How to make high quality images with the hottest p

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How the printing system makes high-quality images (Part 2)

3 The four essentials of dealing with color. When adjusting defects such as insufficient local color saturation of the original, you should master the following four points:

(I) do not add or subtract too much color. First, the basic color addition should not be too large, and the levels in the basic color should be maintained, and the levels should not be merged due to excessive color addition; Second, the amount of opposite color correction should not be too large, and the relationship between light and shade should be maintained in the color, so that the color can be simplified due to excessive opposite color correction

(II) maintain the relationship between color quantity and light quantity. When adjusting a certain color, the color quantity of the bright part shall not exceed the color quantity of the middle note part, and the color quantity of the middle note part shall not exceed the color quantity of the dark part. Maintain the relationship between color quantity and light quantity grade. At present, some printing materials adjust the colors of the bright parts too deeply and too heavily, and deal with the colors of the dark parts too bright and too bright, thus losing the normal relationship between colors and giving people an uncomfortable feeling

(III) master the spatial distance change law of color. In terms of chromatics, due to the influence of space atmospheric medium on our line of sight, objects at different distances will have different changes in shape and color. The principle of spatial perspective is that the object is near, far and small, while the object that is near is clear, the object that is far is fuzzy, the color perception that is near is strong, and the object that is far is weak, which is the result of color spatial perspective. Therefore, when adjusting a certain color, it is necessary to master the change law of color expression space distance, which is warm in the near and cold in the far; Near pure, far gray; The near contrast is bright, the far contrast is fuzzy, the near contrast is strong, and the far contrast is weak. For example, in a landscape album, the operator added some yellow to the purple and blue of the distant mountains and turned them into turquoise green. As a result, the color changes of the spatial distance were completely distorted. The customer shook his head after looking at them. These are not what we want to see. They do not conform to the original color. As a result, it is required to scan and print again. Practice has proved that it is important to adjust the color according to the change law of color space distance

(IV) master the change law of color temperature and temperature. In the natural scenery photographed by color photography, we found that the color of the light receiving surface of the object produced and developed by the technical department of Jinan new era assaying Instrument Co., Ltd. all year round is inseparable from the change in the temperature of the light source color, while the color of the dark surface is closely related to the change in the temperature of the surrounding environment color. Therefore, when carrying out color adjustment, it is necessary to master the change law of this kind of color. Two issues should be noted. First, the light receiving surface of the object image has three parts: high light, bright surface and middle note surface. The hue of the bright surface is mainly the combination of light source color and solid color. The temperature of the hue is transferred by the temperature of the light source color; The color of the highlight part is generally the hue and chromaticity of the light source color; The light received by the middle note surface of the object image is not direct light, but side light, which is more complex and rich in hue and chromaticity. Its hue is the combination of light source complementary color, solid color and environment color, and its color sense is mainly solid color. Second, the hue of the dark side of the object image is mainly the mixture of the environment color and the inherent hue. The temperature of the hue is transferred by the temperature of the environment color, and the color of the dark part always has the complementary color tendency of the light source color. Therefore, we should pay attention to the dark color is not the deepening and darkening of solid color

for the relationship between cold and warm colors in photographic pictures, only the standardized scanning color separation method of restoring the original can achieve satisfactory results

deal with the skin color of the characters

at present, there are many problems in the reproduction quality of the close shot bust pictures in many journals, magazines, pictorials, picture books and some advertisements, some of which are of poor quality. For example:

(1) some skin colors are seriously distorted, and some face colors are orange, black tea, or even vegetable green, gray black

(2) some skin colors are rough, stiff and disjointed, and there is no continuous and excessive tone among bright, medium and dark tones, which seems to lack the beauty of changing curves; Due to the use of GCR process, the dark part is reversed. The yellow and red versions are light and become just a very deep black version

(3) some skin colors are reversed in the dark due to the GCRI process. The yellow and red versions are light, and become just a very dark black version

(4) it is obvious that some skin colors are wrong in color correction. Due to excessive color correction of the green version, the eye flesh and tooth flesh are corrected to red flesh color, and a circle of black tea edges are exposed at the junction between the hair edge and the skin color

