JP2006005449A - Method, apparatus, and program for generating gradation correction curve - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method, apparatus, and program for generating a gradation correction curve generating a gradation correction curve with excellent correction accuracy even in the case of application of the method, program and apparatus to an image output apparatus whose gradation characteristic is not clear. <P>SOLUTION: The method for generating the gradation correction curve includes: a measurement value acquisition step of acquiring a measured value of a physical quantity with respect to colors as to a plurality of color patches outputted from the image output apparatus on the basis of a series of input values different from each other; a gradation curve extraction step for extracting a plurality of gradation curves representing gradations of colors outputted from the image output apparatus by each of a plurality of kinds of extraction methods; a gradation correction curve generating step of generating a plurality of the gradation correction curves for correcting the gradations represented respectively by a plurality of the extracted gradation curves to a prescribed target gradation; and a gradation correction curve selection step of selecting one gradation correction curve among a plurality of the gradation correction curves generated by the gradation correction curve generating step. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a gradation correction curve creation method, a gradation correction curve creation apparatus, and a computer for causing a computer to operate as a gradation correction curve creation apparatus. The present invention relates to a tone correction curve creation program.

  Conventionally, image data representing an image is subjected to color conversion processing that matches the characteristics of the image output device that is to output the image, and further subjected to gradation correction processing that corrects the gradation of the color, and then the image data is converted. An image having a preferable color is created by outputting to an image output device. In this gradation correction processing, for example, a gradation correction curve is formed in a format such as LUT (lookup table) for each color of C (cyan), M (magenta), Y (yellow), and K (black). A process of converting each image data of CMYK based on each gradation correction curve is performed.

  As a method for creating the above gradation correction curve, Patent Document 1 describes a basic method for creating a gradation correction curve using a color chart composed of density patches of C, M, Y, and K. ing. Below, the gradation correction curve preparation method described in this patent document 1 is demonstrated.

  First, image data representing a color chart composed of a plurality of density patches for each of C, M, Y, and K is generated by a personal computer or the like, and the image data is sent to an image output device.

  When image data is sent from the personal computer, the image output device outputs a color chart based on the image data.

  The operator measures the density of each density patch of C, M, Y, and K constituting the color chart output by the image output device with a densitometer or the like, and uses a keyboard or mouse to send the measurement result to a personal computer. Enter a density value.

  In the personal computer, the density value of the input density patch is associated with the value of the image data when the density patch is generated, and the gradation of the color of the image output by the image output device is acquired. Further, a gradation correction curve for correcting the gradation to the target gradation is created.

  According to the method of Patent Document 1, an operator can easily create a tone correction curve without measuring empirical knowledge by simply measuring the density value of each density patch and inputting it to a personal computer. it can.

  By the way, the gradation correction processing described above is performed mainly in a high-quality image output system that outputs a high-quality image such as a proof system for simulating printing before printing. Therefore, conventionally, a program and an apparatus for creating a gradation correction curve to which the gradation correction curve creating method described in Patent Document 1 is applied are prepared for each image output system.

However, in recent years, the quality of images output from inexpensive image output devices such as printers has also increased rapidly, and even the familiar image output devices can easily perform gradation correction processing to further improve the output quality. There is a growing demand for it. In the case of such an inexpensive image output device, it is costly and expensive to prepare a program for creating a gradation correction curve dedicated to each device. It is preferable that one program or the like is applied in common.
JP 2001-245171 A

  However, the tone correction curve creation program and device that have been used in the past are specially created for each image output system, and output a specific type of image having tone characteristics within a predetermined prediction range. It is assumed that this is applied to the device. Therefore, if an attempt is made to divert a program or the like created for a specific type of image output device to an image output device whose gradation characteristic tendency is completely unknown, the gradation characteristic of the image output device exceeds the predicted range. If this is the case, there is a problem that the correction accuracy of the created gradation correction curve is extremely lowered.

  In view of the above circumstances, the present invention provides a gradation correction curve creation method, a floor, and a gradation correction curve that can create a gradation correction curve with good correction accuracy even when applied to an image output apparatus with unknown gradation characteristics. It is an object of the present invention to provide a tone correction curve creation device and a tone correction curve creation program capable of operating a computer as such a tone correction curve creation device.

The gradation correction curve creation method of the present invention that achieves the above object is a gradation correction curve creation method for creating a gradation correction curve that defines gradation correction of an image color.
For each of a plurality of color patches output based on a series of different input values by an image output device that outputs an image, a measurement value acquisition process for acquiring a measurement value in which a physical quantity related to color is measured;
A gradation curve extraction process for extracting a plurality of gradation curves representing the gradation of colors output by the image output device based on the input value and the measured value by each of a plurality of types of extraction methods;
A gradation correction curve creating process for creating a plurality of gradation correction curves for correcting the gradation represented by each of the plurality of gradation curves extracted in the gradation curve extraction process to a predetermined target gradation;
And a gradation correction curve selection process for selecting one gradation correction curve among a plurality of gradation correction curves created in the gradation correction curve creation process.

  Note that the gradation curve representing the gradation of the color according to the present invention may be extracted from the relationship of “measurement value with respect to input value”, or “measurement value that is opposite to that relationship” It may be extracted from the relationship of “input values to”, or may be extracted in units of physical quantities different from the physical quantities represented by these input values and measured values.

  In recent years, there has been a demand for the development of a gradation correction curve creation method for creating a highly accurate gradation correction curve that can be commonly applied to various types of image output apparatuses. Usually, the image output device is, for example, a device having a gradation close to the target gradation, a device having a gradation that is uniformly deviated from the target gradation, There are various gradation characteristics such as those that deviate from the target on the density side, and those that are close to the target in the intermediate area but deviate from the target on both the low density side and the high density side. Depending on the gradation characteristics, the extraction method suitable for the gradation curve extraction differs. Therefore, when one gradation correction curve creation method is commonly applied to various types of image output apparatuses, the gradation curve is extracted by one extraction method as in the conventional gradation correction curve creation method. If the extraction method is not suitable for the gradation characteristics of the image output apparatus, the correction accuracy of the gradation correction curve created based on the extracted gradation curve is degraded, and the image output apparatus It becomes impossible to correct the gradation of the color of the output image to the target gradation.

