ADOBE AFTER EFFECTS 7.0
User Guide
418
Original (left), and with effect applied (right)
The gamma of any curve is its slope, expressed as the ratio of the logarithms of the output to input values. For
example, a gamma value of 1.0 equals an output-to-input ratio of 1:1. Moving the midpoint of the curve up (in an
RGB readout) lowers the gamma value; moving the midpoint down raises the gamma value. Gamma specifies
contrast that affects the midtones in a range.
You can adjust the brightness, contrast, and gamma in an image. Use Levels to adjust the gamma to change the
brightness values of the middle range of gray tones without dramatically altering the shadows and highlights.
Adjust the following controls for the Levels effect:
Channel
Specifies the color channel to be modified.
Histogram
Shows how the pixel values are distributed in an image. The horizontal axis of the histogram represents
the brightness value. The vertical axis represents the number of pixels at each brightness level. No pixels can be
darker than the output black level, and no pixel can be brighter than the output white level.
Input Black
Specifies the threshold of the black value for the input image. Pixels below the input black level are
mapped as black on the input image. The input black value is represented by the upper left triangle below the
histogram.
Output Black
Specifies the limit of the black value for the output image. The output black value is represented by the
lower left triangle below the histogram.
Gamma
Specifies the gamma value, which is represented by the middle triangle below the histogram.
Output White
Specifies the limit of the white value for the output image. The output white value is represented by
the lower right triangle below the histogram.
Input White
Specifies the threshold of the white value for the input image. Pixels below the input white level are
mapped as white on the input image. The input white value is represented by the upper right triangle below the
histogram.
Levels (Individual Controls) effect
The Levels (Individual Controls) effect functions like the Levels effect but allows you to adjust the individual color
values for each channel. This allows you to add expressions to individual properties or keyframe one property
independently of the others. To see each control individually, click the arrow next to the channel color to expand it.
This effect works with 8-bpc, 16-bpc, and 32-bpc color.
Original (left), and with effect applied (right)
Summary of Contents for AFTER EFFECTS 7.0
Page 1: ...Chapter 1 User Guide...
