Texas Instruments TMS320C64x DSP Benutzerhandbuch
Video Input Filtering
3-27
Video Capture Port
SPRU629
3.5.2
Chrominance Resampling Operation
Chrominance resampling computes chrominance values at sample points
midway between the input luminance samples based on the input co-sited
chrominance samples. This filter performs the horizontal portion of a conver-
sion between YCbCr 4:2:2 format and YCbCr 4:2:0 format. The vertical portion
of the conversion must be performed in software.
midway between the input luminance samples based on the input co-sited
chrominance samples. This filter performs the horizontal portion of a conver-
sion between YCbCr 4:2:2 format and YCbCr 4:2:0 format. The vertical portion
of the conversion must be performed in software.
The chrominance resampling filters calculate the implied value of Cb and Cr
in between luminance sample points based upon nearby co-sited Cb and Cr
samples. The resulting values are clamped to between 01h and FEh and sent
to the Cb and Cr capture buffers. Chrominance resampling is shown in
Figure 3–12.
in between luminance sample points based upon nearby co-sited Cb and Cr
samples. The resulting values are clamped to between 01h and FEh and sent
to the Cb and Cr capture buffers. Chrominance resampling is shown in
Figure 3–12.
Figure 3–12. Chrominance Resampling
YCbCr 4:2:2 co-sited
input samples
chroma-resampled
capture results
Luma (Y)
sample
sample
–
Chroma (Cb/Cr)
samples
samples
a
b
c
d
e
f
g
h
i
j
k
l
Cb’
ef
= (–3Cb
c
+ 101Cb
e
+ 33Cb
g
–3Cb
i
) / 128
Cr’
ef
= (–3Cr
c
+ 101Cr
e
+ 33Cr
g
– 3Cr
i
) / 128
3.5.3
Scaling Operation
The
½
-scaling mode is used to reduce the horizontal resolution of captured
luminance and chrominance data by a factor of two. For applications that
require only CIF or lower resolutions, this reduces the video capture buffer
memory requirements (and the bandwidth needed to write the buffer) by a
factor of two. Vertical scaling must be performed in software. (The bandwidth
to load in the buffer is again reduced by 50% over the nonhorizontal scaled
case.)
require only CIF or lower resolutions, this reduces the video capture buffer
memory requirements (and the bandwidth needed to write the buffer) by a
factor of two. Vertical scaling must be performed in software. (The bandwidth
to load in the buffer is again reduced by 50% over the nonhorizontal scaled
case.)
The filtering for the luminance portion of the scaling filter changes depending
on if chrominance resampling is also enabled. (By changing the luminance filter,
the chrominance filters can remain the same.) The resulting values are
clamped to between 01h and FEh and sent to the Y, Cb, and Cr capture buffers.
Scaling for co-sited capture is shown in Figure 3–13 and scaling for chromi-
nance resampling is shown in Figure 3–14.
on if chrominance resampling is also enabled. (By changing the luminance filter,
the chrominance filters can remain the same.) The resulting values are
clamped to between 01h and FEh and sent to the Y, Cb, and Cr capture buffers.
Scaling for co-sited capture is shown in Figure 3–13 and scaling for chromi-
nance resampling is shown in Figure 3–14.