Intra-frame coding is a

data compression In information theory, data compression, source coding, or bit-rate reduction is the process of encoding information using fewer bits than the original representation. Any particular compression is either lossy or lossless. Lossless compressi ...

technique used within a

video Video is an Electronics, electronic medium for the recording, copying, playback, broadcasting, and display of moving picture, moving image, visual Media (communication), media. Video was first developed for mechanical television systems, whi ...

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 effective delta coding. It is one of the two classes of predictive coding methods in

video coding A video coding format (or sometimes video compression format) is a content representation format for storage or transmission of digital video content (such as in a data file or bitstream). It typically uses a standardized video compression algo ...

. 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 A prediction (Latin ''præ-'', "before," and ''dicere'', "to say"), or forecast, is a statement about a future event or data. They are often, but not always, based upon experience or knowledge. There is no universal agreement about the exact ...

s (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 like Portable 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. The term intra-frame coding refers to the fact that the various lossless and

lossy compression In information technology, lossy compression or irreversible compression is the class of data compression methods that uses inexact approximations and partial data discarding to represent the content. These techniques are used to reduce data size ...

techniques are performed relative to information that is contained only within the ''current frame'', and ''not relative'' to any other frame in the video sequence. In other words, no temporal processing is performed outside of the current picture or frame. Non-intra coding techniques are extensions to these basics. It turns out that this block diagram is very similar to that of a JPEG still image video encoder, with only slight implementation detail differences. Inter frame has been specified by the

CCITT The ITU Telecommunication Standardization Sector (ITU-T) is one of the three sectors (divisions or units) of the International Telecommunication Union (ITU). It is responsible for coordinating standards for telecommunications and Information Commu ...

in 1988–1990 by H.261 for the first time. H.261 was meant for teleconferencing and ISDN telephoning.

Coding process

Data is usually read from a video camera or a video card in the

YCbCr YCbCr, Y′CbCr, or Y Pb/Cb Pr/Cr, also written as YCBCR or Y′CBCR, is a family of color spaces used as a part of the color image pipeline in video and digital photography systems. Y′ is the Luma (video), luma component and CB and CR are t ...

data format (often informally called YUV for brevity). The coding process varies greatly depending on which type of encoder is used (e.g.,

JPEG JPEG ( ) is a commonly used method of lossy compression for digital images, particularly for those images produced by digital photography. The degree of compression can be adjusted, allowing a selectable tradeoff between storage size and im ...

or H.264), but the most common steps usually include: partitioning into

macroblock The macroblock is a processing unit in image and video compression formats based on linear block transforms, typically the discrete cosine transform (DCT). A macroblock typically consists of 16×16 samples, and is further subdivided into transform ...

s, transformation (e.g., using a DCT or

wavelet A wavelet is a wave-like oscillation with an amplitude that begins at zero, increases or decreases, and then returns to zero one or more times. Wavelets are termed a "brief oscillation". A taxonomy of wavelets has been established, based on the num ...

), quantization and

entropy encoding In information theory, an entropy coding (or entropy encoding) is any lossless data compression method that attempts to approach the lower bound declared by Shannon's source coding theorem, which states that any lossless data compression method ...

Applications

It is used in codecs like ProRes: a group of pictures codec without inter frames.

External links

* http://www.cs.cf.ac.uk/Dave/Multimedia/node248.html MPEG Video compression {{Computer-stub

Coding process

Applications

See also

External links