On 09/15/2014 06:33 PM, marti.ma...@littlecms.com wrote: > > Hi, > >> So it's not a platform difference, but a rounding error that affects >> all platforms? For 8-bit editing, the error makes no difference. But >> for 16-bit editing, 0.0003162277 times 65535 is 20.7240. So it looks >> like at 16-bit integer, errors up to nearly 21 can be expected when >> converting zero and near-zero channel values between different ICC >> profiles, yes? > > No, 16 bit have 16 bit of precision, 32 bit floating point have 7 digit > precision and a wide domain, that is, you have +/-0.000001 but you also > have the exponent. The range is huge and this is useful for things like > raw photo where intensity varies broadly, and also have the negative > numbers. But still, 16 bits gives you 1/65535 which is 0.00001 and just > one order of magnitude below. If you want to go always from 0 to 1.0 > with no negatives and no highlights, maybe 16 bits is more adequate. On > float you can have an epsilon of +-0.000001 and this means zero can be > slightly negative. > > I did some investigation on how to better the float precision. I think > it can be done in some cases, for example in transforms holding only > matrix to matrix, both matrices can be multiplied and this would avoid > the quantization in the middle.
That would be wonderful! The same matrix-to-matrix multiplication could also be used at 16-bit integer? > This would greatly enhance some kind of > transforms, but still the main problem is in CLUT based transforms which > involves profile elements using floating point extension. This is quite > uncommon as per today. > > In November, at DevCon we at the ICC are going to announce iccMAX, what > would correspond to ICC V5. This new spec will handle floating point > area more in depth. Right now in V4 is a sort of experimental thing that > IMHO is not very well solved. The degree lcms will support iccMAX is > still an unknown. > > http://www.color.org/DevCon/ Hmm, iccMAX sounds interesting - all kinds of new stuff handled by ICC profiles. > > > But of course those are long term plans. > > Best regards > Marti > Best regards, Elle ------------------------------------------------------------------------------ Want excitement? Manually upgrade your production database. When you want reliability, choose Perforce. Perforce version control. Predictably reliable. http://pubads.g.doubleclick.net/gampad/clk?id=157508191&iu=/4140/ostg.clktrk _______________________________________________ Lcms-user mailing list Lcms-user@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/lcms-user
