The upsampling and downsampling performed during the chroma format conversion is implemented with low pass filters for the interpolation and anti-aliasing.
The chroma resampling function offers a horizontal filter with a maximum of 10 taps and two phases, as well as a vertical filter with a maximum of 10 taps and two phases. For conversions requiring up/down sampling in both horizontal and vertical directions, 2D separable filters are offered.
The number of taps selected must be even (4, 6, 8, or 10). Depending on the conversion type and filter size selected, a subset of the coefficients can be used by setting the unnecessary coefficients to zero.
Each coefficient has 16 bits in 2's complement format: 4 integer bits (one sign bit) and 12 fractional bits. The sign bit is the MSB. For example, a coefficient with a value of 1 is represented with this bit vector
[0001000000000000].
The coefficients should sum to exactly 1 to achieve unity gain. If they sum to less than 1, some loss of dynamic range is observed.