kdu_subband::get_conservative_slope_threshold

This function is provided for block encoders to estimate the number of coding passes which they actually need to process, given that many of the coding passes may end up being discarded during rate allocation.

The function returns a conservatively estimated lower bound to the distortion-length slope threshold which will be used by the PCRD-opt algorithm during final rate allocation (usually inside kdu_codestream::flush). The coder is responsible for translating this into an estimate of the number of coding passes which must be processed. The function returns 1 if there is no information available on which to base estimates — such information will be available only if kdu_codestream::set_max_bytes or kdu_codestream::set_min_slope_threshold has been called.