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Just for Color: Hue/Saturation

The third of three essential color correction tools in After Effects is Hue/Saturation. This one has many individualized uses:

  • Desaturating an image or adding saturation (the tool's most common use)
  • Colorizing images that were created as grayscale or monochrome
  • Shifting the overall hue of an image
  • De-emphasizing (or completely knocking out) an individual color channel

The Hue/Saturation control allows you to do something you can't do with Levels or Curves, which is directly control the hue, saturation, and brightness of an image. The HSB color model is merely an alternate slice of RGB color data. All real color pickers, including the Apple and Adobe pickers, handle RGB and HSB as two separate but interrelated modes that use three values to describe any given color.

In other words, you could arrive at the same color adjustments by using Levels and Curves, but Hue/Saturation gives you direct access to a couple of key color attributes that are otherwise difficult to reach. To desaturate an image essentially brings the red, green, and blue values closer together, reducing the relative intensity of the strongest of them; a saturation control lets you do this in one step, without guessing.

Often, colors are balanced but merely too "juicy," and lowering the Saturation value somewhere between 5 and 20 can be a direct and effective way to make an image adjustment come together (see Figure 22). It's essential to understand the delivery medium as well, because film is more tolerant and friendly to saturated images than television is.

Figure 22

Figure 22 For footage that's already saturated with color, even a subtle boost to gamma or contrast can send saturation over the top. There's no easy way to control this situation with RGB tools, such as Levels and Curves, but moving over to the HSB model allows you to single out saturation and dial it back.

The other quick fix that Hue/Saturation affords you is a shift to the hue of the overall image or of one or more of its individual channels. The Channel Control menu for Hue/Saturation includes not only the red, green, and blue channels but also their chromatic opposites of cyan, magenta, and yellow. When you're working in RGB color, these secondary colors are in direct opposition; for example, lowering blue gamma effectively raises yellow gamma, and vice versa.

The HSB model includes all six individual channels, which means that if a given channel is too bright or oversaturated, you can dial back its Brightness and Saturation levels, or you can shift Hue toward a different part of the spectrum without unduly affecting the other primary and secondary colors. This is even an effective way to reduce blue or green spill.

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