typedef unsigned char BitContext

Context variable.

Documentation

Context variable. Variables of type BitContext hold a single byte describing how to encode or decode message bits with similar statistical properties. This single byte simultaneously represents the current estimate of the bit probability distribution (which is determined by the frequencies of 1s and 0s already coded with this context) and the confidence in this estimate (which determines how fast the estimate can change.)

A coding program typically allocates hundreds of context variables. Each coding context is initialized to zero before encoding or decoding. Value zero represents equal probabilities for 1s and 0s with a minimal confidence and therefore a maximum adaptation speed. Each message bit is encoded using a coding context determined as a function of previously encoded message bits. The decoder therefore can examine the previously decoded message bits and decode the current bit using the same context as the encoder. This is critical for proper decoding.

Alphabetic index HTML hierarchy of classes or Java


DjVu is a trademark of LizardTech, Inc.
All other products mentioned are registered trademarks or trademarks of their respective companies.