2.0 Functional Description
Fusion 878A
2.6 Automatic Chrominance Gain Control
PCI Video Decoder
2-22
Conexant
100600B
2.6 Automatic Chrominance Gain Control
The Automatic Chrominance Gain Control (ACGC) compensates for reduced
chrominance and color-burst amplitudes. Here, the color-burst amplitude is
calculated and compared to nominal. The color-difference signals are then
increased or decreased in amplitude according to the color-burst amplitude
difference from nominal. The range of chrominance gain is 0.5–2 times the
original amplitude. This compensation coefficient is then multiplied by the
saturation adjust value for a total chrominance gain range of 0–2 times the
original signal. Automatic chrominance gain control may be disabled.
2.7 Low Color Detection and Removal
If a color-burst of 25 percent (NTSC) or 35 percent (PAL/SECAM) or less of the
nominal amplitude is detected for 127 consecutive scan lines, the color-difference
signals U and V are set to 0. When the low color detection is active, the reduced
chrominance signal is still separated from the composite signal to generate the
luminance portion of the signal. The resulting Cr and Cb values are 128. Output
of the chrominance signal is re-enabled when a color-burst of 43 percent (NTSC)
or 60 percent (PAL/SECAM) or greater of nominal amplitude is detected for 127
consecutive scan lines. Low color detection and removal may be disabled.