PHOTOSHOP system settings and discussion (below)

2, color separation settings

Separation settings control the generation of CMYK color versions, which include black print generation methods, UNDER COLOR REMOVAL or gray component substitutions and GRAY COMONENT REPLACE, and total ink control. To perform accurate and effective color separation on an image, it is especially important to adjust the color separation settings in addition to the tone color adjustments.

When PHOTOSHOP converts an RGB image to CMYK mode, the program changes the RBG value to the CMYK value (using the RGB SETUUP, CMYK SETUP setting parameters, including the color separation setting in the CMYK setting), and the monitor and printing ink settings determine the screen color. Matching the printing color as much as possible, the color separation setting determines which precise CMYK is selected to replace the RGB color. Once the image is already in CMYK mode, PHOTOSHOP displays the CMYK image on the RGB display through internal conversion, and stores the color separation settings and ink set in the color separation table.

(1) The black color generation and color separation type color separation is a process of converting three additive colors (red, green, blue) into three subtractive colors (cyan, magenta, and yellow), and theoretically speaking, cyan, magenta, yellow, etc. The amount of mixing can be black, because the ink hue impure, resulting in blue, Lu, yellow three-color mixing is not black but gray-brown. In order to overcome this defect, it was necessary to remove some overlapping parts of cyan, magenta, and yellow during color separation, and add black to create a black plate.
A certain color is converted from RB mode to DMYK mode, and GCR (gray component instead of GRAY COMPONENT REPLACE) or UCR (background color removal UNDER COLOR REMOVAL) can be used. In the UCR background removal, the black plate is used to increase the dark tone area and the neutral color area; in the GCR gray component replacement, the black plate is used for a larger color range and the color is better than the UCR color separation. The use of GCR can better maintain the balance of printing ash. However, where to use the separation method is determined by the type of paper and printing requirements.

(2) Adjusting the black generation method and the color separation method In most cases, the PHOTOSHOP color separation default item can produce very good results. However, sometimes it is necessary to use the color separation dialog box to change the black print generation method, set a new total amount of ink, and change the background color removal mode. The settings made work when the image is converted from RGB mode to CMYK mode. However, non-POSTscript printers (such as HP DESKJET, CANON BUBBLEJEET, EPSON COLOR STYLE, etc.) produce their respective black amounts, and the separation settings do not work for these printers, that is, they do not affect the output.
Select the menu color separation setting command (FILE/COLOR SETTINGS/DMYK SETUP) under the PHOTOSHOP software. In the SEPARATION OPTIONS area, you can set color separation options, as shown in Figure 5. The appearance of gray gradations in the neutral image of the adjustment image can be displayed. In the figure, the horizontal axis represents the neutral gray value, from 0% (white) to 100 (black), and the vertical represents the generation of a certain gray scale. Neutral gray is generated according to various ink amounts, resulting in gray values ​​and cyan values. Roughly equal.

(3) Choose color separation type PHOTOSHOP lack of GCR to generate color separation, when you need to use UCR, click the select button to change the black generation mode. When using GCR for color separation, select the amount of black print, the total amount of ink, and the base color removal option. You can choose from a few black generation BLACK GENERATION settings. Among them, NONE does not produce a black version, LIGHT produces a smaller amount of black, HEAVY produces a relatively large amount of black, MEDIUM produces a moderate amount of black, and MAXIMUM directly substitutes the gray component for a black version, resulting in the largest amount of black. In most cases, MEDIUM can produce better results.
Using a custom CUSTOM allows you to manually adjust the black generation curve, see Figure 7.
If you need to use a custom item, first select one of the black generation options (LIHGT, HEAVY, MEDIUM, MAXIMUM) that is closest to the requested black generation, and you have a starting point for the black generation curve. That is, how large is, for example, the amount of black produced. The use of LIGHT, MEDIUM, HEAVY starts from 40%, 20%, and 10%, respectively, to generate a black version. Select Custom in the black generator, locate a point on the curve, drag the point to adjust the black curve, and the blue, yellow, and yellow curves will automatically adjust with the newly generated black curve.

(4) Select black ink amount and total ink amount control The black print generation will be based on total black amount control in the color separation setting. The default black edition is limited to 100%, and the total ink amount is limited to 400%. These limits determine how the CMYK curve is formed.

(5) UCA Underlay Gain UCA (UNDER COLOR ADDITION) The background gain is used to remove the black (K) component of the shadow cloud region and add it to the color component (CMY). This school building is richer and darker. Shadows. Increasing the UCA value increases the amount of CMY in the shaded area.

To print a color separation image, you need to convert the RGB, LAB, and other modes of the image to CMYK mode. If the printer supports POSTscript LEVEL 2 language can interpret and print LAB mode images, and can well reproduce the colors. PHOTOSHOP uses the LAB mode as the intermediate value to complete the transition from one color mode to another color mode. Because LAB mode provides a color value that defines all other modes, it is a device-independent color mode. When the image is converted from RGB mode to CMYK mode, PHOTOSHOP first changes RGB to LAB (using the monitor setting MonITOR SETUP to create a color table) and then to CMYK mode. When the image is in the CMYK mode, it needs to be converted to the RGB mode printing sample color patch network expansion value obtained.


Using the PHOTOSHOP application menu command FILE - PAGE SETUP can be found in the TRANSFER FUNCTION dialog box, which can be set TRANSFER FUNCTION does not affect the separation of RGB to CMYK, only when the file is sent to the RIP interpretation of the publishing, it will take effect . Its advantage is that it can accurately high-speed dot size, and then easily hostile to various printing conditions, but this adjustment curve can only be included in the EPS or DCS format, and can not be included in the TIFF format.

Create a TRANSFER curve-correction of the dot percentage of the output film or directly control the percentage of the final printed dot. The TRANSFER curve can be used to authorize as many as 13 control points to generate a custom precise curve.

Use the PHOTOSHOP menu command FILE - PAGE SETUP to bring up the Print Page Setup dialog. Select the TRANSFER button in the dialog box to enter the percentage value of the dots of each color gradation into the corresponding text box. If the dot area is set to 50%, but the film is lost to 53%, to correct the value, 50% of the value is input at 47%. In this way, when the output is performed, the color image of the 50% dot on the screen image is output. Can output 50% outlets. At this time, the input in the 50% box is 47%. The other boxes are input in the same way. Finally, the TRANSFER curve is stored. Select OVERRIDE PRINTER`S DEFAULT FUNCTIONS in the TRANSFER function dialog box and select INCLUDE TRANSTER FUNCTION in the Save EPS Format dialog box.

The function of the TRANSFER FUNCTION setting is to compensate for the exposure error of the imagesetter. It can be adjusted as follows: The imagesetter outputs a standard scale before the TRANSFER FUNCTION is not adjusted, and then the dots on the densitometer output film are enlarged. Store the processed image in EPS or DCS format. Note that INCLUDE TRANSFER FUNCTION is selected in the Save File dialog box. The versatility of the TRANSFER FUNCTION function can be used regardless of the dot shape or the number of screen lines, as long as the value of each tone of the film can be used, if you want to adjust the percentage of the dots of the final print and the screen design. If the percentage of outlets is the same, the percentage of outlets in the final print can also be measured and the TRANSFER FUNCTION curve can be produced.

4. Compensation for dot gain in non-image software

In fact, many colors are set in graphics software and typesetting software years. However, in these softwares, there is no compensation function for dot-net expansion, and it is necessary to consider expanding the color effect in coloring. At this time, the amplification rules of dot-nets should be known. In addition, the percentage of input dots is also better than the printing color, because the color effect on the chromatogram is the point after the dots are enlarged.

Source: Seal