(Another post in a series on using the settings in the YRGBK script)
The Saturation and Color Density sliders in the YRGBK script can be used to adjust the amount of color in your final separation. Although both adjustments appear to have a similar effect, the results of each are very different and they can be used together.
The color density slider adjusts the Black point, or how dark the darkest pixels will be, for all color channels. Each color channels black point can be set individually using the Custom Colors dialog, while the Color Density slider adjusts all the channels together.
The Black point of the color channel determines the amount of ink being printed overall, and is balanced with the color of the ink itself. If we are using a duller, less saturated ink we can increase the density of the channels to compensate. If our inks are pure primary colors we can decrease the density levels. With the Color Density setting set to 0, the black point for all channels is set entirely by the custom color sliders.
The Auto check box automatically sets the darkest pixels to black in each color channel. This setting overrides the values applied in the Custom Colors dialog, so the results can be unbalanced if the image does not contain a full set of primary colors. The Auto setting is useful, however, if you intend on customizing your colors. The Color Density slider increases the Auto amount for all color channels.
The Saturation slider applies to the mid range values in a channel. The Darkest pixels in a channel are not made any darker, but the amount of ink overall is adjusted. The default setting is 50, which means that pixels in the 50% range will be set to 50%, or no adjustment.
Dynamic Range and Coverage.
Dynamic range is the difference between the lightest and darkest values on a channel or in an image. A print with good dynamic range will have high contrast and be able to reproduce the full range of values in an image.
Coverage is how well an ink deposit covers the substrate. For screen printing on textiles it is nice to have an ink printing at 100% coverage where the color is brightest. Most printers will try to achieve a solid print in areas covered by a single color. If the channel itself is coming in below 100%, the print pressure will be increased to create a good ink surface. The resulting dot gain from increasing the print pressure will reduce the dynamic range.
We can anticipate this by setting the solid areas on a color channel to 100%, allowing for complete coverage while maintaining the range of values the color can reproduce. This is only possible where a color in the image is a pure primary, or we are using a custom ink color.
How is this used?
If our inks are duller or our image brightly colored, it can help to increase the density of the colors. Pushing the darkest values closer to 100% increases the dynamic range of each channel, increasing the range of colors that can be achieved.
If the separation itself is too dull or too colorful overall it can be helpful to adjust the Saturation slider. Since this adjustment does not affect the black point the dynamic range and maximum density of the colors are not changed.
Finally, if we are planning on using custom colors, the Auto setting can be used with the density slider to quickly set the black point for all channels so the densest areas of color are printing at 100%. In this case the Saturation slider value can actually be reduced in order to maintain the mid range.