Color Index Map Compression for Screen Content Video
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Solution Overview
Problem
Current video coding standards, such as H.264 and HEVC, are inefficient for encoding screen content videos due to their high bit rate requirements caused by significant non-zero transform coefficients and sharp edges, which are not effectively addressed by existing schemes.
Innovation Solution
A prediction-based approach for compressing the color index map, where each index map is decomposed into a binary map and a sequence of unpredictable indices, allowing for prediction of color indices from neighboring pixels, reducing the need for direct coding and thereby minimizing bit transmission.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If conventional video coding standards (H.264, HEVC) are used to encode screen content video, then the encoding process can be performed with existing infrastructure, but the bit rate becomes excessively high due to sharp edges and significant non-zero transform coefficients
Solution Approach 1:
The patent segments the color index map into multiple prediction modes (e.g., planar prediction, directional prediction, palette prediction) and applies different prediction strategies to different regions of the screen content. This segmentation allows the encoder to handle different types of screen content (natural video regions vs. graphics regions) with appropriate methods, reducing overall bit rate while maintaining quality
Solution Approach 2:
The patent changes the parameter representation by using color index maps instead of direct pixel values, and further transforms the index map into prediction residuals. This parameter transformation enables more efficient compression by exploiting the statistical properties of screen content color distributions and prediction errors
2Productivity
If a multi-stage index prediction scheme is applied to screen content coding, then some compression gain can be achieved, but the scheme does not use a second color index map derived by adding boundary rows and columns, limiting its effectiveness
Solution Approach 1:
The patent performs preliminary actions by constructing boundary rows and columns around the color index map before the main prediction process. These boundary elements are pre-calculated and stored, enabling more accurate prediction for edge pixels and improving overall compression efficiency without significantly increasing computational complexity during the main encoding phase
Solution Approach 2:
The patent introduces an intermediary color index map that serves as a bridge between the original image data and the final compressed representation. This intermediate map allows for multiple prediction stages and facilitates the application of different prediction modes, improving compression while keeping the complexity manageable through structured processing
Data Source
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AI summary
Embodiments are provided for compressing a color index map in video coding applications including screen content images. An embodiment method includes obtaining, at a video codec device, an image block, and generating a color index map comprising a plurality of entries and representing the image block. Each one of the entries is assigned a color index indicating a respective color. The method further includes assigning, in a correct prediction map, a first bit-value for each one of the entries that is predictable by a neighboring entry in the color index map, and a second bit-value for each one of the entries that is unpredictable by any neighboring entry in the color index map. Further, an actual value from the color index map for the each one of the entries that is unpredictable by any neighboring entry is added in a sequence of non-predictable color indices.