How to make high quality images in the printing system (1)
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At present, most printing units are equipped with image-making desktop systems. However, due to the fact that many units, especially the image producers of small and medium-sized enterprises, the technical level is still not high, and affected by other objective factors, the quality of many color pictures is produced and printed. Satisfactory, there is still a distance compared with the printing level of international publications, which can only be regarded as the middle and lower level. Not only did many American editors, photographers, etc. complain that the current color maps of pictorials, albums, and periodicals are not good, and the originals cannot be restored. The colors are seriously distorted. Some colors become pattern blocks, and some are light and dark, and the layers are upside down. Even some pre-press production processes have severely cast color on the characters and landscapes on the manuscript. All of these ills, except for the poor quality of some of the originals, are mostly caused by improper scanning color separation techniques. This is a pre-press production process using low-grade platform scanners (about 20%), scanning color separation quality is inferior; second, because the operator lacks physical and chemical concepts and standardized reduction scanning color separation operation methods, relying only on screen color Subjective adjustments have made the advanced technology and powerful functions of high-end professional scanners and electric extensions high-end networking not fully utilized; third, the lack of aesthetics and correct analysis of the original drawings by operators, and cannot be correctly based on the characteristics of various originals. The parameter settings and the appropriate adjustments. Of course, there are very few cases where customers do not know what to do and who are commanded.
Practice has proved that color map copy printing, its scanning color separation technology is the key to quality, because on the one hand, the current computer plate making the input of graphic art such as simulated color photos and reversal films must first be scanned and transformed. For the digital image, it can be transmitted in the digital process flow of the prepress system. In this scanning and conversion process, there are two key technologies to master. First, how to apply the scanner, from the original scanning The best color level information is obtained. Second, the image file input from the scanner is usually in RGB format. Before outputting the color separation film, the file needs to be converted into CMYK format, that is, color space conversion. This step is color separation. The key to processing. It should set the dot gain value, gray balance parameter, black tone tone, and select GCR or UCR color separation mode according to the printing suitability of ink, paper, etc. Only when these parameters are correctly set, it is possible to output high quality points. Color film. On the other hand, the scanning color separation is technical and artistic, and it is necessary to rationally set and adjust the gray balance, tone contrast, color correction and sharpness parameters according to different types of originals, and also from the aesthetic aspect. Handle the relationship between color tone, saturation, spatial distance, light and dark, light and shadow changes. The level of these two aspects of the operator has a great impact on product quality. Therefore, in order to improve the image quality of current color prints, it is necessary to make up the key technology of scanning color separation to improve the quality of operators. The following is a brief introduction to the main problems and solutions in the current color processing, color, level and tone processing for reference.
Handle the contrast of the photographic image
Some customers responded that the contrast of the photographic prints was not good. Some of the highlights were not bright, the dark ones were not dark, the photos were not strong, and the contrast was not good. Some of the highlights were white, and the darkness was black. There are too many losses. There are both objective reasons for the insufficiency of the network to copy the congenital, as well as the setting of the tone and the subjective factors of improper adjustment. Because of the current photography creation, various pre- and post-processing are used to emphasize the contrast of colors and colors, and different mirrors are used.
Head and technique exaggerate the image. At present, high-quality photos with a maximum density of 2.50 can effectively represent a range of 0.20-2.20. The color reversal film has a maximum density of 3.50, and the normal exposure has an effective density range of 0.20 to 3.20. The color reproduction is limited by the printability of paper, ink, etc., and the maximum density of the tone range that can be reproduced by the high-grade coated paper is only 1.8-1.9. For this reason, it is necessary to compress the tonal range of the manuscript during copying, and it is necessary to lose a part of the layer by compression, so the printed matter is unlikely to reproduce the contrast effect of the high-quality photographic picture, especially the color reversal film. Copying can only make full use of the whiteness of the paper and the maximum density of the four-color ink superimposed on this color space to achieve maximum print density contrast and visual contrast between light and dark. This should be explained to the customer and understood.
