KR20020041698A - Method for correcting color difference influenced by scanner characteristic and computer readable medium stored thereon computer executable instruction for performing the method - Google Patents

Abstract

PURPOSE: A method of compensating color differences caused by scanner characteristics is provided to extract color errors between color tables inputted by scanning an original color table and a color chart, to confirm the extracted color errors as compensation values of a scanner, and to apply a compensation value of a color corresponding to a color value when a substantial image is inputted, thereby compensating a color of a scanned image near to a color of the substantial image. CONSTITUTION: A program sets an original color table on a computer(S10). The program displays a color value measured by a counter, and makes out a color chart(S11). The program scans the color chart by a scanner, and makes an input color table(S12). The program extracts an error of colors between the original color table and the input color table(S13). The program stores the analyzed error in a compensation color table(S14). If an image is scanned, the program applies the compensation color table to inputted data to compensate a color of the image(S15).

Description

TECHNICAL FOR CORRECTING COLOR DIFFERENCE INFLUENCED BY SCANNER CHARACTERISTIC AND COMPUTER READABLE MEDIUM STORED THEREON COMPUTER EXECUTABLE INSTRUCTION FOR PERFORMING THE METHOD }

The present invention relates to a method for correcting color differences caused by the characteristics of a scanner. More particularly, a color chart is created by setting an original color table that is a color reference on a computer and displaying color values measured by a measuring instrument. Creates an input color table by scanning and stores the error of the color between the original color table and the input color table in the corrected color table. When the actual image is scanned, the color generated by the characteristics of the scanner by applying the correction value of the corrected color table to the input color data. To correct the difference.

A scanner is a device that converts analog images into digital data information and generates data that can be processed on a computer. The scanner includes a drum scanner, a charge coupled device (CCD) scanner, and a barcode scanner. Scanners for image input have different hardware characteristics depending on the type and supplier of the scanner. Accordingly, even if the same image is inputted to the scanner, the color values input by the type and supplier of the scanner are different.

Therefore, calibration through a profile or the like is required before inputting an image through the scanner. In this case, the profile refers to the process that is executed automatically when logging in to the system, and the calibration refers to the correction of the color displayed on the monitor when the input from the scanner or the output from the color printer is different from the actual color. Say that.

A monitor is a type of output device of a computer, which refers to a computer display and parts that are packaged as a related physical object. The monitor is calibrated by adjusting a gamma value of the monitor. In this case, the gamma value of the monitor is to match the reproducibility of the color. When the picture or photo is read by the scanner, the value of the gamma value is used to match the difference between the actual original and the original image. A picture file may have been displayed on different monitors. When gamma value can be reproduced the same color. In addition, even if the same monitor displays the same picture file according to the program, the picture quality of the color is different. However, the gamma value can be adjusted.

The above calibration requires that the user can operate in the same manner each time the scanner is used.

In addition, in order to output the same image as the original, color errors caused by hardware characteristics such as printing must be corrected. In this process, color correction of the scanner as an input means must be preceded.

In order to solve the above problems, the present invention extracts the error of the color value between the original color table and the color table inputted by scanning the color chart, which is determined as a correction value of the scan, and when the actual image is input. An object of the present invention is to correct a color of an image to be scanned to approximate a color of an actual image by applying a correction value of a color corresponding to the color value.

1 is a view showing a color chart according to an embodiment of the present invention.

2 is an overall procedure flow diagram according to an embodiment of the present invention.

3 is a diagram illustrating a process of modeling color chart information into a two-dimensional sheet and three-dimensional cubic according to an embodiment of the present invention.

4 is a diagram illustrating a method of extracting an error of color with a Bezier curve according to an embodiment of the present invention.

<Description of the symbols for the main parts of the drawings>

10 ... Color chart 40 ... Curve before correction

20 ... Two-dimensional modeling 50 ... Curves corrected using Bezier curves

30 ... cubic modeling cubic

According to another aspect of the present invention, there is provided a method of correcting a difference in color caused by a characteristic of a scanner, the method including: (a) setting an original color table as a reference for color on a computer; (b) creating a color chart by displaying the color values measured by the instrument; (c) scanning the color chart with a scanner to create an input color table; (d) extracting an error of color between the original color table and the input color table; (e) storing the analyzed error in a corrected color table; And (f) correcting the color by applying the correction color table to input data when the image is scanned.

In the present invention, the color table is characterized by a scanner characterized in that the cubic through modeling the RGB to CMY two-dimensional sheet and CMY to CMYK three-dimensional modeling.

