Image Processing Sub-Sampling for Edge Artifact Reduction
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional image compression methods, such as JPEG, compromise image quality by either deteriorating character images or generating visually unnatural color artifacts at edges due to sub-sampling of color difference components, especially in documents with hatching patterns or halftone images.
Innovation Solution
An apparatus and method that determine the attributes of image areas and apply different sub-sampling processes to color difference components based on these attributes, selecting appropriate sub-sampling methods for each area to optimize compression, thereby improving image quality by avoiding undesirable effects like color clouding and moiré.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If sub-sampling of color difference components is applied to increase compression ratio, then compression ratio is improved, but color difference components deteriorate considerably generating color cloud artifacts at edge portions
Solution Approach 1:
The patent applies different sub-sampling rates to different regions of the image based on their characteristics. Edge portions with high color difference components are processed with lower sub-sampling rates (e.g., 4:2:2 or 4:4:4) to preserve color accuracy, while non-edge areas use higher sub-sampling rates (e.g., 4:1:1) to maximize compression. This local differentiation resolves the contradiction by maintaining color quality where needed while achieving high compression elsewhere.
Solution Approach 2:
The patent segments the image into different regions based on edge detection and color difference component analysis. By dividing the image into edge portions and non-edge portions, the system can apply appropriate sub-sampling strategies to each segment, preventing color cloud artifacts in edge regions while maintaining high compression ratios in non-critical areas.
2Device complexity
If uniform compression processing is applied to entire document image, then processing simplicity is maintained, but image quality deteriorates in specific areas like character regions or edge portions
Solution Approach 1:
The patent implements area attribute determination to identify different regions (character areas, photo areas, edge portions) and applies compression processing tailored to each area's characteristics. This allows high compression ratios in photo areas while maintaining quality in character areas, resolving the contradiction between processing simplicity and image quality preservation.
3Productivity
If conventional sub-sampling methods are applied to hatching patterns or halftone images, then compression ratio is increased, but undesirable effects like tincture change or moiré are generated
Solution Approach 1:
The patent detects hatching patterns and halftone images through area attribute determination and applies appropriate sub-sampling processes specifically suited for these patterns. By identifying the local characteristics of hatching and halftone regions, the system can select compression parameters that maintain pattern integrity and prevent moiré effects while still achieving high compression ratios.
Data Source
AI summary
In an image processing apparatus for encoding image data and a method of controlling the same, whether an attribute of each of a plurality of areas in image data corresponds to an edge in an image based on the image data is determined, and one of a plurality of sub-sampling processes is selected according to the determination for each of the plurality of areas. Note that the plurality of sub-sampling processes can sub-sample color difference components of each of the plurality of areas by different processes. By the sub-sampling process selected as that corresponding to each of the plurality of areas, each of the plurality of areas is sub-sampled to encode the image data.