Silk screen printing platemaking process (11)

Regardless of the type of electronic color separation machine, the basic flow of signals is similar. As shown in Figure 2-83. When the original is affixed on the scanning drum, a beam of light from the illumination source is emitted to a pixel of the color-transparent original (the same applies to the reflective original), and the transmitted light representing this pixel enters the scanning head optical system. Holes and spectrophotometry are converted into four beams of color light, which are then filtered by a color filter to illuminate four photomultiplier tubes to obtain four corresponding electronic signals, namely yellow, magenta, and cyan main signals and a virtual light signal. These signals are amplified by the preamplifier and then enter the color computer logarithmic compression circuit (there is also the combination of these two circuits placed in the scan head), the logarithmically compressed main signal is called the original color density of the analog signal. The size of the signal is linearly related to the color density of the original, and the virtual light signal enters a fine-level circuit, producing fine detail-emphasizing signals. The logarithmically transformed main signal enters the color correction circuit. Generates a color correction signal and corrects the main signal of each channel. The main signal after correction is sent on the one hand to the black version of the calculation circuit to generate the black version signal and the background color removal signal. On the other hand, the three main signal and the black version of the signal are respectively passed through the color separation switch to the level correction circuit, resulting in Level correction signals for highlights, highlights, midtones, and shadows are used to perform corresponding gradation correction and background color removal on the selected main signal of a certain color; the main signal of the gradation correction is scaled after being finely emphasized. The signal enters the proportional computer and is first converted into memory after analog-to-digital conversion. The scaling is then taken from the memory at a different speed from the time when the memory is loaded to achieve the requirements of vertical scaling (horizontal scaling is used The computer controls the scan head and the recording head to feed different speeds of the transverse feed motor, and then converts it back to a color computer after digital-to-analog conversion to calibrate the range of recording film density. Afterwards, the inverse logarithmic conversion and the film linearization compensation circuit are sent to the final amplification circuit, and finally the electro-optical conversion is performed to perform exposure recording on the soft film corresponding to the pixel of the scanning point of the color document and the corrected optical signal. Complete a color separation scan. The above operations and corrections are completed in a flash. Whether it is photoelectric conversion, analog calculation, proportional calculation, or electro-optical conversion, the speed is extremely fast.

The universal electronic color separation machine generally does not use a proportional computer, but simply changes the scanning drum of different diameters to make extreme changes. However, regardless of the versatile or popular type of color separation machine, in terms of circuit theory, it includes a scanning head system for photoelectric conversion and logarithmic compression, color correction, black edition calculation, level correction, subtle level emphasis, and recording density determination. A color computer system that performs arithmetic processing such as standard, inverse logarithmic conversion, and linearization compensation, and a recording head system that performs electro-optical conversion after the final amplification.

At present, some new color separation machines, in addition to the features of stepless change, use of control masks for electronic cutting, text insertion, puzzles, etc., can also use laser as the recording light source, and electronic dot generators can be used to directly connect nets with miniaturization. The computer controls the basic operations of the color computer quickly and accurately, and the color display technology is used to determine the pre-adjustment control amount of the color separation machine.

The electronic color separation process includes a direct plus positive chart, a direct plus screen negative, a continuous positive adjustment chart and a continuous tone adjustment chart, etc. Each has its own characteristics and can be selected based on the manuscript, layout design, equipment materials and quality requirements. Choose.

If the manuscript is of good quality, high quality and speed are required, and special graphics are not to be used, it is better to use a direct plus positive drawing process. The characteristics of the direct plus positive chart process is that it is of good quality and can realistically reflect the quality effect of electronic color separation, and the response is timely and can be corrected in time; the high speed, scanning and color separation of a set of 16 open and 4 color positives is only 15 minutes. Around, simplifies the process flow; saves raw materials, and directly adds the net positive drawing without copying, not only saves the film, but also saves man-hours and simplifies the operation; it is conducive to standardized operation, because when scanning plus mesh positives, yellow, product, The percentages of cyan and black dot sites can be directly fixed in length, and are not affected by the transfer of intermediate dots. Not only is the single-image plate version suitable for use, but also the multi-pictures are combined in one layout, which also has its uniqueness.

The shortcomings are: can not do rounding, hollowing out, set of words in the figure, etc. (Although can also be done, but the procedures are cumbersome, more harm than good); followed by dirty draft correction is not easy, poor quality manuscript to make up for limitations.

