Today, I’m talking about color space. About a month ago I covered some color terms specific to color printing. I’m expanding on that information today and covering a couple other colors spaces. If you’re wondering what RGB means and what it’s good for, I hope to help you out. Also, this is simplified; this is not technical nor exhaustive. Seriously, I could go on for a while.
How color is perceived
Light waves enter your eye and are perceived as color and value. This is possible through the rod and cone cells of your eye. Rod cells are responsible for seeing in dim light and contribute little to color vision. Cone cells are the photoreceptors that pick-up color. There are three flavors: short-wave sensitive, medium-wave sensitive and long-wave sensitive. Roughly, these pick up light waves in the blue, green and red spectrums. Our eyes see many more colors than most color models are able to reproduce.
CIELAB, or LAB color
CIELAB is a color space that is able to mathematically represent nearly all the colors that the human eye can perceive. It is an absolute color space, meaning it describes color independent from reproducible models. It is used to convert between color spaces. The L stands for Lightness, the a and the b are the color components green-red and blue-yellow. If you use Photoshop, the three LAB values are related to this color space.
The main color models: RGB and CMYK
RGB and CMYK are probably the main color spaces that designers use to describe color.
RGB: Each RGB color is represented by three numbers, one each for Red, Green and Blue. The RGB color space is an additive system, which means that as colors are turned on in various amounts, they come closer to white. White is what the eye sees when all colors are present. TVs, computer monitors and cameras use this color space. Since each device is calibrated differently, a particular RGB color doesn’t reliably appear the same on every device. You can see the difference if you watch the bank of TVs on the wall at Best Buy.
CMYK: Each CMYK color is represented by four numbers, one each for the standard printing colors of Cyan, Magenta, Yellow and Black. The CMYK color space is a subtractive model, which means that as more color is applied to the paper, the more light is absorbed and the closer the color appears to black.
Each of these systems (and many more) assign a number to a particular wavelength so that it can be described mathematically, and in the case of RGB and CMYK, reproduced. Because of the limitations of color mixing, both RGB and CMYK can’t reproduce every color seen, and fall short in particular colors. The range of colors that can be reproduced by a system is called its color gamut. CMYK in particular has difficulties with green. I had my own personal experience with the limitation of CMYK greens. I had a piece of green fabric that I used as the backdrop for a photo shoot. When the final product came back from the printer, I was disappointed to find that the lovely shade of green had printed as a dull teal. Well. Live and learn.
Lab color: A derivative of CIELAB color space, LAB color describes color using three variables related to a color’s lightness and its place on the green-red and blue-yellow scales. An absolute color model, it is not device dependent.
RGB: An additive color system using three variables corresponding to the colors red, green and blue. It is a color space used by computer monitors and cameras.
CMYK: a subtractive color system using four variables corresponding to the colors cyan, magenta, yellow and black. This color system is used in four-color process printing.
Additive color: a color that is mixed by adding or turning on colors. When all colors are present, the final color is white.
Subtractive color: a color that is mixed by subtracting light through absorption and therefore failing to reflect it. When all colors are absorbed, the result is black. Printing uses subtractive color mixing, as do paint and dyes.
Gamut: the range of colors possible in a particular color space.
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