Transmission original analysis (5)

3. The relationship between middle control and dot gain

After pre-scanning the person's photo automatically, which part of the face should be used as the detection and adjustment point for the mid-tone control? The law that I summarize in practice is: 1 The facial forehead is used as the middle control point because the forehead is prominent on the face and has a large area. It is yellow flesh and has a stable hue. 2 Using the M version as a benchmark, convert the density of the forehead in the range of 0.95, 1.00, 1.05, 1.10, 1.15 to the percentage of outlets to 50% or less, and Y, C version to the M version. decline. Because one is more than 50% of the dot value in the printing when the increase is more; Second, the forehead is brighter, if the M version exceeds 50%, it will be red hair net, not transparent; Third, the ratio of the forehead skin color is Y is greater than bright yellowish flesh.

Practice has proved that the adjustment of the above adjustment can not only compensate for the increase in the midtone dots in printing, but also ensure bright and true skin color, which is of great significance.

As for Shunguang Film, the forehead skin color density is below 0.90. After A1 is automatically set, the percentage value converted into dots is about 40%, which is ideal. For the backlight, the forehead skin color density is above 1.30, and the percentage of converted dots is more than 55%. Since the entire face is in the backlight, the three-color version is balanced accordingly, so there is no problem. It is only necessary to make some lighter adjustments.

The determination of the midtones is influenced by the light source being photographed. For positive light originals (rays are illuminated from the front), the face forehead is usually used as a midtone control zone. Forehead part of the light area is larger, bright light, coupled with the small part of the muscle, so the yellow skin color, which requires the value of the magenta version is lower than the yellow version, the basic value is: magenta 40% to 50% Yellow is more than 7% to 12.5% ​​of magenta, and the cyan version is roughly half that of magenta. For the elderly, the values ​​for yellow and blue are larger, and for children, the value for the yellow version is slightly lower for young women. This data combination in the midtones is not static, and for some photo manuscripts with very strong light sources, the midtones should be reduced in value, so as to meet the light intensity and lightness correspondence.

After controlling the black and white fields and midtones, we should also be confident in the color composition of the cheeks, lips, teeth, and eyes of portraits. The cheeks are rich in muscles and capillaries, so the skin color is red, usually M and Y. Flat, or yellow slightly larger than about 2% of magenta. The data relationship of the yellow version changes greatly. For children, magenta can be about 10% higher than yellow.

(c) Electronic color separation

The image with characters as the subject matter occupies a considerable proportion in color reproduction. The ideological realm of the characters and the features such as skin color, appearance, form, and personality of the faces are all important components of the main body of the screen. The reproduction of people's skin color, whether domestic or foreign, is the most difficult to deal with, regardless of the technology used, because people are very familiar with the skin color of the characters, and are also the most sensitive. Therefore, how to deal with good skin color, especially facial skin color, is crucial. . The treatment of skin color also follows a regular pattern. If you master the basic copying rules of skin color processing, you can print high quality prints featuring people as the subject.

1. Physiological characteristics of facial skin color and tone of facial skin tone

The average skin area of ​​adults is about 1600 cm2, the epidermis is about 0.1 to 0.3 mm thick, and the dermis is about 0.3 to 2.4 mm thick. The skin color contains a variety of pigments, such as serum proteins, melanin, oxygen complex hemoglobin, etc., and their respective light transmittance is not the same. As shown in Fig. 8-2-3, the distribution of the spectral transmittance of the skin pigment is shown. The solid line indicates the oxygen hemoglobin, the dashed line indicates the serum protein, and the solid line indicates the melanin. Therefore, the skin color is not a single surface color, but has a special translucent feeling, combined with the gloss of the epidermis, forming a complex color.

In addition, the spectral reflectance of skin color varies from person to person, and changes in gender, age, health status, race, and season can all cause differences in the spectral reflectance of skin color. Different subjects were measured and their averages were found. It was found that the spectral ratio of the most bright part of people's faces at 650um was about 605, and that of the darkest part at 430um was about 20%. For example, the upper curve in Figure 8-2-3 shows the spectral reflectance of a woman's complexion. It can be seen that the female complexion is slightly brighter. Figure 8-2-4 shows the curve of the age-influenced skin color. Women (W) are less than 30 years old and have a higher reflectivity than men (M) are less than 30 years old; same-sex ages are older than younger people. The reflectance is low; therefore, the amount of color used for copying cannot be the same. Fig. 8-2-5 shows the curve of skin color changes due to different races. The middle curve in the graph represents the skin color reflectivity of Asians. It is not difficult to see that although the reflectances of the three curves are different, the shapes are generally the same. From this, it can be seen that although the skin color of the race is different, their main wavelengths are the same, so the orange color at 590um is used as the basic tone in the copying process. Figure 8-2-6 shows the seasonal change of facial skin color. The upper curve in Figure 8-2-7 shows the brightest skin color in the face, and the lower curve is the spectral reflectance of the darkest skin color. The curved segment near 575um is a physiological feature that shows the low serum protein response.

According to the above analysis, in the process of copying, the treatment of the facial skin color of a person cannot be done in a uniform manner. Should be based on different characters of gender, age, ethnicity and other characteristics, to deal with a variety of character skin tone. The color of young children's skin is based on white, tender and red, with a delicate, full and delicate leather, and a smooth, light-dark contrast. Young women are based on the radiant flesh of white hair, and their skin is delicate and soft. The color of the young male is dark red, especially the working people who are often exposed to the sun. Their complexion looks rosy and healthy. Because men's muscles are plump, strong, and the contrast of skin tones is strong. The color of the old fishermen is dark and their wrinkles are visible. It should be based on the dark reddish brown color in the black and the color should be thick and heavy. Only by grasping the tone of facial skin color and mastering the relationship between the shade ratios of the three primary colors and the relationship between them, can we truly reproduce the characteristics and personality of various characters.

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