A color model is an orderly system for creating a whole range of colors from a small set of primary colors. The two most common color models are the RGB model (Red-Green-Blue) for computer display and the CMYK model (Cyan-Magenta-Yellow-blacK) for printing.

RGB Color Model Additive color model For computer displays Uses light to display color Colors result from transmitted light Red+Green+Blue=White

CMYK Color Model Subtractive color model For printed material Uses ink to display color Colors result from reflected light Cyan+Magenta+Yellow=Black

Notice that the colors in the RGB model are much brighter than the colors in the CMYK model. It is possible to attain a much larger percentage of the visible spectrum with the RGB model. That is because the RGB model uses transmitted light while the CMYK model uses reflected light. 

For you work to display at its best, choosing the right color model is critical.

RGB Color

The RGB model forms its gamut from the primary additive colors of red, green and blue. When red, green and blue light is combined it forms white. Computers generally display RGB using 24-bit color. In the 24-bit RGB color model there are 256 variations for each of the additive colors of red, green and blue. Therefore there are 16,777,216 possible colors (256 reds x 256 greens x 256 blues) in the 24-bit RGB color model.

In the RGB color model, colors are represented by varying intensities of red, green and blue light. The intensity of each of the red, green and blue components are represented on a scale from 0 to 255 with 0 being the least intensity (no light emitted) to 255 (maximum intensity). For example in the above RGB chart the magenta color would be R=255 G=0 B=255. Black would be R=0 G=0 B=0 (a total absence of light).

CMYK or "Process Color"

The CMYK printing method is also known as "four-color process" or simply "process" color because in the CMYK color model colors are represented as percentages of cyan, magenta, yellow and black. 

For example in the above CMYK chart the red color is composed of 14% cyan, 100% magenta, 99% yellow and 3% black. White would be 0% cyan, 0% magenta, 0% yellow and 0% black (a total absence of ink on white paper).

When In Doubt, Save Images As RGB

The RGB model displays a much larger percentage of the visible spectrum than the CMYK model. Once an image has been converted from RGB to CMYK, the extra RGB data will be lost.

Because of this fact, you want to scan or shoot images (with a digital camera) using the appropriate color model for their primary purpose. If the images will be used primarily for print then use CMYK. If they will be used primarily for screen displays, then use RGB. You can always convert from RGB to CMYK (or vise-versa) but it is best not to.

If you can afford the time, money and disk space to scan or shoot both versions of an image where both are needed, then this is the best solution. This is especially true if you will be using the same images for both printed material (such as a catalog) and the web (such as an online catalog). A little planning can go a long way here.

But if you are not sure, then I generally recommend saving images in RGB mode and creating CMYK copies for printed material as needed.

Bottom Line: Use RGB For Screen Displays and CMYK For Print

It is important to choose the right color model for the job. If your images will be printed, then convert them to CMYK. If your images are to be displayed on a computer, then make sure you use RGB color so the full gamut will be available for display. Because both models can be available at the same time while using an application, it is easy to make a mistake and choose the wrong palette or set of color swatches.

The following chart shows how all the various parts fit together - vector vs. bitmap graphics, some of the various software applications used to create them (Adobe® Illustrator®, CorelDRAW®, Macromedia® FreeHand®, Adobe Photoshop®, Corel PHOTO-PAINT® and Paint Shop Pro™), the four basic file formats and the two most common color models used in computer graphics for print media and the web: