Google Inc.

Linfeng Zhang

Yaowu Xu

Jingning Han

Ching-Han Chiang

James Zern

An encoded bitstream is decodable by a processor configured to execute instructions to store, in a first line buffer, first values of a first scan-order diagonal line scanned immediately before a current scan-order diagonal line of a transform block; and store, in a second line buffer, second values of a second scan-order diagonal line scanned immediately before the first scan-order diagonal line. The first values of the first line buffer and the second values of the second line buffer are interleaved in a destination buffer. Using the destination buffer, a probability distribution is selected for coding a current value of the current scan-order diagonal line. The current value is entropy decoded from the bitstream using the probability distribution. One of the second line buffer or the first line buffer is replaced with current values of the current scan-order diagonal line for coding values of an immediately subsequent scan-order diagonal line.

Efficient context model computation design in transform coefficient coding

A transform type is obtained for decoding the transform block of transform coefficients. A template for entropy-decoding values related to the transform coefficients is selected based on the transform type. The template indicates, for a to-be-coded value, positions of already coded values. A context for selecting a probability distribution for entropy decoding a current value of the values is determined using the template. The current value is entropy decoded from a compressed bitstream using the probability distribution.

A processor is configured to maintain, for encoding current values related to the transform coefficients a first line buffer and a second line buffer. The current values are arranged along a current scan-order anti-diagonal line. The first line buffer includes first values of a first scan-order anti-diagonal line. The second line buffer includes second values of a second scan-order anti-diagonal line. The processor is further configured to interleave the first values and the second values in a destination buffer; select, using the destination buffer, a probability distribution for coding a current value of the current values; entropy encode, in a compressed bitstream, the current value using the probability distribution; and replace, for coding values of an immediately subsequent scan-order anti-diagonal line to the current scan-order anti-diagonal line, one of the second line buffer or the first line buffer with the current scan-order anti-diagonal line.

A memory of an apparatus includes instructions executable by a processor to select a backward scan order for traversing, along scan-order anti-diagonal lines, a block of values related to the transform coefficients; select a template for entropy-coding the values, the template indicating, for a to-be-coded value, scan positions of already coded values, the scan positions arranged in at least two template anti-diagonal lines; maintain, for coding first values, where the first values are arranged along a current scan-order anti-diagonal line, a first line buffer and a second line buffer; for a current value of the current scan-order anti-diagonal line, determine a context using the first line buffer and the second line buffer, and entropy encode, in a compressed bitstream, the current value using the context; and replace one of the second line buffer or the first line buffer with the current scan-order anti-diagonal line.

Coding a transform block using level maps is disclosed. A method includes determining a lower plane of values, processing the lower plane in a backward scan order, and selecting a template for entropy-coding the values of the lower plane. The method also includes, for a current value of the lower plane, selecting, based on the template anti-diagonal lines, two or more line buffers, each of the two or more line buffers corresponding to a respective scan-order anti-diagonal line, determining a context using the two or more line buffers, and entropy encoding the current value using the context. Each value is a respective 'up-to' value of a transform coefficient. The backward scan order visits the values of the lower plane along scan-order anti-diagonal lines. The template indicates scan positions of coded values of the lower plane, the scan positions are arranged, in the template, along template anti-diagonal lines.

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Palo Alto, CA, United States of America

Linfeng Zhang