing mechanism based on the multipath system showing a state in which a second scan is being performed. 3 shows a portion printed on the printing sheet P01 using the recording head C01. The recording head C01 discharges ink while reciprocating in the main scanning direction to form an image on the recording medium P01. In the sub-scan direction side of the recording head, the recording head front part is called the recording head front part C02, and the rear part of the recording head C01 opposite to the recording head front part C02 is called the recording head rear part C03.

First, a first scan is performed. In this embodiment, two-pass printing is performed. Therefore, the first scan prints only for half of the recording head length, and after the second scan, prints for the recording head length. In the recording head, data corresponding to the recording scan of the first pass image is transmitted to the rear portion C03 of 1/2 of the length of the recording head C01. The recording head C01 performs recording scan in the main scanning direction and prints the image in the first scanned image forming range A01. After the first scan is finished, the paper conveying apparatus conveys the printing paper in the sub-scanning direction by 1/2 of the length of the recording head C01, and the first scanned image forming range A01 is moved to A01 '.

Thereafter, a second scan is performed. In the recording head C01, data corresponding to the recording scan of the second pass image is transmitted to the entire recording head. The recording head C01 performs recording scanning in the main scanning direction again, and prints data corresponding to the recording scanning 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 recording head C01. Subsequently, in the third scan, data corresponding to the recording scan of the first pass image is transmitted to the entire recording head. After the third scan, the data corresponding to the recording scan transmitted to the recording head is switched between the first pass image and the second pass image, and repeats the same recording scan as the second scan to form a printed image. do.

4 shows the state on the paper of the first and second scanned image forming ranges A03. 4 shows a state at the time of the second scan showing the printing state of the paper while the recording head is in the middle of the paper. The part which completed two recording scans corresponds to the image formation completion range. 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 in which two passes of printing have been completed.

According to the present embodiment, when generating a pass image, the distribution ratio of pixel values of the input image is periodically varied and distributed according to the spatial position. By distributing pixel values of the input image while adding spatially periodic fluctuations, periodic fluctuations are revealed according to spatial positions throughout the path. This configuration adds variation to the input to the dot separation method error diffusion processing unit 209 and suppresses interference of dots between paths generated when a similar dot pattern occurs. In addition, even in the case where the deviation between paths occurs during printing, the effect of less density change is provided. Due to these synergistic effects, the image is less likely to deteriorate with the variation of the ink droplets during image formation.

In addition, this embodiment can be implemented using a general-purpose computer widely used. Therefore, there is no need to prepare a dedicated architecture or a special processing device, and it provides an important feature of easily realizing the present embodiment using a general purpose device.

At this time, the dot separation method error diffusion processing unit 209 according to the present embodiment uses a three-value quantization method, but this method is not limited thereto. A two-value quantization method may be used, and of course, a higher value quantization method can be used.

In addition, it is not necessary to use the dot separation system error diffusion processing of this embodiment. By distributing the spatially periodic pixel values, also in the quantization processing by the dither matrix method, the same effect as the error diffusion processing unit 209 of the dot dispersion method can be obtained. For example, in the present embodiment, when the dither matrix method is used, each path is independently quantized using a multivalue dither that outputs three values.

As described previously, the dot forming process is not necessarily performed, but when the dot forming process is performed, a different dot arrangement method may be used for each pass. For example, a method of performing the above processing in which the arrangement shown in FIG. 11 is performed for the first pass may be used, and dots are placed in the second pass at positions exclusive of the arrangement shown in FIG. 11. . When printing data is generated by applying the embodiment of the present invention, it is possible to perform dot forming processing independently for each path, unlike the exclusive mask method. For this reason, it is possible to use different dot arrangements between paths in the dot formation process, and more flexible dot arrangements can be performed. By inventing the arrangement of the dots, the print quality can be improved.

In this embodiment, each process is performed for each image, but the configuration is not limited to the above. If it is desired to reduce the number of reads from the buffer and writes to the buffer so that the consumption and processing time of the memory can be suppressed, the processing may be performed in raster units.

An ink jet printer functioning as an image forming apparatus according to the present embodiment is shown as an example, and of course, this embodiment can be applied to an apparatus for forming an image by performing a recording scan in a plurality of times, such as a laser printer.

As described above, according to the present embodiment, the density unevenness of the image formed by the multipath recording method can be suppressed.

