JP2006159601A - Image processor and processing program for printing, and printer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce banding phenomenon by imparting a density variation to a portion of low density variation where banding phenomenon becomes conspicuous. <P>SOLUTION: A feature amount is created based on the resolution of each pixel of an input image such that the sum SUM of gray levels of adjacent (neighboring) pixels is distributed to the gray level of an original pixel at a predetermined distribution ratio, and that feature amount is reflected on the resolution of the original pixel to increase difference between adjacent gray levels thus imparting a density variation. Since the feature amount is reflected only when the difference of gray level is below a predetermined level, banding phenomenon is reduced efficiently without losing coordination of input and output images. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a printing image processing apparatus that converts image data into printing information, and in particular, discharges and outputs fine particles (dots) of a plurality of colors of liquid ink onto printing paper (recording material) to generate predetermined characters and images. The ink jet printer is suitable for an ink jet printer for drawing.

Such an inkjet printer is generally inexpensive and can easily obtain a high-quality color printed matter. Accordingly, along with the widespread use of personal computers and digital cameras, it has become widespread not only in offices but also in general users.
In general, such an ink jet printer prints while a moving body called a carriage having an ink cartridge and a print head integrated with each other reciprocates on the print medium (paper) in the right and left directions in the paper feed direction. By ejecting (injecting) liquid ink particles from the head nozzle in the form of dots, predetermined characters and images are drawn on the printing paper to create a desired printed matter. The carriage is equipped with four color (yellow, magenta, cyan) ink cartridges including black (black) and a print head for each color, so that not only monochrome printing but also full-color printing combining each color is easy. (Furthermore, 6 colors, 7 colors, or 8 colors in which light cyan, light magenta, etc. are added to these colors are also put into practical use).

  In addition, in this type of ink jet printer in which printing is executed while the print head on the carriage reciprocates left and right in the paper feed direction (width direction of the printing paper), printing is performed to print the entire page cleanly. Since it is necessary to reciprocate the head several tens of times to 100 times or more, it takes significantly longer printing time than other types of printing apparatuses such as laser printers using electrophotographic technology such as copiers. There are disadvantages.

  On the other hand, in an ink jet printer that does not use a carriage with a long print head having the same dimensions as the width of the printing paper, it is not necessary to move the printing head in the width direction of the printing paper, so-called one pass. Therefore, high-speed printing similar to that of the laser printer is possible. The former inkjet printer is generally referred to as a “multi-pass printer”, and the latter inkjet printer is generally referred to as a “line head printer”. In a multi-pass printer, a nozzle head on which nozzles are mounted is moved (scanned) in the width direction of the print medium, for example, and the print medium itself is moved (scanned) in the length direction, for example. For example, only the print medium is moved (scanned) in the length direction.

  By the way, a print head indispensable for such an ink jet printer is formed by arranging fine nozzles having a diameter of about 10 to 70 μm in series at a constant interval or in multiple stages in the printing direction. The ink ejection direction of some nozzles is tilted, or the nozzle position is arranged at a position deviating from the ideal position, and the dots formed by the nozzle are shifted from the target point, A so-called “flight curve phenomenon” may occur.

  As a result, a printing defect referred to as a so-called “banding (streaks) phenomenon” may occur in the printing portion corresponding to the defective nozzle portion, and the print quality may be significantly reduced. That is, when the “flying curve phenomenon” occurs, the distance between adjacent dots becomes non-uniform, and “white streaks (when the printing paper is blank)” occurs in a portion where the distance between adjacent dots is long. A “dark streak” occurs in a portion where the distance is short. The appearance of “streaks” in this way is called “banding phenomenon”.

  In particular, such banding phenomenon is caused by the fact that the print head is fixed (one-pass printing) and the number of nozzles is much larger than that of the multi-pass printer, as compared with the case of the “multi-pass printer” as described above. It is more likely to occur in the “line head type printer” (in a multi-pass type printer, there is a technique for making white stripes inconspicuous by using the print head reciprocating many times).

Therefore, in the present situation, in addition to the improvement in the hardware part as described above, a technique for reducing such “banding phenomenon” by using a so-called software method such as print control as described below. Are used together.
For example, in Patent Documents 1 to 4 shown below, for example, by scanning the nozzle head a plurality of times in the same region, ink is ejected from different nozzles at the same location or in the vicinity thereof, and the output characteristics of the individual nozzles become inconspicuous. Technology is disclosed. Further, in Patent Documents 5 and 6 shown below, in an inkjet printer that has a plurality of nozzle heads and performs printing by scanning the nozzle heads a plurality of times, a plurality of nozzle heads with different characteristics are applied to the same region. A technique is disclosed in which the number of times of printing of individual nozzles in a certain area is reduced by printing, and the output characteristics become inconspicuous.
Japanese Patent No. 3176182 Patent No. 3176183 Japanese Patent No. 3176184 Japanese Patent No. 3478573 JP 2001-18374 A JP 2001-150701 A

  However, although any of the printing image processing techniques described in the above-mentioned patent documents can be applied to a multi-pass printer that scans the nozzle head itself, it is generally not applicable to a line head printer that does not scan the nozzle head. . Therefore, there is a demand for a printing image processing technique that can reduce the banding phenomenon even in a line head type printer that does not scan the head.

  The present invention has been made paying attention to the above-described problems, and an object of the present invention is to provide a printing image processing apparatus that can reduce the banding phenomenon even with a line head type printer.

  [Invention 1] In order to solve the above problem, an image processing apparatus for printing according to Invention 1 includes an input image acquisition means for acquiring image data having a gradation for each pixel, and an image acquired by the input image acquisition means. Of the data, the gradation difference changing means for changing the gradation difference between the pixels of the predetermined range of image data while maintaining the visual characteristics of the predetermined range of image data, and the gradation difference changing means between the pixels And binarization processing means for converting the gradation of the image data in which the difference is changed into the density of the printed dots.

The visual characteristic of the image data referred to in the present invention is the so-called appearance of the image, and is expressed by words such as hue or shade. In other words, maintaining the visual characteristics of image data within a predetermined range means that the appearance of an image after printing is retained in the same manner as that of acquired image data. Further, the dot referred to in the present invention means fine particles of liquid ink ejected from the nozzle. Details of the binarization processing will be described in detail later, but this means that the gradation of the image data is converted into a density and a dot diameter corresponding to the density is set.
The dot diameter means the radius or diameter of the fine particles of liquid ink ejected from the nozzle. When the dot diameter increases, the density in a certain range composed of a plurality of dots increases (in numerical values), As the dot diameter becomes smaller, the density becomes lighter (smaller in numerical value).

