KR20010076770A - Mapping Method of RGB for Color Coincidence on Monitor and Printer - Google Patents

Abstract

The present invention relates to a monitor RGB to printer RGB mapping method for performing color matching on a color image on a color monitor and a color image output from a color printer. Conventionally, in a monitor, a user subjectively converts an RGB of an image and sends the value to a driver of a printer, and the printer driver converts the RGB into a CMYK, which is a printer signal, and prints it. In this case, the color of the printed image is different from that of the monitor due to the hardware characteristics of the monitor and the printer.

In order to solve this problem, the present invention compares the color of the monitor with the color obtained after outputting it to the printer with respect to the standard sample present in the RGB color space, so that the color of the monitor matches the color printed on the printer. Correct the color. This correction information value is stored, and then all color values of the printout are corrected. By outputting the corrected image to the printer, you can obtain an image of the same gray scale and color as the image on the monitor.

Description

Mapping Method of RGB for Color Coincidence on Monitor and Printer}

The present invention relates to a monitor RGB to printer RGB mapping method for matching the color of the color image on the color monitor and the color image output from the color printer, and more specifically, when outputting the color original image on the color monitor to the printer. It relates to a mapping method from the monitor's RGB to the new printer RGB to get the color of the image as it appears on the monitor, from the monitor's RGB to the printer driver.

1 is a view showing an image output process of a conventional color printer. When the original image (1) of RGB (Red, Green, Blue) of the color monitor is input to the printer driver (2) of the color printer, the printer driver (2) converts RGB to CMYK (Cyan, Magenta, Yellow, Black). Convert. This CMYK signal is printed by the printing mechanism 3 of the color printer to obtain a reproduced image 4. In general, the printer driver 2 uses the following Equation 1 when converting an RGB signal into a CMYK signal.

C = (255-R) / 255 * 100

M = (255-G) / 255 * 100

Y = (255-B) / 255 * 100, where C, M, Y: range of values from 0 to 100

That is, as shown in Equation 1 above, RGB and CMY are directly complementary to each other. In other words, if two colors of CMY are mixed, one color of RGB is created and vice versa. This relationship can be represented by the color triangle of FIG. As shown in FIG. 2, one color may be represented by two colors around the color, and the color of the diagonal position at each vertex of the triangle becomes a complementary color. In addition, when the maximum value of CMY is used, ideally black color is output. However, in practice, each ink spectrum over a wide area is distributed, so that brown color is output instead of black color. In order to overcome these disadvantages and increase the number of colors that can be expressed and to reduce the amount of ink, a CMYK color space including black is recently used.

As the usage of the black ink, there are Gray Component Replacement (GCR), Under Color Removal (UCR), and the like. The configuration of the CMYK color space using the GCR is made as in Equation 2 below.

K = minimum (C, M, Y)

C '= C-K

M '= M-K

Y '= Y-K

Here, C, M, and Y are the original ink concentrations, and C ', M' and Y 'are the concentrations of the respective inks that are deformed after considering K. As can be seen from the above equation, the ink with the smallest value when printing CMY shows the degree of gray of the color to be reproduced. This gray part is replaced with black and the remaining amount of ink is adjusted by removing the amount of black ink used.

UCR, another method of using black, is a method of printing using black only in the dark part or the neutral part without using CMY.

The printer driver 2 converts the RGB original image into a CMYK signal in the same manner as above, and the printing mechanism 3 prints using CMYK ink. However, if you look at the printed image, you may find that it is slightly different from the color of the image on the monitor. This color distortion occurs because of the mechanical characteristics of the printer and the characteristics of the printed ink. The printer driver used today, of course, provides a control bar that allows the user to adjust the contrast, contrast and individual colors on the driver. However, such a function depends on the subjective tendency of the user and also requires a lot of time and effort for accurate reproduction.

Accordingly, the present invention has been made to solve the above-described problems of the prior art, and after outputting the RGB standard sample image of the color monitor, the color value is changed on the monitor by looking at the output and the RGB to color printer of the color monitor. Create a table for RGB mapping, after which all the images go through the calibration process by the mapping table to obtain a new RGB image and convert it to a CMYK signal for output, ultimately the color of the image on the monitor and the printed image. It is to provide a monitor RGB and printer RGB mapping method for matching the colors of the colors.

