*From*: Roberto Michelena <colorsync@xxxxxxxxx>*To*: argyllcms@xxxxxxxxxxxxx*Date*: Fri, 4 Nov 2005 10:06:24 -0500

Graeme, Let me ask this which has been floating on my mind for some time: When you do a reverse interpolation (as in your -G option), will it be 100% coincident with it's corresponding forward one? In other words, Lab->CMYK->L'a'b will result in perfect match between Lab and L'a'b when both are made from the same table (A2B), using the reverse mapping method as in "-G" option? To put it in perspective (why is it important): Take a pair of devices and their measurements, e.g. Press and Proofer. You get two profiles, ICCPress and ICCProof with also contain the measurements (albeit smoothed) in their A2B tables. Make a link via standard method, abscol; ICCLink1 Make a link via -G method, abscol; ICCLink2 process a set of arbitrary CMYKpress source values through ICCLink1 and you get CMYKproof1 process the same set through ICCLink2 and you get CMYKproof2 Now process CMYKProof1 through ICCProof A2B and you get LabProof1 Do the same with CMYKProof2 and you get LabProof2 Process CMYKpress through ICCPress A2B and you get LabPress comparing LabProof1 to LabPress, and LabProof2 to LabPress, should yield a closer match for LabProof2, right? this would indicate the reverse interpolation (-G) is more precise than the double interpolation incurred when building B2A and then linking to it. (it'd be interesting to see this numbers!) The question is, will LabProof2 be an exact match to LabPress? in other words, the reverse interpolation is mathematically coincident with the forward one? Because if not, the link created by -G (ICCLink2) could still be improved by pure mathematical iteration (function to optimize: deviation from LabPress) without the need of reprinting targets. I mean, we are always assuming (and I believe it's a fine assumption) that the prediction of LabPress and LabProof given by interpolation on their respective A2B tables is the most exact tool we have. Not that it's exact, but it is more accurate than all other tables and interpolations we use. So if we make these match in a link, that link would be as accurate as one can get without further printing, right? -- Roberto Michelena

- » [argyllcms] interpolation reversibility
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