When Separate RGB/Lab to CMYK source is turned on, the original RGB colors in the document are converted to the source CMYK profile selected in Job Properties before being converted to the output profile of the printer (as defined by the Output profile print option). The color reproduction from converting RGB colors to the CMYK source and then the output color space is similar to converting the RGB content to that CMYK source profile.

For example, the color reproduction from converting RGB colors to the CMYK source in the Fiery server is similar to converting an RGB image to a CMYK profile in Photoshop. Another useful technique with Separate RGB/Lab to CMYK source is to take a high-quality ICC profile for another press, define that as the source CMYK profile in the Fiery server and simulate the color appearance of RGB colors by the other press.

This feature is also used with PDF/X workflows in which all color spaces are converted to CMYK source before they are converted to the output color space. These workflows require device dependent colors (RGB, Grayscale) and device independent colors (ICC colors, L*a*b*) to achieve a color match to the CMYK content in the document. With the introduction of PDF/X-4 allowing transparency in a PDF/X document, the feature also supports CMYK overprinting included in designs that have transparency effects. A best practice for rendering transparency is to turn on the Separate RGB/Lab to CMYK source print option because rendering transparency requires complex processing policies to achieve the desired appearance.

Turning off the Separate RGB/Lab to CMYK source print option manages all RGB colors with the output color profile. This workflow renders the RGB colors with the full gamut of the output device and is recommended when you need the most vibrant color achievable with the print system.