In addition, it can be improved from the tone setting and adjustment of the scanning color separation. The difficulty here is that one needs to compress and adjust the ever-changing range of the original tone to the tone range that the printed matter can reproduce; the second is to compress and adjust each sheet. In the case of an original, it is necessary to determine the level of compression of the part, and the level of the part should be highlighted so as to emphasize the level of the main part, and to determine to what extent it is best to emphasize and compress it. This requires both the ability to analyze the original and the correct method of operation. The general solution has the following points:
1. Many high quality photographic images currently have a wide range of densities and cannot be placed completely into the linear region of the assembly. Therefore, first of all, according to the density contrast and tone thickness of each photographic picture, determine the brightest (whitest) and darkest (black part) as the starting point and end point of the gradation setting, and try to correspond to the original density range. Set the maximum dot value of the color separation sheet so that the contrast of the printed matter is as close as possible to the contrast of the image.
2. The white field setting can't be too flat, and the Taiping will make the printed product high gray and gray. It can't be too embarrassing, otherwise it will cause high-level loss, and the signal noise is large, and it is easy to produce coarse particles. The main method is:
(1) The picture with the medium-tone, density contrast standard, the extremely high-light setting of the net, and the high-level light of the required level is set as the base white, that is, the offset printing is C5%, M3%, Y3%; the OPP film gravure is C7%, M5%, Y5%.
(2) For the picture with bright tone and light color density, the white point setting dot value can be slightly larger, and the base white is set at the brightest and whitest place to deepen the color level of the bright tone.
(3) The picture with dark tone as the main color and deep color density can be used to set the second high light to highlight the brightness and lightening (lightening) of the highlight.
3. The black field setting can't be too shallow. Too light will make the printed product dark and not thick, and the strength is not enough; it can't be too deep, too deep will make the printed product dark and dark, and the level is upgraded. The essentials are:
(1) For the picture of the density contrast standard, to restore and copy, the black field setting should select the picture to darken the pure black part, the transmission density is set to 2.70-3.00, and the color photo density is set to 1.80-1.90. The basic black offset printing process is C95%-98%, M85-88%, Y85-88%, K75%-80%. The OPP film gravure printing process is C90-95%, M80-85%, Y80-85%, K65-70%.
(2) The picture with small contrast of density and thin color tone should be deepened and copied. The black field setting should select the black part of the picture, and the transmission density is set to 2.30-2.50. The color photo density is set to 1.50-1.60, and the base black is set.
(3) The density contrast is large, the color tone is heavy, and the light is reduced (brightened). The darkest and darkest parts of the picture can be selected, and the density value can be increased. The transmission density is set to 3.00-3.50, and the color photo density is set. Set to 2.00-2.30, set the base black.
4. The key to the success of the dark copy is the correct black version setting. At present, the common problems are that the operator does not pay attention to the setting and adjustment of the black film. Second, the dark color of most pictures is often not found. To neutral black, affecting the accuracy of the black version setting; the third is that the black version is a short price adjustment skeleton curve, that is, a small point in the C version 50%, thus causing the picture intermediate level is not enough, the stereoscopic effect is not strong . Practice has proved that the effective use of the black version can not only enhance the contrast of the picture, but also enhance the dark and medium levels. The essentials are:
(1) The black field selection point should be selected as far as possible in the neutral black part of the black object to ensure the accuracy of the black version of the dot value setting.
(2) Black dot value setting: The offset printing process is preferably 75%-80%. The OPP film gravure process is 65%-70%.
(3) The effective use of the black version is not to add a black version to the three primary colors, but to match the UCR. The amount of ink in the three primary colors should be reduced in the black part to make room for the addition of a uniform black version. The black version opens the dark tone level and enhances the contrast of the photographic images. Generally, 20%, C78%, M68%, Y68%, and K90% are removed.
(4) The starting point of the black version is extended to 35%-40% of the C version, which can increase the middle and dark tone of the picture and the three-dimensional sense. Of course, the black version of the tone is extended, and the color part is deepened. Pay attention to the corresponding reduction.
Handle white and black in the color map
The white and black in the color picture are not only the important colors in the picture, but also have black and white tones, which make the color thick and pure. Color scientists believe that the world is not absolutely white, nor is it absolutely black. No matter how bright "white" is, or how dark it is, it has a certain color tendency, but in the specific picture, exaggerated white and exaggerated black can appear. Therefore, we must pay attention to the black and white color in the color picture when copying, which is an important part of improving the artistic effect of the image.
