JPEG Image Compression Using Predicted DC Coefficients
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Solution Overview
Problem
High memory requirements and increased file size of JPEG images due to block-based compression, which is burdensome for systems with limited resources and storage in social networking and cloud services.
Innovation Solution
An apparatus and method that estimates a quantized DC coefficient of a target block using AC coefficients and pixel values of adjacent decoded blocks, reducing file size through Huffman encoding of estimation error values.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If block-based compression is used for JPEG images, then compression efficiency is improved, but encoded file size increases
Solution Approach 1:
The patent changes the encoding parameter from directly encoding the quantized DC coefficient to encoding the prediction error (difference between actual and predicted DC coefficient). This parameter transformation reduces the encoded file size because the prediction error is typically smaller in magnitude and requires fewer bits to represent, while maintaining compression efficiency through the predictive coding approach
Solution Approach 2:
The patent performs preliminary prediction of the DC coefficient using neighboring block information before the actual encoding step. By predicting the DC coefficient value in advance using spatial correlation from adjacent blocks, the method prepares a reference value that minimizes the subsequent prediction error, thereby reducing the file size of encoded data
2Reliability
If the whole decoded video is stored in memory, then playback quality is maintained, but memory requirements increase significantly
Solution Approach 1:
The patent segments the image processing into independent 8x8 blocks that can be decoded and processed separately. Each block's DC coefficient can be predicted using only neighboring block information that has already been decoded, eliminating the need to store the entire decoded image in memory. This block-based segmented approach maintains playback quality while significantly reducing memory requirements
Solution Approach 2:
The patent extracts and utilizes only the necessary neighboring block information (specifically the DC coefficients of adjacent blocks) required for prediction, rather than storing or processing the entire decoded image. This selective extraction of essential data maintains playback quality through accurate DC coefficient prediction while minimizing memory usage by excluding unnecessary data
Data Source
AI summary
An apparatus and method for compressing Joint Photographic Experts Group (JPEG) images estimates a quantized DC coefficient of a target block to be decoded using AC coefficients of the target block and a pixel value of already decoded neighboring block adjacent to the target block, thereby reducing the encoded file size while maintaining the JPEG file format.