Intra-frame coding: Difference between revisions

Revision as of 21:40, 12 January 2022

Revision as of 21:49, 12 January 2022

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{{Technical|date=June 2019}}

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'''Intra-frame coding''' is a [[data compression]] technique used within a [[digital video|video]] frame, enabling smaller file sizes and lower bitrates, with little or no loss in quality. Since neighboring pixels within an image are often very similar, rather than storing each pixel independently, the frame image is divided into blocks and the typically minor difference between each pixel can be encoded using fewer bits. It is used in codecs like [[ProRes 422|ProRes]]: a [[group of pictures]] codec without [[inter frame]]s.

Intra-frame prediction exploits spatial redundancy, i.e. correlation among pixels within one frame, by calculating prediction values through extrapolation from already coded pixels for effective [[delta coding]]. It is one of the two classes of predictive coding methods in [[video coding]]. Its counterpart is inter-frame prediction which exploits temporal redundancy. Temporally independently coded so-called intra frames use only intra coding. The temporally coded [[predicted frame]]s (e.g. MPEG's P- and B-frames) may use intra- as well as inter-frame prediction.

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== Coding process ==

Data is usually read from a video camera or a video card in the [[YCbCr]] data format (often informally called [[YUV]] for brevity). The coding process varies greatly depending on which type of encoder is used (e.g., [[JPEG]] or [[H.264/MPEG-4 AVC|H.264]]), but the most common steps usually include: partitioning into [[macroblock]]s, transformation (e.g., using a [[Discrete cosine transform|DCT]] or [[Discrete wavelet transform|wavelet]]), [[Quantization (image processing)|quantization]] and [[entropy encoding]].

== Appplications ==

It is used in codecs like [[ProRes 422|ProRes]]: a [[group of pictures]] codec without [[inter frame]]s.

== See also ==