A typical printing press uses 4 colors of ink to create full-color photographic images. The four inks are placed on the paper in layers of dots that combine to create the illusion of many more colors. CMYK refers to the 4 ink colors used by the printing press. C is cyan (blue), M is magenta (red), Y is yellow, and K is black, the key plate or keyline color. Cyan, Magenta, Yellow and Black are called subtractive colors. Combining them all gives the color black. Subtracting one or more of these colors will yield any other color. When combined in various percentages, these four inks will create an entire spectrum of colors, including those used in color photographs.
In many instances, computers use a different color model called RGB (Red-Green-Blue) that is the contrast of CMYK. Hence, sometimes desktop publishing becomes difficult while converting the RGB colors into CMYK. It is important to ensure that the colors being printed look the same as what appears on the monitor. In printed materials, this light combination cannot be directly reproduced; so computer-generated images must be converted to the CMYK equivalent in ink colors. In RGB, the convergence of the three primary additive colors produces white. In CMYK, the convergence of the three primary subtractive colors produces black.
In RGB, the overlapping of additive colors (red, green and blue) results in subtractive colors (cyan, magenta and yellow). In the CMYK, the overlapping of subtractive colors (cyan, magenta and yellow) results in additive colors (red, green and blue). Additionally, the colors in RGB are much brighter than the colors in CMYK. It is possible to attain a much larger percentage of the visible spectrum with RGB, which is due to the fact that RGB uses transmitted light while the CMYK uses reflected light.
The CMYK printing method is also known as “four-color process” or simply “process” color. All of the colors in the printable portion of the color spectrum can be achieved by overlapping “tints” of cyan, magenta, yellow and black inks. A tint is a screen of tiny dots appearing as a percentage of a solid color. When various tints of the four colors are printed in overlapping patterns it gives the illusion of continuous tones - like a photograph.
It is important to choose the right color model for the job. Use RGB for screen displays and CMYK for print. If your images will be printed, then convert them to CMYK and manually bring them into gamut before printing. 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. Sometimes, the CMYK color model can also be used as YMCK or CYM, these are the subtractive color model used in color printing. These color model is based on mixing pigments of the colors C- Cyan, M – Magenta, Y- Yellow and K- Key (black) in order to make other colors.