Just for giggles, I modified Firefoxes qcms's lcms-compare program, that benchmarks little cms against qcms, to also benchmark Argyll's imdi code. qcms seems to have optimized intel sse3 code to do matrix shaper RGB->RGB conversions, and its speed advantage over lcms was justified as one reason for removing lcms from Firefox and replacing it with qcms. (The other reason was the spurious claim that lcms had security issues.) The test converts just over 16 million 8 bits per sample RGB pixels (ie. a 256 * 256 * 256 * 3 grid), and I used the sRGB profile as the source and destination. I'm running this on an intel MacBook with OS X. The last 1.xx version of lcms was used (I'm not sure if 2.xx of lcms is likely to be faster). The results I got were: lcms 267 argyll 65 qcms 32 So qcms is about twice as fast as Argyll's imdi, but note that Argyll is doing a completely general tetrahedral transform written in portable C code, vs. qcms's processor specific, matrix only transform code, so I'm not too disappointed with this (a 64 bit compile of Argyll's imdi may go faster again too, as might lcms.) Then I tested cLUT versions of the sRGB profile: lcms 301 argyll 69 qcms n/a qcms refused to work ! So not only does it not support ICC V4 profiles as lcms does, it can't actually handle a normal range of ICC V2 RGB profiles (in fact it crashed, which may mean that there is a bug in rejecting profiles it doesn't like.) Graeme Gill.