User guide

January 2013 Altera Corporation Video and Image Processing Suite
User Guide
8. Chroma Resampler MegaCore Function
Chroma Resampler
The Chroma Resampler MegaCore function resamples video data to and from
common sampling formats. The human eye is more sensitive to brightness than tone.
Taking advantage of this characteristic, video transmitted in the Y’CbCr color space
often subsamples the color components (Cb and Cr) to save on data bandwidth.
Functional Description
The Chroma Resampler MegaCore function allows you to change between 4:4:4, 4:2:2
and 4:2:0 sampling rates where:
■ 4:4:4 specifies full resolution in planes 1, 2, and 3
■ 4:2:2 specifies full resolution in plane 1; half width resolution in planes 2 and 3
■ 4:2:0 specifies full resolution in plane 1; half width and height resolution in planes
2 and 3
All modes of the Chroma Resampler assume the chrominance (chroma) and
luminance (luma) samples are co-sited (that is, their values are sampled at the same
time). The horizontal resampling process supports nearest-neighbor and filtered
algorithms. The vertical resampling process only supports the nearest-neighbor
algorithm.
The Chroma Resampler MegaCore function can be configured to change image size at
run time using control packets.
Horizontal Resampling (4:2:2)
Figure 8–1 shows the location of samples in a co-sited 4:2:2 image.
Conversion from sampling rate 4:4:4 to 4:2:2 and back are scaling operations on the
chroma channels. This means that these operations are affected by some of the same
issues as the Scaler MegaCore function. However, because the scaling ratio is fixed as
2× up or 2× down, the Chroma Resampler MegaCore function is highly optimized for
these cases.
Figure 8–1. Resampling 4.4.4 to a 4.2.2 Image
1234
1
2
Sample No 567
8
+
+
+
+
+
+
+
+
3
4
= Y’
+
= Cb
+
= Cr
+
+
= CbCr
+
+
= Y’CbCr
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+