JP2006121398A - Image processor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve user's convenience by shortening a calculation time by reducing the number of tables for calculating an input image as compared with the conventional technique and making an output result high in quality. <P>SOLUTION: An image processor having a means for multi-valued error diffusion and a means of storing a pattern representing a specified gradation with a plurality of pixels has a means of printing a specified pattern, a means of measuring colors of the chart, and a means of changing the pattern according to the colorimetric data. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an image processing apparatus having means for printing a specific chart, measuring the color, and calibrating a printing unit.

  Some printers that use dots to print, such as inkjet printers, treat multiple dots as a group of pixels, and form an image by combining the pattern (hereinafter, halftone dot pattern) and multilevel error diffusion There is.

In addition, some current business inkjet printers include means for correcting individual differences for each head that ejects ink. This is a technique generally called head shading. In many cases, a specific chart is printed by a printing device to be corrected, read by a scanner, and a value to be corrected is calculated based on the data. Then, the output result is corrected by calculating the correction amount as a table to the input image.
Japanese Patent Laid-Open No. 5-220977

  However, depending on the correction table made by this method, the gradation is compressed, and there is room for improvement in that it is easy to create a pseudo contour in the output image.

  In addition, it is necessary to calculate the correction table for the input image for this processing, and there is room for improvement that extra processing time is required.

  An object of the present invention is to improve the convenience of the user by reducing the number of tables to be calculated for an input image to shorten the calculation time and making the output result higher quality than the prior art.

  In order to achieve the above object, the present invention provides means for printing a specific chart in an image processing apparatus having means for performing multilevel error diffusion and means for storing a pattern expressing a specific gradation by a plurality of pixels. And means for colorimetric measurement of the chart and means for changing the pattern according to the colorimetric data.

  According to the present invention, a high-quality output result can be obtained and the calculation time can be shortened.

  Hereinafter, specific examples related to the present invention will be described.

  FIG. 1 is a block diagram showing the configuration of an image processing apparatus and an image printing apparatus in this embodiment.

  First, the apparatus in this embodiment is roughly divided into three parts. One is a scanner unit that reads an image and converts it into an image signal, a main device unit that performs various calculations, and a recording device unit that receives print data from the main device unit and performs printing.

  Hereinafter, each member will be described.

  Reference numeral 101 denotes a recording apparatus main control unit for controlling the entire recording apparatus, which includes an MPU, a ROM, a RAM, and the like.

  A print buffer 102 stores raster data before being transferred to the print head. Reference numeral 103 denotes a print head that ejects ink in accordance with a signal from the print buffer. As shown in FIG. 4, which will be described later, it comprises a plurality of ink tanks and ink nozzles. Reference numeral 104 denotes a paper supply / discharge motor unit that conveys printing paper and performs paper supply / discharge.

  Reference numeral 105 denotes an I / F signal line that connects the main apparatus and the recording apparatus unit, and is, for example, as in the Centronics specification. A data buffer 106 temporarily stores print data received from the main apparatus.

  A system bus 107 connects the recording unit main control unit and each member.

  Reference numeral 108 denotes a main apparatus main control unit that controls creation of a print image and main calculation, and includes an MPU, ROM, RAM, and the like. The expected maximum density, threshold value, etc. at the time of multilevel error diffusion described later are stored here. Reference numeral 109 denotes an I / F unit with the recording unit. Reference numeral 110 denotes a display unit that displays various information to the user, such as a CRT. Reference numeral 111 denotes an I / F unit for communication with the reading unit. Reference numeral 112 is for a user to perform an operation, such as a keyboard or a mouse. Reference numeral 113 denotes a system bus that connects the main device main control unit and each member.

  Reference numeral 114 denotes a main control unit of the reading unit, which includes an MPU, a ROM, a RAM, and the like. Reference numeral 115 denotes an I / F unit that performs communication with the main apparatus. Reference numeral 116 denotes a reading unit which is composed of a CCD or the like. Reference numeral 117 denotes a motor control unit that conveys the read document. A reading device storage unit 118 is an image data storage unit that temporarily stores an image read by the CCD before sending it to the main device. Reference numeral 119 denotes a system bus that connects the main control unit of the reading apparatus and each member.

