RGB vs CMYK – or, Why do My Colors Look Different When Printed?
Every industry has acronyms that nobody else knows. Today I’m demystifying the printer terms RGB and CMYK.
RGB stands for Red Green Blue, and refers to the color format used by computer screens and digital cameras. Computer monitors are made up of millions of red, green, and blue lights. Because computer screens use emitted light, RGB is additive and the combination of Red, Green and Blue is white. RGB is very flexible – it can display a very wide range of color.
CMYK stands for Cyan Magenta Yellow Key, and refers to the color format used by most printing systems. Contrary to computer screens, printed media don’t emit light – they rely upon reflected light. Cyan, Magenta, and Yellow ink or toner reflects only a certain shade of color. You could also say that each shade of ink or toner absorbs all light except cyan, magenta, yellow or black. As we add these colors together, less and less light is reflected, until the color is black. To avoid having to always use a composite of 3 colors to make black, we add the fourth color, black, which is referred to as key. CMYK can display a wide range of color, but not as wide as RGB.
Implications:
Anything that originated as RGB, for instance pictures from a camera, or any document that the designer created using the RGB color scheme, must first be converted to CMYK before being printed. Because RGB is a light source, while CMYK is only reflected light, printed pieces will generally be darker than objects on the computer screen. RGB can display more colors than CMYK, so some colors cannot be translated from RGB to CMYK with any degree of accuracy. For convertible colors, there are several different conversion methods. Furthermore, because of the conversion, printed material will ALWAYS look different than the original RGB design. Finally, because of the several different conversion methods, RGB originals will print differently depending on the method used to make the conversion.
As you can see, RGB is not the best design medium for printed work, due to the inherent inconsistencies. What you see on your computer monitor will not exactly match what is printed. For this reason, good print designers and printers will request CMYK artwork when applicable.