Adjusting quantization to preserve non-zero AC coefficients
First Claim
1. In a video encoder, a method comprising:
- identifying one or more AC coefficients of each of plural blocks in a video picture;
identifying a threshold quantization step size, such that the identified one or more AC coefficients of each of the plural blocks are nonzero after quantization according to the threshold quantization step size, wherein identifying comprises determining a smallest AC coefficient and iteratively evaluating the smallest AC coefficient with respect to candidate quantization step sizes until the threshold quantization step size is identified and, for each of the plural blocks, the one or more AC coefficients are the one or more highest amplitude AC coefficients of the block, and wherein determining the smallest AC coefficient comprises determining the smallest AC coefficient of the highest amplitude AC coefficients;
compressing at least a portion of the video picture comprising the plural blocks using the threshold quantization step size; and
outputting results of the compression.
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Accused Products
Abstract
A video encoder identifies one or more AC coefficients of each of plural blocks in the picture. The encoder identifies a threshold quantization step size such that the identified AC coefficient(s) of each of the plural blocks are nonzero after quantization according to the threshold quantization step size. The threshold quantization step size is such that quantization according to the next higher quantization step size would result in at least one of the identified AC coefficient(s) of at least one of the plural blocks being zero. For example, identifying the threshold quantization step size comprises identifying n top AC coefficients in each of four blocks of a macroblock, determining the smallest AC coefficient among the identified n top AC coefficients of the four blocks, and iteratively evaluating the smallest AC coefficient with respect to candidate quantization step sizes until the threshold quantization step size is identified.
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Citations
17 Claims
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1. In a video encoder, a method comprising:
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identifying one or more AC coefficients of each of plural blocks in a video picture; identifying a threshold quantization step size, such that the identified one or more AC coefficients of each of the plural blocks are nonzero after quantization according to the threshold quantization step size, wherein identifying comprises determining a smallest AC coefficient and iteratively evaluating the smallest AC coefficient with respect to candidate quantization step sizes until the threshold quantization step size is identified and, for each of the plural blocks, the one or more AC coefficients are the one or more highest amplitude AC coefficients of the block, and wherein determining the smallest AC coefficient comprises determining the smallest AC coefficient of the highest amplitude AC coefficients; compressing at least a portion of the video picture comprising the plural blocks using the threshold quantization step size; and outputting results of the compression. - View Dependent Claims (2, 3, 4, 5)
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6. In a video encoder, a method comprising:
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identifying one or more AC coefficients of each of plural blocks in a video picture; for a macroblock comprising four blocks of the plural blocks, identifying a threshold quantization step size for the macroblock such that, for each the four blocks of the macroblock, the identified one or more AC coefficients of each of the plural blocks are nonzero after quantization according to the threshold quantization step size; and compressing the macroblock using the threshold quantization step size for the macroblock; and outputting results of the compression; wherein the identifying the threshold quantization step size comprises; determining an AC coefficient count n, where n is an integer greater than or equal to 1; identifying n highest amplitude AC coefficients in each of the four blocks of the macroblock; determining the smallest AC coefficient among the identified n highest amplitude AC coefficients of the four blocks. - View Dependent Claims (7, 8, 9, 10, 11)
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12. In a video encoder, a method comprising:
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identifying a smooth region of a video picture; for a portion of the smooth region, selecting a threshold quantization step size so as to preserve a gradient across the smooth region by retaining one or more AC coefficients for the portion that would otherwise be quantized to zero according to a next higher quantization step size, wherein the one or more AC coefficients for the portion include the n highest amplitude AC coefficients of each of plural blocks in the portion, where n is an integer greater than or equal to 1; compressing the portion using the threshold quantization step size; and outputting results of the compressing; wherein selecting further comprises determining a smallest AC coefficient of the n highest amplitude AC coefficients and iteratively evaluating the smallest AC coefficient with respect to candidate quantization step sizes until the threshold quantization step size is selected. - View Dependent Claims (13, 14, 15, 16, 17)
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Specification