  In this embodiment, an ink jet printer is used as a recording apparatus. An ink jet printer is a printer of a system that discharges ink droplets from nozzles and records them on recording paper.

  This type of printer has a certain degree of variation in ejection for each print head and for each printing apparatus, and a technique called head shading is used to suppress this. For example, it is a thing like Unexamined-Japanese-Patent No. 5-220977.

  FIG. 2 shows the flow of image data in this embodiment. When image data is input, color correction is first performed in S201 (S201 ′), and then separated into four colors of CMYK in S202 (S202 ′). Thereafter, multilevel error diffusion is performed in S203 (S203 ′), and binarization is performed by replacing each pixel of the resulting image with a corresponding halftone dot pattern in S204 (S204 ′).

  FIG. 3 shows an example of a halftone dot pattern used for development. In this embodiment, two types of ink, dark ink and light ink, having different densities are used to print one of the four colors of CMYK. Therefore, as the halftone dot pattern, two patterns for dark ink and light ink are prepared for each gradation as shown in FIG. Further, in this embodiment, the number of gradations for each ink color is uniformly 8 gradations, but this may have finer gradations, or the number of gradations may be different for each color. .

  In this embodiment, the gradation of multi-level error diffusion is equally spaced. However, this may not necessarily be equally spaced, and the halftone may be dense, or the highlight portion and shadow portion may be dense. Is possible.

  Further, FIG. 3-2 shows the correspondence between each initial pattern and the threshold value of each gradation. As this initial pattern, a pattern having a less noticeable graininess is selected in advance. A representative value is determined for each initial pattern, and an intermediate value between the representative values of the gradations is set as a threshold value for multilevel error diffusion.

  Next, the calibration method will be described.

  First, FIG. 4 is a color measurement chart for use in calibration. For each gradation, a patch composed of only a single pattern candidate used for each gradation is prepared for each color. This pattern candidate includes other patterns excellent in graininess in addition to the initial setting selected as the default. In this embodiment, assuming that 32 types of pattern candidates are prepared for each color, the total number of patches is 129 of 32 types × 4 colors + 1. The last addition is a pure white pattern, because it is one type.

  Information necessary for calibration is obtained by measuring the color of each patch.

  FIG. 5 is a table showing the correspondence between the color number counter bits and the colors used in the calibration process.

  FIG. 6 shows how the calibration is performed by correcting the threshold value according to the flowchart of FIG.

  First, in step S601, a specific chart, in this embodiment, a color chart for calibration as shown in FIG. 4 is printed.

  In step S602, the chart is read by a scanner. At this stage, the result is stored as an 8-bit RGB JPEG image. In step S603, the color number counter and the error code counter are cleared for initialization.

  In step S604, the set density value of each color gradation is read out to the memory. In this embodiment, this value is determined in advance for the media used in the printing apparatus. The maximum density that can be satisfactorily satisfied if the apparatus is within the standard by taking into account the individual differences of the printing apparatus. It is set to a density value that is evenly divided up to the density.

  Next, in S605, the average value of each patch of the corresponding color is obtained for each RGB channel. Here, for the sake of simplicity, based on the RGB values, cyan according to the conversion formulas Log 10 ((255-R) / 255), Log 10 ((255-G) / 255), Log 10 ((255-B) / 255), Conversion is made for each of magenta and yellow, and this is used as the average density of each patch.

  In S606, a pattern that is closest to the set density value of each gradation is selected one by one for each gradation. At this time, if a corresponding pattern is not found within a certain range, it is opened. The certain range is determined in advance for each gradation, for example, within ± 0.2 of the density value from the set value.

  Thereafter, in S607, it is confirmed whether or not all patterns have been searched. If it is completed, the process is passed to S608, and if not, the process is passed to S612.

Next, in S608, based on the density obtained in S605, the representative value of each pattern selected in S606 is calculated. Taking the cyan patch as an example, the formula used for the calculation is as follows, with the expected maximum density being Cmax and the paper density being the C _PAPER patch measured density being C _B.

