Escape Pixel Coding in Palette Video Compression
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Solution Overview
Problem
Traditional video coding techniques are inefficient for compressing screen content with discrete-tone characteristics, such as text or computer graphics, as they assume continuous-tone and smooth images, leading to suboptimal compression performance.
Innovation Solution
The use of palette-based coding techniques, where a palette of dominant pixel values represents a block of video data, with escape pixels encoded using a combination of Golomb rice and exponential Golomb coding with parameter 3, allowing for efficient encoding and decoding of screen content.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If traditional video coding techniques are used for screen content, then continuous-tone image assumptions are applied, but compression efficiency deteriorates due to discrete-tone characteristics
Solution Approach 1:
The patent changes the fundamental parameter assumption from continuous-tone to discrete-tone image characteristics. It introduces a palette-based coding approach where pixel values are represented as indices into a discrete palette table, fundamentally altering how screen content is parameterized and encoded to match its discrete nature rather than treating it as continuous-tone.
Solution Approach 2:
The patent applies different coding strategies to different pixel types within the same block. Escape pixels (those not representable by the palette) are coded differently from palette-indexed pixels. This local differentiation allows the encoder to adapt to the specific characteristics of each pixel, improving overall compression efficiency for discrete-tone content.
2Measurement precision
If escape pixels are coded using traditional methods, then encoding complexity increases due to encoder-dependent parameters and division operations, but decoding accuracy may be compromised
Solution Approach 1:
The patent extracts the maximum quantized escape pixel value as a separate syntax element that is explicitly coded and transmitted in the bitstream. By taking out this critical parameter and encoding it directly rather than deriving it through complex encoder-dependent calculations, the patent ensures the decoder receives the exact value needed for accurate reconstruction without requiring complex encoding operations.
Solution Approach 2:
The patent uses Golomb-Rice coding, a simple and computationally inexpensive entropy coding method, for encoding escape pixel values. This disposable coding approach prioritizes decoding speed and simplicity over highly optimized encoding, allowing rapid decoding with minimal computational resources while maintaining accuracy.
Data Source
AI summary
In one example, a device includes a memory configured to store video data and a video decoder configured to decode an exponential Golomb codeword representative of at least a portion of a value for an escape pixel of a palette-mode coded block of video data, the video decoder is configured to decode the exponential Golomb codeword using exponential Golomb with parameter 3 decoding, and decode the block using the value for the escape pixel.