  According to the image processing apparatus for printing according to the first aspect of the present invention, the difference in gradation between pixels of the predetermined range of image data is changed while maintaining the visual characteristics of the predetermined range of image data in the acquired image data. In addition, since the gradation of the image data in which the difference between each pixel is changed is converted into the density of the print dots, a change is given to a portion of the image data in which the pixel density is not changed or the change is gradual. This makes it possible to reduce the banding phenomenon.

  The “banding phenomenon” here refers to a phenomenon in which “white streaks” and “dark streaks” occur due to “flight bend phenomenon” or the like. “Flying bend phenomenon” is different from the non-ejection phenomenon of some nozzles. Ink is ejected, but the ejection direction of some of the nozzles is tilted. The phenomenon that ends up. Also, “white streaks” cause a phenomenon in which the distance between adjacent dots is continuously larger than a predetermined distance due to the “flying curve phenomenon” or the like, and the background color of the print medium becomes noticeable in a streak shape. A “dark streak” refers to a phenomenon in which the distance between adjacent dots becomes smaller than a predetermined distance continuously due to the “flying curve phenomenon” or the like. The color disappears, or the distance between the dots becomes shorter, so it looks relatively darker. Further, some of the dots that have been separated overlap with normal dots, and the overlapping part is conspicuous as a dark streak The part (area) that is

  In general, the “banding phenomenon” is easily noticeable in a portion where the pixel density does not change or a portion where the change is slow. The printing image processing apparatus according to the first aspect of the present invention makes it possible to make the “banding phenomenon” inconspicuous by giving an intentional change in pixel density to such a portion.

  [Invention 2] The printing image processing apparatus according to the invention 2 is the printing image processing apparatus according to the invention 1, wherein the gradation difference changing means is a gradation degree for each pixel of the image data acquired by the input image acquisition means. And a feature amount reflecting means for reflecting the feature amount created by the feature amount creating means on the image data obtained by the input image obtaining means. It is a feature.

  According to the image processing apparatus for printing according to the second aspect of the present invention, the feature amount is created based on the gradation for each pixel of the acquired image data, and the feature amount is reflected in the acquired image data. It is possible to change the difference in gradation between the pixels of the image data in the predetermined range while maintaining the visual characteristics of the image data.

[Invention 3] The printing image processing apparatus according to Invention 3 is the printing image processing apparatus according to Invention 2, wherein the feature amount reflecting means has a periodicity of the gradation of the image data at least in a direction crossing the printing scanning direction. The feature amount is reflected in the image data so as to have
According to the image processing apparatus for printing according to the third aspect of the invention, since the gradation of the image data changes so as to wave at least in the direction intersecting the print scanning direction, banding is performed by changing the image density in that direction. The phenomenon can be reduced.

[Invention 4] The printing image processing apparatus according to Invention 4 is the printing image processing apparatus according to Invention 2 or 3, wherein the feature amount reflecting means is such that the gradation of the image data has periodicity in the printing scanning direction. The feature amount is reflected in the image data.
According to the image processing apparatus for printing according to the fourth aspect of the present invention, the gradation of the image data changes so as to undulate in the print scanning direction, so that the banding phenomenon can be reduced by changing the image density in that direction. Is possible.

[Invention 5] The printing image processing apparatus according to Invention 5 is the printing image processing apparatus according to any one of Inventions 2 to 4, wherein the feature amount reflecting means is configured such that the gradation levels of neighboring pixels of the image data have a predetermined cycle. The feature amount is reflected in the image data so as to be alternately larger and smaller.
According to the image processing apparatus for printing according to the fifth aspect of the present invention, it is possible to effectively reduce the banding phenomenon by changing the image density to be printed for each pixel.

[Invention 6] The printing image processing apparatus according to the invention 6 is the printing image processing apparatus according to any one of the inventions 2 to 5, wherein the feature amount reflecting means has a periodic noise different from that of the acquired image data. The superimposed image data is output.
According to the image processing apparatus for printing according to the sixth aspect of the invention, it is possible to effectively reduce the banding phenomenon by changing the print image density according to periodic noise different from the acquired image data.

[Invention 7] The printing image processing apparatus according to Invention 7 is the printing image processing apparatus according to any one of Inventions 2 to 6, wherein the feature quantity creating means is a pixel level within a predetermined range of the acquired image data. A feature amount is created from the furniture.
According to the printing image processing apparatus of this invention 7, it is possible to appropriately reflect the feature of the gradation of the pixel of the acquired image data in the feature amount for each predetermined range.

[Invention 8] The image processing apparatus for printing according to the invention 8 is the image processing apparatus for printing according to the invention 7, wherein the feature amount creating means calculates a feature amount from a sum of gradation levels of neighboring pixels of the acquired image data. It is characterized by creating.
According to the printing image processing apparatus of the present invention 8, it is possible to hold the sum of the total gradation levels of neighboring pixels, and to match the printed image with the acquired image.

[Invention 9] In the printing image processing apparatus according to Invention 9, in the printing image processing apparatus according to Invention 8, the feature amount reflecting means previously calculates a sum of gradation levels of neighboring pixels obtained by the feature amount creating means. The distribution is performed on the original pixels according to the set distribution ratio.
According to the printing image processing apparatus of aspect 9, it is possible to effectively reduce the banding phenomenon by changing the pixel density of the printed image while maintaining the sum of the total gradations of neighboring pixels. .

[Invention 10] In the printing image processing apparatus according to Invention 10, in the printing image processing apparatus according to Invention 8, the feature amount reflecting means previously calculates a sum of gradations of neighboring pixels obtained by the feature amount creating means. By dividing by a set ratio, the value is added to or subtracted from the gradation of the original pixel.
According to the printing image processing apparatus of the tenth aspect, it is possible to effectively reduce the banding phenomenon by changing the pixel density of the printed image while maintaining the sum of the total gradation of neighboring pixels. .

