JP3604412B2 - Simplified white point evaluation method and white point simple evaluation chart for self-luminous color monitor - Google Patents

Description

[0001]
[Industrial applications]
The present invention relates to the evaluation of the white point of a self-luminous color monitor that reproduces a natural color image by controlling the amounts of at least three primary color signals and the mixing ratio thereof, and more particularly to the self-luminous color monitor. The present invention relates to an evaluation method for evaluating a mixing ratio of primary color signals forming a white point in an observation environment. The invention also relates to an evaluation chart used for the evaluation method.
[0002]
[Prior art]
As the self-luminous color monitor, for example, a so-called color CRT that reproduces a natural color image by emitting light from R (red), G (green), and B (blue) phosphors, a color liquid crystal display using a backlight system, and the like. It has been known. In these color monitors, it is necessary that the color appearance reproduced by the monitor is always constant. In particular, the white point is the reference.
[0003]
Even if the data of the three primary color signals supplied to the monitor is always constant, the color of the image reproduced on the monitor will not be constant unless the output for them is constant. Also, even if the data of the primary color signal is constant and the output is constant, the color of the ambient light on the monitor causes color adaptation to the evaluator, and the white thing does not look white. However, there is a disadvantage that the colors reproduced in the image look different.
[0004]
Conventionally, as a method of evaluating the white balance of a color monitor, a method of displaying a white raster on a screen and evaluating using a measuring instrument, a method of subjectively evaluating the color of the white raster, or a method of evaluating the color of the screen by a natural image There are known methods for subjectively evaluating the quality of a subject. However, no method has been proposed for evaluating a white point in consideration of an observation environment at a place where a color monitor is placed, for example, illumination intensity, illumination color, and the like.
[0005]
[Problems to be solved by the invention]
When trying to use the above white balance evaluation method for white point evaluation, regarding the evaluation of white point by white raster, it is necessary to use a measuring instrument or the like, and even in the case of subjective evaluation, the presence or absence of color shift is As you can see, it is not possible to evaluate where the white point will be.
[0006]
In the case of the method using a measuring instrument, it is convenient to keep the balance of the display color of the monitor in a certain state, but it is not considered the adaptation of the observer, and the color that actually looks “white” (ie, the white point) In order to find), it is first necessary to obtain a colorimetric value that gives a white point by subjective evaluation.
[0007]
In the subjective evaluation using the white raster, the correction of the white point requires the evaluator to control the ratio of each primary color signal while looking at the white raster to find a point that looks white. However, in this method, it takes time to correct and the white raster on the screen adapts as time elapses, and the "color close to achromatic color" displayed there is felt as achromatic, so it should be originally calculated It is difficult to accurately determine the white point.
[0008]
SUMMARY OF THE INVENTION The present invention has been made in order to solve the above-mentioned problems in the evaluation of a white point using a conventional technique, and uses a measuring device for measuring a mixing ratio of primary color signals (that is, output values) forming a white point. It is an object of the present invention to provide an evaluation method and a simple evaluation chart that enable simple and accurate evaluation without any problem.
[0009]
[Means for Solving the Problems]
In order to achieve the above object, a method for easily evaluating the white point of a self-luminous color monitor according to the present invention includes the steps of: adjusting a color development amount of each of at least three primary colors; In the method for evaluating points, an achromatic color graphic of a monitor having a mixing ratio of the input signals of the three primary colors of 1: 1: 1 is displayed on the monitor, and around the achromatic color graphic, Displaying a plurality of low-saturation color graphics forming a hue circle such that saturation increases with distance from the achromatic color graphics on the monitor by changing the mixing ratio of the input signals of the three primary colors ; These color graphics are compared to evaluate a mixing ratio of primary color signals forming an achromatic axis under the observation environment of the monitor.
