Ross Vision - Gamma; Hue Rotate

Ops 19–6 • Appendix B: Color Correction Parameters Vision Operator’s Manual (v12.0 MD)
Figure 19.6 Effects of Increased and Decreased Cb Offset
Gamma
The previous corrections are all linear. No matter which correction was applied, the output versus
input mapping is still a straight line. Gamma corrections introduce non-linear corrections to a
video signal. A gamma correction can be described as taking a point on the output versus input
video signal line and pulling it perpendicularly away from the line. The result is a Bezier curve
between the start, the new point and the end point. The following graph (Figure 19.7) illustrates
the effect of adding positive and negative gamma corrections to a video signal.
Figure 19.7 Effects of Increased and Decreased Gamma
The point C, called the Gamma Offset point can be any point along the AB line. The Gamma
Value indicates how far perpendicularly off the line the Gamma Offset point is moved. Once the
Gamma Offset point and Gamma Value are determined, a Bezier curve is drawn from point A,
through point C and ended at point B.
The Vision switcher can perform gamma corrections to the luminance component of a video
signal. Luminance gamma corrections allow for selective brightening or darkening of portions of
the video signal. Generally, increasing the gamma value brightens the video signal in the location
of the gamma offset point. Decreasing the gamma value, darkens the video signal in the location
of the gamma offset point. Therefore, by moving the gamma offset point, you can select which
part of the input video signal receives the most brightening or darkening.
Hue Rotate
Hue rotate affects the color of the entire video signal by rotating the input video hues. This
produces an output video signal with colors that are shifted from their original hues. The
following diagram (Figure 19.8) shows a color wheel. By rotating colors around the wheel, hue
values will shift. The diagram shows a clockwise rotation where yellows become orange, reds
Input Value
Output Value
Standard
Increased Cb Offset
Decreased Cb Offset
Cb
Max
Cb
Max
Min
B
A
Input Value
Output Value
A
B
C
Output
Max
Input
Max
Min
Standard
Increased Gamma
Decreased Gamma