Иш кетма-кетлиги

Control questions: 
 
1. What indicators can be evaluated of the portable colorimeter YLD-200 
model? 
1. 2. How is color expressed graphically through color coordinates? 
2. 3. What are the disadvantages of the XYZ colorimetric system? 
3. 4. What kind of information do we get through color coverage? 
 
 

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9 - LABORATORY WORK 
EVALUATION OF COLOR RANGE USING A 
SPECTROPHOTOMETER 
The composition of the work. Getting to know the measuring technique used in 
assessing the quality of color copies. Comparison of color printing methods in terms of 
copy 
quality. 
Acquaintance 
with 
GM 
measuring 
devices 
and 
spectrophotometer/densitometer and the technique of working with them according to 
the description of the work and materials available in the laboratory. Measurement of 
areal absorption of dyes in test scales printed in different printing methods, color 
coverage of color printing, gradational feature, color balance "by gray". Determining 
the quality of creating a given color set. 
Tools and equipment: 
Spectrodensitometer ET-120HD 
Theoretical justification. The printing press uses a number of printing methods: offset, 
electrophotography, flow (spray). They are based on completely different processes, 
and they have different capabilities in terms of color rendering capabilities and the 
accuracy of creating small elements of the image. Methodology for estimating the 
accuracy of forming bar elements. Evaluation of color formation is the goal of this 
laboratory work. 
Color and its descriptions. The radiation that illuminates the objects and natural rocks 
that surround us consists of a mixture of monochromatic radiation of different 
wavelengths. Different wavelengths of radiation cause a person to perceive different 
colors. Short-wave radiation has violet and blue colors, and long-wave radiation has 
various shades of red. The spectrum of colors that occurs under natural conditions is a 
rainbow. The world surrounding us is colorful, because objects and natural objects 
absorb monochrome radiation differently. If blue radiation is absorbed, red and green 
rays will reach the eye and the object will appear yellow or fiery, if red and green 
radiation will be absorbed, the object will have a blue color. 
Color can be characterized by hue, saturation, and clarity. Hue represents the similarity 
of color with a certain object of the environment. Saturation shows the difference of 
color from achromatic (white, gray, black) color. We reduce the color saturation by 
adding white radiation to the colored radiation. Color raster printing reduces color 
saturation by reducing the size of the raster dots and thereby increasing the relative 

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area occupied by the white paper. Hue and saturation make up color. Luminance is 
related to the amount of radiation falling on the eye, that is, the brightness of the 
object. We move the object in front of the window to the back of the room and reduce 
its brightness. 
"Primary radiation" - any color can be obtained by mixing certain amounts of red, 
green and blue. The amount of these rays make up the color coordinates. Knowing the 
color coordinates, it can be defined as a point in the color space formed by red, green 
and blue color coordinates. In this case, the color coordinates will depend on which 
colors (red, green and blue) are selected as the primary color. The basic colors 
depending on the device, for example, the color of the radiation of the television screen 
phosphors R, G, B and the standard basic colors used in CIE RGB and CIE XYZ 
standard colorimetric systems are different. For practical dimensions, CIE XYZ is 
used. However, the CIE XYZ system is not flat-contrast because the distance between 
color points in the XYZ color space is not aligned with the visual difference (contrast) 
between colors. Therefore, another system - CIE LAB - is used to study the quality of 
color reproduction and compare the copies with the standard image.
In this system, color L*a*b* coordinates are entered. The L* coordinate defines 
brightness, while α* and β* represent hue. When constructing the color space, 
mutually perpendicular a* and b* axes are placed on the horizontal plane, these 
coordinates are measured from -100 to +100 grids. The L* coordinate is perpendicular 
to the a* and b* planes from the point of intersection of the a* and b* axes. It varies 
from 0 to 100 grids, at the point of intersection with the plane L*=50 (Fig. 13.1) a 
color circle with a radius of 100 units is built in the a* b* plane to facilitate the 
determination of a* and b* coordinates and to determine the color hue and saturation 
(Fig. 13.1). On the color wheel, hue changes along the circle, and saturation changes 
from the center outwards. The circle is usually colored. Additional colors are selected 
on the opposite sides of the diameter of the circle, and an achromatic color is formed 
when they are added. The luminance axis is an achromatic color axis: black at L*=0, 
white at L*=100. L*a*b* coordinates are calculated from XYZ coordinates.

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