RGB vs. CMYK
There are two primary color models used in today’s graphic design, RGB (Red.Green.Blue) and CMYK (Cyan.Magenta.Yellow.Black). The two vary in numerous ways but the most important difference is the size of each one’s color spectrum. The RGB model consists of ~16.8 million colors while the CMYK model consists of only 1 million. Why does this matter? The short answer, graphic devices (i.e. computers, cameras) use the RGB model but printing devices use CMYK. Therefore, the color conversion is of paramount importance. How is it that CMYK only includes such a small color spectrum in comparison to RGB? One must better understand the color theory behind both in order to fully understand the limitations.
What is RGB?
The RGB color model follows the Additive Color Theory (ACT). This method attempts to create colors by combining two or three distinct colors of light in varying quantities. The reason red, green and blue are the chosen colors to mix is biological. The human eye contains cones which correspond to each of these three colors in particular. So, devices such as a computer monitor use this theory’s methodology to project colors that our eyes will perceive as the correct color tone, even if the color’s spectral distribution is inaccurate. Since RGB devices use this visual trickery they are able to produce a much wider range of colors.
What is CMYK?
The CMYK color model relies on the Subtractive Color Theory (SCT). The methodology of this theory is based on the mixture of pigments, such as ink or paint, to create the desired color. It is known that light includes all of the visible wavelengths of color (i.e. a rainbow). So the ideology behind SCT is that mixing specific colors will block out undesired wavelengths and reflect only the desired color. This is an imperfect process, however, as some wavelengths of light are able to reflect through even when combining the colors in perfect quantities. Theoretically, combining Cyan, Magenta, and Yellow in equal parts should create a perfect black. It does not. Pigments of brown are still present. It is this imperfection that forces printing devices to carry color ink as well as black ink cartridges.
Things to consider.
- It is important to understand that neither theory is entirely perfect. Both models are capable of creating colors that cannot be replicated by the other. A color that is not producible by a particular model is said to be “outside the gamut.” For example: a pure cyan color is outside the gamut of RGB, while deep blues and rich reds are outside the gamut of CMYK
- When viewing an RGB image on varied devices there is a chance that the image will appear slightly different. This occurs because each graphic device is color calibrated differently; calibration affects how you perceive an image.
- CMYK printing has an average accuracy rating of eighty-five percent. Numerous factors contribute to this figure, including: machinery, ink types, and gang run printing. The truth of the matter is that even though there is a fifteen percent margin for error, the error would be unnoticeable to the untrained eye. It would be a miniscule variation in color.
Due to the limitations of each color model, it is necessary for an image created in an RGB model to be converted to a CMYK format before printing. This conversion ensures that the quality of the graphic design remains intact when transferred to printed material. There is currently no creation or printing method that can avoid this limitation, but a skilled graphic artist is capable of converting and preserving effectively.