Adaptive Orthogonal Transform Size Selection for Image Coding
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Solution Overview
Problem
Conventional methods for selecting orthogonal transform sizes in image coding lead to increased coding volume and image quality deterioration due to the excessive selection of 4×4 pixel blocks for character images, which results in conspicuous mosquito noise, while also selecting 4×4 blocks for images with edges like tree branches and leaves, leading to inefficient coding.
Innovation Solution
An image coding method that detects edges and flat portions in blocks, using differential absolute values of adjacent pixels to decide on orthogonal transform sizes, selecting 4×4 pixels for blocks with edges and flat portions and 8×8 pixels for blocks without edges or flat portions, thereby optimizing transform size selection and reducing coding volume.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If orthogonal transform per 4×4 pixels is selected for block images including character images, then mosquito noise is reduced and image quality is improved, but coding volume significantly increases
Solution Approach 1:
The patent applies local quality by making the orthogonal transform size adaptive to local image characteristics. Specifically, it detects edges and flat portions within each block and selects 4×4 transform only for blocks containing both edges and flat portions (typical of character images), while using 8×8 transform for other blocks. This localized adaptation reduces mosquito noise in character regions without unnecessarily increasing coding volume in other regions.
Solution Approach 2:
The patent changes the parameter of orthogonal transform size based on detected image characteristics. By detecting edges and flat portions, the system dynamically adjusts the transform size parameter (4×4 or 8×8) to match the local content, selecting 4×4 for character-like patterns and 8×8 for other patterns, thereby optimizing both quality and coding efficiency.
2Manufacturing precision
If orthogonal transform per 4×4 pixels is selected for images with edges like tree branches and leaves, then edge reproduction is improved, but coding volume increases due to excessive use of 4×4 blocks
Solution Approach 1:
The patent applies local quality by making the orthogonal transform size adaptive to local image characteristics. Specifically, it detects edges and flat portions within each block and selects 4×4 transform only for blocks containing both edges and flat portions (typical of character images), while using 8×8 transform for other blocks. This localized adaptation reduces mosquito noise in character regions without unnecessarily increasing coding volume in other regions.
Solution Approach 2:
The patent changes the parameter of orthogonal transform size based on detected image characteristics. By detecting edges and flat portions, the system dynamically adjusts the transform size parameter (4×4 or 8×8) to match the local content, selecting 4×4 for character-like patterns and 8×8 for other patterns, thereby optimizing both quality and coding efficiency.
Data Source
AI summary
It is decided whether a processing target block includes an edge in accordance with an edge detection result of the processing target block. In the case where the edge is included, it is then detected whether there is a flat portion. It is decided whether the processing target block includes the flat portion in accordance with a flat portion detection result. In the case where the flat portion is included, one of a first group of orthogonal transform sizes is selected. In the case where the edge is not included or the flat portion is not included, one of a second group of orthogonal transform sizes greater than the first group of orthogonal transform sizes is selected.