1 is a view showing a printing process according to the prior art,

2 is a diagram illustrating color triangles showing complementary color relations between RGB and CMY;

3 is a view showing an image output using the CMY value,

4 is a view showing an image output using a printer driver;

5 is a cube structure diagram of a reference table consisting of eight points on each axis of RGB.

In order to achieve the above object, the monitor RGB-to-printer RGB matching method of the present invention includes a first step of printing a standard color sample through a printer, and comparing the standard color sample with an image on the monitor so that the two colors match. A second step of adjusting each color value of the second step of storing the adjustment amount of each color value in a reference table, a fourth step of printing a sample image of a standard gray scale through a printer, and the printed standard gray scale A fifth step of finding a gray scale on the monitor that matches the second gray scale value, storing two gray scale values, a sixth step of storing a difference between the two gray scale values as a correction value, and an RGB value of an image to be printed; And a seventh step of correcting the gray scale value using the corrected value and then printing the gray scale value. It is characterized by.

Hereinafter, the "monitor RGB and printer RGB mapping method" according to an embodiment of the present invention with reference to the accompanying drawings in more detail as follows.

The monitor RGB and printer RGB mapping method according to the present invention includes a first step of printing a standard color sample, a second step of adjusting two colors to match each other while comparing the image of the standard color sample with the monitor, and the two colors. The third step of storing the correction values to ensure that the two coincide with each other in the reference table, and the subsequent printed matter is corrected with reference to the reference table and then printed.

The process of outputting a color sample image for color adjustment is as follows. 3 and 4 are diagrams illustrating images used to obtain an aspect of color output from a color printer.

The image of FIG. 3 has three gray bars, wherein the color values C, M, and Y of the first bar 31 are (25, 25, 25), and the color values of the second bar 32 are (50, 50,50, and the color value of the third bar 33 is (75,75,75). When this image is printed to a printer, it must be printed via code that can be directly controlled by the printer rather than through the printer driver. This image is not used on the monitor screen, but only for printer output. At this time, since the output image does not use a printer driver, an image of an objective color value that is not affected by the driver can be obtained.

4 consists of one gray scale bar and 36 square color samples. The gray scale bar 42 has a value between 0 and 255 in which R, G, and B are the same, and a scale ruler 41 for relative positioning is drawn on the grail scale bar 42. A gray gray 43 is wrapped around the gray scale bar 42. In addition, the values of 36 color samples are as follows. The six samples of the first line 44 are the cases where G and B are zero and the values of R are 219, 182, 146, 109, 73 and 36, respectively. The six samples of the next second line 45 are where R and B are zero and the values of G are 219, 182, 146, 109, 73 and 36, respectively. The six samples of the next third line 46 are where R and G are zero and the values of B are 219, 182, 146, 109, 73 and 36, respectively. The six samples of the fourth row 47 are when R is 255, B is 0, and G is 219, 182, 146, 109, 73 and 36, respectively. The six samples of the fifth row 48 are where B is 255, R is 0, and G is 219, 182, 146, 109, 73 and 36, respectively. The six samples of the last sixth row 49 are where G is 0, B is 255, and R is 219, 182, 146, 109, 73, 36, respectively. The image of FIG. 4 is also displayed on a monitor and is also used as the printer's output image to compare it with the printer's output. When the image of FIG. 4 is output to the printer, the image is printed through the driver of the printer.

The following describes the process of adjusting the gray scale.

In order to adjust the gray scale, the image of FIGS. 3 and 4 output to the printer and the image of FIG. 4 displayed on the monitor are compared with each other. The method is as follows.

