Curves effect
The Curves effect adjusts the tonal range of an image. You can also use the Levels effect, but the Curves effect gives you more control. With the Levels effect you make the adjustments using just three controls (highlights, shadows, and midtones), but with the Curves effect you can arbitrarily map input values to output values using a curve defined by 256 points.
You can load and save arbitrary maps and curves to use with the Curves effect.
This effect works with 8-bpc, 16-bpc, and 32-bpc color.
When you apply the Curves effect, After Effects displays a graph in the Effect Controls panel that you use to specify a curve. The horizontal axis of the graph represents the original brightness values of the pixels (input levels); the vertical axis represents the new brightness values (output levels). In the default diagonal line, all pixels have identical input and output values. Curves displays brightness values from 0 to 255 (8 bit) or 32768 (16 bit), with shadows (0) on the left.
John Dickinson provides visual aids on his website that illustrate how to use the Curves effect for color adjustments: www.adobe.com/go/learn_ae_jdcurves.
Use the Curves effect
- Choose Effect > Color Correction > Curves.
- If the image has more than one color channel, choose the channel you want to adjust from the Channel menu. RGB alters all channels using a single curve.
- Use the Bezier tool and the Pencil tool to modify or
draw a curve. (To activate a tool, click the Bezier button
or
the Pencil button 
.)
To smooth the curve, click the Smooth 
button.
To reset the curve to a line, click the Line 
button.The curve type is determined by the last tool used to modify it. You can save arbitrary map curves modified by the Pencil tool as .amp (Photoshop lookup) files. You can save curves modified by the Bezier tool as .acv (Photoshop spline) files.
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