C = 255 × C _B / Cmax
Using the above formula, the representative value of each patch is obtained and used as the representative value of each gradation. By using the above formula, the printing result of the binarized image to which the halftone dot pattern is applied becomes linear with respect to the input value, and it becomes easy to perform image processing that matches human visual characteristics.

  In S609, a threshold value between each gradation is calculated based on the representative value calculated in the previous item.

  In step S610, the color number counter is incremented by one.

  If the color number counter is 6 in S611, the process returns to S604 to continue the process for the next color, and if it is 4, the process is passed to S612.

  In S612, the error code is determined. If the error code is 0, it is displayed in S613 that the calibration is successful. If it is not 0, an error is displayed according to the error code in S614.

It is a block diagram which shows the schematic structure of a present Example. It is a schematic diagram of the flow at the time of performing image processing. It is a conceptual diagram of a halftone dot pattern and a threshold value of each gradation. It is a conceptual diagram of the chart used in the case of calibration. It is a correspondence table | surface with each color and the bit of a color number counter. It is a flowchart which shows the algorithm at the time of performing calibration.

Claims (23)

  In an image processing apparatus having means for performing multi-level error diffusion and means for storing a pattern expressing a specific gradation by a plurality of pixels, means for printing a specific chart, means for measuring the color of the chart, An image processing apparatus having means for changing the pattern according to colorimetric data.   2. The image processing apparatus according to claim 1, wherein the pattern is composed of inks having different densities.   2. The image processing apparatus according to claim 1, wherein the number of gradation levels of the multi-level error diffusion is different for each color.   2. The image processing apparatus according to claim 1, wherein a threshold value of the multi-level error diffusion is different for each color.   2. The image processing apparatus according to claim 1, wherein the number of pixels constituting the pattern is different for each color.   2. The image processing apparatus according to claim 1, wherein the number of gradations of the multilevel error diffusion is increased or decreased by the colorimetric data.   The image processing apparatus according to claim 1, wherein the chart or the printing apparatus is recognized to be defective based on the colorimetric data.   2. The image processing apparatus according to claim 1, wherein the purpose of changing the multi-value error diffusion pattern is correction for maintaining a linear density with respect to an input value.   9. The image processing apparatus according to claim 8, wherein the pattern is composed of inks having different densities.   9. The image processing apparatus according to claim 8, wherein the number of gradation levels of the multi-level error diffusion is different for each color.   9. The image processing apparatus according to claim 8, wherein the multi-value error diffusion threshold value is different for each color.   9. The image processing apparatus according to claim 8, wherein the number of pixels constituting the pattern is different for each color.   9. The image processing apparatus according to claim 8, wherein the number of gradations of the multilevel error diffusion is increased or decreased by the colorimetric data.   9. The image processing apparatus according to claim 8, wherein the chart or the printing device is recognized to be defective from the colorimetric data.   2. The image processing apparatus according to claim 1, wherein the purpose of changing the pattern of multi-value error diffusion is to correct individual differences for each printing apparatus.   The image processing apparatus according to claim 15, wherein the pattern is made of inks having different densities.   The image processing apparatus according to claim 15, wherein the number of gradations of the multi-level error diffusion is different for each color.   16. The image processing apparatus according to claim 15, wherein the multi-value error diffusion threshold value is different for each color.   16. The image processing apparatus according to claim 15, wherein the number of pixels constituting the pattern is different for each color.   16. The image processing apparatus according to claim 15, wherein the number of gradations of the multilevel error diffusion is increased or decreased by the colorimetric data.   16. The image processing apparatus according to claim 15, wherein the chart or the printing apparatus is recognized as having a problem from the colorimetric data.   9. The image processing apparatus according to claim 8, wherein the purpose of changing the pattern of multilevel error diffusion is to correct individual differences for each printing apparatus in addition to maintaining a linear density with respect to an input value. An image processing apparatus.   2. The image processing apparatus according to claim 1, wherein a threshold value for multi-level error diffusion is corrected in accordance with a selected pattern.

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