Adaptive B-picture quantization control
First Claim
Patent Images
1. In a video encoder, a method comprising:
- selecting a picture type for a current picture;
using the selected picture type when selecting between multiple available quantizers for the current picture, each of the multiple available quantizers having a different dead zone ratio, the selected quantizer for the current picture having a larger dead zone ratio, when the selected picture type is a B-picture type, than one or more other quantizers among the multiple available quantizers, wherein a larger dead zone ratio results in larger dead zone regions that each have a size that is a function of a quantization step size (OP) and wherein the size is approximately 0.8* QP on each side of zero for each OP of the selected quantizer;
applying the selected quantizer to the current picture; and
outputting encoded data for the current picture.
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Abstract
The present application is directed to techniques and tools for adapting the quantizer as well as the quantization step size used during video encoding. For example, a video encoder uses a non-uniform quantizer (having a relatively large dead zone ratio) for B-picture types, but uses a uniform quantizer for other types of pictures. In many encoding scenarios, this helps the encoder control bit rate for the B-picture types instead of resorting to higher quantization step sizes, which improves overall quality for the B-picture types.
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Citations
16 Claims
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1. In a video encoder, a method comprising:
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selecting a picture type for a current picture; using the selected picture type when selecting between multiple available quantizers for the current picture, each of the multiple available quantizers having a different dead zone ratio, the selected quantizer for the current picture having a larger dead zone ratio, when the selected picture type is a B-picture type, than one or more other quantizers among the multiple available quantizers, wherein a larger dead zone ratio results in larger dead zone regions that each have a size that is a function of a quantization step size (OP) and wherein the size is approximately 0.8* QP on each side of zero for each OP of the selected quantizer; applying the selected quantizer to the current picture; and outputting encoded data for the current picture. - View Dependent Claims (2, 3, 4, 5)
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6. In a video encoder, a method comprising:
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getting a current picture of a video sequence; if the current picture is a P-picture or an I-picture; selecting a uniform quantizer with uniform dead zone for AC coefficients for the current picture; and applying the selected uniform quantizer to the current picture; if the current picture is a B-picture; selecting a non-uniform quantizer with a non-uniform dead zone for AC coefficients for the current picture, wherein the non-uniform dead zone is larger than the uniform dead zone of the uniform quantizers; and applying the selected non-uniform quantizer to the current picture; and outputting encoded data for the current picture. - View Dependent Claims (7, 8, 9)
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10. An encoder comprising:
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a frequency transformer for frequency transforming plural blocks of spatial domain information into plural blocks of transform coefficients; a quantizer for quantizing the transform coefficients; an entropy encoder for entropy encoding the quantized transform coefficients; an inverse quantizer for inverse quantizing the quantized transform coefficients; and a controller for selecting quantizers and quantization step sizes for the quantizing by choosing between plural available quantizers, each of the plural available quantizers having a different dead zone ratio, wherein the controller implements; a first path for increasing dead zone ratio while decreasing quantization step size for a given level of rate-distortion performance; a second path for decreasing dead zone ratio while increasing quantization step size for the given level of rate-distortion performance; and wherein the controller follows the first path if a current picture is a B-picture type and otherwise follows the second path. - View Dependent Claims (11, 12, 13, 14, 15, 16)
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Specification