Adjust color separation type and black version generation

For color separation, three additive colors (red, green, and blue) are converted into corresponding subtractive colors (cyan, magenta, and yellow). In theory, equal amounts of cyan, magenta, and yellow can be subtracted to reflect all light reflected from the paper and generate black. However, due to the presence of impurities in all printing inks, the mixing of these colors results in brown soil. To compensate for this deficiency in the color separation process, the printer removes some cyan, magenta, and yellow in equal amounts and adds black ink.

A given color can be converted from RGB mode to CMYK mode in countless ways. However, color output centers typically use one of the following methods to produce a printed black version:

In Underlying Color Removal (UCR), the black ink is used only to replace the cyan, magenta, and yellow inks in the neutral zone (ie, with equal amounts of cyan, magenta, and yellow). This leads to less ink and deeper shadows. Because less ink is used, UCR is used for newsprint and uncoated materials, and they usually have larger dot corrections than coating materials.

In Gray Component Replacement (GCR), black is used to replace the cyan, magenta, and yellow parts of the colored area as well as the neutral area. GCR separations tend to reproduce deep, saturated colors, are better than UCR separations, and can maintain a better gray balance when published.
Select the color separation type based on the requirements of the paper and the printing center.

To adjust the separation type and black generation:

In the Custom CMYK dialog box, select a separation type.
The Separations Options area displays a graphic based on the current settings, indicating how the neutral colors in the image will be separated. This graphic is sometimes referred to as a gray four-color graph, which represents neutral colors with equal amounts of cyan, magenta, and yellow. The horizontal axis represents the neutral color value, from 0% (white) to 100% (black). The vertical axis represents the amount of each ink that will be generated for a given value. In most cases, the cyan curve exceeds the magenta and yellow curves because a little more cyan is required to produce a true neutral color.

If GCR is selected as the separation type, select an option for "Black Generation":
Do not use black prints to create separations.

The Less and More settings weaken and increase the effect of the Medium setting (default). In most cases, "moderate" produces the best results.

"Maximum" maps the gray value directly to the black version. This option is useful for a large number of solid black images on a bright background, such as a computer screen image.

Custom allows you to manually adjust the black version of the curve. Before selecting "Custom", first select the option that is closest to the desired black generation type ("less," "medium," "more," or "maximum"). It gives the black version of the production curve as a starting point. Then select Custom and place the pointer on the curve and drag to adjust the black curve. The cyan, magenta, and yellow curves are automatically adjusted relative to the new black plate curve and the total ink density.

Example of Black Edition: A. No black version (composite image, CMY, K) B. Medium black version (composite image, CMY, K) C. Maximum black version (composite image, CMY, K)
If necessary, specify the values ​​for Black Ink Limits and Total Ink Limits (the maximum ink density your press can support). Check with the color output center to see if these values ​​should be adjusted. .

In the "gray curve", these limits determine the demarcation point of the CMYK curve.

If GCR is selected as the separation type, specify the amount of ground addition (UCA) to increase the amount of CMY added to the shaded area. Verify the preferred value with the color output center. If you are not sure about this value, leave it as 0%.

UCA compensates for ink density loss in the central shaded area. The added ink produces rich black shadows in areas that may appear gradated when printed with only black ink. UCA can also avoid tone separation in the subtle part of the shadow.

source: