Discussion on the Pre-reduction and Post-processing of Scanning Separation Technology
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China's pre-press field has been comprehensively promoted the use of computer-platemaking technology (including color desktop systems and high-end electrical extensions network system), making the graphic arts into a new era. In recent years, some professional plate printing companies have used the DTP system to print out many fine books and won awards at various international book fairs. I see these award-winning books are indeed "printed artwork" and have a high appreciation value, fully embodying the perfect combination of high-tech plate-making printing technology and art. Facts have proved that the printing level of some fine books in China has reached or approached the international advanced level.
However, from the current overall quality of book printing, it is still unsatisfactory. There are generally poor quality, many rework, low efficiency, and even some high-grade books printed and made into inferior products are not satisfactory. Worrying.
Why, then, why do so many platemaking companies have world-class computer-to-platemaking equipment and technology but can't make good products? Why can't we bring into play the advanced nature of new technologies? It really needs us to calm down to study and solve.
Of course, the problems are multifaceted. One of the major problems is that many practitioners have many vague ideas and incorrect operating methods on computer-scanned image scanning and color separation technology. There is no clear theoretical guidance, leading to many blind operations. Sex! E.g:
1. Many practitioners believe that the advanced nature of computer-to-platemaking technology is to look at screen toning, but I do not know this is its advanced aspect, not all. Because we are doing copy work, we still need to follow the copying principle, instead of making creative designs that need to be adjusted on the screen.
Some people think that the scanned document can be modified repeatedly at a later stage, so the requirements for scanning color separation can be greatly reduced, but I do not know that too much image information is lost during scanning, and adjustments are made only after scanning, making it difficult to reproduce good works. , and use Photoshop software to do a variety of changes to adjust and adjust at the expense of the level, because repeated adjustments will reduce the clarity of the image.
Others think that computer-to-platemaking technology is very simple. Even if water understands color knowledge and does not understand the process of making plates, it can also look at the screen to pick up a good product. The result is counterproductive. The tune-out color is not distortion, that is, one sample at a time and one sample at a time. There is no standard or regularity, and the quality fluctuates greatly. It is impossible to have a stable quality.
Practice has proved that computer plate making technology is not magic, nor is it as simple and perfect as people think. It also has many quality problems that are difficult to control. It still requires effective color management and requires standardized and standardized operation methods. Need to understand the LAB, RGB, CMYK color space knowledge and conversion relationship, need to have the ability to correctly analyze the original, need to adjust the operating skills and aesthetic level of non-fitting manuscripts.
That is, the introduction of advanced equipment is only improving the quality and efficiency of 50%, and the other 50% is to rely on scientific management and master the ability and level of new technology to achieve.
2. Many plate-making companies use electric extensions and high-grade roller scanners as simple input devices to swab 40-50 originals on one roller. All black and white field calibrations, color corrections, gradation adjustments, sharpness enhancements, and even zoom ratios were adjusted on the computer using Photoshop image processing software, while the power of the extension printer and roller scanner separation software was not utilized. It is a pity. This type of cart before the inverted operation, the industry called "wild way child operation", will inevitably result in poor quality, rework more. If you are scanning electronic documents for your customers, this operation is also incorrect. You should also be responsible for the customer and follow the standardization.
In summary, these vague ideas and incorrect operation methods cannot produce qualified products. Therefore, we must first have a correct understanding of scanning color separation technology, have a clear theoretical guidance, and then have a standardized method of operation, in order to produce good quality images quickly and well.
Second, the importance of scanning color separation technology
At present, the workflow of the computer-based platemaking system can be divided into five parts: scanning, making, filming, printing, and proofing. The last three parts are relatively stable factors. The task of production is to do a combination of special effects processing and graphics according to the creative design draft provided by the customer. It is a combination of operating skills and responsibilities, requiring the operator to have the ability to proficiently make software and a certain amount of artwork. This assignment is now decentralized. Printing companies, professional plate-making companies, advertising agencies and individual families are all doing it. The scanning color separation technology, first of all it is a variable factor, involves a wide range, in addition to the level and accuracy of the scanner itself, but also consider the product type and ever-changing manuscript features and printability conditions, it is both technical, It is also artistic and difficult; secondly, the scanning separation is the first stage of copying. Regardless of the quality of the original document, it must first be scanned and color-separated. The best color level information should be obtained from the original directly. This is the quality of reproduction. The basics, if there is no high-quality image scanning, the quality will not be able to talk about.
Third, a clear guiding theory
Image scanning color separation technology is the actual operation, is it still theoretical guidance? Practice has proved necessary because if there is no theoretical guidance and no clear ideas for any work, there will be blindness. Only theoretical guidance can reduce blindness and avoid detours.
In the production practice, the author has studied and summarized some computer-guided image scanning color separation technology guidance theory, used this theory as a guide, and adopted corresponding standardization and standardized operation methods, which helped many plate-making companies to produce high quality quickly and well. image. Its guiding theory is:
Under certain printability conditions, the functions of electric extensions (scanners) and image processing software are correctly applied according to the product type and the characteristics of the original document, so that the standard reduction of the color separation at the early stage and the art processing at the later stage are mutually complementary. The perfect combination of technology and art to produce quality images that restore both originals and originals.
The above theory clearly states that the image scanning color separation technology is divided into the concept and operation method of the two aspects of pre-scan restoration and post-art processing. The focus of the two work is different. The former focuses on the construction of standardized documents and the restoration of the original high tone. It belongs to the category of restoration of replication technology; the latter focuses on the adjustment of incompatible manuscripts and the necessary artistic processing to achieve perfection of manuscripts, which belongs to the category of recreating reproduction technology.
In current actual production, the two operations of the pre-scan and post-processing are divided among the major professional plate-making companies by the electric division. The majority of other plate-making companies are completed by the scanning staff. Whether it is the completion of two divisions of work or the completion of one person, the key points of both should be clearly defined in the guiding ideology. This will not only give full play to the advantages of electric extensions or scanners as image input, but also give full play to advanced image processing software such as Photoshop. Sex, make high quality pictures.
Fourth, pre-scan restore
The standard reduction of pre-scan color separation refers to the use of standard transparent, reflective gray scales and color standard test tools for copying experiments based on manuscriptability conditions, using manuscripts as a benchmark, and establishing four standard texts. When scanning, only The calibration of black and white fields, and the use of the four standard documents already established, can achieve a good reduction effect.
1. Create a standard gray balance file
One of the fundamental principles of color reproduction lies in restoring the gray in the original. Therefore, under a certain printing condition, a standard ash scale should be used as a manuscript for copying. Through experiments, C, M, and Y primaries are overprinted with different dot values, so that the levels in the original manuscript can be restored. Gray, the value of this set of gray balance parameters is stored as a standard file, which becomes the basis for restoring the original gray.
2. Create a standard tone level curve file
The tone curve of the tone is the abscissa of the standard gray scale, and the gradation of the dot of the color separation film is the relation curve of the ordinate. Through the scanning and publishing experiments, a standard curve file corresponding to the density values ​​of all levels of gray scales and the tone points of the color separation patches at various levels is established, and used as a standard density contrast original document application. At the same time change the midtone curve, establish a few preset curves, respectively +5%, +10%, -5%, -10%, etc., to be stored for the selection of different density contrast manuscripts.
3. Create a standard color correction
Based on the input gray balance, according to the characteristics of different manuscripts such as transmissive manuscripts, reflection drafts, and prints, the six hues of CMYRGB on the standard transmission and reflection color standards are used for manuscript copy experiments, and the 24-channel color correction parameters are adjusted. After proofing, the six hue of these three types of originals can be accurately restored, then other colors can also be restored. The color correction parameters of these three types of originals are used as the standard color correction files, and are stored thickly for the three originals. Restore selection.
Even if there is no platform scanner for the color correction system, Photoshop's selection function can be used as a supplement, especially when the image RGB mode is converted to the CMYK mode. In this function state, the standard color standard can be used for standard color calibration. Specification, and standard school color quantity parameters are thickly stored, loaded after each image scan, so that it is not necessary to adjust each color gamut of each figure, and the effect of restoring original hue is also achieved.
To establish a standardized color correction document, we should try to achieve both the color saturation and the color hierarchy. Whether the effect and adaptability of this standard color correction quantity is wide can reflect the level of standardization of color correction. The 24 standard color correction parameters should also be continuously revised in the production practice to make color reproduction more accurate.
4. Create a standard sharpening file
The general color separation software for high-grade scanners and high-grade scanners has an automatic sharpening function and automatically sets the sharpening amount according to the magnification. Should be based on this, and then according to the original content characteristics, do different settings for the amount of sharpening. Through experiments, preset several sharpening amounts. Such as: gold and silver bronze utensils, scenery photography, portrait photography, Chinese painting, oil paintings and other sharpening documents, for all types of manuscript selection, in order to achieve fine grain and excellent sharpness effect.
The above four basic standards are interconnected. After a good document is established, stable scanning and color separation can be performed. The author establishes these four standard documents through repeated experiments on various electric extensions and scanners. In practice, the research concludes a law that is called the classic law by peers.
That is, as long as the gray balance curve established by the electric extension and the scanner is accurate, the gray in the image can be restored. At the same time, the complex color (composite color, tertiary color) in the image can also be restored, and it is not necessary to adjust the ratio of the dot values ​​of the three primary color versions in the gray in the later period.
According to scientists, of the more than 100,000 colors that are discernible, more than 80,000 are ash-containing colors. In other words, the thousands of complex colors contained in the image should belong to the category of restoration. This classic law makes our school coloring and color correction work in a regular manner, and can be more scientific, more accurate, and simpler.
Some originals have gray and complex colors that need to be adjusted. Only the brightness of the original is adjusted, that is, the density of the original color is light or heavy. This adjustment should use the Y, M, C tri-color curves for simultaneous darkening or lightening adjustment.
In summary, a standardized recovery file for scanning color separation is established, and the best image information is directly obtained from the manuscript by using an electric extension or a scanner to ensure a good reduction of the color of the image, no matter whether it is a high-end product or a middle or low grade production. The products are the first work. Especially for the production of artistic pictures such as paintings, it is particularly important to reproduce the original beauty of the paintings, the depth of the artistic conception, and the artist's unique temperament, style and characteristics, because the artistic conception in the works is impossible. In the late processing transferred out. This is also the scientific nature of the scanning color separation technology. We should treat it with a scientific attitude and do it carefully and carefully so that we can get twice the result with half the effort.
Fifth, post-art processing
Image scanning