At present, most operators only pay attention to the adjustment of color, while ignoring the treatment of black and white. Therefore, the white object is often treated as a piece of white, completely losing the layered texture of the white object; the black object is treated to be dark, and the layered texture of the black object cannot be highlighted. The solution to this problem is:
1. Improve the understanding of the importance of white and black tones in color pictures
Everyone knows that black and white photos are more visually powerful than color photos, because the difference in reflectivity between black and white is much larger than any color. According to scientists, the contrast between colors, even the most intense contrast between primary colors or complementary colors, is much weaker than the contrast between black and white. For example, the red and green juxtaposition is comparable to black and white, the former can only reach the latter. 40%, the red and blue flat columns are compared with the black and white flat columns. The former can only reach 23% of the latter. The blue and green juxtaposition is compared with the black and white juxtaposition. The former is only 19% of the latter, which is why black and white works sometimes have color The work comes brightly. Therefore, the white and black in the color map are processed during scanning, which not only can realistically express the layered texture of various white and black objects, but also highlight the visual contrast between light and dark.
2. The essentials for dealing with white objects
White is called the extreme color in color, and the white color in the color picture can not only express the texture characteristics of various white objects, but also white and eye-catching, giving brilliance in the bright place.
(1) Various white objects in color photography pictures are extremely rich in color tone due to the influence of light source color. Before processing, it is necessary to fully understand the texture characteristics of various white objects, and then adjust the processing according to different texture characteristics, such as: white Paper, white clouds, white flowers, white silk, white jade, white porcelain, etc., have different texture characteristics, and should be different when setting adjustment. The white of white paper can be handled lightly; while the white of white jade and white porcelain should show the texture of jade and porcelain. For example, the surface of some monochrome porcelain such as shadow green, azure and white glaze is smooth and delicate, and this should be reproduced. For texture, when scanning settings, the blue-gray level of the highlight area should be maintained. However, some of these porcelain catalogues, the porcelain of various white porcelain bowls and white porcelain vases, which are mainly bright and medium-tone, are printed in white, as thin as white paper, with a brightness of only 3%. -5% of the C version, M, Y version are all nets, there are a few even C version of the net, completely lost the porcelain texture.
(2) The white color of art image art has more characteristics, such as oil truck, gouache, and white are covered with pigment on it. White is white and textured. Therefore, the setting should be composed of three primary colors to form neutral white, and only the local extremely high light can be used. The watercolor painting, white is reflected by the white color of the water color itself, and at least one of each watercolor painting is pure white, so that the picture can be bright and clear. Therefore, when setting, the local highlight white can be absolutely net. Leonardo da Vinci once said: "The whitest place in a painting is as valuable as a gemstone." The meaning is that the white place is rarely painted, and it is a special effect pursued by the painter. Therefore, when scanning settings, be sure to show it carefully.
(3) Many white objects of printed products often have color cast and color, which is due to the lack of gray balance awareness of some operators. For high-light white objects that require gradation, they must be set according to the proportion of gray balance dot values, such as C5%-6%, M3%-4%, and Y3%-4%. If the white is warmer, the ratio of the three-color version of the dot value can also be approximated, but it is indispensable for a color version, otherwise it will be biased and exposed.
3. The essentials for dealing with black objects
Black is in the ultraviolet extreme of the spectral band, and it is called the extreme color in color. Processing the black color in the color picture not only can express the texture characteristics of various black objects, but also fully express the thick feeling of the picture and bring out the purity of the color. Bright.
(1) Black objects in color photographs often cause black turbidity due to environmental color. When processing, first understand the texture characteristics of various black objects, and then adjust according to various texture characteristics, such as black steel, black camera, black leather, black sweater, black satin, black hair, etc., the texture characteristics are different, adjust It should be different. Such as black steel metal objects, the amount of color can be heavy but not light, to express its sense of weight, the setting should be based on the black version, the dot value can reach 90%, while the three primary colors are removed, the sum of the four color versions is 320% or so. The black leather coat should not only show the smooth and thick leather, but also have the texture level of the leather coat. When setting, it should make full use of the black version to make the layer texture, the color amount is 85%-90%. The tone can be extended to ensure that the middle and bright layers are rich. Sometimes you need to use the Photoshop lasso tool to tick the skin and adjust it with the black layer curve. As for black satin and other objects, it mainly expresses its smooth and delicate texture. When scanning, the four-color version should be soft and delicate, the contrast should not be too large, and the clarity should not be overemphasized.
