How does the printing system produce high-quality images (1)
At present, most printing units are equipped with a desktop system for image production. However, due to the fact that many units, especially the image production personnel of SMEs, still have a low level of technology, and are affected by other objective factors. Satisfactory. Compared with the printing level of international publications, there is still a certain distance, which can only be regarded as the lower middle level. Not only did I hear many American editors, photographers, etc. complaining that the color pictures of current pictorials, albums, periodicals and magazines are not printed well, and the originals cannot be restored. Even some pre-press production processes severely distorted the characters, landscapes and other colors on the manuscripts. In addition to the poor quality of some manuscripts, most of these deficiencies are caused by improper scanning color separation technology. This is a pre-press production process using low-grade platform scanners (approximately about 20%), and the quality of scanning separation is poor; second, because the operator lacks physical and chemical concepts and standardized operation methods for restoring scanning separation, only relying on screen color Subjective adjustments, so that the advanced technology and powerful functions of high-end professional scanners and high-end networking of electrical extensions have not been fully exerted; third, the operators lack the aesthetic level and the correct analysis ability of the original images, and they cannot be correct according to the characteristics of various originals Parameter setting and proper adjustment. Of course, there are also a very few cases that are caused by customers who do n’t know how to do and blindly command.
Practice has proved that the color separation and scanning technology of color images is the key to good or bad quality, because on the one hand, the current computer platemaking must first input the image art of simulated color photos and reversal films by scanning. It is a digital image that can be transferred in the digital process flow of the prepress system. In this scanning and conversion process, there are two key technologies that need to be mastered. One is how to use the scanner, from the original manuscript from the beginning of scanning Obtain the best color gradation information; the second is that 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, the conversion of color space, this step is color separation The key to handling. According to the printing suitability of ink, paper, etc., it should set the dot expansion value, gray balance parameters, black tone, and choose GCR or UCR color separation mode. Only if these parameters are set correctly, it is possible to output high-quality points. Color film. On the other hand, scanning color separation is technical and artistic. It is necessary to set and adjust the parameters of gray balance, tone contrast, color correction and sharpness from the technical aspects according to different types of manuscripts, but 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, we must make up our mind to improve the key technology of scanning color separation and improve the quality of operators. The following is a brief introduction to the main problems and solutions in the processing of colors, gradations, and gradations in current computer platemaking for reference.
Handle the contrast of photography
Some customers responded that the contrast processing of the photographic prints is not good, some highlights are not bright, the dark tone is not dark, the photo brightness is not strong, and the contrast effect is not good; There is too much loss. There are not only the objective reasons for the inadequate copying of the dots, but also the subjective factors of improper tone setting and adjustment when scanning the color separation. In the current photography creation, various pre- and post-processing is used to emphasize the contrast of tone and color, and different lenses and techniques are used to exaggerate the image. At present, high-quality photos can reach a maximum density of 2.50, which can effectively express the gradation range of 0.20-2.20. The maximum density of color reversal film is 3.50, and the effective density range of normal exposure is 0.20-3.20. The color reproduction is restricted by the printability of paper and ink. The maximum density of the tone range that can be reproduced by high-grade coated paper prints is only 1.8-1.9. For this reason, it is necessary to compress the tone range of the manuscript when copying, and compressing will inevitably lose a part of the layer, so the printed matter is unlikely to reproduce the contrast effect of high-quality photographic pictures, especially color reversal films. 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 the maximum printing density contrast and visual contrast of light and dark, this aspect should be explained to customers to make them understand.
In addition, it can be improved from the tone setting and adjustment of the scanning separation. The difficulty here is that one needs to compress and adjust the ever-changing tone range of the original to the tone range that can be reproduced by the printed matter; the second is to compress and adjust each sheet. When manuscripts, it is necessary to be able to determine what part of the level should be compressed and what part of the level should be highlighted, so as to emphasize the level of the main part, and can determine how best to emphasize and compress it. This requires both the ability to analyze the manuscript and the correct method of operation. The general solutions include the following:
1. Many current high-quality photographic images have a wide range of density and cannot be completely placed in the linear area of ​​the component. Therefore, first of all, according to the density contrast of each photographic picture and the thickness of the tone, determine the start and end points of the tone setting of the brightest (whitest) and darkest (black parts), and try to match the original density range Set on the maximum dot value of the color separation film to make the contrast of the printed matter as close as possible to the contrast of the picture.
2. The setting of the white field can't be too flat, too flat will make the highlight of the printed product become gray and not bright. It should not be too new, otherwise it will cause the loss of high light level, and the signal noise is large, which is easy to produce coarse particles. The main points are:
(1) Focus on the middle-tone, standard contrast picture, the extremely high gloss will set the screen, and set the required level of highlight as the basic white, that is, offset printing is C5%, M3%, Y3%; OPP film gravure is C7%, M5%, Y5%.
(2) For pictures with light tones and light color density, set the dot value of the white field to be slightly larger, and set the base white to the brightest and whitest place to deepen the color gradation of the tones.
(3) The pictures with mainly dark tones and deep color density can be used to screen the sub-highlights to highlight the brightness of the highlights and lighten (lighten) the middle tone.
3. The black point setting should not be too light, too light will make the dark tone of the printed product not thick, and the intensity is not enough; and not too deep, too dark will make the dark tone of the printed product dark, level upgrade. The essentials are:
(1) For the pictures with standard density contrast, to restore and copy, the black setting should select the dark and pure black parts of the picture, the transmission draft density should be set to 2.70-3.00, and the color photo density should be set to 1.80-1.90. The basic black offset printing process is C95% -98%, M85-88%, Y85-88%, K75% -80%. OPP film gravure process is C90-95%, M80-85%, Y80-85%, K65-70%.
(2) For the pictures with low density contrast and light tone, to deepen the copy, the black point setting should select the second black part of the picture, and the transmission draft density should be set to 2.30-2.50. The color photo density is set to 1.50-1.60, and the basic black is set.
(3) The density contrast is large, the color tone is heavy, and to lighten (brighten) the copy, you can select the darkest and darkest part of the picture, and you can increase the set density value, the transmission draft density is set to 3.00-3.50, the color photo density is set Set to 2.00-2.30, set the base black.
4. The key to the success or failure of dark copying lies in the correct black version settings. The current common problems are that the operators do not pay attention to the setting and adjustment of black films; second, the dark tone of most pictures is often not found. To the neutral black, it affects the accuracy of the black version setting; third, the black version uses a short-term skeleton curve, that is, a small point at 50% of the C version, resulting in insufficient mid-tone levels of the picture, and the three-dimensional sense 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 middle tone levels. The essentials are:
(1) Black point selection should be done as much as possible in neutral black parts of black objects to ensure the accuracy of the black dot value setting.
(2) Black dot value setting: 75% -80% is better for offset printing process. OPP film gravure process is 65% -70%.
(3) The effective use of the black version is not to add the black version to the three primary colors, but to match with the UCR. The amount of ink in the three primary colors should be reduced in the black portion to make room for an even black version. The black version opens up the dark tone level and enhances the contrast of photography pictures. 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. Smaller points can increase the middle and dark tone levels and three-dimensional sense of the picture. Of course, the black version is extended and the color part will be deepened. Pay attention to lighten accordingly.
Handle white and black in color pictures
White and black in color pictures are not only important colors in the picture, but with black and white tones, they appear thick and pure. Colorists believe that the world is neither absolutely white nor absolutely black. No matter how bright the "white" is, or how dark the "black" is, it has a certain color tendency, but on the specific screen, exaggerated white and exaggerated black can appear. Therefore, when copying, we must pay attention to the black and white tones in the color image, 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, and ignore the treatment of black and white. Therefore, white objects are often treated as white, and the layered texture of white objects is completely lost; black objects are treated as black, which cannot highlight the layered texture of black objects. The solution to this problem is:
1. Raise awareness 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 reflectance between black and white is much larger than that between any colors. According to the determination of scientists, the contrast between colors, even between the strongest primary colors or complementary colors, is much weaker than that between black and white. For example, when the red-green color is juxtaposed with the black-white color, the former can only achieve 40%, compared with the black and white parallel, the former can only reach 23% of the latter, and the blue and green parallel is compared with the black and white, the former is only 19% of the latter, which is why black and white works are sometimes more colorful than color The work came brightly. Therefore, when processing the white and black in the color image, it can not only express the layered texture of various white and black objects realistically, but also highlight the visual contrast of light and dark.
