Hello Graeme On 11-Jan-2011, Graeme Gill wrote: > The level of accuracy of the forward (A2B) characterisation of the device > is quite important of course, but it comes down to judging where the > color errors are being introduced. "Bumpiness" in the darker areas, > particularly > near the gamut edges, with a visibility that is heavily influenced by > the B2A grid resolution and black generation curve level, are a hint that > there are black topology problems. Currently, grid point accuracy and maximum > gamut size have priority over the black curve, and it is only the black curve > smoothness that results in B2A table smoothness of K value. So nothing > prevents > sudden transitions in the black level at grid points at the gamut edge, > and the resulting device value interpolations of the B2A table can reveal that > the device value interpolated color is very far from the color of the two grid > points that are being interpolated between. Currently the best that can be > done > is to choose a black generation curve that minimises sudden transitions at the > gamut edges. Ink limits (total and black) may also have an influence. Well, accidentally I found now a terrible trick which allows me to generate profiles with a never seen smothness. I know it may sound a blasphemy and it will hurt purists... the trick is simply using an arbitrarily high level for -r in colprof, eg. -r5. I know the major side effect here is having a generated A2B table which won't follow so precisely the device response anymore, and I could hate that... but I tried such a profile for my plain paper tests made with the "offending" -kx and -r5: I don't see the bumps anymore ! And xicclu now shows a K which is monotonically increasing. I'm perfectly aware of what I'm doing: I'm tricking colprof to think the printer combination has a more smooth and predictable behavior, when actually it's not so. I admit this is somehow "hacking", and I know I'm perhaps lossing precision, but I then generated a profile made with the -r5, -qh and a reasonably well chosen k curve (just reasonably, not paranoically): well, I'm perhaps lossing some dE, but when I saw my pictures and graphs printed out FAITHFULLY and COLORFULLY, without any noticeable error, WHO cares of numbers ??? I'm almost convinced I will use this trick, even if to a lesser extent (r=1.5 or so) for quality paper profiles also, to generate smoother profiles, searching for the best compromise between smothness and precision. So I now wonder (since other people might want to follow this approach more or less at their own "risk") if it could make sense for you to "split" the -r behaviour independently for A2B and B2A tables generarion. So one could still chose precise A2Bx tables (eg -r1 =0.5) and artificially smoothed B2Ax ones (eg -r2 =4 or 5). Couldn't this be at least a first, trivial but functional approach to the profile smoothness problem (I read other people too on this ML discussing this topic) ? /&