The Color WheelBefore moving on to weightier matters such as gravity, calculus, and his impending thirtieth birthday, Sir Isaac Newton provided the world of color with one more key concept: if you take the colors of the spectrum and arrange them around the circumference of a wheel, the relationships among primaries become much clearer (see Figure 4-2). Figure 4-2. The color wheelFiguring Saturation and BrightnessSo far, we've talked about color in terms of three primary colors. But there are other ways of specifying color in terms of three ingredients. The most familiar one use the terms of hue (the property we refer to when we talk about "red" or "orange"), saturation (the "purity" of the color), and brightness.Newton's basic two-dimensional color wheel lets us see the relationships between different hues, but to describe colors more fully, we need a more complex, three-dimensional model. We can find one of these in the HSB (Hue, Saturation, Brightness) color cylinder (see Figure 4-3). Figure 4-3. The HSB color cylinder[View full size image] Tristimulus Models and Color SpacesIgnoring the inconvenience of CMYK, all the ways we've discussed of specifying and thinking about color involve three primary ingredients. Color scientists call these tristimulus models. (A color model is simply a way of thinking about color and representing it numerically: A tristimulus model represents colors by using three numbers.) If you go deep into the physiology of color, you'll find that our perceptual systems are actually wired in terms of three different responses to light that combine to produce the sensation of color. So the tristimulus approach isn't merely a mathematical convenienceit's inherent in the way our perceptual systems work.But tristimulus models have another useful property. Because they specify everything in terms of three ingredients, you can (with very little effort) view them as three-dimensional objects with x, y, and z axes. Each color has a location in this three-dimensional object, specified by the three values. These three-dimensional models are called color spaces, a term that gets thrown around a great deal in the world of color.We like to think of the HSB color space as a giant cylinder; the brightness slider in the Apple Color Picker determines which slice of the cylinder we're looking at. But, like any metaphor, there's a good side and a bad side to looking at color this way.The good side. The Apple Color Picker is a great way to start learning about color and how changing a single primary changes your colors.The bad side. The simple HSB model can't really describe how you see colors. For instance, you know that cyan appears much lighter than blue; but in the HSB cylinder, they both have the same brightness and saturation values. Therefore, while the Color Picker is a step in the right direction, we have to go further to understand how to work with color. |