Quantization based on statistics and threshold of luminanceand chrominance

摘要

Embodiments are directed towards modifying a quality of an image without affecting a bit rate associated with a video sequence of images. For each macro-block (MB) or sub-block within a MB for a target image to be encoded, various statistics are determined for a luminance component and chrominance components that provide at least average values for the chrominance components that may then be used to identify saturation thresholds. The saturation thresholds are used to determine a Qlevel. An average Qlevel from at least a previous frame is used to generate a Q modulation factor that may be combined with an activity based modulation factor and/or variance based modulation factor, or used singly. The final quantizer is calculated by bit-rate controller base quantizer multiplied by the Q modulation factor, and may be used to encode a MB or sub-block within a MB.

主权项

1. A processor based method, comprising:
for each macro-block (MB) or sub-block within each MB of a target frame to be encoded, executing instructions within a processor to perform actions, including:
determining statistics based on a luminance component and statistics based on one or more complementary chrominance components, the one or more complementary chrominance components each being based on a difference between a color component and the luminance component;determining at least one saturation threshold using values of the one or more complementary chrominance components, the at least one saturation threshold identifying a condition in which luminance saturation or chrominance saturation occurs;determining a quantization level (Qlevel) based on the at least one saturation threshold and the statistics based on the luminance component;calculating a quantizer modulation factor for the MB or sub-block within the MB by combining the Qlevel with an average Qlevel of a previous frame already encoded;calculating a final quantizer using a base quantizer and the calculated quantizer modulation factor;encoding the MB or sub-block within the MB using at least the final quantizer; andstoring the encoded MB or sub-block within the MB as a bitstream on a storage device or transmitting the encoded MB or sub-block within the MB over a network as a bit-stream;wherein determining the statistics comprises determining an average and a variance of the luminance component within a given MB or sub-block, and an average and a variance of each complementary chrominance component within the given MB or sub-block.