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To implement the standardized scanning color separation method for restoring originals, we must first stabilize the conditions, especially the proofing conditions. E.g:
â‘ Scanner: Scitex EvcrSmart Dro;
â‘¡Printer: Scitex Iris2PRINT 5015 all-digital inkjet printer;
â‘¢ Make the scanner and proofer in the best working state;
â‘£ Adjust the ink hue and solid density value of the printer.
Because the four-color ink used in the Iris proofer is a special ink made of water-soluble materials, the printed samples are brightly colored and have a low solid density. The solvent-based ink used for gravure proofing has a color shift, grayscale, and solid density, which do not match. In order to make Iirs' ink hue and solid density value and dot tone density value simulate the gravure ink hue and solid density value, the following measures should be taken:
â‘ Add appropriate amounts of Y and C inks to M inks, add appropriate amounts of M color inks to C inks, so that the hue of M inks and C inks will increase color shift and grayscale, and the density will also increase accordingly;
②Through the adjustment of the Iris printer software curve, mainly adjust the 100% solid density of CMYK and the dot tone density value of 1/4, 1/2, 3/4, and increase the amount of ink moderately to make it as close as possible to the concave The solid density values ​​and dot tone density values ​​of printing proofing inks have been determined through repeated experiments to determine the standard solid density values ​​of Y1.25, M1.65, C1.80, K1.95, ± 0.05, and achieve stable.
Second, establish the parameter set of scanning and balance curve
One of the key technologies of the standardized scanning color separation method for restoring the original is to establish a parameter set of gray balance curves that conform to the ink hue and solid density values ​​of the Iris proofer, to ensure that the gray and complex colors in the original are restored.
For example, the value of the gray balance curve of the Ever Smart Pro scanning software does not meet the characteristics of the adjusted Iris ink hue and solid density value, and it cannot restore the gray in the original. This problem can be achieved by using Kodak 19-level reflective gray scale as the original, and after multiple scans of color separation and Iris proofing test adjustment, the gray level of the gray scale can be visually restored to obtain a gray balance curve parameter set. At the same time, the point A of the Kodak 19-level gray scale is used as the white field sampling point, and the 19th level is used as the black field sampling point to set the correct density value and dot value. The gray balance parameters are measured after color separation by scanning.
Scan the gray scale printed by Iris after color separation with the above settings.
3. Establish the standard color correction amount for scanning color correction
The second key technology of the standardized scanning color separation method for restoring originals is to establish a set of standard color corrections that conform to the color correction of Iris ink hue and solid density values ​​to suit the restoration of most originals.
For example, the default value of the color correction of the Ever Smart Pro scanning software does not meet the adjusted Iris ink hue characteristics, and the errors in various hue are large. For this, on the basis of inputting the above gray balance parameters, six colors of Y, M, C, R, G, B of Kodak reflection color scale can be used as the original, after multiple scanning and color separation, Iris printing test is carried out, through adjustment The color correction parameters of 24 channels achieve the reduction of six hue. This set of color correction parameters can be used as a standard color correction amount, which can be named and stored for selection by most manuscripts during color correction. The standardized color correction can not only obtain all the color information directly from the original, but also ensure the correct restoration of the original color and reduce blind post-processing. Although this work is more complicated to do, it is a must do well. In the experiment, the white block of Kodak color standard was used as the white field sampling point, and the black color block was used as the black field sampling point. The set density value, dot value and adjusted standard color correction parameters are shown in Table 6-2-1.
Table 6-2-1 Density, dot setting and standard nuclear color parameters of turtles
Item White point set density Set dot value /% Black point set density Set dot value /%
C 0.16 0.0 1.42 95 0 0 0 92 92 95
M 85 100 100 0 0 0 90
Y 85 0 82 85 90 0 0
K 75
Note: Since the M ink in the Iris ink has a small amount of Y ink added, the Y color in the R color is reduced accordingly.
1. Three elements of white spot selection and calibration
â‘ Select the correct sampling point of the white field. For example, you can use the white paper calibration method according to the characteristics of the original, paste a smooth, smooth white paper that is consistent with the thickness of the printed paper next to the manuscript, and use the Set white pt function of the scanner to set the density value to 0.25 , Set the dot value of the CMY three-color version of the white paper and the image with small highlights to 0%;
â‘¡ Determine the basic white. According to the minimum point of gravure engraving cylinder, OPP film proofing and gravure printing that can be transferred out is 5%, the basic white is determined to be C7%, M5%, Y5%; C8%, M6%, C6%, so as to ensure that the image needs the level The whitest and brightest part of the layer is rich;
â‘¢ Follow the gray balance ratio. The level of neutral white is needed in the image so that C is greater than M and Y 2% to 3%. If the white is warm, the ratio of the three color versions C, M, and Y can be close, but there must not be any color version missing.