In the present invention, in the step (d), the extraction of the error may extract the color stored in the original color table and the input color table to calculate the difference between the values corresponding to the position of each table, the extraction of the error is the input color By using the method of giving a level to the color information of the table, the expanded level can be used as an error. The extraction of the error can be done by expressing the color values of the original color table and the input color table as Bezier curves and using the difference between the two curves as errors. Can be.

DETAILED DESCRIPTION Hereinafter, the present invention will be described in detail with reference to examples, and the present invention will be described in detail with reference to the accompanying drawings. However, embodiments according to the present invention may be modified in many different forms, and the scope of the present invention should not be construed as being limited to the embodiments described below. Embodiments of the present invention are provided to more clearly and easily describe the present invention to those skilled in the art.

1 is a view showing a color chart according to an embodiment of the present invention.

Here, the color chart refers to a chart created by displaying color values of pure colors measured by a measuring instrument. In the embodiment of the present invention, cyan, magenta, yellow, and black are 0% to 0%. It was written in 4% increments in the range of 100%, with cyan as C #, often M #, yellow as Y #, and black as K #. Where # represents the numerical value of% of the color.

Color measuring instruments that measure color include objects that measure the color, temperature, and light of objects, and color meters that measure the color of objects include spectrophotometers and chromatic color meters. In the present invention, a color chart having a pure color value can be prepared by using a chromatic colorimeter for measuring a reflected object capable of measuring reflected light on an object surface such as a painted surface, a printed surface, a cloth, or a plastic.

In the exemplary embodiment of the present invention, pure cyan, magenta, yellow, and black, which are measured by a measuring instrument, are divided into 26 levels, and colors having a 4% increase in every step are obtained. If the image is displayed, but the color error is large when inputting the image into the scanner in consideration of the characteristics of the scanner, each step can be further subdivided to create a color chart. Thus, if one wants to correct the color values between 0% and 4% to more accurate color values, each step can be subdivided in increments of 2% or 1%.

Color bits are a predetermined number of contiguous bits that are assigned to each display pixel to determine the color when it is displayed on a monitor. For example, two color bits (2 ² = 4) for four colors. 16 colors require 4 color bits (2 ⁴ = 16), and 256 colors require 8 color bits (2 ⁸ = 256). 2 ⁸ x 2 ⁸ x 2 ⁸ = 256 x 256 x 256 = 16,777,216 Colors are called 24-bit true color systems.

Normally, the pure basic color is expressed in steps of 2 ⁸ = 256, and the color can be corrected by the characteristics of the scanner and the color loss caused by the characteristics of the scanner without making the entire color into the color chart according to the present invention. In the case of one embodiment of the present invention, color correction is possible by setting only the 26 step), thereby saving memory on the computer and bringing a significant improvement in speed, which is a decisive variable in color-intensive work such as graphics.

2 is an overall procedure flow diagram according to an embodiment of the present invention.

Referring to the flow of the overall procedure of the present invention as shown in Figure 2, the steps of setting the original color table (S10), creating a color chart (S11), scanning the color chart to create an input color table ( S12), analyzing the error of the color between the original color table and the input color table (S13), storing the analyzed error in the corrected color table (S14), correcting the corrected color table in the input color data when the actual image is scanned. The correction is made using the value (S15).

In the step S10 of setting the original color table, a color table in which the same color as the color ratio of the color chart created by measuring with a measuring instrument is stored can be used on a computer. Here, the original color table refers to a table used as a reference for inputting a color chart into a scanner, storing the input color information in the input color table, and comparing the same.

In the step S11 of creating a color chart, a color chart of pure color is generated by measuring with a color measuring instrument. The color chart created in this step is input to the scanner and used to correct color errors and color loss that appear due to the characteristics of the scanner.

In the step S12 of scanning a color chart to create an input color table, an input color table is created to compare the color chart information inputted by the scanner with the original color table. Here, the input color table refers to a table storing color information of the color chart input to the scanner.

The most accurate way to specify color is to use a frequency band graph for all colors, but this is not possible, so various methods have been developed to describe colors in specific situations, called color models. The color model defines a three-dimensional color coordinate system and is a subset of the coordinate system that includes all the colors of a particular gamut. RGB (red, green, blue) used for color CRT monitors, YIQ used for broadcast TV color systems, and CMY (cyan, magenta, yellow) used for color printer devices are hardware-dependent color models.

The RGB color model has an additive system, such as light that gets brighter when mixed, and the primary colors are red, green, and blue. In the RGB color model, you can create different colors by mixing the basic colors of red, green, and blue, and by mixing red and green with yellow, by mixing green and blue with cyan, and by mixing blue and red with secondary colors. ) Can be created. If you mix red, green, and blue in the same amount, they become white.