5 four-color version of the negative inspection and correction. Whether it is an electronic color separation process or a photographic color separation process, the revision and inspection of color separation negative films is an important part of perfecting and improving quality and should be given great attention. The following is a description of the two processes:

a. Check the quality of the negative mesh. After the revised version receives the Separation of Yin-net, it is first necessary to conduct a comprehensive inspection and identification of its quality. This can solve the quality problem in time. If you find that the problem is big, you must rework it (review) to avoid rework. If the problem is small, it can be clearly resolved in the amendment.

(a) The basis for checking the quality of separation separation. The basis for checking the quality of Separation Separator is the manuscript. First, the manuscript is compared with the analysis of the manuscript: analyze whether the manuscript density range is standard; analyze the main body of the manuscript; whether the original tone is correct or not. The second is the data provided by the post-process printability conditions. Revised version With the analysis of the pre-process manuscript and the data of the post-process printing applicability condition, it is possible to make a correct judgment on the quality of the separation color negative film.

(b) Check the correctness of the leveling curve of Separation. According to the ladder and the three levels within the image, especially the high and middle levels reflect the rich; original dark, should use the light level curve, then, rich reflection of the level of dark tone, high light level is lost; the original thin We should choose to deepen the level curve. Then, the level of color at all levels has been deepened; to check whether the level of high-light level is correct (the correctness of highlight selection is correct), there are three cases: one is to reflect the correctness. That is, the high-light level texture is rich, not hard, not parallel, and not too flat; the second is too dim, that is, highlights require 5% of the dot sites are net or too small, high-light tone level loss; The three types are Taiping, which means that the parts where highlights need to be netted have dots, so that high-toned color levels are flat and high-brightness does not come out. The second case of the third case is serious, you should re-sweep, if there is a slight error, you can adjust the revision; check the level of the intermediate tone is correct, should be in the 40-60% area of ​​the image to check whether the level of this part is rich , At the same time select a control point, such as 50% of the part, whether the color separation film is 50% or slightly shallower than 50%, indicating that the middle tone, if the character is the main manuscript, you can use the skin color as a benchmark; check whether the tone level is Correctly, in general, the dark tone level is not used as a copying point, but it can be discarded. It is only necessary to check whether the level of the dark tone in the required level is reflected. If the level is not reflected, it indicates that the area of ​​the dark level loss is too large.

(c) Check that the color correction is correct. First check the correctness of color calibration. Generally, only three primary color and three secondary color corrections need to be checked. If the color correction is correct, the color in the image is correct. The second is that the bright contrasting colors and white parts are basically the same. The basic color with a large degree of saturation should be deeper than the black portion or reach 95-100% as compared with the black portion. The third is to check whether the gray balance of the three-color version is correct. Put together the yellow, magenta, and blue color plates, and check whether the cyan outlets are larger than those of the yellow and magenta versions by using a gray scale and a standard gray area within the 40-60% area of ​​the selected image. Balance data.

(d) Check image clarity. Observe whether the outline, level, and texture of the image are clear. In particular, the subtle levels of high-light tone and texture are clearly reflected. If overemphasized,
The impression of embossment is obvious, and black and white edges are likely to appear at the black-and-white contours, indicating that the matching of optical apertures is inappropriate and the fine-level functions are emphasized too much. If the subtle level of emphasis is not enough or the focus is not true, the resolution is poor.

(e) Check whether the specification size and cutting ratio meet the layout requirements, whether the four color plates are the same in size, whether the mesh angle is correct, and whether the image front and back meets the requirements.

(f) Check that the separation plate is clean. Dirty spots, roads, and scars are less.

b. Correction of the negative mesh. The electronic color separation machine has a large number of adjustment means and certain normative data. It is suitable for landscape manuscripts with moderate manuscript density, bright and vivid colors, and rich levels of landscape manuscripts and product advertisements, as well as reflective drafts such as fresh and elegant watercolours and brightly colored gouache. Carefully adjust the color separation film to achieve the desired color correction effect.

For the master made by photographic method, it is generally necessary to make a serious revision so that the printed matter can obtain better results than the proofs.

c. Focus on correcting text. General text changes are relatively large and error prone. Therefore, we must carefully check the positive and negative of the text, whether the position meets the requirements for batch approval. If there are many changes to the text, the blueprint should be sent to school after correcting to avoid mistakes.

d. Check the black and white spots on the repair screen to ensure that the layout is clean and then send it to the printer.



Source: Shandong Printing Network