Third in the troika of essential color correction tools is Hue/Saturation. This one has many individualized uses:

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

The Hue/Saturation control allows you to do something you can't do with Levels or Curves, which is to directly control the hue, saturation, and brightness of an image. The HSB color model is merely a different way of looking at the same color data as exists in the RGB model used by Levels and Curves. All good color pickers, including the Apple and Adobe pickers, handle RGB and HSB as two different modes that use three values to describe any given color, which is the correct way to conceptualize it.

In other words, you could arrive at the same color adjustments using Levels and Curves, but Hue/Saturation gives you direct access to a couple of key color attributes that are otherwise difficult to get at. For example, de-saturating an image is essentially bringing the red, green, and blue values closer together, reducing the relative intensity of the strongest of them. With a complex image, this approach would be difficult and unnecessary when a single slider will do it.

De saturating an image slightly lowering the Saturation value somewhere between 5 and 20can be an effective way to make an image adjustment come together quickly. This is a case where understanding your delivery medium is essential, as film is more tolerant and friendly to saturated images than television.

For footage that is already saturated with color, even a subtle boost to the gamma can cause saturation to go over the top. There's no easy way to control this with RGB controls, 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, so that, for example, lowering blue gamma effectively raises the yellow gamma, and vice versa.

But in the HSB model all six are singled out individually, which means that if a given channel is too bright or over-saturated, you can dial back its Brightness & Saturation levels, or you can shift its Hue toward the part of the spectrum where you want it, without unduly affecting the other primary and secondary colors.