The YIQ color model is used in commercial color television broadcasting in the United States and is a recording of RGB for compatibility and efficient transmission with black and white television. The YIQ color model is closely related to color raster graphics, where raster graphics are a way of creating a screen by viewing an image as a collection of small dots and giving each spot brightness and color.

The CMY color model has a subtractive system used in printing systems and the basic colors are cyan, magenta and yellow. The basic colors of the CMY color model Cyan, purple, and yellow are complementary to the red, green, and blue colors of the RGB color model, and under the white light where red, green, and blue are evenly mixed, the complementary colors are absorbed and the rest are reflected. Therefore, when the color used at the time of printing is blue (cyan + purple), under the white light, the red and purple complementary colors of cyan are absorbed, and only blue is reflected by the paper and appears blue.

Theoretically, a printer should be able to represent all colors with only three color inks, cyan, purple and yellow. In the CMY color model, you can get white if you don't spray ink on white paper, and you get black when you spray 100% ink of cyan, purple and yellow. But in reality it is not possible to get full black with cyan, purple and yellow inks. Therefore, in addition to cyan, purple and yellow, black (marked with black and K) ink is added to the printing process color. As a result, a pure black color can be obtained than black made of three colors of cyan, purple, and yellow, and as a result, the use amount of the basic three inks is reduced, which is economically advantageous.

Since RGB and CMY are complementary colors, the conversion between the two spaces can be converted by the following equation. To convert CMY to RGB, take the complement of white as shown in Equation 1.

C = 1-R

M = 1-G

Y = 1-B

When converting from CMY to RGB, it is the same as Equation 2.

R = 1-C

G = 1-M

B = 1-Y

All values are between 0 and 1 and can be represented as C = 255-R in a 24-bit color system.

Equation 3 is used to convert the CMY color model to a CMYK color model.

K = min (C, M, Y)

C = C-K

M = M -K

Y = Y-K

The assay used is the minimum amount of cyan, purple and yellow. Each of the primary colors will fall by as much as black, which saves ink in cyan, purple, and yellow.

The scanner reads the analog image as digital RGB data information to produce data that can be processed on a computer, and reads analog image as digital CMYK data information (UMAX scanner). If you change the model to color correction and read it as CMYK data, color correction is possible without changing the color model.

When the color value of the color chart input to the scanner is read and stored as an RGB value, it can be modeled as a two-dimensional sheet using Equation 1 and can be modeled in a three-dimensional cubic form using Equation 3 again. . A process of modeling the color chart information into a two-dimensional sheet and three-dimensional cubic is shown in FIG. 3.

Three-dimensional modeling of RGB color values as CMYK color values enables the 3D cubic to be useful because the distribution of colors in the CMYK color cubic space can be known and the fluidity of the colors can be checked. For example, if you want to increase the saturation of blue in the CMYK cubic space, you can increase the cyan or purple color or decrease the yellow color, and to make the red more red, you can increase the yellow and purple color or decrease the cyan color.

Here, saturation refers to the color density or purity of the color, 0% state is white, 100% is pure color itself does not contain white.

In analyzing the error of the color between the original color table and the input color table (S13), the error is extracted by comparing the color information obtained by inputting the color chart with the scanner and the original color table serving as a reference stored in the computer.

The method of extracting an error includes a method of extracting a color difference between an original color table and an input color table, a method of leveling color information of an input color table, and a method of using a bezier curve.

The method of extracting the color difference between the original color table and the input color table is to extract the colors stored in the original color table and the input color table and calculate the difference between the values corresponding to the positions of each table. Can be.

Error value = input color table-original color table

For example, when a color of 24% of the white color of the color chart corresponding to 24% of the original color of the original color table is scanned, the error value of the input color table is 20%. Therefore, when another image for a job is scanned, a color corresponding to 24% of the original color value of the original color table is input through scanning in consideration of an error value of 4% when the cyan value is 20%.

The method of leveling the color information of the input color table is a method of adjusting the brightness of the image to change the tone. Here, the level generally refers to adjusting the light and dark of the entire image or the selected area based on 256 levels. The brightness of the natural world is a continuous concept with no special step values, but in digital images it has 256 levels of brightness. The darkest state is 0 and the brightest state is 256 steps.

For example, in the 0 to 255 brightness levels used in digital images, typical images do not use the brightness area evenly. If you give a level to such an image so that the brightness area can be used evenly between 0 and 255 levels, the contrast will be clearer than the image before the level is given. The extended level here is the error to be extracted.

In CMYK cubic space, the maximum minimum value of each CMYK image data can be obtained, and the level can be given using Equation 5.

