Low-complexity two-dimensional (2D) separable transform design with transpose buffer management

摘要

Methods are provided for reducing the size of a transpose buffer used for computation of a two-dimensional (2D) separable transform. Scaling factors and clip bit widths determined for a particular transpose buffer size and the expected transform sizes are used to reduce the size of the intermediate results of applying the 2D separable transform. The reduced bit widths of the intermediate results may vary across the intermediate results. In some embodiments, the scaling factors and associated clip bit widths may be adapted during encoding.

主权项

1. An apparatus for decoding an encoded video bit stream, the apparatus comprising one or more processors configured to:
entropy decode a block of transform coefficients from the video bit stream; apply a first one-dimensional (1D) inverse transform of a two-dimensional (2D) separable inverse transform to the block of transform coefficients; reduce a bit width of each of a plurality of intermediate results of applying the first 1D inverse transform, wherein a reduced bit width of a first intermediate result and a reduced bit width of a second intermediate result are different, wherein the one or more processors are further configured to reduce the bit width by scaling a bit width of each intermediate result based on a predetermined shift amount; and clipping the scaled bit width of each intermediate result to a predetermined bit width to attain a final bit width, and wherein a final bit width for a first scaled intermediate result is different from a final bit width for a second scaled intermediate result; store the reduced bit width intermediate results in a transpose buffer; and apply a second 1D inverse transform of the 2D separable inverse transform to the reduced bit width intermediate results to recover a block of residual values.