How to make high quality images in the printing system (2)
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3. Four essentials to deal with color. When adjusting defects such as insufficient local color saturation of the original, you should master the following four essentials:
(1) Adding color and reducing color should not be excessive. First, the basic color plus color can not be too large, to maintain the level of the basic color, can not be caused by excessive coloring and level; and second, the color correction of the opposite color can not be too large, to maintain the relationship between light and shade, light and shadow in color The color can be simplified due to the excessive color correction.
(2) Maintaining the relationship between the color quantity of the color and the light quantity level. When adjusting a certain color, the color quantity of the bright adjustment part cannot exceed the color quantity of the middle adjustment part, and the color quantity of the middle adjustment part cannot exceed the dark adjustment part. For the amount of color, it is necessary to maintain the relationship between the amount of color and the brightness and darkness of the light level. Now some prints have adjusted the color of the bright part too deep and too heavy, and the color of the dark part has been processed too brightly, losing the normal relationship of color, giving people an uncomfortable feeling.
(3) Master the law of spatial distance variation of color. From the color point of view, our line of sight is affected by the space atmosphere medium, and objects of different distances will change differently in color. The object's near-large and small is the principle of space perspective, while the object's closeness is clear, the far side is blurred, the color perception is close to the strong, and the far side is weak, which is the result of the color space perspective. Therefore, when adjusting a certain color, it is necessary to grasp the change law of the color expression space distance, near warm, far cold; near pure, far gray; near bright, far blurred, near contrast strong, far The contrast is weak. For example, there is a landscape album, in which a picture with a correct color and rich color changes, the operator adds a yellow color to the purple blue of the distant mountains, and turns into a turquoise color, which causes the color change of the spatial distance to be completely distorted. The customer looked around and shook his head and said that it did not conform to the original color tone, and the result required re-scanning and printing. Practice has proved that it is important to adjust the color according to the spatial distance variation of color.
(4) Master the law of color change and warmth. In the natural scenes of color photography, we find that the color of the object's light surface is inseparable from the change of the light and color of the light source color, and the color of the dark surface is closely related to the change of the surrounding environment. Therefore, when color adjustment is performed, it is necessary to grasp the law of change of color and warmth. Pay attention to two issues. First, the object surface has three parts: high light, bright surface and medium adjustment surface. The hue of the bright surface is mainly the combination of the light source color and the intrinsic color, and the color tone is warm and cold, which is transferred by the warm and cold color of the light source color; The color is generally the hue and chromaticity of the light source color; the light received by the object in the object is not direct light, but side light, which is more complicated and rich in hue and color. The hue is the complementary color, natural color and ambient color of the light source. The combination of color and color is mainly intrinsic color. Second, the hue of the dark side of the object is mainly the mixture of the ambient color and the inherent hue. The warmth and warmth of the hue is shifted by the warmth and warmth of the ambient color, and the color of the dark part always has the complementary color tendency of the light source color. Therefore, it should be noted that the dark color is not the deepening and darkening of the inherent color.
The relationship between the cold and warm colors in the photographic image can only be satisfactorily achieved by the standardized scanning color separation method using the restored original.
Handle the color of the person
At present, there are many problems in the copy quality of close-up photographs of half-length portraits in many journals, pictorials, pictures and some advertisements, some of which are of poor quality. E.g:
(1) Some skin color is seriously distorted, and some face coloration becomes orange, black, and even some become cyan, gray and black;
(2) Some skin color is rough, hard and disjointed, there is no continuous excessive tone between light, medium and dark tone, and it seems that there is no curve of change. Because of the GCR process, the dark part is reversed, and the yellow and red versions are shallow, becoming just one Very deep black version;
(3) Some skin tones are reversed due to the GCRI process, and the yellow and red versions are shallow and become a deep black version;
(4) Some skin colors are obviously seen as wrong color correction. Due to the excessive color of the green version, the eye and meat are red-colored, and some hairs are separated from the skin color by a circle of black tea.