Present value = (255 X (present value-minimum value)) / (maximum value-minimum value)

If you give an excessive level, the color distribution becomes wider, so there are many bright tones and it seems to be covered with a white film as a whole. Therefore, use the maximum value (minimum) for each CMYK, the maximum value (minimum) of the CMYK, Leveling is performed in the appropriate area using the maximum (minimum) value of the maximum (minimum) value of each CMYK or the maximum (minimum) value reduced (increased) by 5% among the maximum (minimum) value of each CMYK.

In the method of using a bezier curve, the error value is represented by the degree of shifting the color information of the original color table and the input color table as a Bezier curve and moving the two curves to coincide.

In the step S14 of storing the analyzed error in the corrected color table, a corrected color table is created to correct the color error and the color loss that appear due to the characteristics of the scanner. Here, the corrected color table refers to the color error between the original color table and the input color table. When scanning another image, the corrected color table is used to correct the error and the reduction of color that appear due to the characteristics of the scanner by using the information of the corrected color table on the input color data. Can be.

One or more pieces of the three error value information detected in step S13 are stored in the same form as the three-dimensional cubic structure of the original color table and the input color table to create a corrected color table.

In the step S15 of correcting the corrected color table using the correction value of the input color data when the actual image is scanned, the error value of the corrected color table corresponding to the color value is applied to the color value of the input color table when the actual image is scanned. This is to reduce the color error that appears due to the characteristics of the hardware of the scanner.

4 is a diagram illustrating a method of extracting an error of color with a Bezier curve according to an embodiment of the present invention. Here, bezier curves are curves that indirectly define the derivatives of the two end points using the position of the two end points representing the three-dimensional curve and the derivatives of two other points not on the curve. Color values with irregularities caused by hardware characteristics can be corrected to the same color values as the original colors.

Curves are graphic representations of tones that are accurate and fluid color corrections. In the curve 20 corrected using the pre-correction curve 10 and the Bezier curve, the x-axis represents the input color and the y-axis represents the color value corrected by the corrected color table information. To see the color value change, draw the tonal area of the color value of the input color table and the corrected color table color value. The tonal area here refers to the area of the tone from the lightest point to the darkest point of the image. The error is a degree of movement when the curve corrected using the curve 10 and the Bezier curve overlapped with each other.

The method for correcting color difference generated due to the characteristics of the scanner of the present invention as described above may be stored in a computer-readable recording medium. Such recording media includes all kinds of recording media on which programs and data are stored so that they can be read by a computer system. For example. Read Only Memory, Random Access Memory, Compact Disk Read Only Memory, Magnetic Tape, Floppy Disk, Optical Data Storage. Programs and data stored on such recording media can be distributed over network coupled computer systems so that the computer can be stored and executed in a distributed fashion.

The terms used to describe the embodiments of the present invention above are used for the purpose of describing the present invention, but are not used to limit the scope of the present invention as defined in the claims or claims.

According to the present invention, it is possible to correct color errors and color loss occurring according to the hardware characteristics of suppliers and types of scanners, and it is possible to correct actual colors irrespective of changes in gamma values on the monitor. The scanner that corrects the color error generated by the color error may be used as a premise in the correction process of the color error generated in the output device such as a printer.

Claims (6)

(a) setting an original color table as a reference of colors on a computer; (b) creating a color chart by displaying the color values measured by the instrument; (c) scanning the color chart with a scanner to create an input color table; (d) extracting an error of color between the original color table and the input color table; (e) storing the analyzed error in a corrected color table; And and (f) correcting the color by applying the correction color table to input data when the image is scanned. The method of claim 1, The color table is a method of correcting color differences caused by the characteristics of a scanner, characterized in that the model is a cubic through the two-dimensional sheeting of RGB and CMYK CMYK CMYK. The method of claim 1, wherein in step (d), The extraction of the error is a method for correcting the difference in color that occurs due to the characteristics of the scanner, characterized in that to calculate the difference between the values corresponding to the position of each table by extracting the color stored in the original color table and the input color table. The method of claim 1, wherein in step (d), The extraction of the error is a method for correcting the difference in color generated due to the characteristics of the scanner, characterized in that the extended level as an error using a method of giving a level to the color information of the input color table. The method of claim 1, wherein in step (d), The extraction of the error is a method of correcting the color difference caused by the characteristic of the scanner, characterized in that the difference between the two curves by representing the color values of the original color table and the input color table as a Bezier curve. A computer-readable recording medium containing a program capable of performing a method of correcting a color difference occurring due to a characteristic of a T scanner for implementing a method according to any one of claims 1 to 5.