Image Stream Coding with Constant-Value Prediction for Sharp Transitions
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Solution Overview
Problem
Existing image and video compression techniques, such as HEVC, are not optimal for content with strong discontinuities like screenshots or synthesis images, as they struggle to accurately predict pixel values across transitions.
Innovation Solution
A method that determines a group of constant pixel values within a block and uses these values to predict pixels in transition areas, adjusting the prediction mode based on the distance between the original pixel value and the predicted value, reducing the need for additional information transmission.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional prediction techniques (intra prediction using neighbouring pixels) are used, then natural images can be compressed effectively, but images with strong discontinuities (screenshots, synthesis images) suffer from high prediction error
Solution Approach 1:
The prediction method dynamically adapts between two prediction modes based on image characteristics. The encoder determines which mode to use by evaluating the image content, switching from conventional neighbouring-pixel prediction to constant-value prediction when strong discontinuities are detected, thereby optimizing prediction accuracy for different image types
Solution Approach 2:
The invention changes the prediction parameter approach by introducing a second prediction mode that uses constant values derived from histogram analysis rather than spatial neighbouring pixels. This parameter change allows the system to handle discontinuous images where conventional spatial prediction fails
2Reliability
If a second prediction mode using constant values is introduced, then prediction accuracy for discontinuous images improves, but device complexity increases
Solution Approach 1:
The constant values are determined locally within each block by analyzing the histogram of previously decoded pixels in that specific block. This local analysis avoids the need for complex global image processing while capturing the essential constant characteristics needed for accurate prediction in discontinuous regions
Solution Approach 2:
The system uses already-decoded pixels within the same block to determine the constant values for prediction, making the prediction process self-sufficient without requiring additional external reference data or complex inter-block processing
3Productivity
If prediction modes are selected based on distance threshold, then compression efficiency improves, but information transmission requirements increase
Solution Approach 1:
The encoder calculates the distance between original and predicted pixel values and uses this feedback to determine whether to switch prediction modes. This feedback mechanism allows adaptive selection of the most efficient prediction approach for each pixel, optimizing compression while minimizing unnecessary mode switching information transmission
Data Source
AI summary
A method and device for coding and decoding a coded data stream representative of at least one image split into blocks. For a current block, a group of pixel values in the block is determined from previously decoded pixels, and for each pixel, a prediction residue is decoded. A prediction value for the pixel is determined according to a first prediction mode by predicting the pixel from at least one other previously decoded pixel belonging to the current block. Information is decoded from the stream indicating whether the pixel is predicted according to a second prediction mode using a prediction resulting from the group of pixel values in the block. When the pixel is predicted according the second mode, the prediction value for the pixel is replaced with a selected value of the group. The pixel is reconstructed using the prediction value associated with the pixel and the prediction residue.