In the first exemplary embodiment of the present invention, an example of using two passes has been described, but any number of two or more passes may be used. As an example, a case of performing three-pass printing will be described. In the path generation unit 208 according to the first exemplary embodiment of the present invention, in addition to the distribution parameter, another distribution parameter whose phase of the waveform is shifted is prepared, and the pixel value is determined by the two distribution parameters. Divide into three Fig. 17 shows an example of the data flow when creating a three-pass image at the time of path decomposition. The input image 1801, the first pass distribution parameter 1802, and the third pass distribution parameter 1806 are respectively input, and the distribution pixel value of the path image is calculated based on the following equation, and the first pass image is obtained. (1807), a second pass image 1808 and a third 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 Assuming 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 addition, the dot separation method error diffusion processing unit 209 of FIG. 5 uses the two-dimensional lookup table shown in FIG. 10 expanded in three dimensions to determine the output value from the input values obtained in three pass images. Search for. After the dot separation method error diffusion processing, the processing of steps S203 to S205 is performed for each pass.

By carrying out the processing as described above, the present embodiment can also be applied in the case of three passes. Thus, this embodiment can be applied not only to 2-pass printing but also to multi-pass printing having an increased number of passes such as 3-pass printing and 4-pass printing.

That is, this embodiment can be applied to printing with a low number of passes, as well as printing with a high number of passes.

In the first embodiment of the present invention, examples of independently performing the same processing for each color have been described. At this time, it is also possible to perform different processing for each color. For example, in the printing by C, M, M, and white, the first exemplary embodiment is applied to a color that is relatively noticeable, such as CMB, and to a color that is relatively inconspicuous, such as Y. The conventional method can be applied. In this way, for example, when high-speed image processing is required, as described above, the first exemplary embodiment is applied to the relatively noticeable color, and the conventional method is applied to the other colors. On the other hand, when high quality printing is required, the first exemplary embodiment is applied to all colors. In this way, the above process can be flexibly selected and performed.

The path generation unit 208 according to the first exemplary embodiment of the present invention does not need to use a distribution parameter, and the pixel value may be distributed using a formula. For example, when distributing in an environment where it is difficult to secure a buffer of distribution parameters, the realization may be more appropriate by using a formula. As an example, when using a mathematical expression for 2-pass printing, a distribution ratio may be changed periodically using a trigonometric function as shown in the following formula.

This expression represents the case where the fluctuations only in the carriage direction. I (x, y) is the input value of the selected pixel, P is the amplitude, and T is the period, and the first pass distribution pixel value D1 and the second pass distribution pixel value D2 are calculated as follows.

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

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

Further, as the direction of the spatial variation, the spatial variation is generated in one of the carriage direction and the paper feeding direction or in the diagonal direction, or is generated in a circular symmetry method, for example, as shown in FIG. The method of expressing the spatial variation is based not only on the method of simply expressing the variation through a certain period, but also the method of changing the period according to the position, or the method of combining a plurality of periodical variations.

In the first exemplary embodiment of the present invention, the dot separation scheme error diffusion processing unit 209 of FIG. 5 has a low concentration of an input pixel value (sum of input values of the first pass and the second pass) before being distributed to the path. If it is a value, the dot placement uses an exclusive table. However, when the pixel value after the input density is distributed in the path is a low concentration value, a table in which dot arrangements are exclusive may be used. In this embodiment, the parameter used in the dot separation method error diffusion processing unit 209 is changed (e.g., as shown in FIG. 19) to perform the error diffusion processing exclusively with the area 2901 which performs the error diffusion processing independently. It can be realized by changing the area 2902.

According to the first exemplary embodiment of the present invention, in the dot separation type error diffusion processing unit 209, a method of using a table has been described. For example, in some circumstances it may be difficult to maintain a table buffer, but in some cases a method other than using the table may be necessary. In this case, this embodiment may be realized through a formula. For example, in the prior art (for example, Japanese Patent Laid-Open No. 2000-354172), the output values of cyan and magenta are determined by comparing input values between cyan and magenta. This application is applied between paths, and this embodiment may be realized by using a formula. For example, P1 may be an input value of the first pass and P2 may be an input value of the second pass, and the output may be determined by the following equation. T1, T2, S1, and S2 represent thresholds, O1 represents a first pass output, and O2 represents a second pass output. At this time, the following formula is an example which performs the output corresponding to the 1st Example of this invention to the last. In the case where the possible values of the input value and the output value are different, it is natural to change the following equation accordingly.