[Invention 11] The printing image processing apparatus according to the invention 11 is the printing image processing apparatus according to any one of the inventions 2 to 10, wherein the feature amount reflecting means is a gradation level of a neighboring pixel of the acquired image data. The feature amount is reflected when the difference between them is equal to or less than a predetermined value.
According to the printing image processing apparatus of the eleventh aspect, it is possible to effectively reduce the banding phenomenon by changing the pixel density of the printed image only in the portion where the difference in the gradation of neighboring pixels is small.

[Invention 12] The image processing program for printing according to Invention 12 changes the difference in gradation between each pixel of the image data in the predetermined range while maintaining the visual characteristics of the image data in the predetermined range among the acquired image data. It is characterized by having a computer realize this.
According to the printing image processing program of the twelfth aspect of the present invention, the difference in gradation between pixels of the predetermined range of image data is changed while maintaining the visual characteristics of the predetermined range of image data in the acquired image data. Since the gradation of the image data in which the difference between each pixel is changed is converted to the density of the print dot, the change is applied to the portion of the image data where the pixel density is not changed or the change is gradual. Banding phenomenon can be reduced.

[Invention 13] A printing apparatus according to Invention 13 comprises the printing image processing apparatus according to any one of Inventions 1 to 11.
According to the printing apparatus of the thirteenth aspect, the effects of the printing image processing apparatuses of the first to eleventh aspects can be realized as a printing apparatus.

Next, a first embodiment of an image processing apparatus for printing according to the present invention will be described with reference to the drawings.
FIG. 1 shows an inkjet printer 2 of this embodiment and a personal computer 1 for driving the inkjet printer 2. In this printing system, for example, the image data of the digital still camera 4 is read by the personal computer 1 or the ink jet printer 2, and the image data can be printed by the ink jet printer 2. A device driver 3 for driving the ink jet printer 2 is built in the personal computer 1, and the device driver 3 is appropriately driven by application software to drive the ink jet printer 2, that is, perform printing. Do.

  The ink jet printer 2 of the present embodiment is the above-described line head type printer, and the nozzle head unit has a plurality of nozzles N for discharging black (K) ink in a straight line as shown in FIG. A group of black nozzles 50 arranged, a group of yellow nozzles 52 in which a plurality of nozzles N that exclusively discharge yellow (Y) ink are linearly arranged, and a plurality of nozzles N that similarly eject magenta (M) ink exclusively. A magenta nozzle group 54 arranged in a straight line and a cyan nozzle group 56 in which a plurality of nozzles N that specifically discharge cyan (C) ink are arranged in a straight line are superposed in the print scanning direction so as to be integrated. It is configured. Therefore, according to the command signal from the device driver, the print medium is moved in the print scanning direction with respect to the head unit while ejecting and outputting liquid ink from each nozzle of the head unit, thereby printing the image data in one pass. It becomes possible. FIG. 3 shows a state in which the flight bending phenomenon occurs in the sixth nozzle N6 from the left of the black nozzle group 50 among these nozzle groups, and as a result, ink is ejected obliquely from the nozzle N6. As a result, a dot is formed in the vicinity of the normal nozzle N7 next to it.

  The device driver 3 is configured by software. A typical hardware configuration of the personal computer 1 for operating the device driver 3 and the application software 4 is shown in FIG. In this hardware configuration, a PCI bus, an ISA bus, or the like is provided between the CPU 60 that is a central processing unit that performs various controls and arithmetic processing, the RAM 62 that constitutes the main storage device, and the ROM 64 that is a read-only storage device commission. And an external storage device 70 such as an HDD, an output device such as the inkjet printer 1, CRT, LCD monitor, etc. via an input / output interface (I / F) 66. 72, an operation panel, an input device 74 such as a mouse, a keyboard, and a scanner, and a network L for communicating with a print instruction device (not shown).

  When the personal computer 1 is turned on, a system program such as BIOS stored in the ROM 64 or the like is stored in various dedicated computer programs stored in advance in the ROM 64, CD-ROM, DVD-ROM, or flexible disk (FD). ), Or various dedicated computer programs installed in the storage device 70 via a communication network such as the Internet are loaded into the RAM 62, and in accordance with instructions described in the program loaded into the RAM 62. Each function described later can be realized on software by the CPU 60 performing predetermined control and arithmetic processing using various resources. The device driver may be provided in a printer control unit provided in the ink jet printer, or may be provided in a completely separate computer system. Similarly, application software for driving the device driver may be executed in a printer control unit provided in the inkjet printer, or may be executed in a completely separate computer system. Good. Further, functions equivalent to device drivers and application software may be configured by hardware.

  As described above, since the device driver of the present embodiment is configured by software, the procedure of the arithmetic processing will be described. FIG. 5 is a functional block diagram of the device driver, and FIG. 6 is a flowchart of arithmetic processing for realizing it. In this device driver, first, in step S1, image data is acquired as an input image from application software. In this input image acquisition step, the input image data is represented by, for example, a gradation (luminance value) for each color (R, G, B) per pixel in 8 bits (0 to 255). In the case of multi-value RGB image data, the image data is converted into the four CMYK colors to be printed from now on to obtain multi-value CMYK image data in which the gradation is expressed by 8 bits.

In the next step S2, a feature amount is created from the input image acquired in step S1 according to an individual calculation process described later. In the next step S3, the feature amount created in step S2 is reflected on the acquired input image in accordance with individual calculation processing described later.
In the next step S4, the binary value processing of each pixel is performed on the input image in which the feature amount is reflected in step S3. This binary value processing refers to, for example, so-called binary value processing that pays attention to an arbitrary pixel constituting image data and hits a dot on the target pixel, that is, whether or not liquid ink is ejected from a nozzle. , And error diffusion processing based on a predetermined error diffusion matrix is executed in the same way as normal data conversion for pixel errors caused by the binary value processing. In this error diffusion process, when binary value processing is performed on multi-value data with a certain threshold as a boundary, the difference from the threshold is not discarded, but an error is diffused to a plurality of pixels to be processed. It is intended to be used. For example, if the target pixel to be processed can be expressed by 8 bits (256 gradations) and the gradation is “101”, the gradation is a threshold value (intermediate value) in normal binary value processing. Since it is less than “127”, it is processed as “0”, that is, a pixel not forming a dot, and “101” is discarded as it is. On the other hand, in the case of error diffusion processing, the “101” is diffused to the surrounding unprocessed pixels according to a predetermined error diffusion matrix. Since only the normal binary value processing is less than the threshold value as in the target pixel, it has been processed as “Dot is not formed”, but the pixel value exceeds the threshold value by receiving the error of the target pixel. As a result of handling such as “form dots”, binary value data closer to the original image data can be obtained. When the error diffusion processing for the target pixel is completed in this way, it is determined whether or not a dot is formed at the position of the target pixel as a result of the binary value processing.