2. Essentials for handling white objects
White is called the extreme color in color science. Processing white in color pictures can not only show the texture characteristics of various white objects, but white can also be eye-catching and give brightness in bright places.
(1) A variety of white objects in color photography pictures are affected by the color of the light source, and their hue changes are extremely rich. Before processing, you must fully understand the texture characteristics of various white objects, and then adjust the processing according to different texture characteristics, such as Paper, Baiyun, White Flower, White Silk, White Jade, White Porcelain, etc. have different texture characteristics, so they should be different when setting and adjusting. The white of the white paper can be handled lighter and thinner; the white of the white jade and white porcelain should show the jade texture and porcelain texture, such as some shadow blue, sky blue and white glaze. For the texture, the gray-gray level of the highlight area should be maintained when scanning. However, some of these porcelain albums are printed with a variety of white porcelain bowls, white porcelain vases and other utensils that are mainly bright and middle notes. They are printed in white, as thin as white paper, and the brightness is only 3%. -5% of the C version, the M and Y versions are all screens, and several of them are even screens, completely losing the porcelain texture.
(2) The white color of fine art image works of art is more characteristic. For example, in oil trucks and gouache paintings, white is represented by pigments covering its color. White is both white and textured. Therefore, it is necessary to use the three primary colors to represent neutral white when setting, and only the local extremely high light can be extinguished. In watercolor painting, white is reflected by the white that leaves the water color itself. At least one of each watercolor painting is pure white, so that the picture can be bright and clear. Therefore, when setting, it can be screened against the local high-gloss white. Da Vinci once said: "The whitest place in a painting should be as precious as a gem." It means that the white place is very few in painting, and it is a special effect that the painter pursues. Therefore, when scanning settings, it must be carefully expressed.
(3) At present, the white objects of many printed products often have color cast or dew, which is due to the lack of gray balance awareness by some operators. The high-gloss white objects that need to be layered must be set according to the gray balance dot value ratio, such as C5% -6%, M3% -4%, Y3% -4%. If the white is warm, the proportion of halftone dots of the three-color version can also be close, but a color version is indispensable, otherwise it will be cast and exposed.
3. The essentials of handling black objects
Black is at the ultraviolet extreme of the spectral color band. It is called extreme color in color science. Processing black in color pictures can not only express the texture characteristics of various black objects, but also fully express the heavy sense of the picture, and bring out the pure color. Bright.
(1) Black objects in color photography pictures often cause black turbidity due to the influence of environmental colors. When processing, you should 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 coat, black sweater, black satin, black hair, etc. Time should be different. Such as black steel metal objects, the color volume can be heavy but not light. To show its weight, the black version should be the main setting, the dot value can reach 90%, and the three primary colors should be removed in an appropriate amount. The sum of the four color versions is About 320%. The black leather coat not only needs to show the smoothness and thickness of the leather, but also have the texture level of the leather coat. When setting, the black version should be used to make the layered texture, the color amount is 85% -90%. The tone can be extended to ensure the richness of the middle tone and the bright tone. Sometimes, you need to use the Photoshop lasso tool to check out the skin and adjust it with the black level curve. As for objects such as black satin, the smooth and delicate texture is mainly manifested. The four-color version should be soft and delicate when scanning. The contrast should not be too large, and the clarity should not be overemphasized.
In actual production, the dark tone of the photographic pictures is easy to cast color, making the object black black. Therefore, the UCR / UCA function is used to correct the deviation, so that the three-primary color version achieves the effect of neutral black, and then the black version is mainly used, so as to achieve the pure black effect, and better express the texture level of black objects.
