JP2007028143A - Printing color evaluation system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a system which evaluates and confirms whether a printing color is printed as a standard by simultaneously photographing the printing color with a reference color chart without using a dedicated measuring device in a print creation process. <P>SOLUTION: The system includes a photographing unit (11) which simultaneously photographs the printing color (13) with the reference color chart (14) by a photographing device (12), a conversion unit (21) which converts three primary color signals acquired from a photographing means to color values using a reference color chart database (22), a comparison unit (31) which compares the printing colors and the color standard using the color values obtained from the conversion unit (21) and the color reference database (32), and a display unit (41) which displays the obtained result of the comparison unit (31), and executes color evaluation of the printing colors. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a system for evaluating whether or not a printing color is printed according to a standard in creating a printed matter.

In the color printed matter creation process, it is necessary to print the printed matter with a standard color. Therefore, at the printing site, while performing printing, evaluation and confirmation of whether or not the printed matter is printed according to the standard are performed at any time. As a method for confirming whether the printing is performed according to the standard, visual evaluation, a dedicated densitometer, and a color meter are used. In some cases, a larger-scale system is equipped with a color measurement device attached to a printing machine for evaluation and confirmation.
Japanese Patent Application No. 2004-173812 Japanese Patent Application No. 2004-175225

However, the visual evaluation method is based on human senses, and a correct evaluation is not always performed due to individual differences. In addition, in a method using a dedicated measuring device such as a color meter, an expensive dedicated measuring device such as a densitometer or a color meter must be used.
In view of the above-mentioned points, the present invention uses a commercially available digital camera or camera-equipped mobile phone to photograph a print color simultaneously with a reference color chart, and converts the photographed data into a color value or density, thereby Provides a system for accurately evaluating and confirming whether or not the printing color is printed according to the standard without using a dedicated measuring instrument.

The present invention includes a photographing means for photographing a printing color;
Conversion means for converting the three primary color signals of the photographed image obtained by the photographing means into color values and densities;
Comparison means for comparing the color value and density value obtained by the conversion means with the color value and density value of a preset color reference database to calculate a difference;
Display means for displaying the difference calculated by the comparison means;
A printing color evaluation system comprising:
The print color is photographed at the same time as a reference color chart in which one or more color charts with known color values and density values are arranged,
The conversion means refers to the reference color chart database including the color values of the reference color chart or the three primary color signal data, and converts the three primary color signals of the photographed reference color chart and the three primary color signals of the photographed designated color. Based on the conversion to color values,
The present invention relates to a printing color evaluation system.

  The present invention also relates to the print color evaluation system, wherein the reference color chart database includes three primary color signal data obtained by photographing the reference color chart in advance under two or more photographing conditions and color conversion parameters.

  Further, according to the present invention, the color reference database is a database that stores color references related to a plurality of print colors, and includes color names, CMYK values, XYZ, CIEL * a * b * color values, and density values. It is related with the said printing color evaluation system characterized.

  The conversion unit compares the three primary color signals of the reference color chart captured at the same time as the printing color with the imaging unit and the three primary color signals of the reference color chart captured in the reference color chart database, and the three primary color signals are the closest. The printing color evaluation system characterized in that the photographing condition is retrieved from the reference color chart database, and the three primary color signals of the photographed printing colors are converted into color values using the color conversion parameter of the retrieved photographing condition. About.

  The comparing means compares the color value and density value of the print color converted by the converting means with the color value and density value of a preset color reference database, and calculates the color difference and density difference. The present invention relates to the print color evaluation system.

The present invention also relates to the print color evaluation system, wherein the display means displays at least one of a color difference and a density difference between the print color calculated by the comparison means and the print color reference.

According to the present invention, evaluation and confirmation of whether the printing color is printed according to the standard can be performed accurately by anyone using a commercially available digital camera or camera-equipped mobile phone without requiring a dedicated measuring device. can do.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a diagram showing the configuration of the present invention. This system includes a photographing unit (11) that photographs the print color (13) at the same time as the reference color chart (14) by the photographing apparatus (12), and a reference color chart database (22) for the three primary color signals acquired by the photographing means. A conversion unit (21), which is a conversion unit that converts the color into a color value, and a comparison unit that compares the print color with the reference color using the color reference database (32) from the color value obtained by the conversion unit (21). And a display unit (41) which is a display means for displaying the result obtained by the comparison unit (31).
The photographing device (12) may be a photographing device capable of obtaining RGB three primary color signals of a photographed image, such as a commercially available digital camera or camera-equipped mobile phone.
Examples of the display unit (41) include a printer and a display.

FIG. 2 is a diagram illustrating an example of a reference color chart and an example of adjacent photographing with a printing color. Color chart 1 (C1) to color chart 8 (C8) are eight color charts whose color values are known in advance. Cut out the center of the reference color chart (P1). By placing the reference color chart (C0) on the print color (P0), the print color (P1) and the reference color chart (C1 to C8) can be photographed adjacent to each other. There is no particular limitation on the number of colors to be arranged in the reference color chart and the colors to be arranged. By increasing the number of colors, highly accurate color conversion can be performed.
The size and shape of the reference color chart are not particularly limited as long as there is an area that can be separated into three primary color signals after photographing.
Examples of combinations of eight colors include combinations of cyan, magenta, yellow, black, red, green, blue, white, and the like. Also, in the color evaluation of printed matter, solid colors (100% halftone dots) of cyan, magenta, yellow, and black are often used, so peripheral colors that approximate the reference color are arranged around the reference color to be confirmed. A plurality of reference color charts may be prepared. For example, a reference color chart in which color charts that include a standard cyan 100% solid color and have a density centered on the standard cyan 100% solid color is arranged. Similarly, a reference color chart for each standard color including a standard magenta 100%, yellow 100%, and black 100% solid color chart in which color charts having different densities around the standard solid colors are arranged.