  Next, the calculation process of FIG. 7 performed in steps S2 and S3 of the calculation process of FIG. 6 will be described. In this calculation process, first, in step S11, pixel data for one line is acquired from the input image data acquired in step S1 of the calculation process of FIG. In this case, one line indicates a pixel row arranged in the nozzle arrangement direction of the nozzle head unit, in the print medium, that is, the width direction of the print medium, and the pixel data itself indicates the gradation of each color of each pixel. To the gradation P of each pixel, which is pixel data, suffixes 0, 1, 2,... Are added in order from the left end of the pixel data, and this is handled as a variable I.

In step S12, the variable I is initialized to zero. In step S13, the sum SUM of adjacent (neighboring) pixel data (gradation levels) P _I and P _{I + 1} is obtained. In step S14, the sum SUM of the pixel data (gradation degree) obtained in step S13 is distributed to the original pixels. Specifically, the distribution ratio RATIO is 0.6 in this case, and the value obtained by multiplying the sum SUM of the gradations by RATIO is the pixel data (gradation degree) PI of the pixel _I, and the sum SUM of the gradations ( A value obtained by multiplying 1−RATIO) is defined as pixel data (gradation degree) P _I-1 of the pixel (I-1). That is, the sum of the gradation levels of adjacent pixels is distributed to the original pixels with a predetermined distribution ratio.

Next, the process proceeds to step S15, and the gradation levels P _I and P _I-1 obtained in step S14 are clipped (truncated) to an 8-bit gradation level 0 to 255. Next, the process proceeds to step S16, and 2 is added to the variable I. Next, the process proceeds to step S17, where it is determined whether or not the variable I added by 2 in step S16 is greater than or equal to the image width. If the variable I is greater than or equal to the image width, the process proceeds to step S18. If not, the process proceeds to step S13. In step S18, it is determined whether or not the pixel data for one line acquired in step S11 is the final line of the image. If the acquired pixel data for one line is the final line of the image, an arithmetic process is performed. If not, the process proceeds to step S11.

According to this calculation process, for example, as shown in FIG. 8, among the pixel data for one line of the input image, the gradation levels P ₀ and P ₁ of the pixel of the variable I = ₀ , ₁ are 100 and 90, respectively. In this case, the sum SUM of the gradations is 190, and when it is distributed to the original pixels with the distribution ratio RATIO = 0.6, the gradations P ₀ and P ₁ of the pixel of the variable I = ₀ , ₁ are 114, It becomes 76. Similarly, when the gradation levels P ₂ and P ₃ of the pixels of the variable I = ₂ and ₃ are 80 and 90, respectively, the sum SUM of gradation levels is 170, which is the original with a distribution ratio RATIO = 0.6. Are distributed to the pixels, the gradation levels P ₂ and P ₃ of the pixels of the variable I = ₂ and ₃ become 102 and 68, respectively. Further, when the gradation levels P ₄ and P ₅ of the pixels of the variable I = 4 and ₅ are 110 and 130, respectively, the sum SUM of the gradation levels is 240, which is the original distribution ratio RATIO = 0.6. When distributed to the pixels, the gradation levels P ₄ and P ₅ of the pixels of the variable I = 4 and ₅ are 144 and 96, respectively. Further, if the gradation levels P ₆ and P 7 of the pixels of the variable I = 6 and ₇ are 140 and 140, respectively, the sum SUM of the gradation levels is 280, which is the original distribution ratio RATIO = 0.6. If distributed to the pixel, gradient P _6, P ₇ pixel variables I = 6, 7 is respectively 168,112.

  At this time, for example, the gradation difference between the pixels of the input image corresponding to the variable I = 0, 1 is 10 in absolute value, whereas the sum SUM of gradations that is the feature amount is distributed with the distribution ratio RATIO. The gradation difference reflected on the original pixel is 38 in absolute value. Similarly, the gradation difference between pixels of the input image corresponding to the variable I = 1, 2 is 10 in absolute value, whereas the gradation difference after reflecting the feature amount is 26 in absolute value. Yes. The gradation difference between adjacent pixels in the input image shown in the example of FIG. 8 is small as 0 to 20 in all cases, but the sum SUM of gradations that is a feature amount is distributed with a distribution ratio RATIO to obtain the original difference. The gradation difference between adjacent pixels after reflection on the pixels is 26 to 76, both of which are larger than the original values.

  In general, the “banding phenomenon” such as “white streaks” and “dark streaks” associated with the “flight curve phenomenon” described above is easily noticeable in a portion where the pixel density does not change or a portion where the change is slow. On the other hand, according to this calculation process, while maintaining the visual characteristics of the image data in the predetermined range among the acquired image data, the difference in gradation between the pixels of the image data in the predetermined range is changed. Since the gradation of the image data in which the difference between the pixels is changed is converted into the density of the printed dots, the banding phenomenon is caused by changing the portion of the image data where the pixel density does not change or changes slowly. Can be reduced.

In addition, since the feature amount is created based on the gradation level of each pixel of the acquired image data and the feature amount is reflected in the acquired image data, the predetermined range of the image data is maintained while maintaining the visual characteristics. It becomes possible to change the difference in gradation between each pixel of the image data.
Further, at least printing is performed by reflecting the feature amount in the image data so that the gradation of the image data has periodicity in at least the direction intersecting the print scanning direction, that is, the nozzle arrangement direction of the line head type ink jet printer. Since the gradation of the image data changes so as to wave in the direction intersecting the scanning direction, that is, the nozzle arrangement direction, it is possible to reduce the banding phenomenon by changing the image density in that direction.

In addition, by reflecting the feature amount in the image data so that the gradation levels of neighboring pixels in the image data are alternately large and small, the printed image density is changed for each pixel, thereby effectively reducing the banding phenomenon. It becomes possible to do.
In addition, as a result of reflecting the feature amount, it is possible to output image data on which periodic noise different from the acquired image data is superimposed, and according to periodic noise different from the acquired image data. It is possible to effectively reduce the banding phenomenon by changing the print image density.

