A Quick Color Quiz

By Gary David Bouton

Dateline: August 9, 2004
Volume 2, Number 13
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With 16.7 unique colors to choose from on your monitor, it's likely that you've overlooked the primary colors that in combination are responsible for all these colors. Let's take a trip back to school and review the basic colors from which all others are derived.

Q: What are the primary additive colors?
A: Red Green, and Blue. Blended together at full intensity, you get white; the colors are additive.

As you can see in the first illustration, red, green, and blue, when combined, create white. Additionally, when these colors are blended on equal amounts at less than full intensity, shades of grey are produced. Also, complementary colors are formed, yellow, cyan, and magenta, when only two of the three primary colors are used. We get all the colors we see on the monitor by blending equal and unequal amounts of two or three primary additive colors. Using a less than 100% amount of a single primary color results in a tint.

Q: What are the subtractive primary colors (pigments)?
A: Cyan, Magenta, and Yellow, with usually an option for black. The three primary subtractive colors, when combined, usually don't produce a pure black, because these are physical colors (such as paints or dyes), and physical colors contain impurities, so the addition of black helps to "goose" the resulting color blend. The subtractive primary colors are also known as th CMYK color space, and it it used extensively in printing.

Q: What is a color space?
A: It is the boundary within which all colors can be expressed with a particular color model. RGB is a color model and it has its limitations. IOW, all the colors you see in real life cannot be expressed using the RGB color space. Sure, you can see a lot of colors (this is why digital photography is so popular), but the RGB color space cannot match the space of the human eye. The CMYK color space intersects the RGB color space at certain points, and even extends to embrace some colors that RGB cannot, but overall, CMYK is a narrower color space than RGB, and its colors look somewhat duller because it is subtractive in nature.

Q: What is a spot color?
A: A spot color is a special dye or pigment that lies outside of the CMYK color space. We frequently see fluorescent colors on a detergent box, and this is done by first applying the cyan, magenta, yellow, and black printing plates, reserving white space for the spot color on the package, and then applying the spot color printing plate. Some (expensive!) packaging has been known to use up to five spot color plates and no CMYK plates.

Q: What is a complementary color?
A: It is the opposite color on a color wheel. As you can see in the illustration below, yellow is the complementary color to blue, cyan to red, and magenta to green. These complementary colors are made up of their neighboring (primary) colors.

Q: What is LAB color?
A: LAB is a color space that engenders all other color spaces. LAB consists of one channel of luminance, and two chromacity (color) channels. By using the LAB color model in your work, you can isolate only the brightness (luminance) aspect of a color picture. LAB color most closely imitates the spectrum of visible light that the human eye can see. It's useful as an intermediary color space when converting, say, RGB to CMYK–you are assured by using the LAB space that no colors are clipped. See the illustration below for the LAB color space and how some of Adobe's and other color spaces fit within LAB. As you can see, the Adobe RGB color space is the largest, the CMYK color space approximately fits within it, and the RGB color space, popular with inexpensive digital cameras, offers a fairly narrow color space.

Q: Are all colors equal in intensity?
A: No. If you look at figure 4 again, you will notice that LAB color forms a tongue-shapes curve when red intensity is plotted against green. Our eyes are more sensitive to green than other colors, and therefore more green is dedicated to the color space.

Do you have any other questions about color? Write to me in the forum, and I'll try to answer the question for all in a later column.

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Gary David Bouton is the moderator of "The Inside Track", a forum dedicated to Photoshop users of all platforms. Additionally, Gary moderates the 3D forum at TalkGraphics, and has a series of tutorials posted on beginning trueSpace. In addition to being an illustrator, author, and all around swell guy, Gary has a new book on Photoshop, "Inside Photoshop CS" and he wouldn't mind at all if you picked up a copy on Amazon.