  According to the gradation correction curve creation method of the present invention, a plurality of gradation curves are extracted by each of the plurality of extraction methods, and therefore the gradation curve is also extracted by an extraction method suitable for the gradation characteristics of the image output apparatus. . Accordingly, a tone correction curve that matches the tone characteristics of the image output device is selected from a plurality of tone correction curves created based on each of the plurality of tone curves, and output by the image output device. It is possible to apply a gradation correction curve that corrects the gradation of the color of the image to be accurately performed.

  In the gradation correction curve creation method of the present invention, the gradation curve extraction process is a process of extracting a gradation curve by interpolating values between adjacent measurement values, and each of a plurality of types of interpolation methods. A process of extracting a plurality of gradation curves is preferable.

  Examples of interpolation methods for extracting gradation curves based on multiple measurement values include, for example, a polynomial approximation method that smoothly connects measurement values as a whole, and a quasi-Hermitian method that creates a curve that passes all measurement values. Has been widely used. For example, for unstable image output devices with varying measurement values, a polynomial approximation method is applied to extract the overall gradation tendency while ignoring the variations in the measurement values, and image output with excellent stability For the apparatus, a gradation curve is extracted by an extraction method suitable for the gradation characteristics of the image output apparatus by applying a quasi-Hermitian method that extracts a gradation curve in which all measured values are accurately reflected. Therefore, a highly accurate gradation correction curve can be created.

  Further, in the gradation correction curve creating method of the present invention, the gradation curve extraction process converts the measurement value into a second physical quantity unit different from the first physical quantity expressed by the measurement value. It is also preferable that the gradation curve is extracted in the unit of the physical quantity of 2, and the gradation curve is also extracted in the original unit of the first physical quantity that has not been converted to the unit of the second physical quantity.

  Since the shape of the extracted gradation curve is changed by changing the unit of the measurement value, the shape of the gradation correction curve created based on the gradation curve is also changed. Therefore, a plurality of gradation correction curves can be created by extracting gradation curves in a plurality of units.

  In the gradation correction curve creation method of the present invention, it is preferable that the first physical quantity is a density and the second physical quantity is a half-tone value.

  If there is a variation in the measured value of the color patch density, converting the measured value to halftone values will cause the gradation of the measured value after unit conversion to be lost due to dot gain, etc. There is a tendency to become smaller. In the case of a highly stable image output device with little variation in measured values, an image output device that is inferior in stability by applying a gradation correction curve that is created in units of density and accurately reflects the measured values In this case, the gradation of the color of the image output by the image output device is accurately applied by applying a gradation correction curve that is created in units of halftone values and emphasizes overall smoothness. A gradation correction curve to be corrected well can be selected.

  In the gradation correction curve creation method of the present invention, the gradation correction curve selection process is a process of selecting a gradation correction curve having a curve distortion of a predetermined value or less from among a plurality of gradation correction curves. Is preferred.

  By applying this preferred form of the gradation correction curve creation method, it is possible to reduce gradation problems such as tone jump.

  In the gradation correction curve creation method of the present invention, the gradation correction curve selection process may be configured such that, among the plurality of gradation correction curves, each of the plurality of measurement values acquired in the measurement value acquisition process is in accordance with the gradation correction curve. It is preferable that the gradation represented by the corrected plurality of correction values is a process of selecting a gradation correction curve that reproduces the target gradation at a predetermined reproduction rate or higher.

  By selecting a gradation correction curve that accurately reproduces the target gradation, the image output apparatus can output an image having a visually desirable color.

In addition, the gradation correction curve creating apparatus of the present invention that achieves the above object is a gradation correction curve creating apparatus that creates a gradation correction curve that defines gradation correction of an image.
For each of a plurality of color patches output based on a series of input values different from each other by an image output device that outputs an image, a measurement value acquisition unit that acquires a measurement value in which a physical quantity related to color is measured;
A gradation curve extraction unit that extracts a plurality of gradation curves representing gradations of colors output by the image output device based on the input value and the measurement value by each of a plurality of types of extraction methods;
A gradation correction curve creating section for creating a plurality of gradation correction curves for correcting the gradation represented by each of the plurality of gradation curves extracted by the gradation curve extracting section to a predetermined target gradation;
And a tone correction curve selection unit that selects one tone correction curve from among the plurality of tone correction curves created by the tone correction curve creation unit.

  According to the gradation correction curve creating apparatus of the present invention, a plurality of gradation curves are extracted by each of a plurality of types of extraction methods based on an input value and a measured value, and a plurality of gradation correction curves corresponding to each of the gradation curves are obtained. Is created. Therefore, a gradation curve is extracted even by an extraction method suitable for the gradation characteristic of the image output apparatus, and a gradation correction curve that accurately corrects the gradation of the color of the image output by the image output apparatus can be selected. .

  Note that only the basic form of the gradation correction curve creation device is shown here, but this is only for avoiding duplication, and the gradation correction curve creation device referred to in the present invention has the above basic configuration. Not only the form but also various forms corresponding to each form of the above-described gradation correction curve creating method are included.

