CMYK settings in Photoshop

The image processing software Photoshop (file/color setting/CMYK setting/CMYK mode/built-in) is a very important function for setting printing parameters. It can be set in terms of ink color, dot gain, color separation parameters, etc. . These parameters are set up for the equipment characteristics of a four-color offset system. It can also be used to create output files for other output methods (such as color inkjet), and to simulate offset printing processes for color separation.
The details of the setting parameters and their respective parameters are described in detail below, which is very important for personnel of foreign printing technology.
1.Ink Options: This item contains the following two items:
(1) Ink Color: This option provides the selection criteria for ink color. Options include Custom and some commonly used offset ink standards. Commonly used offset ink standards include, for example, SWOP (Specifications for Web Offset Publications) commonly used in the United States, Toyo inks commonly used in Japan, and Eurostandard commonly used in Europe. According to print papers such as coated paper, uncoated paper and newsprint, there are different standards. Users should know if their presses use these inks or which ones they prefer, and if they are close, they can use them. If the ink used deviates too far from the ink standard set in the options, you must develop your own ink standards.
The Custom option is used to create your own ink standard. This option includes 9 calibration blocks, yellow, blue, green, red, green, blue, synthetic black, black, black, and black [Y, M, C , MY (R), CY (G), CM (B), K (CMY), W, K], the first six colors have the greatest impact, they represent the six corners of the CMYK color space, respectively. The basic method for customizing the special ink color: print the used ink on its own printing system with the calibrated nine solid color blocks, measure the tristimulus value XYZ of each color block using a colorimeter, and then use the formula X=X / (X + Y + Z) and Y = (X + Y + Z) calculate the chromaticity coordinates x and y, respectively, where Y is the luminance coordinate, the value is small 0-100, X, y take 0-1. The measured Yxy is then filled in the color coordinates of the individual patches and named and stored. This completes the creation of a specific ink color. In addition, you can use the setting button at the bottom of the dialog box to select the L"a"b" chroma space as the chroma value of each test patch. Yxy and L"a"b" are two expressions of the absolute chroma space. , two spaces can be converted between each other.
Normally, when printing on coated paper, approximately SWOP (Coated) or Eurostandard (Coated) is used. For printing on offset paper, SWOP (Uncoated) or Eurostandard (Coated) may be used. Printing newspapers may be approximated using SWOP (Newsprint) or Eurostandard ( Newsprint). Domestic ink standards are not completely consistent with foreign inks, and their ink color is not added to the ink table in advance, and similar ink cannot be found in the table. In this case, custom ink color can be used. Another situation is to use a spot color ink to replace the primary color ink to produce special effects. For example, some packaging prints use spot color red instead of magenta ink, which looks better and more vivid than magenta.
At present, a variety of non-offset color output technology is used more and more widely, such as the color inkjet output method, which uses inkjet ink also divided into four colors CMYK. Since many inkjet output software does not have the ability to automatically separate colors based on the characteristics of paper and ink, offset color separation settings can be used for simulation. The determination of the ink color standard is similar to the above-described offset ink color determination method, except that the test color mark must be produced under certain conditions such as a machine, an ink, a paper, and an ink-jet speed currently used.
(2) Dot Gain (network expansion). There are two ways to set up dot gain in Photoshop 5.0:
a. Standard (standard mode): The network expansion has the greatest influence on the midtones, and the expansion rate of the 50% outlets is the largest. The dot gain value set in the standard mode is the enlarged value of the 59% dot. For example, setting a 20% dot gain ratio means that the midtone dot will be printed at 70% (50%+20%). In addition, the effect of dot gain on color printers is equally large, and different paper, inkjet speeds, and printer models will all lead to very different dot gains.
b. Curves: In this mode, the dot expansion can be set in all the same [composite channel] and CMYK four-color channels. It can set the corresponding dot gain values ​​for up to 13 levels. Accuracy is higher than standard mode. In the "all the same situation, when the expansion rate of each channel of CMYK is forced to the same value, it is actually the expansion of the standard mode, the expansion of the network points from a point of 50% to a range of the entire gray ladder. This type of setting needs to be used. Go to the gray scale and use the density meter to measure the number of gray points at each level of the gray gradient above the gray scale, and fill in the table respectively.If the 20% gray scale of the original gray scale is printed, the measured network point is 30%. Enter 30 in the dialog box 20%.
If you use four color channels to set their dot gain values ​​(don't choose the "all the same" method), it not only gives dot gain parameters for each color ink, but also compensates for the gray balance of the ink. The acquisition must test all CMYK four-color rulers one by one, and measure and fill in the same form as the gray scale.
