ADOBE AFTER EFFECTS 7.0
User Guide
395
Channel effects
Alpha Levels effect (Pro only)
The Alpha Levels effect increases or decreases the transparency of a matte. Use Alpha Levels to adjust pure black or
pure white areas of a matte to be semitransparent, or to adjust grays (semitransparent areas) to be pure black and
white. Alpha values are converted using Input limits, Output limits, and the Gamma value.
This effect works with 8-bpc and 16-bpc color.
Original (left); matte created with Fractal Noise effect on a solid layer (center); result (right)
Adjust the following controls for the Alpha Levels effect:
Input limits, Output limits
Specify where transparency begins and ends.
Gamma
Affects the range of gray values that are converted. A Gamma value of 1 produces a gradual (linear) distri-
bution of gray values. A Gamma value less than 1 creates darker gray values and more transparency. A Gamma value
greater than 1 creates lighter gray values and less transparency.
To convert grays in a matte to pure black or white (Pro only)
1
Set the Input Black Level to a gray value. Alpha values at this level or lower become fully transparent (black).
2
Set the Input White Level to a gray value. Alpha values at this level or higher become fully opaque (white).
3
Leave the Output Black Level set to 0 and the Output White Level set to 255.
4
If necessary, adjust the Gamma value to increase or decrease transparency.
To convert pure black and white in a matte to gray (Pro only)
1
Leave the Input Black Level at 0 and the Input White Level at 255.
2
Set the Output Black Level slider to a gray value. Alpha values below this value rise to this value.
3
Set the Output White Level to a gray value. Alpha values above this value are lowered to this value.
Arithmetic effect
The Arithmetic effect performs various simple mathematical operations on an image’s red, green, and blue channels.
This effect works with 8-bpc color.
Summary of Contents for AFTER EFFECTS 7.0
Page 1: ...Chapter 1 User Guide...
