Does painless RGB to CMYK conversion exist?

Jun 1, 2005 12:00 AM, By Julie Shaffer

Not without color management!

Doing it properly with desktop publishing applications
Desktop publishing applications such as QuarkXPress or Adobe InDesign also offer a way to convert color between color modes from the print or export options. Sometimes RGB to CMYK conversion is done incidentally from a desktop publishing application, as, for example, when RGB images are placed in QuarkXPress layouts, then output with the "Print Colors" option set to "Composite CMYK." If Quark Color Management has not been enabled, this will convert any RGB image in the document to the CMYK color space using a built-in algorithm rather than ICC profiles. The resulting conversions often aren’t very pretty.

But when color management is set up properly in desktop publishing applications, placed RGB images can be converted quite successfully to CMYK. Adobe, in particular, has made consistent color settings between its Creative Suite tools a priority. All CS tools (including InDesign, Illustrator, Photoshop, Acrobat and Distiller) can use the same "color settings file" (.csf). This allows users to color manage content within all the CS applications in the same way. And with the latest version of the Adobe Creative Suite (CS2), all applications that can export PDF files will share common "Adobe PDF Settings," so a PDF file can be created from Illustrator in the same way as Distiller or InDesign. It is possible, then, to set up master color and PDF setting files and use them with all instances of the Adobe applications within a workgroup. A printing company might share these settings with its clients, so it won’t matter where color is being converted with an Adobe-based tool—it will be done consistently and to a master specification. Now we’re on the road to painless.

There is an ever-growing number of color management aficionados who recommend storing, manipulating and color correcting images in the RGB color space for CMYK conversion just prior to final output. This works even for stalwart CMYK prepress professionals, because imaged editing tools like Photoshop allow the user to accurately preview and manipulate CMYK data while working within an RGB image mode. The benefits of an RGB workflow are many. It is far easier to maintain an accurate gray balance in RGB images, because equal amounts of RGB indicate a balanced gray. Edits to RGB images won’t result in out-of-range shifts, either, as maximum blacks and minimum whites will be set to the right level automatically when CMYK conversion is accomplished using a good profile. RGB files are smaller and easier to store, and retouching or color edits to RGB images need only be done once, even if the image will be separated later for any number of different printing processes.

Server-based options
Several server-based image/workflow management tools make color conversion a highly automated and consistent process. Adobe now offers an array of server solutions, including the Adobe Graphics Server. The Adobe Graphics Server integrates database-driven digital asset management and color management, automating the process of managing and repurposing images. Users of the Graphics Server can create scripts to automatically convert color mode and attach ICC profiles as required, relieving the desktop computer user from that time-consuming task.