US 2023/0147376 A1 · Adaptive Quantization and Dead Zone Modulation

Abstract

Methods are provided for improving the quality and compression factor of compressed images. The methods include determining frequency-band-specific quantization levels on a block-by-block level. This results in an adaptive dead zone, allowing certain blocks to be represented by fewer nonzero elements while other blocks are represented by more nonzero elements. Accordingly, the quality of the encoded image is improved while maintaining or improving the compression ratio. The adaptive quantization level is determined by comparing a post-quantization energy level to a threshold energy criterion for each frequency band within a block. Where the energy threshold criterion is not satisfied via these methods, additional methods can be applied to improve the image quality. The methods described herein allow the effective compression ratio of the image to be adapted on a block-by-block, frequency-sensitive basis in order to more effectively allocate encoded image bits where they will have the most effect on image quality.

Claims26

Dependent claims

A method for encoding an image, the method comprising:

generating, based on a block of pixels of the image, a set of coefficients indicative of image contents of the block of pixels at a plurality of spatial frequencies, wherein each coefficient in the set of coefficients is for a respective spatial frequency in the plurality of spatial frequencies;
scaling the set of coefficients according to a first set of scaling factors to generate a first set of scaled coefficients;
performing an assessment of a plurality of quantization levels, wherein performing the assessment comprises, for each respective quantization level of the plurality of quantization levels:
quantizing a subset of the first set of scaled coefficients according to the respective quantization level to generate a quantized subset of the first set of scaled coefficients, wherein the subset of the first set of scaled coefficients are for spatial frequencies within a first band of spatial frequencies;
and
determining a post-quantization energy of the quantized subset of the first set of scaled coefficients;
generating a scaled and quantized version of the set of coefficients based on the assessment of the plurality of quantization levels;
and
generating an encoded version of the image based on the scaled and quantized version of the set of coefficients.

6 more elements

An article of manufacture including a non-transitory computer-readable medium, having stored thereon program instructions that, upon execution by a computing device, cause the computing device to perform operations comprising:

generating, based on a block of pixels of the image, a set of coefficients indicative of image contents of the block of pixels at a plurality of spatial frequencies, wherein each coefficient in the set of coefficients is for a respective spatial frequency in the plurality of spatial frequencies;
scaling the set of coefficients according to a first set of scaling factors to generate a first set of scaled coefficients;
performing an assessment of a plurality of quantization levels, wherein performing the assessment comprises, for each respective quantization level of the plurality of quantization levels:
quantizing a subset of the first set of scaled coefficients according to the respective quantization level to generate a quantized subset of the first set of scaled coefficients, wherein the subset of the first set of scaled coefficients are for spatial frequencies within a first band of spatial frequencies;
and
determining a post-quantization energy of the quantized subset of the first set of scaled coefficients;
generating a scaled and quantized version of the set of coefficients based on the assessment of the plurality of quantization levels;
and
generating an encoded version of the image based on the scaled and quantized version of the set of coefficients.

6 more elements

Dependencies are inferred from the claim text.

Adaptive Quantization and Dead Zone Modulation

Life of this patent

Adaptive Quantization and Dead Zone Modulation

Life of this patent

Abstract

Claims26