2. Two elements of black spot selection and calibration
â‘ Select the correct black sampling point. The sampling point of the black field is selected at the darkest part of the dark tone, and the Sedark pt function is adopted, and the density value is set to 1.83. Because the dark tone of the gravure printing process should not be set deep, on this basis, consciously increase the set density value, manually enter the density of 1.93, and the dot value is C90%, M81%, K66%.
Because the dark tone has a larger color cast (bluer) and the particles are coarser, the point selection with the mouse is very different, especially the black dot value changes greatly, so try to choose a neutral black part.
â‘¡ Determine the base black. According to the engraving cylinder and gravure proofing and printing, the maximum dot value that can be transferred is preferably 90% to 93%, and the basic black is set to C90%, M81%, Y80%, K66%.
Because the rule of increasing dots in gravure proofing and printing increases with the percentage of dots, it increases linearly, and the more the dark tone increases, the more urgent it is. Therefore, the dark tone setting should be compressed more.
3. High light calibration rule of scanning color separation in gravure electro-engraving process
According to the rule of dot change of engraving cylinder and OPP proofing, the highlight part of the ink is thin, and the small dots are easy to shrink. Therefore, when scanning the color separation highlight setting, the basic white setting for the high-gloss white that needs gradation should be slightly larger, and the minimum dot value It is 6% ～ 7%, which is conducive to the reproduction of small dots when the engraving drum dots are transferred to the OPP film, thus ensuring the richness of highlight color gradation.
4. Set the correct black dot value
In the printing process, the dot value of the black version increases the most, and sometimes the dots in the 70% to 75% area will increase so that it is almost unclear.
â‘ The quality of black ink is not good. If you want to print black characters and lines in black, you need to increase the amount of ink. The larger the amount of ink, the more the dots increase;
â‘¡Electric carving only has three mesh angles, generally using an angle of black and magenta, which requires increasing the width of the black version of the mesh. The net hole is wide, the net point increases more;
③ The black version and the magenta version use the same angle. In order to prevent moiré, the number of black lines should be thinned, generally 90 lines and 100 lines. The thinner the network cable, the more the dots increase.
Taking into account the above-mentioned rule of increasing the black dots, it is not appropriate to set the dark dots of the image dark. In order 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%.
5. Gravure process
After the engraved gravure cylinder dots are sampled or printed by OPP film, the dot gradation of the dots expands linearly. The darker the dots, the more the ink content increases, and the more dots expand. Therefore, it is not advisable to lengthen the dot tone of the gravure cylinder by electrical separation or desktop scanning color separation. It is important to control the dot value of the dark tone part to prevent the OPP film from printing samples or printing dark tone levels. At the same time it will affect the deepening of the middle notes. The gravure printing process for flexible packaging such as food and seed bags is preferably 60% to 70% of the black version and 65%.
6. Correct sharpness adjustment
According to the characteristics of the printed manuscript, it is necessary to not only produce no angular patterns, but also reproduce the level of detail and clear texture of the image. We make full use of the clarity function of the scanning software and make the following adjustments based on the default values:
â‘ Adjust the Smooth Internet function on the main menu to 3;
â‘¡ From the setting of this project, the default value of Sharp is 2, enhanced adjustment is 3, and Smooth is 4;
â‘¢ The setting of the expansion item is small, and the Radius sharpening radius is adjusted from the default value 4 to 3 to reduce the width of the black and white edges. Intensity strengthens the emphasis value of white and black borders from 2 to 3; Thresholdl threshold and Value in Grain particles (this function can suppress color noise and limit image graining) are adjusted to 4 to make the bright and medium particles fine ; The default value of Clip trimming is set to No Effect, adjust the trimming value of white border to 3, and the trimming value of black border to 5, so that the outline of the image will not be embossed, and the coarse particles will be smooth , While the sharpness enhancement of the bright tone is maintained.
The Clip trimming function has two functions. First, it can limit the sharpening value to the edge trimming, limit the edge level of the high-contrast area, that is, control the width of the black and white edges, and trim the excessively obvious black and white edges and thick spots. ; Second, the signal lower than the edge trimming value is not affected, and all the sharpness enhancement effects in the low-contrast area can be maintained. Clip has white edge trimming and black edge trimming.
Gravure plate-making scanning color separation process
Section 2 Gravure plate separation and color separation process 1. Stable scanning conditions