In addition, by creating a feature amount from the gradation of pixels in a predetermined range of the acquired image data, it is possible to appropriately reflect the feature of the gradation of pixels of the acquired image data in the feature amount for each predetermined range. it can.
In addition, by creating a feature value from the sum of the gradation levels of neighboring pixels in the acquired image data, it is possible to retain the sum of the total gradation levels of neighboring pixels, and a printed image can be obtained. Can be matched to the image.

Also, by distributing the sum of the gradations of neighboring pixels to the original pixels according to a preset distribution ratio, the pixel density of the printed image can be reduced while maintaining the sum of the total gradations of neighboring pixels. By changing it, it becomes possible to effectively reduce the banding phenomenon.
Next, a second embodiment of the printing image processing apparatus of the present invention will be described. The printing system of this embodiment is the same as that of FIG. 1 of the first embodiment, and the nozzle head unit of the line head type printer is also the same as that of FIGS. 2 and 3 of the first embodiment. Further, the schematic configuration of the personal computer is the same as that of FIG. 4 of the first embodiment, and the arithmetic processing constituting the device driver is the same as that of FIGS. 5 and 6 of the first embodiment.

In the present embodiment, the arithmetic processing performed in steps S2 and S3 of the arithmetic processing in FIG. 6 is changed from that in FIG. 7 of the first embodiment to FIG. In this calculation process, first, in step S21, pixel data (gradation degree) for one line is acquired from the input image data acquired in step S1 of the calculation process of FIG. 6 as in the first embodiment. To do. At the next step S22, the step S21 adjacent obtained in (neighboring) compares the values of pixel data (gradation degree), adjacent pixel data (gradation degree) P _I, the difference between P I _{+ 1} There is stored as the correction unnecessary portions D _N the predetermined value TH larger portion. Defining the correction unnecessary portions D _N is the same as the variable I, the neighboring pixel data (gradation degree) P _I, the difference between P I _{+ 1} is the predetermined value TH larger portion is number from the left end of the image Means.

In step S23, the variable I is initialized to zero. At the next step S24, if the variable I and the correction unnecessary portions D _N is determined whether they match, the variable I and the correction unnecessary portions D _N coincides proceeds to step S28 If not, the process proceeds to step S25. In step S25, the sum SUM of adjacent pixel data (gradation levels) P _I and P _{I + 1} is obtained, and then the process proceeds to step S26. In step S26, the sum SUM of the pixel data (gradation degree) obtained in step S25 is distributed to the original pixels in the same manner as in the first embodiment, and then the process proceeds to step S27. Specifically, the distribution ratio RATIO is 0.6 in this case, and the value obtained by multiplying the sum SUM of the gradations by RATIO is the pixel data (gradation degree) PI of the pixel _I, and the sum SUM of the gradations ( A value obtained by multiplying 1−RATIO) is defined as pixel data (gradation degree) P _I-1 of the pixel (I-1). In step PS27, the gradation levels P _I and P _I-1 obtained in step S26 are clipped (truncated) to 8-bit gradation levels 0 to 255, and then the process proceeds to step S28.

  In step 28, 2 is added to the variable I. Next, the process proceeds to step S29, where it is determined whether or not the variable I added by 2 in step S28 is greater than or equal to the image width. If the variable I is greater than or equal to the image width, the process proceeds to step S30. If not, the process proceeds to step S24. In step S30, it is determined whether or not the pixel data for one line acquired in step S21 is the final line of the image. If the acquired pixel data for one line is the final line of the image, an arithmetic process is performed. If not, the process proceeds to step S21.

According to this arithmetic processing, in addition to the operation and effect of the first embodiment, a portion where the difference between neighboring pixel data (gradation levels) P _I and P _{I + 1} is greater than a predetermined value TH is not necessary for correction D _N. stored as, when the variable I and the correction unnecessary portions D _N match does not update the original pixel of the feature quantity consisting of the sum of the gradient sUM. That is, in this embodiment, by reflecting the feature amount when the difference in gradation of neighboring pixels in the acquired image data is equal to or less than a predetermined value, the difference in gradation of neighboring pixels is reduced. Therefore, it is possible to effectively reduce the banding phenomenon by changing the pixel density of the printed image.

  Next, a third embodiment of the printing image processing apparatus of the present invention will be described. The printing system of this embodiment is the same as that of FIG. 1 of the first embodiment, and the nozzle head unit of the line head type printer is also the same as that of FIGS. 2 and 3 of the first embodiment. Further, the schematic configuration of the personal computer is the same as that of FIG. 4 of the first embodiment, and the arithmetic processing constituting the device driver is the same as that of FIGS. 5 and 6 of the first embodiment.

In the present embodiment, the arithmetic processing performed in steps S2 and S3 of the arithmetic processing in FIG. 6 is changed from that in FIG. 7 of the first embodiment to FIG. In this calculation process, first in step S31, pixel data (gradation degree) for one line is acquired from the input image data acquired in step S1 of the calculation process of FIG. 6 in the same manner as in the first embodiment. To do. In step S32, the variable I is initialized to zero. In step S33, the sum SUM of adjacent (neighboring) pixel data (gradation levels) P _I and P _{I + 1} is obtained. Next, the process proceeds to step S34, and the noise amount N, which is the feature amount of the present embodiment, is obtained from the sum SUM of adjacent pixel data (gradation levels) obtained in step S33. Specifically, the noise amount N is obtained by dividing the sum SUM of pixel data (gradation levels) by a predetermined ratio N_RATIO set to 30, for example.

At the next step S35, the pixel data (gradation degree) P _I adjacent, P of the I _{+ 1,} the left side of the pixel data (gradation degree) P _I is right pixel data (gradation degree) P I _{+ 1} determines whether larger or not, the process proceeds to step S36 if the left side of the pixel data (gradation degree) P _I is right pixel data (gradation degree) larger than P I _{+ 1,} step S37. Otherwise Migrate to In step S36, a value obtained by subtracting the noise amount N as the feature amount from the original pixel data (gradation degree) P _I on the left side is set as new left pixel data (gradation degree) P _I, and the original pixel data on the right side is obtained. A value obtained by adding the noise amount N as the feature amount to (gradation degree) PI _{+ 1} is used as new right pixel data (gradation degree) PI _{+ 1} , thereby obtaining the noise amount N as the feature amount. After reflecting the pixel data (gradation degree), the process proceeds to step S38. In step S37, a value obtained by adding the noise amount N as the feature amount to the original pixel data (gradation degree) P _I on the left side is set as new left pixel data (gradation degree) P _I, and the original data on the right side is obtained. A value obtained by subtracting the noise amount N, which is the feature amount, from the pixel data (gradation degree) PI _{+ 1} is used as new right pixel data (gradation degree) PI _{+ 1} , so that the noise amount N is the feature amount. Is reflected in the original pixel data (gradation degree), and then the process proceeds to step S38.

