This module computes the bit rate (bit per pixel) needed to encode
the input fimage that is, to perform lossless compression on it\index{coding!image}.

Several algorithms are considered, and the bit rate returned by the 
function is the best bit rate over all the following algorithms :
entropy coding, arithmetic coding, predictive arithmetic coding.

See the module \verb+arencode2+ for more information on the arithmetic
coding algorithms.