In addition to some of the manuscript factors, the above problems are mainly caused by improper scanning color separation parameter setting and color processing. The general solution is:
1. Determine the tone of the skin tone. When performing character scanning color separation, regardless of the original, it is necessary to deal with the characteristics of various people's skin color. First, determine the tone of the skin color based on their age, gender, occupation, origin, ethnicity, etc., such as children's skin color, to be white and delicate, Delicate and rosy. "Beauty photo" is a skin color after makeup, the skin is white and rosy, the color is exaggerated, and the change is rich. For example, the original color cast should be corrected according to the character's skin color characteristics. Only when the key tone is correct, there will be no large distortion.
2. Control dark skin color is not reddish. The dark tone of most originals is reddish brown. After the black field is set, the Y and M color versions are deeper, and the dot value reaches about 85%, sometimes reaching 90%. The C color version is sensitive to the color of the black tea, often over the school. Therefore, for a darker skin tone with a larger area, one should pay attention to controlling the Y and M versions below 80%, generally 75-78%. Because 80% is a dot jump area, the printing dot is easy to increase; the second is to keep up with the C color version, and slightly deepen the standard color correction amount, while the K version of the tone is slightly extended to make up for the C version. Insufficient, the general ratio, if the M, Y color version is 75% -78%, the C color version should be 30%, and the K version is about 25%, so that the dark part of the skin is calm.
3. Standard tone density, control to adjust the skin tone.
(1) Shunguang film: Most of the face is in the bright and middle tone, and its color density is converted into a dot value of 30%-45%, which is ideal, and the skin color is normally restored.
(2) Side-backing film: Half of the face is in the back-lighting part, and the medium-density density gradually shifts to the dark part. The key technology here is to control the Y and M color versions of the forehead part. Some of the side backlights have a skin density of 0.90-0.95, which translates into a dot value of 51%-53%, because 50% is an offset dot. A jump zone, the printing dot increases the most. Therefore, it is necessary to pay attention to reduce the dot value of the Y and M color plates to between 45% and 48%, so as to avoid the jumping point of the dot, so that the forehead has a bright complexion and a yellow flesh color.
(3) Backlighting film: Most of the face is in the backlight, the density is large, and the skin color is dark. The forehead part is used as the control point, and its color density is converted into the dot value. The Y and M color plates are between 60% and 70%. Therefore, the first step should be to select the lightening curve to scan the color separation, or to use the Photoshop level curve after scanning. The middle part of the adjustment, the lightening (brightening) adjustment of the three-color version, generally should be reduced by 5%, so that the print skin density is in line with the visual effect, and there is room for the print dot to increase.
4. Master the continuous overtones of skin color. When making the tone setting and adjusting with the gradation curve, it should be mastered that the facial skin color should have continuous excessive tone from the bright part to the middle part to the dark part, and it should not be hard and disjointed, especially the tone of the M color version should be softly coordinated. .
5. Use the virtual light filter correctly. In theory, what color light is used for the virtual light filter should be based on the original color definition of the original, and the green (G) filter emphasizes the sharpness of the warm color. The default values of general scanners and electrical extensions are green (G), some are C=C, M=M, Y=Y, and K=Y. Some Y, M, C, and K color versions are all mixed colors of G (5:5). The skin color is soft and the hair is clear, so the red (R) filter is preferred.
In short, for the scanning and production of images in the prepress system, there is deep knowledge and experience, and the quality of the film output directly affects the printing result of the entire image. However, many of our prepress system operators are often difficult to produce high quality images due to the uneven quality and cultural level, as well as the lack of aesthetics, printing knowledge and image production experience. It is one of the main reasons why we can't see high-quality image prints in our daily life. To change this situation and improve the competitiveness of enterprises, especially after we join the WTO, we must face the fierce competition in the world. We must ask all the people in the printing industry (especially the operators of the prepress system) to Diligent study, good at thinking, summing up experience, actively exploring, diligently learning, will be able to master the rules of image production technology and scanning color separation technology, improve color sensitivity and artistic understanding, improve their own aesthetics, improve quality To a new level.