In step PS38, the gradation levels P _I and P _I-1 obtained in step S36 or step S37 are clipped (truncated) to an 8-bit gradation level 0 to 255. In step S39, 2 is added to the variable I. Next, the process proceeds to step S40, where it is determined whether or not the variable I added by 2 in step S39 is greater than or equal to the image width. If the variable I is greater than or equal to the image width, the process proceeds to step S41. If not, the process proceeds to step S33. In step S41, it is determined whether or not the pixel data for one line acquired in step S31 is the final line of the image. If the acquired pixel data for one line is the final line of the image, an arithmetic process is performed. If not, the process proceeds to step S31.

According to this arithmetic processing, as shown in FIG. 11, for example, among the pixel data for one line of the input image, the gradation levels P ₀ and P ₁ of the pixel of the variable I = ₀ , ₁ are 100 and 90, respectively. In this case, the sum SUM of the gradations is 190, and the noise amount N obtained by dividing the sum SUM by the ratio N_RATIO = 30 is 6 (about 3% of the sum SUM of the gradations). If the amount of noise is reduced and the amount of noise is added to the pixel with the smaller gradation, and the amount of noise that is the characteristic amount is reflected in the original pixel, the new gradation degree of the larger left pixel is obtained at the time of acquisition. P ₀ is 94, and the new gradation P ₁ of the smaller right pixel is 96. Similarly, when the gradation levels P ₂ and P ₃ of the pixel of the variable I = ₂ , ₃ are 80 and 90, respectively, the sum SUM of the gradation levels is 170, and the noise amount N = 5 is set to the original pixel. Reflecting the change, the gradation levels P ₂ and P ₃ of the pixel with the variable I = ₂ , ₃ are 85 and 85, respectively. Further, when the gradation levels P ₄ and P ₅ of the pixels of the variable I = 4 and ₅ are 110 and 130, respectively, the sum SUM of the gradation levels is 240, and the noise amount N = 7 is adjusted to the original pixel. As a result, the gradation levels P ₄ and P ₅ of the pixels of the variable I = 4 and ₅ become 117 and 123, respectively. Further, when the gradation levels P ₆ and P 7 of the pixels of the variable I = 6 and ₇ are 140 and 140, respectively, the sum SUM of gradation levels is 280, and the noise amount N = 8 is added to or subtracted from the original pixel. When reflected by, gradient P _6, P ₇ pixel variables I = 6, 7 is respectively 132,148.
At this time, the gradations P ₆ and P ₇ of the variables I = 6 and 7 that are equal to the original pixel data are obtained by dividing the sum of gradations SUM = 280 by the predetermined ratio N_RATIO and using the noise amount N = 8 as the original pixel. By adding and subtracting it, it becomes 132 and 148, respectively, and the difference in gradation is 16 in absolute value. That is, in this embodiment, in addition to the operation and effect of the first embodiment, the sum of the gradations of neighboring pixels is divided by a preset ratio, and the value is added to or subtracted from the gradation of the original pixel. As a result, it is possible to effectively reduce the banding phenomenon by changing the pixel density of the printed image while maintaining the sum of the total gradation of neighboring pixels. In particular, in this embodiment, when the gradation levels of neighboring pixels are the same, the band density can be reduced by forcibly changing the pixel density of those printed images.

  Next, a fourth embodiment of the printing image processing apparatus of the present invention will be described. The printing system of this embodiment is the same as that of FIG. 1 of the first embodiment, and the nozzle head unit of the line head type printer is also the same as that of FIGS. 2 and 3 of the first embodiment. Further, the schematic configuration of the personal computer is the same as that of FIG. 4 of the first embodiment, and the arithmetic processing constituting the device driver is the same as that of FIGS. 5 and 6 of the first embodiment.

In the present embodiment, the arithmetic processing performed in steps S2 and S3 of the arithmetic processing in FIG. 6 is changed from that in FIG. 7 of the first embodiment to FIG. In this calculation process, first, in step S51, pixel data (gradation degree) for two lines is acquired from the input image data acquired in step S1 of the calculation process of FIG. At this time, the pixel data (gradation degree) acquisition method for each line is the same as that in the first embodiment, but in this embodiment, the subsequent two lines are acquired. To the pixel data (gradation degree) P, a suffix L or L + 1 indicating a line is newly added, and when the suffix is L, it means the upper line of the image, and when it is L + 1, it means the lower line of the image. To do. In step S52, the variable I is initialized to zero. Next, the process proceeds to step S53, in which four neighboring (neighboring) pixel data (gradation levels) P _{L, I} , P _L , _{I + 1} , P _{L + 1, I} , P _{L + 1,} vertically and horizontally are adjacent _. Find the sum SUM of _{I + 1} . Next, the process proceeds to step S54, and the noise amount N, which is the feature amount of the present embodiment, is obtained from the sum SUM of the four pixel data (gradation levels) adjacent in the vertical and horizontal directions obtained in step S53. Specifically, the noise amount N is obtained by dividing the sum SUM of pixel data (gradation levels) by a predetermined ratio N_RATIO set to 30, for example.

Next, the process proceeds to step S55, and the value obtained by subtracting the noise amount N as the feature amount from the original pixel data (gradation degree) P _{L, I} on the upper left side is used as new upper left pixel data (gradation degree) P. _{L, I} , the original pixel data (gradation degree) P _L on the upper right side, and the value obtained by adding the noise amount N, which is the feature amount, to _{I + 1} is newly added to the upper right side pixel data (gradation degree) P _L , _{I + 1,} and the value obtained by adding the noise amount N as the feature amount to the original pixel data (gradation degree) P _{L + 1, I} on the lower left side is the new lower left pixel data (gradation degree) P _{L + 1 and I} , the value obtained by subtracting the noise amount N as the feature amount from the original pixel data (gradation degree) P _{L + 1, I + 1} on the lower right side is used as new pixel data (gradation degree) on the lower right side. ) By setting P _{L + 1, I + 1} , the noise amount N that is a feature amount is reflected in the original pixel data (gradation degree).

