1. The influence of lighting source on color discrimination
The color of the color body is presented by light of a specific wavelength, so to accurately compare the color of the color body, the light source is a very important condition. Illumination light sources for color discrimination in the offset printing process include natural light and artificial light sources. In order to accurately distinguish the color, whether it is natural light or artificial light source, the standard light source of pure white light is the most suitable for observing color. Direct sunlight is yellowish, indirect sunlight is better, no color, blue under blue sky, orange-red under incandescent lamp, and slightly blue-violet under fluorescent lamp. Only the proportion of the three primary colors of indirect sunlight is equal to white light. The color body is irradiated with white light, so that the reflection or absorption of the color body to light is relatively standard. It can be seen that whenever natural light is used as the lighting source, it is better to use relatively stable indirect sunlight. Therefore, when installing the machine in the offset printing workshop, it should be considered that the sample stand is placed in the indirect sunlight daylighting position, and the fluorescent lamp reflector should always be kept. Clean, remove dust and dirt, avoid using blue and yellow lamps. The light source illuminates the printed sample in the vertical direction with the 45 ° angle as the observation angle, so the sample table should have a corresponding slope.
2. Whiteness of paper
The ideal paper whiteness when printing is 100% total reflection, especially the color discrimination, you must understand the importance of paper whiteness, especially as one of the main factors to distinguish color, white paper bearing color imprint Whiteness plays a decisive role in the hue, brightness and saturation presented. Generally, the coated paper for printing fine products requires a reflectivity of greater than 85%. The paper used for proofing in offset printing should be the same as the whiteness of the officially printed proof paper, otherwise it is difficult to accurately evaluate the ink color effect. Must first specify the use of paper with sufficient whiteness, in the printing process of the same batch of products, the paper used should have the same color, otherwise, it is impossible to keep the ink color of the product consistent.
Third, the impact of environmental color
Ambient colors also have a significant impact on correct color discrimination. Similarly, when observing, analyzing and discriminating colors, the process of looking at samples must avoid color illusions. A color in a specific environment, human vision is prone to illusion due to psychological effects, need to recognize it, so as to avoid color discrimination errors caused by environmental colors. It is also a kind of green. It is placed in a yellow environment, and the contrast between green and white is bluish; while green is placed in a color environment, it is yellowish. It is also a gray background, reddish in a green environment. The black block of 50% dots is placed in the black field and the environment of 10% dots. You can feel the difference in brightness between the two. These are the results of discoloration caused by the illusion of color. From this reasoning, when distinguishing the colors of a certain color body, the influence of environmental colors must be avoided. When comparing various colors of multiple sets of color printing products, it is necessary to cover other colors.
At the same time, in the solid color block of proofing and printing, it can be juxtaposed together, and the interference of environmental colors should be eliminated to avoid color deviation caused by vision.
4. The relationship between the absorption of paper and the blotting ink layer
Due to the great differences in the absorption of inks by various papers, the absorption of coated paper is small, and the absorption of relief paper and offset paper is large. The paper with large absorption often causes the imprinted ink layer to solidify, and there is a large loss during the drying process. . As the ink binder has penetrated and absorbed into the paper fibers, the gloss of the print will be affected, the surface will become rough, and the color will change accordingly. When printing fine products, it is necessary to pay attention to the use of paper that cannot absorb too much. In addition, in offset printing, the ink color of the blotting ink is different between dry and wet. Offset ink color is a little darker after the ink is wet after printing, and the offset ink color will be lighter after drying. Therefore, when distinguishing colors and looking at samples, we must fully estimate its impact and increase the thickness of the ink layer in advance within the allowable range to compensate for the possible loss of color density. When using paper with poor quality, loose structure and rough surface, in order to avoid the ink color error that may occur when signing, the print can be placed for a certain period of time. After drying, the degree of color is determined. The thickness of the ink layer is controlled by the amount of ink, the general ink volume law:
1. The number of dot lines is 133L / in, 150L / in, 175L / in, etc. The higher the number of dot lines, the more it should be avoided. Too much ink will cause the dots to expand and expand. The amount of ink should be reduced appropriately.
2. Solid products can increase the amount of ink, making the ink layer slightly thicker.
3. The paper surface is relatively rough and has strong absorbability. It is necessary to increase the amount of ink used. The paper surface is relatively smooth and smooth, and the absorption is poor. The amount of ink used can be reduced in an appropriate amount.
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