The gradation correction curve creation program of the present invention that achieves the above object is executed in a computer, and the computer is used as a gradation correction curve creation device for creating a gradation correction curve that defines gradation correction of an image. In the gradation correction curve creation program to be operated,
On the computer,
For each of a plurality of color patches output based on a series of input values different from each other by an image output device that outputs an image, a measurement value acquisition unit that acquires a measurement value in which a physical quantity related to color is measured;
A gradation curve extraction unit that extracts a plurality of gradation curves representing gradations of colors output by the image output device based on the input value and the measurement value by each of a plurality of types of extraction methods;
A gradation correction curve creating section for creating a plurality of gradation correction curves for correcting the gradation represented by each of the plurality of gradation curves extracted by the gradation curve extracting section to a predetermined target gradation;
A gradation correction curve selection unit that selects one gradation correction curve among a plurality of gradation correction curves created by the gradation correction curve creation unit is configured.

  By executing the tone correction curve creation program of the present invention in a computer, the computer can be operated as the tone correction curve creation device as described above.

  In addition, the element such as a measurement value acquisition unit configured on the computer by the gradation correction curve creation program of the present invention may be composed of one program part, and a plurality of one element. These program parts may be configured, and a plurality of elements may be configured by one program part. In addition, these elements may be constructed so as to execute such actions by themselves, or constructed by giving instructions to other programs and program components incorporated in the computer. May be.

  ADVANTAGE OF THE INVENTION According to this invention, even if it is a case where it is a case where it applies to an image output device with unknown gradation characteristics, the gradation correction curve creation method and gradation correction curve which can create a gradation correction curve with favorable correction accuracy It is possible to provide a creation apparatus and a gradation correction curve creation program capable of operating a computer as such a gradation correction curve creation apparatus.

  Hereinafter, embodiments of the present invention will be described.

  FIG. 1 is an overall configuration diagram of an image processing system to which an embodiment of the present invention is applied.

  FIG. 1 shows a color scanner 10, which reads a document image 11 and generates four-color image data composed of C, M, Y, and K. The C, M, Y, and K image data is input to the personal computer 20. In the personal computer 20, the image data obtained by the color scanner 10 is converted into image data for image output suitable for a color printer 30 described later. Here, the description of FIG. 1 is interrupted, and functions provided in the personal computer 20 will be described with reference to FIG.

  FIG. 2 is a functional block diagram of the personal computer 20.

  The personal computer 20 shown in FIG. 1 has functions as a color conversion device 40, a gradation correction device 50, and a gradation correction curve creation device 60.

  The personal computer 20 has a color conversion profile in a look-up table format in which the correspondence between the image data in the color space suitable for the color scanner 10 shown in FIG. 1 and the image data in the color space suitable for the color printer 30 is defined. 41 is prepared in advance. The color conversion device 40 refers to the color conversion profile 41 and converts the image data sent from the color scanner 10 shown in FIG. 1 into image data in a color space suitable for the color printer 30.

  Further, the personal computer 20 is provided with a plurality of patch data representing a plurality of density patches for each color of C, M, Y, and K, and the color printer 30 in FIG. Thus, a color chart formed by a plurality of density patches is output. The gradation correction curve creating device 60 uses the density measurement value obtained by measuring the density of the density patch on the color chart to set the color gradation of the image output by the color printer 30 to a target gradation prepared in advance. A gradation correction curve 51 for correction is created. The processing in the gradation correction curve creating device 60 is processing performed in response to an operator instruction when a new printer is connected to the personal computer 20, for example. A method of creating the gradation correction curve 51 will be described in detail later.

  The tone correction device 50 performs tone correction processing on the image data sent from the color conversion device 40 in accordance with the tone correction curve 51 created by the tone correction curve creation device 60. The image data that has been subjected to gradation correction processing by the gradation correction device 50 is sent to the color printer 30 of FIG.

  This is the end of the description of FIG. 2, and the description will return to FIG. 1.

  The image data input from the color scanner 10 to the personal computer 20 is suitable for the color printer 30 and subjected to color gradation correction processing by the functions of the color conversion device 40 and the gradation correction device 50 shown in FIG. It is converted into image data and further sent to the color printer 30. In the color printer 30, print output based on the sent image data is performed, and a print image 31 is formed.

  In the image processing system shown in FIG. 1, a color printer 30 is shown as an example of an image output apparatus that outputs an image based on image data. However, the color printer 30 may be an electrophotographic color printer, An ink-jet color printer may be used, and the printing method is not questioned. The image output apparatus is not limited to a printer, and may be a printing machine. However, here, description will be made on the assumption that an image processing system including the color printer 30 is an example of the image output apparatus according to the present invention.

  Here, the feature of the image processing system shown in FIG. 1 as an embodiment of the present invention resides in the processing contents executed inside the personal computer 20, and the personal computer 20 will be described below.

  3 is an external perspective view of the personal computer 20 shown as one block in FIG. 1, and FIG. 4 is a hardware configuration diagram of the personal computer 20. As shown in FIG.

  The personal computer 20 has an appearance configuration, a main body device 21, an image display device 22 that displays an image on a display screen 22a in accordance with an instruction from the main body device 21, and a main body device 21 in accordance with various key operations. A keyboard 23 for inputting information and a mouse 24 for inputting an instruction corresponding to, for example, an icon or the like displayed at that position by designating an arbitrary position on the display screen 22a are provided. The main body device 21 has an FD loading port 21a for loading a flexible disk (hereinafter abbreviated as FD) and a CD-ROM loading port 21b for loading a CD-ROM.

  As shown in FIG. 4, the main unit 21 includes a CPU 211 that executes various programs, a main memory 212 that is read for execution by the CPU 211 and programs stored in the hard disk device 213, and various programs. And a hard disk device 213 in which data and the like are stored, the FD 100 are loaded, the FD drive 214 that accesses the loaded FD 100, the CD-ROM 110 is loaded, and the CD-ROM drive 215 that accesses the loaded CD-ROM 110 The input interface 216 is connected to the color scanner 10 (see FIG. 1) and receives image data from the color scanner 10, and the output interface 217 that sends image data to the color printer 30 is built-in. Also shown in FIG. Image display device 22, a keyboard 23, a mouse 24 are connected to each other via a bus 25.

