Convert 4:4:4 to 4:2:2 - 2.3 English

Video Processing Subsystem Product Guide (PG231)

Document ID
PG231
Release Date
2022-04-27
Version
2.3 English

This conversion is a horizontal 2:1 decimation operation, implemented using a low-pass FIR filter to suppress chroma aliasing. In order to evaluate output pixel ox,y, the FIR filter in the core convolves COEFk_HPHASE0, where k is the coefficient index, ix,y are pixels from the input image, and [ ]Mm     represents rounding with clipping at M, and clamping at m. DW is the Data Width or number of bits per video component. Ntaps is the number of filter taps.

 

Equation 3-11      pg231-designing00020.jpg

 

In phase 0, COEF00_HPHASE0 is the coefficient applied to the most recent input sample in the filter. This Figure illustrates coefficient use for a 5 tap filter example, with simplified nomenclature a= COEF00_HPHASE0, b= COEF01_HPHASE0, c= COEF02_HPHASE0, d=COEF03_HPHASE0, and e= COEF04_HPHASE0.

Figure 3-14:      4:4:4 to 4:2:2 Coefficient Configuration

X-Ref Target - Figure 3-14

coeffconfig2.PNG

The predefined filter coefficients are [0.25 0.5 0.25].