Types and instruments of the most flaming color me

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Types and instruments of chromaticity measurement (II)

II. Three elements of chromaticity measurement standardization

lighting, geometric conditions of observation, and standard white are the three main factors to realize color measurement

the calculation of parameter values of each surface color system depends on the type of lighting. A. B, C and D65 light sources are simulated incandescent lamps, sunlight at noon, sunlight on overcast days or cloudy noon sunlight respectively, especially D65 light source. Its radiation distribution is obtained through a complex averaging process after many measurements of eye spectra at different times, climates and places. C light source and D65 light source are the most useful for the printing industry

the power of standard light source C in the ultraviolet region is very small, which is irrelevant for non fluorescent colors. However, for the fluorescent color, when illuminated by C light source, the fluorescence of the color is less than that in the real sunlight. With the wide application of fluorescent additives in white pigments, there is a great need for a light source that can better express sunlight, including the ultraviolet region. Therefore, CIE recommended the standard light source D65 in 1963. The spectral range defined for D65 is 300 ~ 830nm, and the color temperature is 6500k. It is one of a series of D light sources. Because many inks and papers show fluorescence, D65 light source is important for the printing industry. If ultraviolet light is not required, it can be removed by filter

the influence of fluorescence on the measurement results can be explained through table 2-2. Although paper and yellow ink show obvious fluorescence properties, they do not have much impact on the overall measurement results. When the light source contains ultraviolet components, as expected, the paper and yellow ink appear bluer, and the l* value of the paper is slightly larger. This change tendency is correct, but the l* of yellow ink decreases slightly, showing a wrong change tendency

table 2-2 effect of ultraviolet on measured data

parameters paper Cyan Magenta yellow

with or without ultraviolet, with or without ultraviolet, with or without ultraviolet, with or without ultraviolet

x( λ) 88.77 86.46 19.23 19.27 37.40 37.36 67.90 67.13

y( λ) 86.61 85.56 24.90 25.00 20.70 20.65 74.60 73.79

z( λ) 98.85 95.29 72.31 71.95 26.30 25.80 10.80 10.55

L* 94.57 94.12 60.56 60.97 55.95 56.22 94.36 94.42

u* -10.76 -10.44 -51.50 -59.97 107.92 109.66 25.88. After the operation, be sure to turn off the power switch 5 25.44

v* - 12.09-9.5-15.79 -77.00-20.86-20.55 106.48 104.23

in the printing industry, D50 light source is recommended when observing the transmission samples of originals, and D65 light source is recommended when observing the reflection samples such as printed matter. The color temperature of the two light lakes is different, which should be noted

when measuring translucent tissue samples, it is of special significance to lining a white surface under the samples

for most cases, a white surface should be lined, which is closest to the standard observation state. However, for some quality control measurements, a black surface may be preferable

if a very smooth reflecting surface is observed, the color of the object depends on the incident angle of the light relative to the surface and the observation angle of the eye relative to the incident light. If the light enters from only one direction, in order to avoid seeing the mirror image of the light source, you can properly rotate the surface, so that you can see the color of the object surface. If this reflecting surface is illuminated from different directions, and in a room, the reflecting surface of the object is illuminated by light from many windows or by many artificial light sources, it is impossible to find a direction to completely avoid the specular reflection of the light source. If you observe the reflective surface under a large light source, such as the sunlight on a cloudy day or under a uniformly illuminated ceiling lamp, you will always see the color of the surface under the partial mirror reflection of the new industrialization road with Chinese characteristics. Specular reflection is produced by the surface of an object. Unless the object is metal, the reflected light is always similar to the color of the light source. If the color of illumination is white, specular reflection usually adds white light to the surface color. Unless the reflecting surface itself is white, its effect always reduces the saturation of color. This is why glossy surfaces look more saturated under directional illumination than under slow illumination

for a completely rough surface, no matter what the incident angle of each beam of light, if it does not enter the surface, some of it will enter the eyes, and this part of the light is not affected by the pigment (unless it is metal). Therefore, when observing a rough surface in white light, the saturation always decreases due to surface reflection. For this reason, rough surfaces are generally not as saturated as glossy surfaces unless the glossy surface is illuminated with very diffuse light

most surfaces are neither completely rough nor very shiny. The influence of geometric conditions of illumination and observation is between the above two extreme conditions. The color saturation is lower than that of shiny surface and higher than that of rough surface. The difference in surface properties has a great impact on the color feeling of objects

obviously, the geometric conditions of illumination and observation play an important role in the color effect. According to the needs of practical applications, the International Commission on illumination has recommended some geometric conditions for illumination and observation for colorimetric measurement applications

when measuring the reflectance (transmission) parameters, the International Commission on illumination recommends the ideal diffuse reflectance (transmission) body as the standard white. The ideal non reflector is the ideal isotropic diffuser, which has the same luminous density in all directions of the reflection space, so the standard white is a completely matt white surface, which meets the following conditions:

① all the light incident on the surface is reflected into space, so all wavelengths of light within the visible spectrum are not absorbed

② the reflected light is completely diffuse, Matt and evenly scattered in all directions. The brightness produced by 1LX illumination in all directions is equal to 104cd/m2

③ the above two characteristics are completely independent of the direction of incident light

standard white can be pressed with barium sulfate powder. The Nanjing municipal government proposed that if barium sulfate is very pure, the light absorption rate is very low, only about 2%, which is quite similar to the ideal diffuse reflection standard white, and has nothing to do with the wavelength in the visible spectrum range. The absorption rate increases when the wave length is less than 410nm. There are precise regulations for the barium sulfate used to produce this white standard. During measurement, the difference between the ideal matte white surface and the actual white standard is compensated by the correction method. It must be emphasized that the Y stimulus value of ideal diffuse reflection is specified as 100. In all color objects (non phosphors) under any illumination, the luminous density of ideal diffuse reflector is the highest, which is the benchmark parameter for calculating the three stimulus value

in terms of standard white, ideal diffuse reflector is only a choice, which may be suitable for evaluating textiles and paints, but in some applications, ideal diffuse reflector may not be suitable as standard white. For example, when evaluating ink, it is generally a better choice to take the paper used as standard white. This is because if the paper is slightly yellowing, a non selective neutral ink will also be light yellow relative to the ideal diffuse reflector, but the ink itself is not yellowing, so it is better to take the unprinted paper as the standard white evaluation ink; But the ideal diffuse reflection standard white is suitable for evaluating paper

for a realistic reflective print, it is appropriate to use the ideal diffuse reflector as the standard white to measure the paper, and when evaluating the image surface, it is appropriate to use the representative white on the picture as the standard. This representative white (set the stimulus value as yn) may not only be a different color, but also be significantly darker than the ideal diffuse reflector. The ideal diffuse reflector will have a value Y/yn significantly higher than the unit value for the known signal (size/amplitude (set the stimulus value as y), which indicates that the brightness of the standard diffuse reflector is greater than that of the white in the image

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