Image Encoding Apparatus Using Variable-Length Quantization and Bit Recovery
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Solution Overview
Problem
Existing image encoding methods, such as DCT-based methods like JPEG and MPEG2, are unsuitable for high-speed image processing due to high circuit speed requirements and result in significant image quality drops when dealing with complex images like steep edges, as they require large quantization steps to maintain edge components.
Innovation Solution
An image encoding apparatus that encodes blocks of pixels into fixed-length data by performing variable-length encoding and quantization, analyzing pixel importance, and strategically storing loss bits in free regions based on pixel importance, to minimize image quality degradation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a large quantization step is used for the entire pixel block to maintain edge components, then edge preservation is improved, but image quality deteriorates due to loss of detailed information
Solution Approach 1:
The patent applies local quality by differentiating quantization steps across different regions of the pixel block. Specifically, it uses a first quantization step for edge components and a second quantization step for non-edge components, where the first quantization step is larger than the second. This allows edge components to be preserved with larger quantization steps while maintaining image quality in non-edge regions with smaller quantization steps, thereby resolving the contradiction between edge preservation and image quality.
2Productivity
If variable-length encoding is used to adapt to image content, then encoding efficiency is improved, but output data length becomes variable requiring padding to achieve fixed length
Solution Approach 1:
The patent applies discarding and recovering by intentionally discarding certain bits during encoding (using a discarding coefficient to determine which bits to discard) and then recovering them through strategic allocation in the output data structure. The variable-length encoded data is padded with discarded bits to achieve fixed length, and the decoding process recovers the original data by removing the padding. This approach maintains encoding efficiency while managing the fixed-length requirement through controlled bit discarding and recovery.
3Speed
If complex images with steep edges are encoded using fixed quantization steps, then encoding speed is improved, but image quality drops due to excessive quantization of detailed regions
Solution Approach 1:
The patent applies dynamics by making the quantization step dynamic rather than fixed. It calculates edge components for each pixel block and adjusts the quantization step accordingly: using a first (larger) quantization step for edge components and a second (smaller) quantization step for non-edge components. This dynamic adjustment allows the encoding process to adapt to local image characteristics, maintaining encoding speed while preserving image quality in detailed regions.
Data Source
AI summary
An encoding apparatus comprises an acquiring unit that acquires image, a divider that divides the image into blocks, and an encoding processor that encodes a block. The encoding processor includes a variable-length encoder that performs quantization on each of pixels in a block so that a code length is no greater than the fixed length, and performs variable-length encoding on quantized block; a determiner that, based on a difference between the code length and the fixed length, determines a size of a free region for filling the fixed length; an analyzer that analyzes each of the pixels and calculates an index value indicating an importance; and a multiplexer that, based on the index values, multiplexes the encoded block data and the bits lost due to the quantization to generate the fixed-length encoded block data.