bt848kpf ETC-unknow, bt848kpf Datasheet - Page 44

• Manufacturer Part Number: bt848kpf
• Description: Single-chip Video Capture For Pci
• Manufacturer: ETC-unknow

F
Low Color Detection and Removal
34
UNCTIONAL
D
ESCRIPTION
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 zero. When the low color detection is active, the reduced
chrominance signal is still separated from the composite signal to generate the lu-
minance 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 con-
secutive scan lines. Low color detection and removal may be disabled.
Coring
The Bt848 video decoder can perform a coring function, in which it forces all val-
ues below a programmed level to be zero. This is useful because the human eye is
more sensitive to variations in black images. By taking near black images and turn-
ing them into black, the image appears clearer to the eye.
minance level is below the selected limit, the luminance signal is truncated to the
black value. If the luma range is limited (i.e. black is 16), then the coring circuitry
automatically takes this into account and references the appropriate value for
black. Coring is illustrated in Figure 17.
Figure 17. Coring Map
Four coring values can be selected: 0, 8, 16, or 32 above black. If the total lu-
L848A_A
32
16
8
0
0
8
Luma Value
Calculated
16
32
Single-Chip Video Capture for PCI
Bt848/848A/849A
Brooktree
®