[0010]
Further, the white point simple evaluation chart of the self-luminous color monitor according to the present invention is used to evaluate the white point of the self-luminous color monitor that reproduces a color image by adjusting the color development amounts of at least three primary colors. In the white point evaluation chart, an achromatic color figure of a monitor in which the mixing ratio of the three primary color input signals is 1: 1: 1 is arranged, and the achromatic color figure is further surrounded around the achromatic color figure. A plurality of low-saturation color graphics forming a hue circle such that the saturation increases with distance from the color graphics are arranged by changing the mixing ratio of the input signals of the three primary colors .
[0011]
The achromatic color of the monitor is, for example, a color CRT monitor in which the mixing ratio of the input signal to the three colors R (red), G (green), and B (blue) is 1: 1: 1. is there. In addition, a plurality of color graphics having low saturation are colors in which the ratio between the maximum value and the minimum value of the mixed amount of the input signal does not exceed 2: 1 or under a certain environment, for example, in the dark. , For example, a color giving the same chromaticity value as that of the C light, and a color whose saturation does not exceed 5. Here, there is no guarantee that a color in which the mixing ratio of the input signals is 1: 1: 1 or a color that gives the same chromaticity value as the standard light, for example, the C light, is subjectively felt as “achromatic”. The “achromatic color” is included in the achromatic color of the monitor or a plurality of low-saturation colors around the monitor.
[0012]
[Action]
According to the present invention, the evaluation is performed by selecting an object that feels "achromatic" from a plurality of low-saturation color graphics including achromatic colors, each of which has a different mixing ratio of the primary color signals. The lower white point can be accurately evaluated. Further, since the mixing ratio of the primary color signals (that is, the input signals) constituting the color figure is known, the white point can be easily corrected. By arranging a plurality of low-saturation color graphics including achromatic colors on a background having a light emission level of 0 (zero), that is, a background visually viewed as black, the influence of the background color and adaptation to the screen is reduced. can do.
Further, since it is expected that the adaptation direction of the visual system shifts to the hue direction due to the light color of the ambient light, the work of selecting a figure that looks achromatic can be facilitated. Further, since the achromatic color always exists inside the hue circle, the selection can be easily performed.
[0013]
【Example】
FIG. 1 shows an embodiment of the white point simple evaluation chart according to the present invention. The simplified evaluation chart 10 includes a plurality of circular figures 12 each having a color close to an achromatic color, and a plurality of circular figures 12 each having a different color are arranged side by side on a background 11 having no light emission state, that is, a light emission level 0 (zero). It is configured by arranging.
[0014]
FIG. 2 shows a color reproduction space of a self-luminous color monitor centered on input signals of three colors of R (red), G (green), and B (blue). The color on the straight line V connecting the origin P of the color space and the point W is the color that should be the achromatic color of the monitor, and the mixture ratio is R: G: B = 1: 1: 1. I have. The point W indicates a point where R, G, and B all have the maximum gradation value.
[0015]
FIG. 3 shows an enlarged view of the cut surface 21 when the color reproduction space of FIG. The colors corresponding to the coordinates in the color reproduction space indicated by the 25 colored circles 30 in the figure indicate the colors of the 25 color graphics 12 used in the simplified evaluation chart 10 shown in FIG.
[0016]
FIG. 4 shows a case where the simple evaluation chart 10 according to the present invention is applied to the white point evaluation of the color CRT 41. In order to reproduce the chart 10 on the color CRT 41, for example, the following procedure is performed. Now, the display color of the color CRT 41 is controlled by three primary color signals of R, G, and B, and the control value is set such that the minimum value of each drive signal current for the primary color signals (R, G, B) is 0. (Zero), when the maximum value is set to, for example, 255 and the interval is represented by “tone values” obtained by dividing the interval at equal intervals, the unit of each axis in FIG. 2 can be represented by a tone value.
