The third key technology of the standardized scanning color separation method for restoring manuscripts is correct white point and black point selection.
According to the characteristics of gravure plate making of product packaging products, using the three elements of the white point and black point selection calibration method developed by the author to calibrate the selected points, a fast and accurate calibration density value can be obtained.
1. Grasp the three elements of the white point selection 1 Select the correct white field sampling point. According to the characteristics of the “Fruit” drawing of the manuscript, a white paper calibration method was adopted, and a smooth, clean white paper consistent with the thickness of the printed paper was attached next to the manuscript. The density value was set using the scanner's Set white pt function. 0.25, set the value of the extremely high light CMY trichrome version in white paper and images to 0%.
2 determine the basic white. According to the gravure engraving roller, OPP film proofing and gravure printing can be transferred to the minimum point of 5%, to determine the basic white is C7%, M5%, Y5%, so as to ensure that the image needs the level of the whitest brightest part of the rich.
3 Follow the gray balance ratio. The image needs a neutral white level, so that C is greater than M and Y2 to 3%. If the white warm, C, M, Y three-color version of the ratio can be close, but you can not lack any one color version, if a lack of color version, highlight white must be color cast, dew.
2. Grasp the three elements of the black field selection point calibration 1 Select the correct black field sampling point. The black field sampling point is selected in the darkest shade, and the Set dark pt function is used to set the density value to 1.83. Since the gravure process dark tone should not be set to depth, therefore, on this basis, consciously increase the set density value, with a manual input density of 1.93, outlet value is C90%, M81%, Y66%.
Due to the darker color cast (bluish), the particles are coarser, and there is a large selection of points with the mouse. In particular, the black dot value changes greatly. Therefore, try to select the neutral black part.
2 determine the basic black. According to engraving roller and gravure printing and printing can be transferred out of the maximum dot value of 90 ~ 93%, the basic black is set to C90%, M81%, Y80%, K66%.
Because the law of gravure proofing and printing dot gain is proportional to the proportion of dot percentages, it grows in a straight line, and the darker tone increases more and more urgently. Therefore, the dark tone setting should be made larger.
3. Set the correct black dot value In the gravure printing process, the dot value of the black dot increases most. Sometimes the dots in the 70 to 75% zone will increase to barely noticeable. This is due to:
1 black ink quality is not good. If you want to print black letters and lines, you need to increase the amount of ink. The larger the amount of ink, the more dots will increase.
2 There are only three screen angles in the electric carving, generally adopting an angle between black and magenta, which will increase the width of the black version of the network. The network is wide, and the number of outlets increases.
3 The black version and the magenta version use the same angle. In order to prevent the occurrence of moiré, the number of black screen lines must be increased, usually 90 lines and 100 lines. The finer the network cable, the more the network points increase.
Considering the above black dot increase rule, it is not appropriate to set the black dot value of the image dark tone. To better reproduce the dark tone level of the original, the black dot value is set between 65% and 70%, and the sampling point is 66%.
4. Correct sharpness adjustment According to the characteristics of the printed manuscript “fruit”, not only the moire but also the level of detail and clear texture of various fruits are reproduced. We fully use the sharpness function of the scanning software. Make the following adjustments based on the default values:
1 Adjust the Smooth Descreen function on the main menu to 3.
2 In the basic project settings, the Sharp default value is 2, the enhanced adjustment is 3, and the Smooth is 4.
3 In the extended project settings, the Radius sharpening radius is adjusted from the default value of 4 to 3 to reduce the black and white edge width; Intensity intensity increases the white and black edge emphasis from 2 to 3; Grain particles (this function can be suppressed The Threshold threshold and Value value in color noise, limiting image graining are both adjusted to 4 to make the light and medium grain fine; the Clip trimming default is No Effect, and the white trim value is adjusted to 3, The black trimming value is set to 5, so that the image outline is neither embossed nor reversed, while the coarser particles are trimmed flat, while the sharpness enhancement enhancement is maintained.
The Clip trimming function has two functions. One is that the unsharpness value can be limited to the edge trimming, and the edge level of the high contrast region can be limited, that is, the width of the black and white sides can be controlled, and the black and white sides and the rough points that are too obvious can be trimmed off. Secondly, the signal below the edge trimming value is not affected, and all sharpness enhancement effects in the low contrast region can be maintained. Clip features white trimming and black trimming.
Through the above adjustments, the best of both worlds is achieved, so that the sample has no moire, but it also truly reproduces the fruit-rich detail level and clear texture. Sharpness adjustment parameters are shown in Figure 5.
V. Conclusions The standardized “scanning” method for the original manuscript of the printed manuscript was used to test the color of the manuscript, and the original color, level, and sharpness of the manuscript were simulated and detailed. This method has been used in practical production and has achieved ideal results, from which the following laws can be derived:
1. The manuscript with moderate density contrast and normal hue can be corrected by the standardized scanning color separation method. The tone levels, gray and color in the original document can be correctly restored without any adjustment.
2. In the standard ... In the scanning color separation, image processing, the above two concepts must be clear. If the concept is clear, we can do a good job on the standardization of restoration work on the one hand, and on the other hand, carefully analyze the defects of the manuscript and understand the requirements of customers, and make appropriate adjustments. In this way, the effect of scanning and separating the color of each original can be made predictable, so that high-quality products can be reproduced quickly and well.

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