Implementation - 2.4 English

Video Processing Subsystem Product Guide (PG231)

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2.4 English

Between the three supported sub-sampling formats (4:4:4, 4:2:2, 4:2:0), there are six conversions available. Conversion is achieved using a FIR filter approach. Some require filtering in only the horizontal dimension or in only the vertical dimension, and in some cases in both the horizontal and the vertical dimensions. These are detailed in Table: Chroma Resampling Configuration along with default filter information.

Table 3-4: Chroma Resampling Configuration


Filter Configuration

4:4:4 to 4:2:2

Horizontal anti-aliasing

4:4:4 to 4:2:0

Separable 2-D anti-aliasing

4:2:2 to 4:4:4

Horizontal Interpolation

4:2:2 to 4:2:0

Vertical anti-aliasing

4:2:0 to 4:4:4

Separable 2-D Interpolation

4:2:0 to 4:2:2

Vertical Interpolation

Three implementation options are offered for each conversion operation:

DSP48 based filter with programmable coefficients and programmable number of taps. 2D filters must be separable. Coefficients are in the range [-8, 8), represented in 16-bit signed, fixed-point format with four integer bits and 12 fractional bits.

The predefined fixed coefficient, non-programmable filter with power of two coefficients (using only shifts and additions for filtering therefore no DSP48s are used). Default coefficients implement linear interpolation for the interpolation and anti-aliasing low pass filters.

The simplest, lowest footprint solution is to simply drop (decimation) or replicate (interpolation) samples. For down sampling, some samples are passed directly to the output, but others are dropped entirely as appropriate. For up converters, replication of the previous input sample occurs.