Coefficient Coding Method, Encoder, Decoder, and Method for Transmitting Bitstream High Bit Depth Video Coding with Reversed Last-Significant-Coefficient Position

This patent covers a coefficient coding technique for video compression in which the position of the last non-zero transform coefficient inside a block can be signalled in reverse, measured from the lower-right corner of the block, with the choice controlled by a sequence-level flag tied to high-bit-depth and high-quality content.

The Problem

In every modern video codec, each block of pixels is transformed (typically by an integer DCT or DST), quantised, and entropy-coded as a stream of integer transform coefficients. To save bits, encoders only transmit coefficients up to the position of the last non-zero (significant) coefficient in a scanning order; everything after that is implicitly zero. The position of that last significant coefficient is signalled by its X and Y coordinates inside the block, encoded as a prefix and an optional suffix. For ordinary low-bit-depth content, most of the energy concentrates near the top-left of the block, so writing the coordinate from the top-left is efficient. But for the new generation of “triple-high” content (high bit depth, high quality, high bitrate, including lossless), the distribution of significant coefficients changes. Many more coefficients are significant, and the last one is much closer to the lower-right corner. Encoding that distant position with a prefix-and-suffix scheme designed for the small-coordinate case wastes bits and slows entropy coding throughput.

What This Invention Does

The invention provides a coefficient coding method, encoder, decoder, and bitstream that introduce a last-significant-coefficient position-reverse flag and a sequence-level flag controlling its use. At the sequence header, the encoder signals whether the video meets a preset condition (high bit depth, high quality, high bitrate, high frame rate, or lossless). When the flag is set, each block can additionally signal a reverse flag. When the reverse flag is set, the coordinates of the last significant coefficient are measured as horizontal and vertical distances from the lower-right corner of the block instead of the top-left. The decoder reconstructs the actual position with the formula LastSignificantCoeffX = (1 << log2ZoTbWidth) - 1 - LastSignificantCoeffX (and the same for Y). All coefficients up to that position are then decoded in the preset scanning order to recover the block. The patent claims the decoder method, the matching encoder method, the bitstream that carries the flags, and a non-transitory storage medium storing a program and bitstream.

Key Features

• Reverse-position signalling for last-significant coefficient. A single flag per block lets the encoder choose to express the last-significant-coefficient position as a distance from the lower-right corner of the block, which is shorter to encode when significant coefficients fill most of the block.
• Sequence-level gating. The reverse mode is enabled only when a sequence-level flag indicates that the video is high bit depth, high quality, high bitrate, high frame rate, or lossless, avoiding any cost in conventional content.
• Prefix-plus-suffix coordinate model. The coordinate is still expressed using a Golomb-Rice-style prefix and an optional suffix, but with the reverse option folded in via a single subtraction, keeping the entropy path simple to implement in hardware.
• Throughput improvement claim. The patent expressly targets throughput and coding speed, not only compression efficiency, which is the operative measure for real-time codec ASICs in professional cameras and post-production workflows.
• Codec-pool-style claim form. The patent covers a decoder method, an encoder method, a bitstream, and a non-transitory computer-readable storage medium storing the program and bitstream, the claim set standards bodies require for inclusion in a codec patent pool.

Who Is Behind It?

The applicant is Guangdong Oppo Mobile Telecommunications Corp., Ltd., the Dongguan-based smartphone and consumer electronics manufacturer that is an active participant in the JVET video coding standardisation work. The named inventors are Fan Wang and Zhihuang Xie. The Australian patent attorney is Spruson and Ferguson in Sydney. The application is a divisional of AU 2021440177, which is the national phase of PCT/CN2021/086710 filed 12 April 2021.

Why It Matters

The next-generation video coding standards under development by JVET and the Alliance for Open Media (AOMedia) are explicitly being designed to handle professional and consumer content beyond standard 8-bit HD, including 10-bit and 12-bit colour, HDR, high frame rate, and visually lossless or mathematically lossless modes. Smartphone makers like Oppo are simultaneously moving their cameras and screens up that ladder. Holding patents on the bitstream tools that make high-bit-depth coding efficient gives Oppo currency in the cross-licensing arrangements through which video codecs are pooled and royalty rates are set. For Australian post-production houses, broadcasters, OTT services, and consumer device sellers, the practical implication is that any future codec adopted on Australian shores that contains a “reverse last coefficient” tool keyed to a sequence-level high-quality flag may engage this patent and the broader Oppo IP portfolio.

Related Concepts

Last-coefficient signalling is one of many small bitstream tools that distinguish recent codecs like HEVC and VVC from earlier generations such as H.264/AVC, and from the royalty-free AV1 codec developed by the Alliance for Open Media.

Improvements that target throughput at high bit depth and lossless modes are particularly relevant to professional acquisition and post-production cameras, where codec performance is implemented in ASIC hardware and where standards-essential patents on coefficient coding feed into the broader patent pool licensing system that funds codec development.

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AU 2026201849 was published in the Australian Official Journal of Patents on 2 April 2026 and is open for public inspection. Patent applications represent inventions that are sought to be protected and do not necessarily reflect commercially available products.