  Here, one embodiment of the tone correction curve creation program of the present invention is applied to the CD-ROM 110, and tone correction curve creation for operating the personal computer 20 as the tone correction curve creation device 60 of FIG. The program is stored. The CD-ROM 110 is loaded into the CD-ROM drive 215, and the gradation correction curve creation program stored in the CD-ROM 110 is uploaded to the personal computer 20 and stored in the hard disk device 213. Then, when the gradation correction curve creation program is activated and executed, the personal computer 20 shown in FIG. 2 performs the gradation correction curve creation device 60 which is an embodiment of the gradation correction curve creation device of the present invention. Works as.

  Next, a tone correction curve creation program executed in the personal computer 20 will be described.

  FIG. 5 is a conceptual diagram showing the CD-ROM 110 in which an embodiment of the gradation correction curve creation program of the present invention is stored.

  The tone correction curve creation program 300 shown in FIG. 5 includes a measurement value acquisition unit 310, a tone curve extraction unit 320, a tone correction curve creation unit 330, and a tone correction curve selection unit 340. Details of each element of the gradation correction curve creation program 300 will be described later.

  FIG. 6 is a functional block diagram of the gradation correction curve creating device 60 shown in FIG.

  The gradation correction curve creation device 60 includes a measurement value acquisition unit 410, a gradation curve extraction unit 420, a gradation correction curve creation unit 430, and a gradation correction curve selection unit 440. These measurement value acquisition units 410, the tone curve extraction unit 420, the tone correction curve creation unit 430, and the tone correction curve selection unit 440 are included in the tone correction curve creation program 300 shown in FIG. Each of the curve extraction unit 320, the gradation correction curve creation unit 330, and the gradation correction curve selection unit 340 is configured on the personal computer 20. As described above, each element of the gradation correction curve creation device 60 shown in FIG. 6 corresponds to each element of the gradation correction curve creation program 300 shown in FIG. 5, but each element of FIG. Unlike the hardware and the combination of the OS and application program executed by the personal computer 20, each element shown in FIG.

  Hereinafter, by describing each element of the gradation correction curve creation device 60 shown in FIG. 6, each element of the gradation correction curve creation program 300 shown in FIG. 5 will also be described.

  In FIG. 1, a color printer 30 is shown as an image output device that outputs an image based on image data. However, various image output devices can be connected to the personal computer 20. When a new image output device is connected to the personal computer 20, the tone correction curve creating device 60 shown in FIG. 6 is used to correct the color tone of the image output by the image output device to the target tone. An instruction to create a tone correction curve is given.

  In the personal computer 20, a plurality of patch data having a series of different data values for each color of C, M, Y, and K are prepared. The plurality of patch data is first sent to the color conversion device 40 shown in FIG. 2 and subjected to color conversion processing by the color conversion device 40, and then sent to the color printer 30 shown in FIG. The printer 30 outputs a plurality of density patches as a color chart 401 based on each of the plurality of patch data. When the color chart 401 is output, the density is measured for each density patch forming the color chart 401 by the operator, and the density measurement value is input to the personal computer 20 using the mouse 24 shown in FIG. . The input concentration measurement value is acquired by the measurement value acquisition unit 410. The measurement value acquisition unit 410 corresponds to an example of a measurement value acquisition unit in the present invention. The density patch corresponds to an example of the color patch according to the present invention, and “density” corresponds to an example of “physical quantity relating to color” and “first physical quantity” according to the present invention, and the density of the density patch was measured. The “concentration measurement value” corresponds to an example of the “measurement value” in the present invention.

  The gradation curve extraction unit 420 represents the gradation of the color of the image output by the color printer 30 based on the data value of the patch data and the density measurement value of the density patch output based on the patch data. Extract the tone curve.

  Here, since an image output device having various gradation characteristics is connected to the personal computer 20 shown in FIG. 1, when an attempt is made to extract a gradation curve by one extraction method, the extraction method is the image output device. If it is not suitable for the tone characteristics, the tone curve cannot be extracted with high accuracy. As a result, the correction accuracy of the gradation correction curve created based on the gradation curve also deteriorates, and the color gradation of the image output by the image output device cannot be corrected to the target gradation. End up. Therefore, in the present invention, a plurality of gradation curves are extracted for each image output device by a plurality of extraction methods. In the present embodiment, the relationship between the “density value with respect to the data value” (hereinafter referred to as the first relationship) and the relationship between the “data value with respect to the concentration measurement value” (hereinafter referred to as the first relationship), which is opposite to the first relationship. (Referred to as a second relationship), a relationship of “net% conversion value with respect to data value” in which the unit of density measurement value of the first relationship is converted into a mesh% value (hereinafter referred to as a third relationship), and a third relationship Using each of the inverse relations of “data values with respect to half-tone conversion values” (hereinafter referred to as fourth relation), a polynomial approximation method as an interpolation method for interpolating between values, and Each of the quasi-Hermitian methods is adopted, and a gradation curve is extracted by a total of eight extraction methods. This “net% conversion value” is an example of the “second physical quantity” in the present invention, and the polynomial approximation method and the quasi-Hermitian method are examples of a plurality of types of interpolation methods in the present invention. The gradation curve extraction unit 420 corresponds to an example of the gradation curve extraction unit in the present invention.

  The tone correction curve creation unit 430 creates a plurality of tone correction curves for correcting the tone represented by each of the plurality of tone curves extracted by the tone curve extraction unit 420 to a target tone prepared in advance. To do. The tone correction curve creation unit 430 corresponds to an example of a tone correction curve creation unit in the present invention.