When P1 + P2≤T1

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

When T1 <P1 + P2≤T2

If P2≤P1, (O1, O2) = (1,0),

Otherwise, (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.

As an example of applying a specific threshold value to the above equation, the following calculation may be performed.

When P1 + P2≤124

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

When 124 <P1 + P2≤251,

If P2≤P1, (O1, O2) = (1,0),

Otherwise, (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.

Each threshold used in the above formula is an example 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.

In the first exemplary embodiment, the case where the table buffer is used in the dot separation scheme error diffusion processing unit 209 of FIG. 5 will be described. However, in some circumstances, when it is difficult to hold using a table buffer, a method other than the method of using the table may be necessary in some cases. In this case, this embodiment may be realized using a formula. For example, P1 may be referred to as an input value of the first pass and P2 may be referred to as an input value of the second pass, and its output may be determined by the following equation. T1, T2, and S1 are thresholds, O1 is the output of the first pass, and O2 is the output of the second pass. At this time, the following equation is only an example of outputting corresponding to the first exemplary embodiment of the present invention. In the case where the possible input value and the possible output value are different from each other, of course, the above equation is changed accordingly.

For the input P (= P1, P2), the following equation is used.

If P≤T1,

When P1 + P2≤S1

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

When S1 <P1 + P2

If P2≤P1, (O1, O2) = (1,0),

Otherwise, (O1, O2) = (0,1).

If T1 <P≤T2, then P = 1,

If T2 <P, then P = 2.

An example in which a specific threshold value is applied to the above equation may be shown as follows. Regarding the input P (= P1, P2), the following equation is used.

If P≤192,

When P1 + P2≤124

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

When 124 <P1 + P2

If P2≤P1, (O1, O2) = (1,0),

Otherwise, (O1, O2) = (0,1).

If 192 <P≤255, P = 1,

If 255 <P ≦ 319, P = 2.

Each threshold value used in the said formula is an example in the present Example to the last. For example, it is of course 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.

In the dot separation type error diffusion processing unit 209 of FIG. 5 according to the first exemplary embodiment of the present invention, this embodiment is not necessarily limited to the case where this error diffusion method is used. For example, the present embodiment may be realized by using different parameters between paths used for error diffusion, such as a parameter for determining the threshold of quantization used in the error diffusion, a parameter for changing the threshold, and the like.

For example, a method of realizing the present embodiment using different error diffusion thresholds will be described. A high threshold T == 170 is used for the first pass and a low threshold T == 85 for the second pass. In normal cases, these thresholds are used to perform error diffusion without change. In the low concentration part, error diffusion is performed while replacing a threshold value for every error diffusion of a predetermined region.

When printing data is generated by applying the present embodiment, a quantization process is performed after generating a path. Therefore, at the time of the quantization process, different parameters can be used between passes, and more flexible parameter settings can be made as compared with the conventional method. That is, more optimal quantization parameters can be applied, and print quality can be improved. In the case of using the same parameters between passes, assigning inputs having similar variations between passes yields similar quantization results for dot patterns between passes. At this time, the dot patterns easily interfere with each other between the paths, which is a cause of deterioration of image quality. In view of the above, when using different parameters between passes at the time of quantization, quantization results with relatively different dot patterns can be obtained even when an input having similar variation between passes is assigned. As a result, the dot pattern hardly interferes with each other between the paths, which helps to improve image quality.

In addition, it goes without saying that the embodiment of the present invention can be made through the following configuration. In other words, a computer-readable storage medium having recorded thereon software program code having computer-executable instructions for realizing the above-described embodiments is supplied to a system or apparatus, and the computer (or CPU or MBP) of the system or apparatus is provided with the storage medium. Read and execute the program code stored in the program. In this case, the program code itself read out from the storage medium realizes the functions of the above-described embodiment, and the storage medium storing the program code constitutes the present invention.

As a storage medium for supplying program codes, for example, a flexible disk, a hard disk drive, an optical disk, a magneto-optical disk, a CD-ROM, a CD-R, a magnetic tape, a nonvolatile memory card, a ROM, a DVD, or the like can be used. Can be.

Further, the present invention is not limited to the case where the function of the above-described embodiment is realized by the computer executing the read program code, but also an operation in which some or all of the actual processes are running on the computer according to the instruction of the program code. It goes without saying that the processing performed by the system OS and the processes include the case of realizing the functions of the above-described embodiments.

