Computer color matching principle introduction - Huaqiang Electronic Network

First, the color mode computer color is roughly divided into color number archive search, reflection spectrum matching and three stimulus value matching three ways.
(1) Color number archive search.
That is, the varieties produced in the past are classified according to the color value, and the paint formula and process conditions are compiled into a file and stored in the computer. When necessary, the color difference is smaller than a certain value by inputting the color measurement result of the standard sample or directly inputting the code. All the formulas of the value are all output, which has the advantages of avoiding the fading problem when the sample is saved and the search is more comprehensive, but many new colors often only provide approximate formulas, and it is still necessary to adjust the experience in this case.
(2) Reflection (transmission) spectral matching.
The final determination of the color of the paint film is still the reflection spectrum (solid color) or transmission spectrum (transparent color), so that the reflection (transmission) spectrum of the product can match the reflection (transmission) spectrum of the standard, which is the most perfect color matching. It is also called unconditional matching. The reflection (transmission) spectrum generally uses a wavelength range of 400-700 nm, taking one data point every 10 nm.
(3) Tristimulus values ​​match.
The color matching result obtained in this way is not the same as the standard in the reflection (transmission) spectrum, but the same color can still be obtained because the tristimulus values ​​are equal. Since the tristimulus values ​​are determined by certain lighting conditions and observer color perception characteristics, the so-called tristimulus values ​​are equal and in fact conditional. Conversely, if one of the lighting conditions and the observer's two conditions does not match the premise of achieving the equi-color, then the equi-color is destroyed and the chromatic aberration occurs, which is also the color matching method. origin. Most computer color matching operations are based on CIE standard lighting conditions D65 and CIE standard observers. The output formula refers to a formula that can be adjusted to the same color as the standard under these two conditions. However, in order to predict the color difference that may occur after the light source is changed, the color difference data under the conditions of CIE standard illumination condition A cold white fluorescent lamp CWF or trichromatic fluorescent lamp TL-84 can also be provided. Conditional equivalence of each formula II. When the color theory is applied to the opaque paint film, in addition to part of the surface reflection, some light is absorbed and scattered. The absorption of light is mainly caused by pigments. Different pigments are selected. The absorption spectrum is different, resulting in a variety of colors in the paint film. At the same time, the more the amount of pigment, the more light is absorbed, and the less light is reflected, it can be seen that there is a relationship between the concentration of the pigment and the reflectivity of the film. Experiments have found that the relationship between reflectance and concentration is complex and not a simple ratio. To calculate the pigment concentration required for a coating, it is best to establish a transition function between the reflectivity and the concentration, which is a simple relationship with the reflectance and a linear relationship with the pigment concentration.
In fact, this theory is more complicated. In 1939, Kubelka and Munk induced a relatively simple theory from the theory of complete radiation. The color exhibited by the surface of the object is related to the reflectance (p) of the surface to the light, the absorption coefficient (K) of the opaque surface, and the scattering coefficient (S) of the opaque surface. The relationship between these three parameters is

When actually using the computer to adjust (match) color system color matching, the system configuration should have a full set of paint color matching software and basic database establishment and analysis software. As long as the data of the target color is input (by color measurement), the system can automatically select the color paste and the base paint according to the basic database, and at the same time give a plurality of formulas for the user to select. These formulas can be arranged according to the color difference between the pre-matched color and the target color, or can be arranged according to the formula cost. The colorizer selects a feasible formula according to the actual situation, and then performs color matching.
When using the computer toning system to do the coloring, the work that must be done beforehand is also necessary to make the various materials (color paste or pigment paste, base paint or white paint, additives, etc.) used in the color making the same thickness. The dry coating film is then used to measure the color of the coating film by a spectrophotometer, that is, the color paste data is input into the computer and stored, which is the establishment of the basic database.
A complete database setup is very complicated, but this work is the basis of color grading. On the one hand, if there is no raw material data such as color paste and base paint in the system, that is, the system does not know the various raw materials used for the color palette, and the formula cannot be produced. On the other hand, the formulation of the system and the prediction of the color difference between the color to be matched and the target color are calculated based on the data of various raw materials used in the coloring of the input system, if these data cannot be reflected. The essential characteristics of raw materials, that is, they cannot be equivalent to raw materials, then the coloring is equivalent to the use of other raw materials, and the color of the formula produced by the system will definitely be far from the target color. Therefore, when building a basic database, every step of the operation requires carefulness and strives for accuracy.
After the basic database is built, it is very convenient to use the computer toning system to color. It is worth noting that the database established can only represent a certain batch of raw materials (color paste, base paint, additives, etc.). In principle, if the batch of raw materials changes, the database should be re-established, otherwise it is difficult to ensure the color correction. accuracy. On the other hand, don't think that if you use the formula of the system to remove the color, you can definitely call out the test color with the target color difference equal to the predicted color difference. In fact, the color difference between the test color and the target color that is actually called may be better. Large, this requires recipe correction. When correcting the recipe, the system will automatically correct the recipe as long as the recalled test color data (by color measurement) is entered into the system. Generally, after 1-3 corrections, a satisfactory formula can be obtained.