In step PS56, the gradation levels P _{L, I} , P _L , _{I + 1} , P _{L + 1, I} , P _{L + 1, I + 1} obtained in step S55 are clipped to 8-bit gradation levels 0-255. (Truncate). In step S57, 2 is added to the variable I. Next, the process proceeds to step S58, where it is determined whether or not the variable I added by 2 in step S57 is greater than or equal to the image width. If the variable I is greater than or equal to the image width, the process proceeds to step S59. If not, the process proceeds to step S53. In step S59, it is determined whether or not the pixel data for two lines acquired in step S51 is the final line of the image. If the acquired pixel data for two lines is the final line of the image, an arithmetic process is performed. If not, the process proceeds to step S51.

According to this arithmetic processing, for example, as shown in FIG. 13, the gradation levels P _L , 0, P _{L, 1} , P _L of the pixels of the variable I = 0, 1 out of the pixel data for two lines of the input image. _{When +1,0} and P _{L + 1,1} are ₁₀₀ , ₉₀ , ₁₁₀ , and ₁₁₀ , _respectively , the sum SUM of the gradations is 410, and the noise amount N obtained by dividing it by the ratio N_RATIO = 30 is 12 ( Therefore, the amount of noise is reduced from the upper left and lower right pixels, and the amount of noise is added to the upper right and lower left pixels, and the original pixels are feature amounts. When a certain amount of noise is reflected, the new gradations P _L , 0, P _{L, 1} , P _{L + 1,0} , and P _{L + 1,1} of the pixel of the variable I = 0, ₁ are 88, 102, 122, respectively. , 98. Similarly, when the gradations P _L , 2, P _{L, 3} , P _{L + 1,2} , and P _{L + 1,3} of the pixel with the variable I = 2, ₃ are 80, 90, 90, 100, respectively. , The sum of gradations SUM is 360, and when the noise amount N = 10 is added to or subtracted from the original pixel, the gradations P _L , 2, P _{L, 3} , P of the pixel with the variable I = 2, 3 are reflected. _{L + 1,2} and P _{L + 1,3} are 70, 100, 100 and 90, respectively. Further, when the gradation levels P _L , 4, P _{L, 5} , P _{L + 1,4} , and P _{L + 1,5} of the pixel with the variable I = 4, ₅ are 110, 130, 90, 120, respectively, The sum SUM of the gradation levels becomes 450, and when the noise amount N = 14 is added to or subtracted from the original pixel, the gradation degrees P _L , 4, P _{L, 5} , P _L of the pixels of the variable I = 4, 5 are reflected. _+1,4 and P _{L + 1,5} become 96, 144, 104 and 106, respectively. Further, when the gradation levels P _L , 6, P _{L, 7} , P _{L + 1,6} , and P _{L + 1,7} of the pixel with the variable I = 6, ₇ are 140, 140, 120, 100, respectively, The sum SUM of the gradation levels is 500, and when the noise amount N = 15 is added to and subtracted from the original pixel, the gradation levels P _L , 6, P _{L, 7} , P _L of the pixels with the variable I = 6, 7 are reflected. _+1,6 and P _{L + 1,7} are ₁₂₅ , ₁₅₅ , 135 and 85, respectively.
At this time, in the direction intersecting the print scanning direction, that is, the nozzle arrangement direction, or the print medium width direction, for example, between the pixels of the variable I = 0, 1 of the lower line L + 1 and the variable I = 5. , 6 and between the pixels of variable I = 6, 7; between the pixels of variable I = 1, 2 of the upper line L; between the pixels of variable I = 2, 3; and between the pixels of variable I = 4, 5 And the difference in gradation between the pixels of the variable I = 6, 7 is large. Further, in the print scanning direction, that is, in the print medium length direction, for example, between the pixels of the upper line L and the lower line L + 1 of the variable I = 0, and the upper line L and the lower line of the variable I = 2. The difference in gradation is large between the pixels of L + 1, between the pixels of the upper line L and the lower line L + 1 with the variable I = 5, and between the pixels of the upper line L and the lower line L + 1 with the variable I = 7. That is, in the present embodiment, in addition to the operations and effects of the first and third embodiments, the feature amount is reflected in the image data so that the gradation of the image data has a periodicity in the print scanning direction. As a result, the gradation of the image data changes so as to undulate in the print scanning direction, so that the banding phenomenon can be reduced by changing the image density in that direction.

If the printing image processing apparatus according to the first to third embodiments described above is provided in the printing apparatus, the above-described effects can be realized as a printing apparatus.
In the first and second embodiments, the feature amount composed of the sum of the gradation levels is distributed to the original pixels at a predetermined distribution ratio. For example, the larger one of the original pixels has a smaller gradation level. In addition, the smaller one of the gradation levels of the original pixels may be increased. Conversely, for example, the one with the larger gradation of the original pixel may be further increased and the one with the smaller gradation of the original pixel may be further decreased.

In the third embodiment, the feature amount composed of the sum of the gradation levels is divided by a predetermined ratio, and the value is subtracted from the higher gradation level of the original pixel, and the gradation level of the original pixel is decreased. In contrast to this, on the contrary, for example, the feature amount may be summed to the one with the larger gradation of the original pixel, and the feature amount may be decreased from the one with the smaller gradation of the original pixel.
In addition, the feature amount creation method and the original pixel data reflection method may be changed according to, for example, acquired input image data.

In the second embodiment, the feature amount is reflected when the difference in gradation between adjacent (neighboring) pixels is equal to or smaller than a predetermined value. That is, when the difference in gradation is larger than the predetermined value, the feature amount is simply reflected. Although the reflection is not performed, for example, the feature amount may be reflected forcibly on both sides of the pixel to which the feature amount is not reflected to change the density.
Further, when the density is changed in a wave shape by reflecting the feature amount in the pixel data, the wave period may be changed or the amplitude may be modulated in accordance with the gradation of the input image.

  In the first to fourth embodiments, the example in which the feature amount is reflected in the image data so that the gradation of neighboring pixels of the image data alternately becomes larger and smaller in a predetermined cycle is shown. The form is not limited to this, and the range of the target pixel reflecting the feature amount may be widened, and the feature amount may be reflected so that the gradation of the pixel changes smoothly in a sine wave shape.