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

1 Set the tone of your skin tone. When scanning and color separation of characters, regardless of the original, it should be processed according to the characteristics of the skin color of various characters. First, determine the tone of the skin color based on their age, gender, occupation, origin, nationality and other characteristics. For example, the skin color of children should be white, delicate, delicate and ruddy. "Beauty photo" refers to the skin color after makeup. The skin is white and ruddy, the color is boastful, and the changes are rich. If the original is biased, it should be corrected according to the character's skin color characteristics. Only if the tone is correct, there will be no major distortion

2. Case 1 of control darkness: after confirming that the installation levelness of the instrument meets the requirements of the regulations, the testing machine should first check whether the friction force of the working part is too large. If so, adjust the clearance of the guide wheel to eliminate the friction force, and clean the working oil cylinder if necessary. If there is still a positive difference after eliminating the influence of the friction force, loosen the fastening screw of the connecting shaft sleeve between the swing rod and the push plate in the force measuring part (reading mechanism), adjust the push plate to the inside, and fix the solid screw, The small dial shall be verified step by step and repeated several times until it is qualified. If the small dial is qualified, but the large and medium dial are still out of tolerance, the weight of B thallium and C thallium shall be appropriately increased until the color of the qualified part is not red. The dark tone skin color of most originals tends to be reddish brown. After the black field setting, the Y and M color versions tend to be darker, and the dot value reaches about 85%, sometimes 90%. The c-color version is sensitive to black tea color correction, and is often over calibrated. Therefore, for dark tone skin with large area, first, pay attention to control the Y and M versions below 80%, which is generally%. Because 80% is a point jump area, the printing point is easy to increase; Second, the color C version should keep up with the standard color correction. It should be slightly deepened on the basis of the standard color correction. At the same time, the gradient of the K version should be slightly extended to make up for the deficiency of the C version. Generally, if the M and Y color versions are 75%-78%, the color C version should be 30% and the K version should be about 25%, so as to make the dark skin calm

3. Regulate the shade density and control the color of middle note tone

(I) smoothing film: most of the face is in bright and middle note, and its color density conversion to point value is mostly 30%-45%, which is ideal, and the normal set skin color restoration is better

(II) side backlight film: half of the face is in the backlight part, and the middle note density gradually moves to the darker part. The key technology here is to control the Y and M color plates on the forehead of the middle note. The forehead skin color density of some side backlights is at 0 95, the converted point value is 51%-53%. Since 50% is another jumping area of offset printing point, the printing point increases the most. Therefore, pay attention to lighten the point value of Y and M color plates to 45%-48% to avoid the jumping area of this point, so that the forehead skin color is bright and yellow

(III) backlight film: most of the face is backlight, with high density and dark skin color. With the forehead as the control point, the color density is converted into the point value, and the Y and M color plates are between 60%-70%. Therefore, first, the lightening level curve should be selected to scan the color separation, or after scanning, the middle note part of the Photoshop level curve should be used to lighten (brighten) the tricolor plate, which should generally be lightened by 5%. In this way, not only the skin color density of the print conforms to the visual effect, but also the print point should be increased

4. Master the continuous excessive tone of skin color. When setting the gradient and adjusting with the hierarchical curve, it should be understood that the skin tone of the face should have a continuous and excessive tone from the bright part to the middle note part to the dark part, and it should not be too hard Host size: 430*315*855mm sections, especially the tone of m-color version should be soft and harmonious

5. Correct selection of virtual light filter. Theoretically, what color light should be selected for the virtual light filter should be based on the clarity of the main tone of the original. The green (g) filter emphasizes the clarity of the warm tone. Generally, the default values of scanners and electrical extensions are green (g), and some are c=c, m=m, y=y, k=y. Some of the Y, m, C and K color versions are g (5:5) mixed colors. The skin color should be soft and the hair should be clear, so the red (R) filter is better

in a word, there is deep knowledge and experience in the scanning and production of images in the prepress system. The quality of film output directly affects the printing results of the whole image. However, many operators in our prepress system are often difficult to produce high-quality images because of their uneven quality and educational level, as well as their lack of aesthetics, printing knowledge and image production experience. This may be a main reason why we can not see high-quality image prints in our daily life. In order to change this situation and improve the competitiveness of enterprises, especially in the face of fierce global competition after China's entry into the WTO, we must require all the staff in the printing industry (especially the operators of the prepress system) to study harder, be good at thinking, sum up experience, actively explore and ask more questions, so that we can master the laws of image making technology and scanning color separation technology, Improve the awareness of color sensitivity and artistry, improve their aesthetic views, and raise the quality to a new level

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