Image Encoding Device Quantization Matrix Selection
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Solution Overview
Problem
The existing image encoding schemes, such as HEVC, suffer from deterioration of subjective image quality when blocks undergo both orthogonal transformation and those that do not, due to variations in quantization roughness across pixels.
Innovation Solution
An image encoding and decoding device that determines whether to apply orthogonal transformation or transformation skip to blocks, using a quantization matrix with equal roughness for all elements on the encoding side, and transmitting a second quantization matrix to the decoding side for blocks that undergo orthogonal transformation, to maintain consistent quantization accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If orthogonal transformation is applied to some blocks but not others, then compression efficiency is improved, but subjective image quality deteriorates due to quantization roughness variations
Solution Approach 1:
The patent applies different quantization matrices to different blocks based on whether orthogonal transformation was applied. Blocks with orthogonal transformation use one quantization matrix while blocks without transformation use another, allowing local optimization of quantization roughness for each block type to maintain consistent visual quality across the entire image
Solution Approach 2:
The patent changes the quantization parameter (quantization matrix) based on the transformation application status. By selecting different quantization matrices for different blocks, the system adjusts the quantization roughness parameter to compensate for the presence or absence of orthogonal transformation, thereby maintaining uniform subjective image quality
Data Source
AI summary
An image coding device is provided with a determination unit which determines whether to apply an orthogonal transform to a transform block obtained by dividing a prediction difference signal indicating a difference between an input image and a predicted image or perform a transform skip by which the orthogonal transform is not applied, and an orthogonal transform unit which performs processing selected on the basis of the determination, the image coding device comprising a quantization unit which, when the transform skip is selected on the basis of the determination, quantizes the transform block using a first quantization matrix in which the quantization roughnesses of all elements previously shared with a decoding side are equal, and when the orthogonal transform is applied to the transform block on the basis of the determination, quantizes the transform block using the first quantization matrix or a second quantization matrix that is transmitted to the decoding side.