[0017]
The cut surface 21 shown in FIG. 2 passes through three points, for example, (R, G, B) = (255, 255, 180), (255, 180, 255), and (180, 255, 255). . The straight line V passes through the center of gravity of this triangle and becomes the normal to this plane. The coordinates of the center of gravity (that is, the gradation value) are (230, 230, 230), which is point 31 in the drawing. This color is arranged at the center of the simplified evaluation chart 10 as the color of the figure 12a at the center of the chart 10. Since five circular figures 12 are arranged in the vertical and horizontal directions in the chart 10 shown here, the size of the chart 10 is 1024 × 1024 pixels, and a gap of at least 6 pixels is provided between the figures. If a margin of 50 pixels is created on the top and bottom, the radius of each circular figure will be 90 pixels.
[0018]
The color of the outermost circular figure is the color on the outer periphery of the triangle of the cut surface 21. For example, from the point 32 of (255, 218, 218), 16 colors are taken at equal intervals along the outer circumference. The colors indicated by the points 32 are arranged above and outside the center of the simplified evaluation chart 10, and the remaining 15 colors that have just been determined are sequentially set as the colors of the figure outside the chart 10, and the positional relationship is made to correspond to FIG. And place them. The remaining eight colors are equally spaced in the direction along the sides of the triangle, starting from an intermediate color connecting the points 31 and 32 in FIG. In this manner, the white point evaluation chart 10 having a double hue circle with low saturation around the achromatic color of the monitor 41 is completed.
[0019]
Hereinafter, a method for evaluating a white point using the above-described simple evaluation chart will be described.
[0020]
Now, the color of the figure placed at the center of the evaluation chart 10 is a color of R: G: B = 1: 1: 1, which is a color that should be felt as an achromatic color. However, there is no guarantee that this point will actually feel achromatic. If the white point of the CRT 41 displaying the chart 10 is set to a point having a correlated color temperature of 6500 [K], when the CRT 41 is observed under a light source having the same correlated color temperature of 6500 [K], Is adapted to the light from the light source, the color of the center of the evaluation chart 10 looks a little more reddish than white. Under this environment, a point that appears white is a color of the figure at the lower left of the center, that is, a color having a higher B (blue) ratio.
[0021]
Further, when the CRT 41 is observed under an illumination environment using an incandescent lamp, when the same chart 10 is displayed on the CRT 41 with the same settings, the color of the graphic above the central graphic, for example, (R, G, B) = The color of (255, 218, 218) is felt as white. This is because the color temperature of the ambient light is lower than the former environment (about 2800 [K]), and the sensitivity of the visual system to long-wavelength light is relatively lower than that of the former environment. The color with a high ratio of) is perceived as white.
[0022]
As described above, from among a plurality of color graphics close to achromatic color including achromatic color, a color graphic which is actually seen as achromatic under the environment is selected. Then, since the tone values of R, G, and B constituting each figure are known when the evaluation chart 10 is created, the originally set achromatic axis of the monitor 41 and the subjective achromatic color at the time of observation are set. The deviation from the axis is grasped as a mixture ratio of the signals constituting the figure selected just now.
[0023]
Adaptation of the visual system, in particular here chromatic adaptation, takes place in a direction colored by the light color of the ambient light, in such a direction that objects that should originally appear "white", for example paper or cloth, feel "white". In other words, the sensitivity of the cone of the visual system corresponding to the wavelength having a relatively high energy among the wavelengths included in the ambient light works to relatively decrease. On the other hand, the spectral distribution of light emitted from the self-luminous color monitor hardly changes because it is hardly affected by ambient light. As a result, the position of a figure that looks achromatic changes due to the adaptation of the visual system.
[0024]
By arranging the color of each figure around a color that may be achromatic and forming a hue circle around it, it is expected that the direction of adaptation of the visual system will shift to the hue direction due to the light color of ambient light. Therefore, it is easy to select a figure that looks achromatic. Further, since the achromatic color always exists inside the hue circle, the selection can be easily performed. Originally, the white of the monitor should always look white. Further, it is desirable that the ratio of each primary color signal of the input signal is (1: 1: 1). To correct the white point, the ratio of the input signal giving the output current value that gives the color of the currently selected figure may be corrected so as to be (1: 1: 1).
