BT848 ETC, BT848 Datasheet - Page 51

• Manufacturer Part Number: BT848
• Description: Single-Chip Video Capture for PCI
• Manufacturer: ETC

Bt848/848A/849A
Single-Chip Video Capture for PCI
Brooktree
YCrCb Sub-sampling
Gamma Correction
®
YCrCb to RGB
Conversion
Removal
The 4:2:2 YCrCb data stream from the video decoder portion of the Bt848 must be
converted to 4:4:4 YCrCb before the RGB conversion occurs, using an interpola-
tion filter on the chroma data path. The even valid chroma data pass through un-
modified, while the odd data is generated by averaging adjacent even data. The
chroma component is upsampled using the following equations:
Bt848 provides gamma correction removal capability. The available gamma values
are:
Furthermore, gamma correction removal is not available when YCrCb data is out-
put.
The 4:2:2 data stream is horizontally sub-sampled to 4:1:1 using the following
equations:
For n = 0, 4, 8, etc.:
modes. In these modes, the video data is first planarized and placed in the FIFO as
4:2:2 planar or 4:1:1 planar data. The FIFO data is then vertically sub-sampled to
4:1:1 for YUV9 and 4:2:2 for YUV12 formats. The vertical sub-sampling is per-
formed via RISC instructions that are executed by the DMA controller.
the YUV12 format. Line 2 of Cr/Cb data is discarded and hence 4:2:2 vertical
sub-sampling is achieved. In the YUV9 format, lines 2–4 of Cr/Cb data are dis-
carded and hence 4:1:1 vertical sub-sampling is achieved.
For n = 0, 2, 4, etc.
RGB Conversion:
Gamma correction removal capability is not programmable on a field basis.
Vertical sub-sampling is supported by Bt848’s YUV9 and YUV12 planar
Table 7 shows an example of a 4 pixel line for YUV9 and YUV12 formats. In
Cb
Cr
Cb
Cr
R = 1.164(Y–16) + 1.596(Cr–128)
G = 1.164(Y–16) – 0.813(Cr–128) – 0.391(Cb–128)
B = 1.164(Y–16) + 2.018(Cb–128)
Y range = [16,235]
Cr/Cb range = [16,240]
RGB range = [0,255]
NTSC: RGBout = RGBin
PAL: RGBout = RGBin
Cb
Cr
n
n+1
n
n
n+1
n
= Cr
= (Cr
= Cb
= (Cb
= (Cr
= (Cb
L848A_A
n
n
n
n
+ Cr
n
+ Cb
n
+ Cr
+ Cb
n+2
n+2
n+2
)
n+2
)
)/2
)/2
2.8
2.2
Video Data Format Conversion
F
UNCTIONAL
D
ESCRIPTION
41