  The tone correction curve selection unit 440 selects one tone correction curve from the plurality of tone correction curves created by the tone correction curve creation unit 430. In the present embodiment, a gradation correction curve that reproduces a gradation close to the target gradation with a curve distortion of a predetermined value or less is selected. The gradation correction curve selection unit 440 corresponds to an example of the gradation correction curve selection unit in the present invention.

  The gradation correction curve creation device 60 is basically configured as described above.

  FIG. 7 is a flowchart showing a series of procedures until the gradation correction curve is selected by the gradation correction curve creating apparatus 60. Hereinafter, a series of processes from creating a plurality of gradation correction curves and selecting one gradation correction curve from among them will be described in detail using this flowchart.

  First, when an instruction to create a gradation correction curve is input by an operator, the personal computer 20 displays a plurality of pieces of patch data representing a plurality of density patches for each of C, M, Y, and K single colors in FIG. To the color printer 30 shown. The color printer 30 outputs a color chart 401 shown in FIG. 6 composed of a plurality of density patches based on the sent patch data (step S11 in FIG. 7).

  FIG. 8 is a diagram showing a color chart 401 also created in the color printer 30 and shown in FIG.

  In the color chart 401, 21 density patches are formed for each of C, M, Y, and K single colors. Each density patch is assigned a patch number for identifying each density patch. This batch number is stored in the personal computer 20 in association with a data value for outputting a density patch to which the patch number is assigned.

  Subsequently, the density of each density patch constituting the color chart 401 shown in FIG. 8 is measured. This measurement itself is an operation performed by the operator using, for example, a colorimeter equipped with a density measurement mode, away from the gradation correction curve creating device 60 of FIG. When the operator measures the density measurement value which is the density of the density patch, the operator inputs the patch number and the density measurement value to the personal computer 20 using the keyboard 23 shown in FIG. The input density measurement value is acquired by the measurement value acquisition unit 410 in FIG. 6 together with the data value associated with the patch number (step S12 in FIG. 7). The process of acquiring the density measurement value in step S12 in FIG. 7 corresponds to an example of the process of acquiring the measurement value in the gradation correction curve creation method of the present invention.

  The data value and density measurement value acquired by the measurement value acquisition unit 410 are sent to the gradation curve extraction unit 420.

  In step S2, the concentration measurement value is input to the personal computer 20 by using a colorimeter having a function of outputting the measurement data as a signal as it is, and connecting the colorimeter and the personal computer 20 with a signal cable. Thus, the measurement value may be input to the personal computer 20 as it is.

  The operations in steps S11 and S12 described above are not the operations of the main processing for creating the gradation correction curve, but are the preparation operations for creating the gradation correction curve.

  FIG. 9 is a schematic diagram showing the processing contents of steps S13 and S14 in the flowchart of FIG. In the following, in addition to FIG. 6 and FIG. 7, FIG. 9 will be used together to describe the main process for creating a gradation correction curve performed in the gradation correction curve creating apparatus 60.

  The personal computer 20 includes an image output device having various gradation characteristics, such as an image output device in which the gradation on the high density side tends to be crushed and an unstable image output device in which the density measurement value is likely to change due to the influence of temperature or the like. Is connected. Since the extraction method for accurately extracting the gradation curve differs depending on the gradation characteristics of the image output apparatus, the gradation curve is extracted by a plurality of extraction methods in the present invention.

  In the gradation curve extraction unit 420 of FIG. 6, gradation curves representing the gradation of the color of the image output from the color printer 30 of FIG. 1 based on the data value and the density measurement value are respectively extracted from a plurality of extraction methods. Are extracted (step S13 in FIG. 7).

In the present embodiment, eight gradation curves are extracted by the following eight extraction methods.
First_A method: A gradation curve is extracted by using a polynomial approximation method as an interpolation method for interpolating between values based on the first relationship (the relationship of the density measurement value to the data value).
First_B method: Based on the first relationship, a quasi-Hermitian method is adopted as an interpolation method.
Second_A method: A polynomial approximation method is employed as an interpolation method based on the second relationship (the relationship of the data value to the concentration measurement value).
Second_B method: Based on the second relationship, a quasi-Hermitian method is adopted as an interpolation method.
Method 3_A: A polynomial approximation method is employed as an interpolation method based on the third relationship (relationship of half-tone conversion value to data value).
Method 3_B: Based on the third relationship, the quasi-Hermitian method is adopted as the interpolation method.
Method 4_A: A polynomial approximation method is employed as an interpolation method based on the fourth relationship (relationship of halftone conversion value to data value).
Fourth_B method: Based on the fourth relationship, the quasi-Hermitian method is adopted as the interpolation method.

  First, a method of extracting a gradation curve by the first_A method and creating a gradation correction curve for the gradation curve will be described.

  Part (A) of FIG. 9 shows a first graph representing the first relationship in which the horizontal axis represents the data value (input value) and the vertical axis represents the concentration measurement value (output value). . The curve that smoothly connects the points on the first graph and the vicinity of the points represents the gradation of the color of the image output by the color printer 30 shown in FIG. 1, and the gradation curve P extracted in step S13 of FIG. It is. In the first_A method, the gradation curve P is extracted based on the first relationship.

  First, the vertical axis and the horizontal axis of the first graph shown in Part (A) of FIG. 9 are interchanged, and the concentration measurement value (output value) is shown on the horizontal axis and the vertical axis is shown in Part (B) of FIG. A first inverse graph associated with each data value (input value) is acquired.

Subsequently, the points between the points on the first inverse graph are interpolated by a polynomial approximation method, and a smooth first inverse curve P ^-1 passing through the points on the first inverse graph or near the points is created. Since the polynomial approximation method is a method that has been widely used in the past, the description thereof is omitted in this specification.

