vc2_bit_widths.quantisation
: VC-2 Quantisation¶
The vc2_bit_widths.quantisation
module contains an implementation of
VC-2’s quantisation scheme along with functions for analysing its properties.
Quantisation & dequantisation¶
The VC-2 quantisation related pseudocode functions are implemented as follows:
-
forward_quant
(coeff, quant_index)¶ Quantise a value according to the informative description in (13.3.1)
-
inverse_quant
(quantized_coeff, quant_index)¶ Dequantise a value using the normative method in (13.3.1)
-
quant_factor
(index)¶ Compute the quantisation factor for a given quantisation index. (13.3.2)
-
quant_offset
(index)¶ Compute the quantisation offset for a given quantisation index. (13.3.2)
Analysis¶
The following functions compute incidental information about the behaviour of the VC-2 quantisation scheme.
-
maximum_useful_quantisation_index
(value)¶ Compute the smallest quantisation index which quantizes the supplied value to zero. This is considered to be the largest useful quantisation index with respect to this value.
-
maximum_dequantised_magnitude
(value)¶ Find the value with the largest magnitude that the supplied value may be dequantised to for any quantisation index.
See Quantisation and affine arithmetic for a proof of this method.