Sample adaptive offset control
Offset values, such as Sample Adaptive Offset (SAO) values in video coding standards such as the High Efficiency Video Coding standard (HEVC), may be improved by performing calculations and operations that improve the preciseness of these values without materially affecting the signal overhead needed to transmit the more precise values. Such calculations and operations may include applying a quantization factor to a video sample and at least some of its neighbors, comparing the quantized values, and classifying the video sample as a minimum, maximum, or one of various types of edges based on the comparison. Other sample range, offset mode, and/or offset precision parameters may be calculated and transmitted with metadata to improve the precision of offset values.
1. A decoding method, comprising:
extracting a quantization factor and coded pixel values from a coded video stream for derivation of sample adaptive offset (SAO) offset values for coded luma data and for derivation of SAO offset values for coded chroma data,
decoding the coded pixel values to produce reconstructed pixel data,
scaling the reconstructed pixel data by applying the quantization factor to produce scaled pixel values,
rounding the scaled pixel values;
evaluating the rounded pixel values,
classifying a reconstructed pixel at a current location into a category based on the evaluation,
deriving a first SAO offset value for luma data based on the classification,
performing SAO filtering on a luma component of the reconstructed pixel data using the derived first SAO offset value as an input identifying an offset in the SAO filtering operation,
deriving a second SAO offset value for chroma data based on the classification, and
performing SAO filtering on a chroma component of the reconstructed pixel data using the derived second SAO offset value as an input identifying an offset in the SAO filtering operation.
2. The method of claim 1 , wherein the function applied to scaled pixel data is a rounding function.
3. The method of claim 1 , wherein the function applied to scaled pixel data is a floor or ceiling calculation function.
4. The method of claim 1 , wherein rounding scaled pixel values rounds to whole number pixel values.
5. A decoding method, comprising:
extracting a quantization factor and coded pixel values from a coded video stream for derivation of sample adaptive offset (SAO) offset values for coded luma data,
decoding the coded pixel values to produce reconstructed pixel data,
scaling the reconstructed pixel data by applying the quantization factor to produce scaled pixel values,
rounding the scaled pixel values;
evaluating the rounded pixel values,
classifying a reconstructed pixel at a current location into a category based on the evaluation,
deriving an SAO offset value based on the classification, and
performing SAO filtering on a luma component of the reconstructed pixel data sing the derived SAO offset value as an input identifying an offset in the SAO filtering operation.