Of course, the present invention also includes the case where the above embodiments are realized by the following processes. That is, the program code read out from the storage medium is recorded in the memory installed so as to be provided in the function expansion board inserted into the computer or the function expansion unit connected to the computer. Then, according to the instruction of the program code, the CPU or the like provided in the function expansion board or the function expansion unit performs part or all of the actual processing.

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 of a configuration example of a print system according to the first exemplary embodiment of the present invention.

2 is a flowchart illustrating processing according to the first exemplary embodiment of the present invention.

Fig. 3 is a schematic diagram showing the structure of printing by the multipass method and showing the state during the second scan.

FIG. 4 shows superposition on a recording medium for the first and second scanned image forming ranges of FIG. 3.

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

6 is a diagram for explaining path generation processing.

7 is a flowchart for describing path generation processing in detail.

8 is a diagram for specifically describing path generation processing.

9 is a flowchart for explaining 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 that depends on the correspondence between the quantization level and the dot arrangement used to determine the arrangement of the dots.

FIG. 12 shows an ideal multi-pass recording system shown in the state in which ink droplets of a uniform ejection amount are ejected in a uniform direction.

Fig. 13 shows a plurality of (three times) main scanning by a recording head by a multipath recording method, and two recording scans (passes) of a recording scanning area having a unit of four pixels which is half of eight pixels in the longitudinal direction. The state of completion by performing is shown.

Fig. 14 shows the states at the top, the middle and the bottom to complete the recording of the same area using the Houndstooth check pattern and the opposite Houndstooth check pattern.

Fig. 15 shows an example of dot arrangement of low concentration portions when error diffusion is independently performed on two passes.

Fig. 16 shows an example of dot arrangement in a low concentration portion when dot separation method error diffusion is performed for two passes.

17 shows an example of creating a path image for three paths using distribution parameters.

18 shows an example of a distribution parameter of circular symmetry.

19 shows an example of determining whether the pixel value after the lookup table of FIG. 10 is distributed in the path is a low concentration value.

Claims (13)

An image processing apparatus for generating recording data used in an image forming apparatus that performs image formation by performing multiple recording scans of the same image area on a recording medium, A dividing unit for dividing the input image data into the image data for each of the recording scans in accordance with a distribution ratio for dividing the image data for each recording scan to form the image data; A quantization unit that quantizes the image data for each recording scan based on the divided image data for each recording scan; A generation unit for generating record data for each record scan based on the image data for each quantized record scan; And the distribution ratio periodically varies depending on a spatial position of a pixel value of the image data. The method of claim 1, And the division ratio is a division ratio that periodically varies in the main scanning direction of the recording head of the image forming apparatus. The method of claim 1, And the division ratio is a division ratio that periodically varies in the sub-scanning direction of the recording head of the image forming apparatus. The method of claim 1, And the division ratio is a division ratio that periodically varies in the main scanning direction and the sub scanning direction of the recording head of the image forming apparatus. The method of claim 1, And said dividing ratio is a dividing ratio varying in rippled or circular symmetry. The method of claim 1, And the division ratio is a division ratio which varies at an angle with respect to the main scanning direction or the sub scanning direction of the recording head of the image forming apparatus. The method of claim 1, And the quantization unit performs quantization based on an error diffusion process. The method of claim 7, wherein And the quantization unit performs quantization based on an error diffusion process of a dot separation method. The method of claim 1, The quantization unit performs quantization based on a dither matrix method. The method of claim 1, And the dividing unit performs the dividing on a color component of a part of each color component constituting the image data. The method of claim 1, And the dividing unit performs the dividing on all the color components among the color components constituting the image data. An image processing method for generating recording data used in an image forming apparatus that performs image formation by performing multiple recording scans of the same image area on a recording medium, Dividing the input image data into the image data for each of the recording scans in accordance with a distribution ratio for dividing the image data for each recording scan to form the image data; Quantizing the image data for each of the recording scans based on the divided image data for each of the recording scans; Generating recording data for each recording scan based on the image data for each of the quantized recording scans, And the distribution ratio of the dividing step changes periodically according to the spatial position of the pixel value of the image data. A computer readable storage medium storing a computer program having computer executable instructions for causing a computer to execute the image processing method according to claim 12.

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