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Ancillary Data Capture
Note that edge pixel replication only comes into effect when the full BT.656 stream is being captured. If
VCXSTART is greater than 0, then only some of the leading edge replicated pixels are used by the filter. If
VCXSTART is greater than m, then none of the leading edge replicated pixels are used. Similarly, if
VCXSTOP is less than the number of samples before EAV, then none or only some of the trailing edge
replicated pixels are used by the filters.
SAV
d
c
b
Leading edge replicated pixels
Figure 3-12
shows an example of a capture window that is smaller than the BT.656 active line. Sample a
is the first sample in the horizontal capture window and sample n is the last sample. In this case, any
filtering done on the first sample location uses the m leading edge captured pixels (m is 3 in this example),
and any filtering done on the last sample location uses the m trailing captured pixels. (From an
implementation standpoint, the mirroring and filtering can still begin and end with SAV and EAV, but the
samples before VCXSTART or after VCXSTOP must not be saved to the YCbCr buffers.)
Figure 3-12. Capture Window Not Requiring Edge Pixel Replication
XSTART
SAV
a-4 a-3
a-4 a-3 a-1
Leading edge replicated pixels
3.6
Ancillary Data Capture
The BT.656 and some Y/C specifications includes provision for carrying ancillary (non-video) data within
the horizontal and vertical blanking regions. Horizontal ancillary (HANC) data appears between the EAV
code and SAV codes. Vertical ancillary (VANC) data, also called vertical blanking interval (VBI) data,
appears during the active horizontal line portion of vertically blanking (for example, after an SAV with
V = 1). Ancillary data blocks are always preceded by an ancillary data header 00h, FFh, FFh.
60
Video Capture Port
Figure 3-11. Edge Pixel Replication
a
b
c
d
e
a
b
c
d
e
Luma (Y)
-
sample
a-2 a-1
a
b
c
d
e
Active line
a
b
c
d
e
Luma (Y)
-
sample
n - 4 n - 3 n - 2
Active line
n - 4 n - 3 n - 2
Chroma (Cb/Cr)
-
samples
XSIZE
n-4 n-3 n-2
n-1 n
n-4 n-3 n-2
n-1 n n+1 n+2 n+3
Trailing edge replicated pixels
Chroma (Cb/Cr)
-
samples
www.ti.com
n - 1
n
EAV
n - 1
n
n - 1 n - 2 n - 3
Trailing edge replicated pixels
n+1 n+2 n+3
n+4
EAV
SPRUEM1 – May 2007
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