In actual production, because the darkness of the photographic picture is easy to color, the object black is not pure. Therefore, the UCR/UCA function is used to correct the deviation, so that the three primary color versions achieve the effect of neutral black, and then the black version is mainly used, thereby achieving the black pure effect and better expressing the texture level of the black object.
(2) The dark tone of art pictures is an important part of the art of image modeling. The black color is varied due to the characteristics and styles of various paintings. The scanning settings should be treated differently. For example: Chinese painting is ink The main color is pure ink. The ink painting should adopt the GCR process and make a long black version, which makes the whole picture layer rich, and the black version of the coke ink can reach 95%-100%. Among the color ink paintings, whether it is heavy color or light color painting, UCR technology should be adopted, K95%, C70%, MY60%, and the sum of four colors is about 280%. However, some of the reproductions of Chinese paintings still use the three primary colors, and the black version is a short-tuning skeleton process, which causes the color cast and color of the ink to be improved as soon as possible.
Some inks and gouaches use black and other colors in combination, not pure black. Therefore, the setting should be based on three primary colors, C95%, M, Y85-88%, K70%, which cannot be made like the black version in the photographic picture. So deep. The darkness of some watercolors is almost a unique taste expressed in pure black. Therefore, the setting should also be reproduced in black version, generally 75%-80%. At the same time, the UCR method is used to reduce the amount of ink of the three primary colors. Since the color ink of the watercolor painting is elegant, the dot values after removal are C65%, M55%, and Y55%. The sum of the four colors is preferably from 250% to 260%.
Handle the normal relationship of color
At present, the color processing of some color prints is very messy and cannot restore the original color. Many customers (including artists such as painters and photographers) are not satisfied. A photographer also wrote an article saying: "In color printing, I often see In order to make the picture colorful, regardless of the normal relationship between the colors, regardless of the specific position of a specific color in the picture, it is adjusted very purely, although it is gorgeous, but the whole picture appears to be chaotic."
This is the fact that most operators do not have the ability to master the standardized scanning color separation and lack of artistic understanding of color. They only look at the color of the display screen, which is caused by subjective random adjustment, and often adjusts too much and the amplitude is too large. The solution is:
1. Do a good job of standardization and data color management. This is the most important basic work. Even with software automated color management, this foundation must be in place to give the entire process a stable environment. The method steps are:
(1) Firstly, formulate the technical parameters and quality standards of the post-process photo, print, and proof, and stabilize it.
(2) Using the standard gray scale ruler, color scale and original for color restoration test, establish a set of gray balance parameter sets to ensure the gray and complex color restoration in the original.
(3) Based on the input gray balance, the quasi-calibration color quantity of the color correction is established, and the restoration of the six color phases of R, Y, G, C, B, and M is achieved to ensure the restoration of the original color. After doing the above work, when scanning the color separation, as long as the correct black and white field settings are used, the original color can be restored. It is not necessary or necessary to perform post-processing, but it is adjusted by Photoshop software tools only to satisfy the customer. Some defects in the original are adjusted as required.
2. Make full use of the scanner to get the best image. At present, the image scanning and color separation operation is going to go out of a misunderstanding, that is, the high-end professional scanner and the electric extension are regarded as simple input devices, and their powerful professional functions are not used. Or use it badly, and the black and white field calibration, level adjustment, color correction, and definition of sharpness are all adjusted by Photoshop software tools. This is not only the adjustment time is long, the quality is unstable, and it is often a person who adjusts one or even one person. Tune one sample at a time, and because the scanned color separation image has only a small amount of color level information, then the Photoshop software tool can not be used to call up a better color level. What's more, the artistic conception and subtle color level changes in graphic art such as painting and photography cannot be adjusted.
Many excellent peers have the experience in practice that "in order to finally print a good product, all the information needed for the product must be obtained from the original when scanning, which is better than recording. The music, the first microphone is better, otherwise the quality can not be discussed."
Nowadays, many good printing units engage in data color management, and use the "standardized scanning color separation method of reducing originals" to achieve the effect of quickly and accurately restore the original. For this reason, the unit stipulates that the customer requests to restore the original and scan the color separation. The image is not allowed to be post-processed. If the quality is not good, it will be re-scanned. When Apple is made, the images scanned by the scanner and the electric extension can only be repaired, cut, or do some special effects. The picture layer, color and definition cannot be adjusted, and no enlargement or reduction is performed. This is to improve quality and efficiency. The only way to go.