First, the first bar bar 31 of FIG. 3 and the gray scale bar 42 of FIG. 4 are closely placed and compared with each other using the two images of FIGS. 3 and 4 printed by a printer. As a result of the comparison, the position of the gray scale bar of FIG. 4 that matches the image color of FIG. 3 is grasped using the ruler 41 of FIG. By using the position of the grasped ruler 41, a portion corresponding to the ruler of the image gray scale portion shown in FIG. 4 displayed on the monitor is clicked with a mouse. At this time, the part clicked with the mouse is set to R, G, B value 190 whose C, M, Y is 25, but the position by the ruler of the actual printed matter is R, G, B shown on the actual monitor. Does not match part of 190. This is because there is a difference between the color of the image on the monitor and the image output from the printer. Therefore, if the difference is corrected in advance on the monitor and output to the printer, color images matching the color of the monitor can be obtained. To do this, you need to get the relative position on the monitor, taking into account the original value and the image of the printer. This process gives us a default value of 190 and a new value between 0 and 255.

By comparing the second image 32 and the third image 33 of FIG. 3 with the gray scale bar 42 of FIG. You get a value of 63 and two other new values.

The method of correcting the gray scale using the information obtained above is as follows. Although three images are used in FIG. 3, in terms of gray scale, 0 and 255 can be considered simultaneously, so five equal parts [255, 190, 127, 63, 0] of gray scales between 0 and 255 on the monitor are displayed. Since it is mapped to the value [255, a, b, c, 0] to the relative position viewed from the side, in order to map the original [255, 190, 127, 63, 0] to the position having the color value as it is, the change value [ 0, a-190, b-127, c-63, 0]. For correction, the change value should be stored and the correction method is to identify which part of [255, 190, 127, 63, 0] belongs to the R, G, and B channels for each pixel of the image. For example, if the R value is 150, 150 is a value between 190 and 127. Therefore, the value between the correction value-(a-190) at 190 and the correction value-(b-127) at 127 is changed to the original 150. You must add it to get the corrected value. To find the correction value between the sections, find the left and right position ratios at both end points of the sections, and then find the correction value using the same position ratio between the corresponding correction values.

Doing the same for G and B in the same way, the image displayed on the monitor will get a new image with the printer's gray scale corrected, and the image will go to the next color correction step.

Hereinafter, a process of adjusting the RGB value of the color sample will be described. This is the part that works with the reference table at the same time.

The reference table is constructed from the 36 color samples of FIG. 4 displayed on the monitor. Reference tables exist in three dimensions in the RGB color space. In this case, the interval between 0 and 255 of the R, G, and B axes is used as an interval divided by eight. The color values of the six samples of the first row in the 36 color samples of FIG. 4 may be made into six sections (51 of FIG. 5) between 0 and 255 on the R axis in the RGB color space. Six color values of the next second line may be represented by six sections (52 of FIG. 5) of the G-axis, and the next third line may represent a section (53 of FIG. 5) by the value of the B-axis. By intersecting the values of each coordinate axis using points on Cartesian coordinates in the two-dimensional plane, two-dimensional intersections can be created. Using this three-dimensional extension method, you can construct a three-dimensional cube of 8 x 8 x 8 points using eight points, including 0 and 255, on the RGB axis, each of which is based on FIG. It has a corresponding RGB color value. In order to construct a more accurate reference table in the RGB color space, points on the RG, GB, and RB planes as well as points on the R, G, and B axes as shown in the 36 samples of FIG. The reference table in the RGB space thus produced is as shown in FIG. 5. FIG. 5 shows the coordinates of a subset in a space of 8 x 8 x 8 points. Each coordinate point in this reference table has space to store R, G, B and new R, G, B values.

Thus, based on the values of the 36 color samples of FIG. 4, the color is directly compared with the image of FIG. 4 output while the reference table is generated. In the monitor, a controller that can adjust R, G, and B on the monitor is used as a color conversion interface so that the change in the color value of the image of FIG. 4 can be well understood. For comparison, for each of the 36 samples output to the printer, use the R, G, and B color controllers so that the color samples from the corresponding monitor will have the same color as the print image. The internal processing that occurs when the color of the monitor is adjusted to be the same as the color of printed matter is as follows.

First, when 36 color samples are converted, the reference table of the RGB color space simultaneously stores not only the existing R, G, and B color values but also the changed color values at the corresponding points. By storing the 36 changed color values, the new coordinate values can be obtained by crossing the coordinates at the remaining points. In this way, 8 x 8 x 8 points have newly changed R.G and B values as well as existing R, G and B values.

