CHAPTER 8 (Geocities web hosting) COLOR MANIPULATION, CHANNELS, AND LAYER
CHAPTER 8 COLOR MANIPULATION, CHANNELS, AND LAYER MODES 299 Subtractive Colors So what s up with those red, yellow, and blue paints you mixed as a child? The red, green, and blue additive primary colors work for transmitted light. But ink or paint on paper follow different rules. As you add colors of transmitted light, the image gets brighter. But as you add shades of paint to a reflecting surface, the image gets darker. That s subtractive color. The paint absorbs light of particular frequencies. The light that doesn t get absorbed is reflected to your eye. In other words, the paint subtracts colors from the white light shining on it. When you mix several colors of paint together, the paint absorbs more and more colors, subtracting from the colors that reach your eye. Reflected color is called subtractive. Each of the additive colors that come from your RGB monitor has an opposite, or complementary color. The complement of blue is yellow, of green is magenta, and of red is cyan. You can see the relationships in Figure 8-1. For subtractive colors, it works best to use those complementary colors as primaries: so the subtractive primary colors are cyan, magenta, and yellow, and the color model based around them is known as CMY. Take some yellow paint and put it on white paper. The white surface reflects the full spectrum of magenta, cyan, and yellow light, while the yellow surface absorbs the magenta and cyan what s left is yellow. But wait! When you shine differently colored lights on a white screen, you re looking at reflected light, but it follows the additive rules. What s up with that? That s confusing, but the reflection is a red herring. The color you see is still coming from transmitted light, even after it s reflected. It s not subtractive color because there s no tinted surface subtracting from the colors you see. The Relationship Between Additive and Subtractive Systems It s convenient to consider these two systems, additive and subtractive, as mirrors of each other. They have their own rules about how colors work, but the rules are exact opposites of each other. For example, if you mix any two of the additive primaries (red, green, or blue), you get one of the subtractive primaries (also called the additive secondaries): magenta, cyan, or yellow, as you saw in Figure 8-1. Conversely, mixing any two subtractive primaries of paint will yield the additive primaries: yellow + magenta = red, yellow + cyan = green, and cyan + magenta = blue. So ultimately, the object of a subtractive approach is to reflect red, green, and blue aiming the RGB colors of light at your eye, just like your monitor does! Tip The GIMP can help you experiment with combining colors, using the Addition and Subtract layer modes and the color picker. That s how Figure 8-1 was made. You ll learn how in the next chapter. There s another way the two approaches mirror each other. If you keep adding transmitted light colors, eventually you ll get white. If you keep mixing colors of paint (subtracting reflected light), you theoretically end up with black. (In practice, with paint you get a muddy dark brown most of the time, but that s just reality refusing to conform to theory. You ll learn more about black in the discussion of CMYK color, and in the section Printing in Chapter 12.)
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