Here, the first inverse curve P ^-1 can lead the gradation curve P passing through the points on the first graph shown in Part (A) of FIG. The process of creating the first inverse curve P ^-1 is synonymous with the process of extracting the gradation curve P.

Further, by interpolating between points on the first graph shown in Part (A) of FIG. 9, the gradation curve P is directly extracted without creating the first inverse curve P ^−1. However, since the first inverse curve P ⁻¹ is used in the process of creating the gradation correction curve that follows, in this embodiment, the first inverse curve P ⁻¹ instead of the gradation curve P is used in step S13. To extract. The process of extracting the first inverse curve P ⁻¹ (ie, extracting the gradation curve P) in step S13 of FIG. 7 corresponds to an example of the gradation correction curve extraction process in the gradation correction curve creating method of the present invention. To do.

The first inverse curve P ⁻¹ extracted by the gradation curve extraction unit 420 in FIG. 6 is transmitted to the gradation correction curve creation unit 430. The tone correction curve creation unit 430 creates a tone correction curve for correcting the tone represented by the tone curve P to the target tone using the first inverse curve P ⁻¹ (step S14 in FIG. 7). .

Part (C) of FIG. 9 shows a target curve T representing a target gradation relating to the color of an image prepared in advance in the personal computer 20. The gradation correction curve C for correcting the gradation represented by the gradation curve P to the target gradation represented by the target curve T uses the target curve T and the first inverse curve P ⁻¹ .
Tone correction curve C = first inverse curve P ⁻¹ (target curve T) (1)
Is calculated by The process of creating the gradation correction curve in step S14 in FIG. 7 corresponds to an example of the gradation correction curve creation process in the gradation correction curve creation method of the present invention.

  FIG. 9D shows a gradation correction curve C created by applying the first_A method.

According to the method of the first_A, since the gradation curve P (actually, the first inverse curve P ⁻¹ ) is extracted without converting the density measurement value into the halftone conversion value, the measurement error or The correction accuracy of the gradation correction curve C to be created may deteriorate due to variations in density and the like. However, when applied to an image output apparatus in which the density measurement value changes smoothly, the first inverse curve P ^-1 having a smooth gradation can be obtained, so that the distortion of gradation during interpolation processing can be suppressed. A highly accurate gradation correction curve C can be created.

  Further, according to the first_A method, the polynomial approximation method is adopted as the interpolation method, and therefore, the gradation curve is extracted with an emphasis on the overall tendency rather than the variation in the density measurement value, and the color reproduction is performed. In the case of an image output device having unstable characteristics, the gradation correction curve C can be created with high accuracy.

  When the first_A method is applied, the gradation correction curve C is created as described above.

  Subsequently, a case where the first_B method is applied as a method of extracting a gradation curve will be described.

In the first_B method, almost the same processing as that of the first_A method is performed. However, a point between points on the first inverse graph shown in FIG. 9B is not a polynomial approximation method but a quasi-Hermitian method. Is interpolated to create the first inverse curve P- ¹ . This quasi-Hermitian method is also a method that has been widely used in the past, and thus description thereof is omitted in this specification.

According to the polynomial approximation method applied in the first_A method, the points on the first inverse graph shown in Part (B) of FIG. 9 and the first inverse curve P ^-1 that smoothly connects the points are created. On the other hand, according to the quasi-Hermitian method applied in the first_B method, a first inverse curve P ⁻¹ that passes through all points on the first inverse graph is created.

As described above, when the quasi-Hermitian method is applied as the interpolation method, the first inverse curve P ^-1 in which all the points are accurately reflected is created, so that a stable image output apparatus having good color reproducibility. In this case, a highly accurate gradation correction curve C is created.

  The n_A method (n is 1 to 4) and the n_B method (n is 1 to 4) described above differ only in the interpolation method. Therefore, in the following, they are referred to as the nth method (n is 1). ~ 4) will be described collectively.

  Next, a case where the second method (the second_A method or the second_B method) is applied as a method for extracting a gradation curve will be described.

In the second method, first, in FIG. 9 Part (A), the vertical axis (output value) is separated at predetermined intervals, the output value y by [Delta] y y = y _1, y _2, ..., and y _n Input values x ₁ , x ₂ ,..., X _{n when changed} are estimated based on each point on the first graph (horizontal axis: data value, vertical axis: concentration measurement value). In this example, the input value x is interpolated using each point on the first graph. These input values _{x 1, x 2, ...,} x n is the new data value, the output value _{y = y 1, y 2,} ..., y n is treated as a new density measurement.

Subsequently, output values (new concentration measurement values) y = y ₁ , y ₂ ,..., Y _{n on} the horizontal axis, and input values (new data values) x ₁ , x _{2 ,.} A second graph associated with each is acquired. This second graph shows the second relationship (the relationship of the data value to the concentration measurement value). Hereinafter, the second graph is regarded as the first inverse graph shown in Part (B) of FIG. 9, and the processing after the first inverse curve P ⁻¹ extraction in the first method is performed to create the gradation correction curve C. Is done.

  Since the shape of the second graph obtained by the second method is different from the shape of the first inverse graph obtained by the first method, when the second method is applied, the first graph is finally obtained. A gradation correction curve C having a shape different from that in the method can be created.

  Next, a case where the third method (the third_A method and the third_B method) is applied as a method for extracting a gradation curve will be described.

  In the third method, first, the density measurement value acquired by the measurement value acquisition unit 410 of FIG. 6 is converted into a unit of halftone value. In converting the measured density value into the net% conversion value in the unit of the net% value, the following Male-Davis equation is used.

However, D ₀ is the measured density of white background
D _s is the solid density measurement
D _t represents the measured density value to be converted to the halftone value.

  Subsequently, the horizontal axis is associated with the data value (input value), and the vertical axis is associated with the halftone conversion value (output value) in which the unit of the density measurement value is converted. A third graph representing the value relationship is acquired.

