How does a printing system produce high-quality images (2)

3. The four ways to deal with color. When adjusting defects such as insufficient local color saturation, you should master the following four methods:

( a ) Additions and subtractions cannot be excessive. First, the additive color of the basic color should not be too large. To maintain the level of the basic color, it is not possible to create a level-parallel level due to an excessive amount of color. Secondly, the color amount of the opposite color cannot be too large. To maintain the change in light and shade, light and shadow in color, , can result in simplification of color due to overuse of the opposite color.

( 2 ) Maintain the relation between the color amount and the light quantity level of a color. When adjusting a certain color, the color amount of the bright-tuning portion cannot exceed the color amount of the middle-regulation portion, and the color amount of the middle-adjustment portion cannot exceed the darkness portion. The amount of color, to maintain the color of the color and the light level of light and shade, depth relationship. Some prints now adjust the brightness of the bright part too much and overly bright the color of the dark part, losing the normal relationship of color and giving people an uncomfortable feeling.  

( C ) master the color space distance changes. In terms of chromatics, our sightlines are affected by the space and atmosphere media, and objects at different distances will undergo different changes in the color of the objects. The near, far, and small objects are the principle of spatial perspective. The closeness of the objects and the distant ones are blurred. The closeness of the color perception is strong and the distance is weak, which is the result of the perspective of the color space. Therefore, when adjusting a certain color, it is necessary to grasp the law of change when the color expresses the spatial distance, which is close to the warm and far cold; the near pure, distant ash; the near-bright, the far-blur, the close contrast, the far The contrast is weak. For example, there is a landscape picture book, in which a scene with a correct tone and rich color changes, the operator added a yellowish-blue color from the distant mountain to a blue-green color, causing a complete distorted color change in the spatial distance. The customer watched and shook his head again and said that the original hue was not met, and the result required rescanning and printing. Practice has proved that it is important to adjust the color according to the variation of the spatial distance of color.

( D ) master the law of color warm and cold changes. In the natural scenes of color photography, we find that the color of the light receiving surface of the object is inseparable from the cold and warm changes of the color of the light source, and the color of the dark surface is closely related to the cool and warm changes of the surrounding environment. Therefore, when making color adjustments, it is necessary to grasp the law of color warming and cooling. Pay attention to two issues. Firstly, there are three parts in the light receiving surface: high light, bright surface, and medium tone surface. The hue of the bright surface is mainly the combination of the light source color and the inherent color. The hue is cool and warm, and the light source color is cool and warm; the high light part. The color is generally the hue and color of the light source color; the light received by the adjusting surface in the object image is not direct light, but is side-emitting light. The hue and color are more complex and abundant. The hue is the light source complementary color, the intrinsic color and the ambient color. For the synthesis, the color is dominated by the inherent color. Second, the hue of the dark side of the object image is mainly the mixture of the ambient color and the natural hue. The warm and cold of the hue is shifted by the warm and cold of the ambient color. The color of the dark part always has the complementary color of the light source color. Therefore, it is important to note that the color of the dark tone is by no means a deepening or darkening of the inherent color.

The relationship between cold and warm colors in photographic photographs can only be achieved with the standardized scanning color separation method using reconstructed originals.  

Handle character skin color

There are many problems in the quality of reproduction of half-length portrait images in many periodicals, magazines, pictorials, photo albums and some advertisements. Some of them are of inferior quality. E.g:

(1) Some skin colors are seriously distorted, and some of the face color has become orange, red brown, and some have become blue, gray and black;

(2) Some skin color is rough, hard disjointed, there is no continuous overtones between light, medium and dark tone, it looks like there is no curve of change; due to the use of GCR technology, the dark part is reversed, and the yellow and red versions are shallow and become only one Deep black version;  

(3) Some skin colors due to the use of GCRI technology, causing the dark part of the reversal, the yellow, red version of the shallow, becomes only a very dark version;

(4) Some skin colors clearly show that the school color is wrong. Because the overprint of the Qingban school is excessive, the eyes and the school of the teeth are turned into red flesh, and some of the edges of the hair and the skin color show a circle of black tea.  

In addition to some of the original factors, the above problems are mainly caused by improper settings of color separation parameters and improper color processing. The general solution is:

1. Determine the tone of the skin tone. When performing character scanning and color separation, no matter how the manuscript is, it must be processed according to the characteristics of various people's skin colors. First, determine the tone of the skin tone by its age, gender, occupation, origin, ethnicity, and other characteristics, such as children's skin color, to be white and delicate, Delicate and ruddy. The "beauty shot" is a skin color that has been revitalized. The skin is ruddy, the colors are pleasing, and the changes are rich. If the original is color-shifted, it should be corrected according to the characteristics of the skin color of the characters. Only the correctness of the key tone will not cause major distortion.

2. Control dark skin color is not reddish. Most of the original dark skin tone reddish brown, after the black field settings, Y , M darker version, the dot value of about 85% , sometimes up to 90% . The C color version is sensitive to red tea and often goes to school. Therefore, for the darker skin tone of the larger area, one must pay attention to control the Y , M version below 80% , usually 75-78% . Because 80% is a dot jump zone, the printed dot is easy to increase; second, the C color version must keep up, and the standard color quantity should be slightly deepened. At the same time, the K version is slightly extended to make up for the C version. The shortcomings, the general ratio, if the M , Y color version in 75% -78% , C color version should be 30% , K version is about 25% , so that dark skin color calm.  

3. Normalize tone density and control skin tone.

( I ) Shunguang Film: Most of the faces are in bright and medium tone, and their color density converted into dot values ​​are mostly in the range of 30% to 45% . Ideally, the normal setting of skin color is better.

( b ) Side backlit film: half of the face is in the backlit position, and the density of the middle tone gradually shifts toward the dark side. The key technology here is to control the Y , M color version of the forehead. The color density of the forehead of some side backlights is 0.90-0.95 , which is converted into the dot value of 51%-53% , because 50% is the offset printing point again. In a jumping zone, the printing outlets increase the most. Therefore, pay attention to reducing the dot values ​​of the Y and M color versions to between 45% and 48% so as to avoid the jumping zone of the dot so that the forehead is bright and yellowish in color.

( C ) Backlight: most of the face is in the inverse