Hue is the color of a channel
Saturation is the amount of a color
Value is the brightness of a color
Gamut is the range of colors a color model can achieve
Use Ink Colors
The Use Ink colors option does just what it sounds like, sets the final channel colors to printable ink color values. By unchecking the Use Ink Colors check box we can display a wider gamut of colors, but they will be outside our printable color range.
The YRGBK script splits the colors in an image into Hues and the Values, with all of the Value information going to the Black, White and Gray channels. The Hues are then split into a set of primary colors, and, if the Use Ink Colors box is checked, assigned printable ink colors. The Black channel is adjusted automatically to work with the colors.
When a color in an image falls outside of the color range generated by a color model the color is said to be “Out of Gamut”. The YRGBK script generates a color model whose Gamut is limited by the ink colors used. Colors which can not be created by the inks are printed using the closest color available. By Unchecking the Use Ink Colors check box we can keep the colors in their original, primary state, generating a separation with a much larger color range.
If, when running a separation through the script you notice a large color shift, it can be helpful to turn Use Ink Colors Off to visualize the whole color gamut.
To generate a Primary color separation:
• Uncheck the Use Ink Colors checkbox in the main window
• Check the Custom Black box
• Check the Custom Colors box
Adjust the Black Values
In addition to setting the color values, the YRGBK script makes adjustments to the Black channel to accommodate the brightness of the ink colors. When Unchecking the Use Ink Colors option, there will not be enough Black generated to render the image fully using the default settings. To fix this:
• Set the custom Black slider in the main window to 100.
• In the secondary Black Generator window, set both the Midtone and Shadow values to 0.
Adjust the Saturation Levels
Color channels are also adjusted for Saturation levels by the script. The Colors in the primary set have a saturation of 100%. Ink colors, on the other hand, have much lower saturation values based on the selected inks.
For most images the default settings are calibrated to generate good results using the Ink colors. For some images we need to adjust the density of the channels to achieve proper saturation levels. The Color levels sliders in the Color Generator dialog adjusts each channels density individually. To reset the color adjustments for a primary color separation:
• In the Main window, set the Color Density to 0
• In the secondary Color Generator window, set all the color sliders to 0, the Midtone to 100, and uncheck the Transition Mask box.
The Use Ink Colors option is checked by default, and in most cases this is where you will want to leave it. This setting will automatically bring your colors into a printable range that works with the default settings in the rest of the script. Often it is easier to customize the color channels after running the script then it is to run a primary color separation and make it printable. A primary color separation generated in this way would need to be manually adjusted to achieve printable results.
That said, in the case where you have large color shifts, unchecking the Use Ink Color dialog can quickly create a wide gamut, fully saturated color separation. Creating a primary color separation in this way can help to visualize a solution, or can be used as a starting point for working the separation up manually.