Video Port/VCXO Interpolated Control (VIC) Port User's Guide

www.ti.com
4.4.2 Chrominance Re-sampling Operation
YCbCr 4:2:2 interspersed
source pixels
YCbCr 4:2:2 co-sited
output results
Luma (Y)
sample
Cb’
f
= (-3Cb
ab
+ 33Cb
cd
+ 101Cb
ef
- 3Cb
gh
) / 128
Cr’
f
= (-3Cr
ab
+ 33Cr
cd
+ 101Cr
ef
- 3Cr
gh
) / 128
Chroma (Cb/Cr)
samples
-
a b c d e f g h i j k l
-
4.4.3 Scaling Operation
2× upscaled output
YCbCr 4:2:2 co-sited
source pixels
Luma (Y)
sample
Y’
d’
= (-1Y
c
+ 17Y
d
+ 17Y
e
- 1Y
f
) / 32
Cb’
d
= (-1Cb
a
+ 17Cb
c
+ 17Cb
e
- 1Cb
g
) / 32
Cr’
d
= (-1Cr
a
+ 17Cr
c
+ 17Cr
e
- 1Cr
g
) / 32
-
Chroma (Cb/Cr)
samples
-
a a’ b b’ c c’ d d’ e e’ f f’
a b c d e f g
g
Cr’
c
= Cr
c
Cb’
c
= Cb
c
Y’
b
= Y
b
Video Output Filtering
Chrominance re-sampling computes chrominance values at sample points corresponding to output
luminance samples based on the input interspersed chrominance samples. This filter performs the
conversion between interspersed YCbCr 4:2:2 format and co-sited YCbCr 4:2:2 format. The vertical
portion of the conversion from YCbCr 4:2:0 to interspersed YCbCr 4:2:2 must be performed in software.
The chrominance re-sampling filters calculate the implied value of Cb and Cr co-sited with luminance
sample points based upon nearby interspersed Cb and Cr samples. The resulting values are clamped to
between 01h and FEh before being output. Chrominance re-sampling is shown in Figure 4-15 .
Figure 4-15. Chrominance Re-sampling
The 2x -scaling mode is used to double the horizontal resolution of output luminance and chrominance
data. This allows processed CIF resolution images to be output at full size. Vertical scaling must be
performed in software. Scaling for co-sited source is shown in Figure 4-16 and scaling for interspersed
source is shown in Figure 4-17 .
For a co-sited source, the source luminance pixels are output unchanged for every even pixel (a, b, c,
etc., in Figure 4-16 ). Odd luminance pixels (a', b', c', etc.) are generated from neighboring source (even)
pixels using a four tap filter. The chrominance source pixels are output unchanged for every other even
pixel (a, c, e, etc.). Other even output pixel (b, d, f, etc.) chrominance values are generated from
neighboring source chrominance pixels using a four tap filter.
For an interspersed source, the luminance is output identically to the co-sited case. Chrominance output is
generated using a four tap filter with one of two different coefficient sets depending on which source
chrominance pixel the output pixel is closest.
Note that because input scaling is limited to 2x, full BT.656 width output is not achieved from CIF source
images. The horizontal location of the reduced image can be adjusted using HOFFSET.
Figure 4-16. 2x Co-Sited Scaling
104 Video Display Port SPRUEM1 – May 2007
Submit Documentation Feedback