2.Separation Options. It is mainly used to set the black version of the method and control the total amount of printing ink. The setting of these parameters directly affects the display of the color of the printed product.
(1) Separation Type: This option is used to set the black version generation method. There are two types: UCR (Under Color Removal) and GCR (Gray Component Replacement). Called achromatic structure).
a. UCR (Background Removal): This method replaces the CMY color component contained in the neutral gray portion of the image with black, leaving the color component of the color portion of the image unchanged. Most of the CMY color components of this dark part are replaced by black ink, while the remaining part retains the original CMY color component.
b.GCR (Grey Component Substitution): This method replaces all gray components in the color component with black. Regardless of color or neutral gray in the image, as long as it contains all CMY color components in accordance with the gray balance ratio, it is black. Replace it. The GCR has changed the composition of the original color structure. Therefore, the degree and scope of the GCR must be strictly controlled according to the printability requirements.
(2) Black Generation (Black Edition): Specifically for the GCR color separation method, controls the tone from which the black color substitution starts, and determines the black substitution curve. The starting point of the gradation of black substitution is called the starting point of GCR, and the range of black substitution is the deepest point from the starting point to the dark tone. In this project there are already established alternative methods, alternative scopes and user-made methods.
Custom
None... - No black color, less CMY image production (Light) - 40% ~ 100% black alternative, short tone black version Medium - 20% ~ 100% black alternative, midtone Black version -10%~100% black alternative, long tone black version Maximum (Maximum) - all black alternative, full black edition short black version is suitable for copying color-based originals, The black version mainly enhances the contrast of the picture, strengthens the tone of the middle tone to the dark tone, stabilizes the color, and reduces the overprinting rate. The black version only makes some contours in the dark tone. The Black Edition is a black version that is normally used. The long tone black edition is suitable for copying originals with non-color and color as auxiliary. This black edition has more gray components instead of black ink, and the color tone is very short.
For medium, for example, its starting point is 20%, then the subtone with less than 29% does not perform black substitution, and the subtone with greater than 20% can see the black component in the CMYK colorimetric value. In addition, if you select Light, the black range will be shrunk. With Heavy and Maximum, the black range will extend toward the bright part and the black component will increase.
Custom black generation, use the gamma curve to set the coordinate plot, in which the black generation amount is the ordinate and the original gradation is the abscissa, generally represented by blue. Use this relationship to edit the graph, you can customize many special black generation methods. For example, if you require the use of a profile black version, you can select a black version of the curve that is smaller than the Light setting and focus the black generation range on the dark tone. You can also control the generation of black prints to optimize extremely bright or dark surrounds. Such as very dark images, the black version of such images is very large, the results further darken the image tone, then, can be appropriately reduced the black version of the scope of production and generation, first select the Light generation curve, and then The starting point is reduced to 55%-60%, and the midpoint is adjusted, and then the amount of production is reduced by about 10% to help normalize the darkest tone image. Similarly, for extremely bright images, to appropriately increase the scope and amount of black generation, first select Medium to generate the curve, and then appropriately increase the amount of production. With these custom curves, the adaptability and effects of image printing can be refined and refined.
(3) Black Ink Limit: Another aspect that affects the shape of the black generation curve is the black ink limit, which is the maximum amount of dark ink that the dark tone portion allows. The BlackGeneration item is used to create the starting point of the black alternative tone, which is the pole used to set the amount of black ink in the dark tone region. It determines whether the blackest version (100% solid black) is produced using the 100% black ink to generate the darkest place, or the blackest place to use 80% black ink and other colors to form a 100% black effect. This parameter is usually set between 85-95%.
(4) Total Ink Limit: This parameter is the total amount of CMYK ink overprint that can be printed by the printer. The value is determined by the printer and substrate used. In principle, the more ink you use, the better the resulting image. However, excess ink can affect the suitability of the printing process. Most printers know the maximum amount of ink that can be printed on their own presses, which can be set accordingly, or average total standing ink of 280%. In addition, in the case of limiting the total amount of ink, it is relatively normal that the black ink limit is set to about 90%.
(5) Under Color Addition: It is the same as Black Generation (Black Edition) and is only applicable to the GCR (Grey Component Substitution) separation mode. Replacing color with a large amount of black will affect the loss of tone details and the appearance of dark tone. UCA will recover some of the color components of the neutral tone region. This process only adds a small amount of color to the neutral portion. The general UCA setting is not large, such as about 10%.
Whenever you use a new CMYK output system and output process, you should reset the parameters of Photoshop's built-in color separation mode, and then save the name for the next call, preferably based on