Saturation

Saturation is another way of creating contrast between objects in a color image. You can think of saturation as a way of measuring how pure colors are. Imagine a can of pure red paint. It would produce a color like the one shown at left in Figure 7.8. Add some white paint to the can, and you'll get a less saturated red, eventually arriving at a totally desaturated white (if you added an overwhelming amount of white paint), as shown in the squares in the top row of the figure. If you added black paint instead, you'd end up with a darker, but also less saturated red, ending up with black, as you can see in the bottom row. This analogy doesn't precisely correspond to the way RGB colors become more or less saturated, but it's a useful way of thinking about the process.

Figure 7.8. Add white or black to red, and all you get is a desaturated red that is lighter or darker than the original color.

Figure 7.8. Add white or black to red, and all you get is a desaturated red that is lighter or darker than the original color.

As I said, this analogy isn't perfect, because the white paint is lighter than the red paint, and the black paint is darker, so, in terms of grayscales, the various degrees of saturation could still be told apart in a black-and-white version of the image, like the one in Figure 7.9.

Figure 7.9. After the saturation has been adjusted, converting the colors to gray doesn't provide an accurate image.

Figure 7.9. After the saturation has been adjusted, converting the colors to gray doesn't provide an accurate image.

However, if parts of an image were exactly the same color and brightness, and varied only in the degree of

This documentiscreatedwithtrialversionofCHM2PDFPilot 2.16.100^je. Figure 7.10 shows at top a gradient consisting of a single color, with the saturation carefully controlled to blend from the pure color (at the left side of the image) to the same color completely desaturated (at the right side of the image). When this saturation gradient is converted to grayscale, the completely uniform gray tone shown at the bottom of the figure results.

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