Image and Video Coding
Summary
Digital image and video coding encompasses a suite of algorithmic and standardised techniques to represent visual information in a compact form while preserving perceptual fidelity. In image coding, spatial redundancy is reduced by partitioning frames into blocks or transform units, applying transforms such as the discrete cosine transform (DCT) or discrete wavelet transform to concentrate energy, quantising transform coefficients to discard less significant components and employing entropy coding to remove statistical redundancy. Video coding extends this framework with temporal prediction, using intra-prediction within frames and inter-prediction across frames to exploit motion coherence, followed by residual transform and quantisation. Successive international standards—from JPEG and JPEG 2000 in still images to H.264/AVC, High Efficiency Video Coding (HEVC) and Versatile Video Coding (VVC) in video—have driven bit-rate reductions of up to 50 per cent per generation. Parallel developments in royalty-free formats such as AV1 support open-source deployment. Recent advances address ever higher resolutions, high dynamic range and screen content, balancing compression gains against encoder and decoder complexity and hardware feasibility. Emerging directions include machine-learning-based coding, content-adaptive quantisation and perceptual optimisation for immersive media, streaming, broadcast, remote sensing and low-bandwidth communications globally.
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Image and Video Coding publication trend
The graph below shows the total number of articles in image and video coding across all publications each year (not limited to Nature Index journals).
Technical terms
Discrete Cosine Transform (DCT): A mathematical transform that represents pixel blocks as sums of cosine basis functions to concentrate signal energy for efficient quantisation.
Discrete Sine Transform (DST): A transform akin to the DCT but using sine basis functions, applied in some coding standards for decorrelation and multiple transform selection.
Quantisation: The process of mapping continuous transform coefficients to a finite set of values, permitting lossy compression by discarding low-magnitude information.
Entropy Coding: A lossless step that assigns shorter codes to more probable symbols to remove statistical redundancy.
Group of Pictures (GOP): A sequence of frames including I-frames (intra-coded) and P/B-frames (inter-predicted) that defines the temporal prediction structure in video coding.
Bit-rate: The amount of data transmitted or stored per unit time, typically in kilobits or megabits per second, which directly impacts quality and bandwidth.
References
- The Development of Fast DST-II Algorithms for Short-Length Input Sequences. Electronics (2024).
- Impact of Video Motion Content on HEVC Coding Efficiency. Computers (2024).
- A Technical Overview of AV1. Proceedings of the IEEE (2021).
- Image Coding.
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