BT848 ETC, BT848 Datasheet - Page 48

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

F
Video Data Format Conversion
38
UNCTIONAL
Video Control Code
Pixel Data Path
D
ESCRIPTION
Status Data
Video Data Format Conversion
The video decoder/scaler portion of the Bt848 generates a video data stream in
packed 4:2:2 YCrCb format. The video data is then color space converted and for-
matted in a 32-bit wide DWORD. Figure 21 shows the steps in converting the vid-
eo data from packed 4:2:2 YCrCb to the desired format. The YCrCb 4:2:2 data is
up-sampled to 4:4:4 format prior to conversion to RGB. It can then be dithered,
have gamma correction removed, or be presented directly to the byte swap circuit.
packed into BtYUV format or converted to planar format and vertically subsam-
pled to achieve the YUV9 format. Alternatively, packed 4:2:2 data may be convert-
ed to planar 4:2:2 and vertically sub-sampled to YUV12 format. The vertical
subsampling is achieved via the appropriate DMA instructions (see the DMA con-
troller section).
packed 4:2:2 data is stripped and the luma component is packed into 8 bits. This
format is otherwise known as gray scale. Table 7 shows the various color formats
supported by the Bt848 and the mapping of the bytes onto 32-bit DWORDs.
In addition to the pixel information, the Bt848’s Video Data Format Converter pro-
vides four bits of video control status code to the FIFO. These four bits of status
code STATUS[3:0] are based on inputs from the video decoder/scaler block of the
Bt848, and convey information about the pixel data and the state of the video tim-
ing (Figure 21). STATUS[3:0] are used to specify the FIFO mode (packed or pla-
nar), provide information regarding the pixel data (respective position of the pixel
and number of valid bytes), to indicate if the pixel data is valid, and to signal the
end of a capture enabled field. See Table 9 in the FIFO section for a full list of the
status codes and descriptions.
In the case where 4:1:1 data is desired, the 4:2:2 data is first down sampled, then
Bt848 also offers a Y8 color format, in which the chroma component of the
L848A_A
Single-Chip Video Capture for PCI
Bt848/848A/849A
Brooktree
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