Image Processing Reference
Headroom & overshoot
Peak white level
Legal video values
Figure 35-10 Legal video values.
Rotating the hue of an image causes some severe bit-rate problems. You will see this in
footage of music concerts where the lighting director changes the stage lights from red to
green. Every pixel in the image has changed color. Because luma is computed using a
matrixed RGB value, there will be some small changes to the luma but most of the change
will be to the chroma. The lighting positions will cause slightly different shadows to be
cast, also affecting the luma channel. The perceived effect for the viewer is a major increase
in macroblock artifacts.
The same argument applies if you are using color correction as a special effect.
Kill That Noise
So a few chapters back we sorted out the T-axis. Then we wrestled with X and Y. Now we
just got Z to toe the line. But our image still has some noise in it. Let's try to find some
ways to eliminate that noise and get it looking just right. In the next chapter we'll cover