(2) The dark tone of fine art pictures is an important part of the image modeling art. The black color in them is varied due to the characteristics and styles of various paintings. Different treatments should be done when scanning settings, for example: Chinese painting is based on ink Mainly, the ink color is pure, and the ink painting in it should use the GCR process to make a long-adjusted black version, so that the entire picture layer is rich, and the black version of the focal ink can reach 95% -100%. The color ink painting, whether it is heavy color or light color painting, should use UCR process, K95%, C70%, MY60%, the total of four colors is about 280%. However, the reproduction of some Chinese paintings today still mainly uses three primary colors, and the black version is a short-tone skeleton process, which causes the color of the ink to be discolored and exposed. It should be improved as soon as possible.
Some inks and gouaches use black in combination with other colors, not pure black. Therefore, the primary colors should be used for setting, C95%, M, Y85-88%, K70%, cannot be made like the black version in the photographic picture So deep. The deep and dark parts of some watercolor paintings are almost a unique taste expressed in pure black. Therefore, it is necessary to use the black version to reproduce when setting, generally 75% -80%. At the same time, the UCR method is used to reduce the amount of three primary inks. Because the color ink of the watercolor painting is light, the dot value after removal is C65%, M55%, Y55%. The sum of the four colors is preferably 250% -260%.
Deal with the normal relationship of color
At present, the color processing of some color prints is very messy, and the color tone of the original cannot be restored. Many customers (including many artists such as painters and photographers) are not very satisfied. A photographer also wrote an article saying: "In color printing, I often see In order to make the picture bright, regardless of the normal relationship between the colors and regardless of the specific position of a specific color in the picture, they are all adjusted very purely. Although the color is gorgeous, the whole picture looks chaotic.
This is caused by the fact that most operators do not master the standardized scanning color separation of restored originals and lack the artistic understanding of colors. They only look at the colors of the display screen and adjust them subjectively and arbitrarily. They often adjust too much and the range is too large. The solution is:
1. Do a good job in standardized and digitalized color management, which is the most important basic work. Even if the software is used to automate color management, it must have this foundation, so that the entire process flow has a stable environment. The method steps are:
(1) First of all, formulate technical parameters and quality standards for post-process phototypesetting, printing and proofing, and make them stable.
(2) Adopt standard gray scales, color scales and manuscripts for color restoration test, and establish a set of grey balance parameter sets to ensure the restoration of grey and complex colors in the manuscript.
(3) Establish the quasi-color correction amount for color correction on the basis of the input gray balance to achieve the restoration of the six hues of R, Y, G, C, B, and M 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 settings are used, the original color tone can be restored, no or little post-processing is required, and the Photoshop software tool is used to adjust it only to meet the customer's Request to adjust some defects of the original.
2. Make full use of the scanner to get the best image. At present, the image scanning and color separation operation must get out of a misunderstanding, that is, use high-end professional scanners and electrical extensions as simple input devices, and their powerful professional functions are useless. Or it is not used well, but the black and white field calibration, gradation adjustment, color correction, and sharpness are all adjusted using Photoshop software tools. This not only takes a long time to adjust, and the quality is unstable. It is often adjusted by one person or even one person. One sample at a time, varied, and because the scanned color separation image has little color gradation information, it is not possible to use the Photoshop software tool to call up a better color gradation. What's more, the artistic conception and subtle changes in color levels in graphic arts such as painting and photography cannot be adjusted.
Many excellent peers have this experience in practice, "In order to finally print a good product, all the information required for the product must be obtained from the original when scanning, which is like recording. For music, the microphone should be good first, otherwise the quality cannot be discussed.
Nowadays, many good printing units engage in data-based color management and use the "standardized scanning color separation method for restoring manuscripts" to achieve the effect of restoring manuscripts quickly and well. The images are not allowed to be post-processed. If the quality is not good, rescan. When the Apple computer is produced, the pictures scanned by the scanner and the extension can only be repaired, cut or do some special processing, and the picture level, color and clarity cannot be adjusted, nor enlarged or reduced. This is to improve quality and efficiency. The only way.
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