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Intra-frame coding is adata compression technique used within avideo 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.
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 effectivedelta coding. It is one of the two classes of predictive coding methods invideo coding. Its counterpart is inter-frame prediction which exploits temporal redundancy. Temporally independently coded so-called intra frames use only intra coding. The temporally codedpredicted frames (e.g. MPEG's P- and B-frames) may use intra- as well as inter-frame prediction.
Usually only few of the spatially closest known samples are used for the extrapolation. Formats that operate sample by sample likePortable Network Graphics (PNG) can usually use one of four adjacent pixels (above, above left, above right, left) or some function of them like e.g. their average. Block-based (frequency transform) formats prefill whole blocks with prediction values extrapolated from usually one or two straight lines of pixels that run along their top and left borders.
Inter frame has been specified by theCCITT in 1988–1990 byH.261 for the first time. H.261 was meant for teleconferencing and ISDN telephoning.
Data is usually read from a video camera or a video card in theYCbCr data format (often informally calledYUV for brevity). The coding process varies greatly depending on which type of encoder is used (e.g.,JPEG orH.264), but the most common steps usually include: partitioning intomacroblocks, transformation (e.g., using aDCT orwavelet),quantization andentropy encoding.
It is used in codecs likeProRes: agroup of pictures codec withoutinter frames.
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