After adjusting 36 samples of the monitor using FIG. 4, a method of correcting by applying an actual image is as follows.

The original image on the monitor gets the corrected RGB values past the gray scale part. Then, the R, G, and B values of each pixel may be located at any point in the table (7 in FIG. 5) divided into 8 parts in the table based on the RGB values of the reference table created above. After the location is found, eight coordinate points surrounding the coordinate point can be obtained as shown in FIG. 5. Using the eight coordinate points, the ratio of the distance to the coordinate point of the image existing in the space can be obtained. To find the ratio of the distance, you can find the position ratio in the direction parallel to the eight points surrounded by each element of the point coordinate of the image. Obtain the position ratio thus obtained and move on to the next task based on it. The next step is to bring the new color coordinates of the eight points around the image coordinates. Then, using the position ratio information from the previous step, the relative coordinate values are obtained in the space formed by eight new color coordinates. Using the position ratio is the same as the previous step. Coordinates with new RGB values are more likely to not form an exact cube. However, it is rare to see a completely distorted form that is completely different from the cube. Therefore, finding a relative point by position ratio is enough to allow a slight error. In this way, the color value of the image can be obtained from the position on the reference table and the relative position of the newly constructed reference table. Next, find the change value of each coordinate axis on these two relative positions. Then, for color correction, the corrected image value is obtained by moving in the opposite direction (8 of FIG. 5) to the color coordinate value inputted from the input in the opposite direction to the conversion value. If you print this image using the printer driver, you can get the output image of the same color monitor.

While the invention has been described above based on the preferred embodiments thereof, these embodiments are intended to illustrate rather than limit the invention. It will be apparent to those skilled in the art that various changes, modifications, or adjustments to the above embodiments can be made without departing from the spirit of the invention. Therefore, the protection scope of the present invention will be limited only by the appended claims, and should be construed as including all such changes, modifications or adjustments.

As described above, according to the present invention, the color of the monitor is compared with the color obtained after outputting the standard sample existing in the RGB color space, and a correction operation for matching the color to the printer is performed on the monitor. Even if all the color values in the RGB color space are received by the correction information values, the existing correction information can be interpolated to obtain an image having the corresponding corrected values. When this image is output to a printer, an image of the same color as the image on the monitor can be obtained. Therefore, the present invention has the effect of matching the color of the output image between the color monitor and the color printer and can be implemented on the printer driver, so that the printing color quality of the printer can be easily improved by software.

Claims (4)

A monitor RGB to printer RGB matching method for matching an image on a monitor with an image printed through the printer, The first step of printing a standard color sample via a printer; A second step of adjusting each color value of the monitor such that the two colors match while comparing the standard color sample with the image on the monitor, A third step of storing the adjustment amount of each color value in a reference table, And a fourth step of correcting the RGB value of the image to be printed using the reference table and then printing. The method of claim 1, wherein the third step is A first substep of obtaining coordinates in RGB space with respect to RGB values of an image to be printed; A second substep of applying the RGB values of the image to a reference table to obtain coordinates in a new RGB space; A third substep of obtaining a difference between a coordinate value of the original image and a new coordinate value; And And a fourth substep of correcting an RGB value of the original image by using a difference value between the two coordinate values. The method of claim 1, further comprising: printing a sample image of standard gray scale through a printer; A sixth step of finding a gray scale on the monitor that matches the printed standard gray scale, and storing two gray scale values; and And storing a difference between the two gray scale values as a correction value, correcting the gray scale value of the image to be printed using the correction value, and then printing the monitor RGB to printer RGB matching. Way. On your computer, The first step of printing a standard color sample via a printer; A second step of adjusting each color value of the monitor such that the two colors match while comparing the standard color sample with the image on the monitor, A third step of storing the adjustment amount of each color value in a reference table, The fourth step of printing a sample image of standard gray scale through a printer, A fifth step of finding a gray scale on the monitor that matches the printed standard gray scale and storing two gray scale values, A sixth step of storing the difference between the two gray scale values as a correction value, and A program for executing a monitor RGB to printer RGB matching method comprising a seventh step of correcting an RGB value of an image to be printed using the reference table and correcting a gray scale value using the correction value A computer-readable recording medium that records the data.