Re: MNG decoder performance very bad

Glenn Randers-Pehrson wrote:

> At 07:48 PM 8/14/03 +0200, you wrote:
> >
> >Time (ms)  Function
> >----------------------------------------------
> >1401,371  _filter_paeth (libmng_filter.obj)
>
> Try using the sub filter or "none" filter when compressing your
> images. The Paeth filter is the slowest PNG filter to decompress.

Medical images are continuous-tone images, and their PNG compression
should work best (in terms of ratio) with as many filters as possible.
Although I did not run any experiment, I expect the "none" filter to
give a poor compression, even if it's fast.

I am sorry to realize that the Paeth filter is so slow. Maybe the best
compromise would be an adaptive filter heuristic that involves
(PNG_ALL_FILTERS & ~PNG_FILTER_PAETH). I believe there is no software to
do this, although the modfications in the existing software should be
easy to do.

Of course, the ideal solution would be to optimize the Paeth filter
decoding. Too bad that I don't have any idea how to do it.

Cosmin


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