In the reference color chart database (22), shooting conditions (221), conversion parameters (222), and RGB three primary color signals (223) of each color chart are stored for each different shooting condition. The conversion parameter (222) for each shooting condition is set in advance from the relationship between the RGB three primary color signals of the reference color chart obtained by shooting for each shooting condition and the color value and density of the reference color chart.
As two or more shooting conditions, for example, shooting is performed under conditions of a shooting device, a shooting mode, and a light source.
The conversion parameter can be obtained by a polynomial approximation method, for example.

  In the color reference database (32), the color name (321), CMYK (cyan percentage of cyan, magenta, yellow, and black in process printing) value (322), color value (XYZ, CIEL * a *) for each color reference. b * etc.) (323) and density value (324) are stored.

FIG. 3 is a diagram showing a flow of the present invention. The system according to the present invention photographs the print color and the reference color chart at the same time (S11). Next, the RGB three primary color signals of the print color portion and the reference color chart portion are extracted from the photographed image data (S21). The RGB3 primary color signal of the extracted reference color chart part is compared with the RGB3 primary color signal of the reference color chart part extracted by comparing the RGB value of the reference color chart for each shooting condition stored in the reference color chart database (S32). A shooting condition having a primary color signal is selected (S31). Next, the RGB primary color signal of the print color portion is converted into a color value by a polynomial approximation method using the conversion parameter stored in the selected shooting condition (S41).
The method of converting RGB 3 primary color signals of print colors into color values (XYZ, CIEL * a * b *, etc.) by polynomial approximation is as follows:
For example, using (Equation 1)

  Variables a, a ′, a ″, b, b ′, b ″, c, c ′, c ″, d, d ′, d ″ are conversion parameters stored in the reference color chart database for each photographing condition. . In this embodiment, a three-variable primary conversion equation is shown, but a three-variable secondary or tertiary may be used. Further, instead of preparing and calculating a variable according to (Equation 1), an ICC (International Color Consortium) compliant profile for each photographing condition may be used.

The method of converting the RGB three primary color signals of the print color to the density value of the print CMYK (cyan, magenta, yellow, black) by the logarithmic approximation method uses (Equation 2),

  Variables a2, a2 ', a2 ", b2, b2', b2" are conversion parameters stored in the reference color chart database for each photographing condition. In addition to the logarithmic approximation method, a function approximation method using a second-order, third-order, or polynomial function may be used.

The comparison means compares the color value and density value obtained by the conversion means with the color value and density value set in advance in the color reference database, and calculates the difference. The difference to be calculated may be a color difference that is a difference in color values, a density difference that is a difference in density values, or a difference in evaluation parameters combining these.
In order to compare the print color with the color reference, a color name or CMYK value is designated (S50), and the color value and density value of the converted print color and the color name stored in the color reference database (S52) or The color value and density value corresponding to the CMYK value are compared, and the color difference and density difference are calculated. (S51).

  The last obtained color difference and density difference are displayed (S61). The information to be displayed may be at least one of a color difference and a density difference, and a print color, a color reference color value, a density value, a color difference between the print color and the color reference, and a density difference are possible. In addition, an instruction for increasing the printing color to the color reference (increasing density or decreasing density) may be displayed from the density difference.

  As described above, this system enables anyone to accurately evaluate and confirm the print color with respect to the color reference without having a dedicated densitometer or measuring device at the printing site where the print color is evaluated and confirmed.

Configuration diagram of this system Example of adjacent shooting of reference color chart and specified color of this system Flow chart for implementing this system

Claims (6)

Photographing means for photographing the print color;
Conversion means for converting the three primary color signals of the photographed image obtained by the photographing means into color values and densities;
Comparison means for comparing the color value and density value obtained by the conversion means with the color value and density value of a preset color reference database to calculate a difference;
Display means for displaying the difference calculated by the comparison means;
A printing color evaluation system comprising:

The print color is photographed at the same time as a reference color chart in which one or more color charts with known color values and density values are arranged,
The conversion means refers to the reference color chart database including the color values of the reference color chart or the three primary color signal data, and converts the three primary color signals of the photographed reference color chart and the three primary color signals of the photographed designated color. Based on the conversion to color values,
Print color evaluation system.
2. The print color evaluation system according to claim 1, wherein the reference color chart database includes three primary color signal data and color conversion parameters obtained by photographing the reference color chart under two or more photographing conditions in advance.
The color reference database is a database that stores color references for a plurality of print colors, and includes color names, CMYK values, XYZ, CIEL * a * b * color values, and density values. Alternatively, the printing color evaluation system according to claim 2.
The conversion means compares the three primary color signals of the reference color chart captured at the same time as the printing color in the imaging means with the three primary color signals obtained by capturing the reference color chart in the reference color chart database, and the imaging conditions for which the three primary color signals are closest to each other. 4. The reference color chart database is searched, and the three primary color signals of the photographed print colors are converted into color values using the color conversion parameters of the retrieved photographing conditions. The printing color evaluation system described in any one.
The comparison unit compares the color value and density value of the print color converted by the conversion unit with the color value and density value of a preset color reference database, and calculates a color difference and a density difference. The printing color evaluation system according to any one of claims 1 to 4.
6. The print color evaluation system according to claim 1, wherein the display means displays at least one of a color difference and a density difference between the print color and the print color reference calculated by the comparison means.

Images