  Further, the target curve T shown in Part (C) of FIG. 9 is converted into the target curve T3 in the halftone conversion value by the equation (2).

Hereinafter, in the same manner as in the first method, the vertical axis and the horizontal axis in the third graph are interchanged, and the horizontal axis of the first inverse graph shown in Part (B) of FIG. 9 is the unit of the net conversion value (output value). The converted third inverse graph is acquired, and interpolation processing is performed using each point on the third inverse graph to create a third inverse curve P- ¹ . The third inverse curve P ^-1 also leads the gradation curve P passing through the points on the first graph shown in Part (A) of FIG. 9 by exchanging the vertical axis and the horizontal axis and using Equation (1). Therefore, the process of creating the third inverse curve P ⁻¹ having undergone unit conversion is also synonymous with the process of extracting the gradation curve P.

Further, using the third inverse curve P ⁻¹ and the target curve T3, the gradation correction curve C3 is created by the equation (1). In this gradation correction curve C3, since the unit of the correction value (vertical axis) is a halftone value, the gradation correction curve C3 is converted into the gradation correction curve C in the unit of density by the equation (2). .

  According to the third method, when the density measurement value is converted into the halftone conversion value, the gradation of the output value is slightly collapsed due to dot gain or the like, but the variation in the output value is suppressed. For this reason, even in the case of an unstable image output apparatus in which density measurement values vary, a tone correction curve with less distortion can be created.

  Subsequently, a case where the fourth method (the fourth_A method and the fourth_B method) is applied as a method for extracting the gradation curve will be described.

  In the fourth method, processing in which the second method and the third method are combined is performed.

  First, the concentration measurement value acquired by the measurement value acquisition unit 410 of FIG. 6 is converted into a half-tone conversion value by Equation (2).

Next, a third graph is acquired in which the horizontal axis is associated with the data value (input value) and the halftone conversion value (output value) in which the unit of the density measurement value is converted. Further, the vertical axis of the third graph (output value) is separated at predetermined intervals, the output value y by [Delta] y y = y _1, y _2, ..., the input value x ₁ when changing the y _n, x ₂ ,..., x _n are estimated based on points on the third graph (horizontal axis: data value, vertical axis: half-tone conversion value).

Subsequently, the horizontal axis represents the output value (new net% conversion value) y = y ₁ , y ₂ ,..., Y _n , and the vertical axis represents the input value (new data value) x ₁ , x _{2 ,.} A fourth graph in which each is associated is acquired. The fourth graph shows the fourth relationship (the relationship of the data value with respect to the dot% conversion value). Hereinafter, this fourth graph is regarded as the third inverse graph in the third method, and the same process as in the third method is performed to create the gradation correction curve C.

  When eight gradation correction curves are created as described above, these gradation correction curves are sent to the gradation correction curve selection unit 440 in FIG.

  First, the gradation correction curve selection unit 440 evaluates the correction accuracy for each of the eight gradation correction curves created by the gradation correction curve creation unit 430 (step S15 in FIG. 7).

  In the present embodiment, a reproduction evaluation method for evaluating how much the gradation expressed by the correction value obtained by correcting the density measurement value according to the gradation correction curve reproduces the target gradation, and the gradation correction curve Two evaluation methods of a distortion evaluation method for evaluating distortion are applied.

  First, the density measurement value acquired by the measurement value acquisition unit 410 of FIG. 6 is corrected to the correction density value according to the gradation correction curve C created by the first_A method, and the corrected density value and the target on the target curve T are corrected. A difference from the density value is calculated. The sum of the differences in the total concentration measurement values is set as the reproduction evaluation value in the first_A method. Similarly, reproduction evaluation values are calculated for each of the eight gradation correction curves C. The smaller the reproduction evaluation value, the correction is made so that the gradation of the color of the image output by the color printer 30 is reproduced closer to the target gradation.

  Subsequently, the distortion of the gradation correction curve is evaluated.

  When the function representing the gradation correction curve C is y = C (x), the distortion S of the entire gradation correction curve is calculated by the following equation.

  Using this equation (3), the distortion evaluation value of each of the eight gradation correction curves C is calculated. A smaller distortion evaluation value represents a curve with less distortion, and it is possible to reduce problems of color gradation such as tone jump.

  When the evaluation value of each gradation correction curve is calculated, the gradation correction curve selection unit 440 in FIG. 6 selects one gradation correction curve from the gradation correction curves (step 16 in FIG. 7). . In this example, the reproduction evaluation value and the distortion evaluation value described above are added at a predetermined ratio, and the gradation correction curve having the smallest total evaluation value (that is, reproducing the target gradation and reducing the distortion) is selected. . The process of evaluating and selecting the gradation correction curve in step S15 and step S16 in FIG. 7 corresponds to an example of the gradation correction curve selection process in the gradation correction curve creating method of the present invention.

  The gradation correction curve selected as described above is sent to the gradation correction apparatus 50 shown in FIG. The tone correction curve 51 is a tone correction that corrects the tone of the color of the image output by the color printer 30 with the highest accuracy among the plurality of tone correction curves created by the tone correction curve creating device 60. By applying the gradation correction curve 51, the color printer 30 can output an image having a preferable color.

  Even when a new printer or the like whose gradation characteristics are unknown is connected to the personal computer 20, if an operator inputs an instruction to create a gradation correction curve, a plurality of gradations can be obtained by a plurality of methods. A correction curve is created, and a tone correction curve suitable for the printer is selected from the plurality of tone correction curves. Therefore, even when applied to a printer whose gradation characteristics are unknown, a gradation correction curve with good correction accuracy can be created.

  Above, description about embodiment of this invention is complete | finished.

  In the above description, an example is shown in which density is applied as an example of the “physical quantity related to color” according to the present invention. However, the “physical quantity related to color” according to the present invention may be a colorimetric value or the like. .

  In the above description, an example of applying the net% value as an example of the “second physical quantity” in the present invention is shown. However, the “second physical quantity” in the present invention is based on the measured value. As long as it is uniquely calculated, it is not limited to the halftone value.

1 is an overall configuration diagram of an image processing system to which an embodiment of the present invention is applied. 2 is a functional block diagram of a personal computer 20. FIG. 1 is an external perspective view of a personal computer 20 shown as one block in FIG. 2 is a hardware configuration diagram of a personal computer 20. FIG. It is a conceptual diagram which shows CD-ROM110 in which one Embodiment of the gradation correction curve creation program of this invention was memorize | stored. FIG. 3 is a functional block diagram of the gradation correction curve creation device 60 shown in FIG. 2. 10 is a flowchart showing a series of procedures until a gradation correction curve is selected by the gradation correction curve creating apparatus 60. It is a figure which shows the color chart 401 also shown in FIG. It is the schematic diagram which showed the processing content of step S13 and step S14 in the flowchart of FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Color scanner 11 Original image 20 Personal computer 21 Main body apparatus 21a FD loading slot 21b CD-ROM loading slot 22 Image display apparatus 22a Display screen 23 Keyboard 24 Mouse 25 Bus 211 CPU
212 Main Memory 213 Hard Disk Device 214 FD Drive 215 CD-ROM Drive 216 Input Interface 217 Output Interface 30 Color Printer 31 Print Image 40 Color Conversion Device 41 Color Conversion Profile 50 Gradation Correction Device 51 Gradation Correction Curve 60 Gradation Correction Curve Creation Device 100 FD
110 CD-ROM
300 Gradation correction curve creation program 310 Measurement value acquisition unit 320 Gradation curve extraction unit 330 Gradation correction curve creation unit 340 Gradation correction curve selection unit 410 Measurement value acquisition unit 420 Gradation curve extraction unit 430 Gradation correction curve creation unit 440 gradation correction curve selection section

Claims (8)

In a gradation correction curve creation method for creating a gradation correction curve that defines gradation correction of an image color,
For each of a plurality of color patches output based on a series of different input values by an image output device that outputs an image, a measurement value acquisition process for acquiring a measurement value in which a physical quantity related to color is measured;
A gradation curve extracting step of extracting a plurality of gradation curves representing gradations of colors output by the image output device based on the input value and the measured value by each of a plurality of types of extraction methods;
A gradation correction curve creating process for creating a plurality of gradation correction curves for correcting the gradation represented by each of the plurality of gradation curves extracted in the gradation curve extracting process to a predetermined target gradation;
A gradation correction curve creation method comprising: a gradation correction curve selection process for selecting one gradation correction curve among a plurality of gradation correction curves created in the gradation correction curve creation process.   The gradation curve extraction process is a process of extracting a gradation curve by interpolating values between adjacent measurement values, and a process of extracting a plurality of gradation curves by each of a plurality of types of interpolation methods. The gradation correction curve creating method according to claim 1.   The gradation curve extraction process converts the measurement value into a second physical quantity unit different from the first physical quantity represented by the measurement value, and extracts a gradation curve in the second physical quantity unit. The gradation correction curve creating method according to claim 1, wherein the gradation curve is extracted even in the original first physical quantity unit that has not been converted to the second physical quantity unit.   4. The gradation correction curve creating method according to claim 3, wherein the first physical quantity is a density, and the second physical quantity is a halftone value.   2. The gradation correction according to claim 1, wherein the gradation correction curve selection process is a process of selecting a gradation correction curve whose curve distortion is a predetermined value or less from the plurality of gradation correction curves. Curve creation method.   The gradation correction curve selection process is expressed by a plurality of correction values obtained by correcting each of the plurality of measurement values acquired in the measurement value acquisition process according to the gradation correction curve, among the plurality of gradation correction curves. 2. The gradation correction curve creating method according to claim 1, wherein the gradation correction curve is a process of selecting a gradation correction curve that reproduces the target gradation at a predetermined reproduction rate or higher. In a gradation correction curve creation device for creating a gradation correction curve that defines gradation correction of an image,
For each of a plurality of color patches output based on a series of input values different from each other by an image output device that outputs an image, a measurement value acquisition unit that acquires a measurement value in which a physical quantity related to color is measured;
A gradation curve extraction unit that extracts a plurality of gradation curves representing gradations of colors output by the image output device based on the input value and the measurement value by a plurality of types of extraction methods;
A gradation correction curve creating section for creating a plurality of gradation correction curves for correcting the gradation represented by each of the plurality of gradation curves extracted by the gradation curve extracting section to a predetermined target gradation;
A gradation correction curve creating apparatus comprising: a gradation correction curve selecting section that selects one gradation correction curve from among the plurality of gradation correction curves created by the gradation correction curve creating section. In a gradation correction curve creation program that is executed in a computer and operates as a gradation correction curve creation device that creates a gradation correction curve that defines gradation correction of an image.
On the computer,
For each of a plurality of color patches output based on a series of input values different from each other by an image output device that outputs an image, a measurement value acquisition unit that acquires a measurement value in which a physical quantity related to color is measured;
A gradation curve extraction unit that extracts a plurality of gradation curves representing gradations of colors output by the image output device based on the input value and the measurement value by a plurality of types of extraction methods;
A gradation correction curve creating section for creating a plurality of gradation correction curves for correcting the gradation represented by each of the plurality of gradation curves extracted by the gradation curve extracting section to a predetermined target gradation;
A gradation correction curve creation program, comprising: a gradation correction curve selection section that selects one gradation correction curve among a plurality of gradation correction curves created by the gradation correction curve creation section.

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