Texas Instruments TMS320C64x DSP - Manual (Page 90)

Video Input Filtering
Video Capture Port 3-28 SPRU629
Figure 3–13. 1/2 Scaled Co-Sited Filtering
YCbCr 4:2:2 co-sited
input samples
1/2 scaled co-sited
capture results
Luma (Y)
sample
Y’
h
= (–3Y
e
+ 32Y
g
+ 70Y
h
+ 32Y
i
– 3Y
k
) / 128
–
Chroma (Cb/Cr)
samples
–
a b c d e f g h i j k l
Y’
f
= (–3Y
c
+ 32Y
e
+ 70Y
f
+ 32Y
g
– 3Y
i
) / 128
Cb’
f
= (–1Cb
c
+ 17Cb
e
+ 17Cb
g
– 1Cb
i
) / 32
Cr’
f
= (–1Cr
c
+ 17Cr
e
+ 17Cr
g
– 1Cr
i
) / 32
Figure 3–14. 1/2 Scaled Chrominance Resampled Filtering
Y’
g
= (–3Y
d
+ 32Y
f
+ 70Y
g
+ 32Y
h
–3Y
j
) / 128
Cb’
f
= (–1Cb
c
+ 17Cb
e
+ 17Cb
g
– 1Cb
i
) / 32
Cr’
f
= (–1Cr
c
+ 17Cr
e
+ 17Cr
g
– 1Cr
i
) / 32
YCbCr 4:2:2 co-sited
input samples
1/2 scaled
chroma-resampled
capture results
Luma (Y)
sample
–
Chroma (Cb/Cr)
samples
–
a b c d e f g h i j k l
Note that because input scaling is limited to
½
, true CIF horizontal resolution
is not achieved if the full BT.656 horizontal line (720 pixels) is captured. A CIF
size line can be captured by selecting a 704 pixel-sized window within the
BT.656 line. This window size and location on the line are programmed using
the VCXSTARTn and VCXSTOPn bits.
Note that when
½
scaling is selected, horizontal timing applies to the incoming
data (before scaling). The VCTHRLD value applies to the data written into the
FIFO after scaling.