In each of the above embodiments, only the example in which the printing image processing apparatus of the present invention is applied to a line head type printer has been described in detail. However, the printing image processing apparatus of the present invention is, for example, a multipass printer. First, it can be applied to all types of inkjet printers.
FIG. 14 shows respective printing methods using a line head type ink jet printer and a multi-pass type ink jet printer. As shown in FIG. 5A, when the width direction of the rectangular printing paper P is the sub-scanning direction of the image data, and the longitudinal direction is the main scanning direction of the image data (printing scanning direction according to the present invention), the line In the head type ink jet printer, as shown in FIG. 5B, the print head 200 has a length corresponding to the paper width of the print paper P, and the print head 200 is fixed to the print head 200. By moving the printing paper P in the main scanning direction, printing is completed in a so-called one pass (operation). It is also possible to perform printing while fixing the printing paper P as in a so-called flatbed scanner and moving the print head 200 in the main scanning direction, or moving both in the opposite direction. It is. On the other hand, in the multi-pass type ink jet printer, as shown in FIG. 5C, the print head 200, which is much shorter than the paper width, is arranged in a direction perpendicular to the sub-scanning direction. The printing paper P is moved in the main scanning direction by a predetermined pitch while reciprocally moving in the sub-scanning direction many times. Therefore, the latter multi-pass type ink jet printer has a drawback that it takes more printing time than the former line head type ink jet printer, but the print head 200 can be repeatedly positioned at an arbitrary position. Among the banding phenomenon as described above, it is possible to cope with a certain degree of reduction of the white streak phenomenon.

  In FIG. 3, each nozzle group 50, 52, 54, 56 provided for each color of the print head 200 has a form in which the nozzles N are continuous immediately before the print head 200 in the longitudinal direction. As shown in FIG. 15, each of these nozzle groups 50, 52, 54, 56 is composed of a plurality of short nozzle units 50a, 50b,... 50n, which are arranged before and after the movement direction of the print head 200. You may comprise as follows. In particular, if each of the nozzle groups 50, 52, 54, 56 is composed of a plurality of short nozzle units 50a, 50b,... 50n, the distance between the actual dots of each nozzle unit 50a, 50b,. Since the distance between dots can be substantially reduced without reducing (pitch), it is possible to easily cope with a high-resolution image.

1 is a configuration diagram of a printing system showing a first embodiment of an image processing apparatus for printing according to the present invention. It is explanatory drawing of the nozzle head unit of the inkjet printer of FIG. It is explanatory drawing of the flight bending phenomenon of the ink discharged and output from a nozzle. It is a schematic block diagram of the personal computer of FIG. FIG. 2 is a functional block diagram of a device driver in the personal computer of FIG. 1. It is a flowchart of the arithmetic processing for achieving the functional block of FIG. It is a flowchart of the subroutine performed by the arithmetic processing of FIG. It is explanatory drawing of the effect | action of the arithmetic processing of FIG. FIG. 7 is a flowchart of a calculation processing subroutine of FIG. 6 showing a second embodiment of the printing image processing apparatus of the present invention. FIG. 7 is a flowchart of a calculation processing subroutine of FIG. 6 showing a third embodiment of the printing image processing apparatus of the present invention. It is explanatory drawing of an effect | action of the arithmetic processing of FIG. It is a flowchart of the subroutine of the arithmetic processing of FIG. 6 which shows 4th Embodiment of the image processing apparatus for printing of this invention. It is explanatory drawing of the effect | action of the arithmetic processing of FIG. It is explanatory drawing which shows the difference in the printing system by a multipass printer and a line head printer. It is a conceptual diagram which shows the other example of the structure of a print head.

Explanation of symbols

1 is a personal computer, 2 is an inkjet printer, 3 is a device driver, 4 is a digital still camera, N is a nozzle

Claims (13)

  Input image acquisition means for acquiring image data having a gradation for each pixel, and image data of the predetermined range while maintaining the visual characteristics of the predetermined range of image data among the image data acquired by the input image acquisition means A gradation difference changing means for changing a difference in gradation between each pixel, and binarization for converting the gradation of image data in which the difference between each pixel is changed by the gradation difference changing means into a density of print dots An image processing apparatus for printing, comprising: processing means.   The gradation level difference changing unit includes a feature amount creation unit that creates a feature amount based on a gradation level of each pixel of the image data acquired by the input image acquisition unit, and a feature amount generated by the feature amount generation unit. The printing image processing apparatus according to claim 1, further comprising: a feature amount reflecting unit that reflects image data acquired by the input image acquiring unit.   The feature amount reflecting means reflects the feature amount to the image data so that the gradation of the image data has periodicity at least in a direction intersecting the print scanning direction. Image processing device for printing.   4. The printing image according to claim 2, wherein the feature amount reflecting unit reflects the feature amount in the image data so that the gradation of the image data has periodicity in the print scanning direction. Processing equipment.   5. The feature amount reflecting unit reflects the feature amount in the image data so that the gradation of neighboring pixels of the image data alternately becomes larger and smaller in a predetermined cycle. The printing image processing apparatus according to claim 1.   6. The image processing for printing according to claim 2, wherein the feature amount reflecting means outputs image data on which periodic noise different from the acquired image data is superimposed. apparatus.   The printing image processing apparatus according to claim 2, wherein the feature amount creating unit creates a feature amount from a gradation of pixels in a predetermined range of the acquired image data. .   The printing image processing apparatus according to claim 7, wherein the feature quantity creating unit creates a feature quantity from a sum of gradation levels of neighboring pixels of the acquired image data.   9. The feature amount reflecting unit according to claim 8, wherein the feature amount reflecting unit distributes the sum of gradations of neighboring pixels obtained by the feature amount creating unit to the original pixels according to a preset distribution ratio. Image processing device for printing.   The feature amount reflecting means divides the sum of the gradation levels of neighboring pixels obtained by the feature amount creating means by a preset ratio, and adds or subtracts the value to the original pixel gradation level. The image processing apparatus for printing according to claim 8.   11. The feature amount reflecting means reflects a feature amount when a difference in gradation of neighboring pixels of the acquired image data is equal to or less than a predetermined value. The image processing apparatus for printing described in the item.   A printing image processing program for causing a computer to change a difference in gradation between each pixel of image data in a predetermined range while maintaining visual characteristics of the image data in a predetermined range among the acquired image data. A printing apparatus comprising the printing image processing apparatus according to claim 1.

Images