[0025]
In the above embodiment, the color of the figure constituting the evaluation chart is a color on a plane intersecting at the point (230, 230, 230) with the achromatic axis V of the monitor as a normal line. It is not necessary to be limited to colors on a plane. To find an achromatic color at each lightness and to obtain a subjective achromatic axis, for example, colors on a plurality of planes parallel to this plane may be used. In this case, there are a plurality of color graphics that are selected as achromatic colors. Alternatively, a plurality of evaluation charts using the colors on each plane may be prepared.
[0026]
Further, the shape, arrangement, and number of the color graphics need not be limited to specific ones.
[0027]
According to the present invention, it is possible to accurately evaluate a white point under an environment where a monitor is observed. In addition, the deviation of the white point of the monitor can be quantitatively evaluated without using a measuring device, and the correction can be easily performed.
Further, since it is expected that the adaptation direction of the visual system shifts to the hue direction due to the light color of the ambient light, the work of selecting a figure that looks achromatic can be facilitated. Further, since the achromatic color always exists inside the hue circle, the selection can be easily performed.
[0028]
[Brief description of the drawings]
FIG. 1 is a schematic diagram showing one embodiment of a simple white point evaluation chart according to the present invention.
FIG. 2 is a schematic diagram showing a color reproduction space of a self-luminous color monitor to which a simple evaluation chart of a white point according to the present invention is applied.
3 is a schematic diagram showing positions on a color plane of each color figure constituting the evaluation chart shown in FIG. 1, and is an enlarged view of a cut surface 21 in a color reproduction space shown in FIG.
FIG. 4 is a front view of a color CRT showing an example when a simple evaluation chart according to the present invention is used for evaluating a white point of the color CRT.
[Explanation of symbols]
Reference Signs List 10 simple evaluation chart 11 background 12 color figure 21 cut surface of color reproduction space 31 position of center color figure color of evaluation chart in monitor color reproduction space 32 on monitor color reproduction space of color of top center color figure of evaluation chart Position 41 CRT
42 screens

Claims (4)

A method for evaluating a white point of a self-luminous color monitor that reproduces a color image by adjusting a color development amount of each of at least three primary colors,
Displaying on the monitor an achromatic color graphic of a monitor in which the mixing ratio of the input signals of the three primary colors is 1: 1: 1 ;
Around the achromatic color figure, a plurality of low-saturation color figures forming a hue circle such that the saturation increases as the distance from the achromatic color figure increases , and a mixing ratio of the input signals of the three primary colors To display on the monitor,
A simple evaluation method for a white point of a self-luminous color monitor, comprising comparing these color graphics and evaluating a mixing ratio of primary color signals forming an achromatic color axis under an observation environment of the monitor. 2. The simple white point evaluation of a self-luminous color monitor according to claim 1, wherein the achromatic color graphic and a plurality of color graphics around the achromatic color graphic are displayed on a background having a light emission level of 0 (zero). Method. In a white point evaluation chart for evaluating a white point of a self-luminous color monitor that reproduces a color image by adjusting a color development amount of each of at least three primary colors,
An achromatic color figure of a monitor in which the mixing ratio of the three primary color input signals is 1: 1: 1 is arranged, and a color figure is arranged around the achromatic color figure as the distance from the achromatic color figure increases. A simple white point evaluation of a self-luminous color monitor characterized by arranging a plurality of low-saturation color graphics forming a hue circle with a high degree of color while changing the mixing ratio of the input signals of the three primary colors. chart. 4. The simple white point evaluation of a self-luminous color monitor according to claim 3, wherein the achromatic color graphic and a plurality of color graphics surrounding the achromatic color graphic are displayed on a background having a light emission level of 0 (zero). chart.

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