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Chroma quantization in video coding

專利號
US11659182B2
公開日期
2023-05-23
申請人
Apple Inc.(US CA Cupertino)
發(fā)明人
Alexandros Tourapis; Guy Cote
IPC分類
H04N19/124; H04N19/30; H04N19/70; H04N19/126; H04N19/186; H04N19/157; H04N19/86; H04N19/136; H04N19/13; H04N19/15; H04N19/159; H04N19/51; H04N19/61; H04N19/96; H04N19/172; H04N19/176
技術領域
chroma,qp,offset,luma,qg,offsets,picture,values,coding,qgs
地域: CA CA Cupertino

摘要

A method of signaling additional chroma QP offset values that are specific to quantization groups is provided, in which each quantization group explicitly specifies its own set of chroma QP offset values. Alternatively, a table of possible sets of chroma QP offset values is specified in the header area of the picture, and each quantization group uses an index to select an entry from the table for determining its own set of chroma QP offset values. The quantization group specific chroma QP offset values are then used to determine the chroma QP values for blocks within the quantization group in addition to chroma QP offset values already specified for higher levels of the video coding hierarchy.

說明書

These categorizations could then be used to specify different chroma QP offset sets for the different categories. For example, in some embodiments, the first category 1611 (all flat) is assigned zero or negative QP offsets. In this scenario, a negative chroma QP offset allows for improved chroma quality allocation in those regions, since the improved chroma quality can be more apparent due to the characteristics of all color components. For the second category 1612 (flat luma, high textured color information) a larger, positive, QP offset could be used. In this case, the larger chroma QP allows better control of chroma components so as to not overwhelm the luma components, while some texture masking from the chroma information could still be exploited to guarantee good subjective quality. For the third category 1613 (high textured luma versus flat chroma), some embodiments use a larger negative chroma QP offset to help in guaranteeing slightly better color quality. Some other embodiments use larger positive chroma QP offset to better exploit luma texture masking. For the fourth category 1614 (high texture across all three components), some embodiments use a zero or a positive chroma QP offset to better exploit luma texture masking and to avoid wasting bits for insignificant improvement in chroma subjective quality. It is worth noting that the exact chroma QP offset values assigned to a quantization group is dependent upon the corresponding luma QP values for that quantization group. Different decisions could be made based on subjective or objective quality and bitrate decision mechanisms in other encoders.

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