Intra Coded Pictures

Intra pictures contain all information necessary for representation, there are neither temporal nor spatial references to surrounding pictures. In principle an I-picture is an individually encoded image file, equivalent to the coding of a single picture by means of JPEG.

The I-pictures provide the only possibility to start the decoding within an MPEG data stream. Each individually representable MPEG sequence is introduced inevitably by an I-picture.

The distance between two I-pictures affects considerably the achievable compression rate. The substantial elements, with which MPEG reduces the data volume, are only available with P- or B-pictures. But the access options increase with a larger number of I-pictures.

In dependency on the picture's contents however the intra coding even may be the better option. This applies always, if the contents changes rapidly, e.g. with a cut for a new scene. In such a case, the mechanisms for movement compensation would fail and the difference to the original pictures becomes too large.

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