[argyllcms] Re: Number of patches - well behaved printer?

  • From: Iliah Borg <ib@xxxxxxxxxxx>
  • To: argyllcms@xxxxxxxxxxxxx
  • Date: Wed, 23 Feb 2011 19:16:34 -0500

Dear Rishi,

> I don't understand how it's not essential to have Dmin & Dmax mapped
> to black & white when shooting a target on film.

Tone curve can't be properly addressed with a profile, and if you are using a 
flatbed scanner or modern pseudo-drums, Dmax is a waste because of flare 
anyway. I shoot film with LF cameras that also flares as hell, so no point in 
either Dmin or Dmax again. However if you bracket as I explained and make a 
composite target you will reach both Dmin and Dmax, as it is with my Leica with 
moderately fast lenses for the scenes that have no more than 9 stops of dynamic 
range and do not have .very light backgrounds. Profiling from a composite 
target allows to reach both Dmin and Dmax; but tone curve still needs to be 
addressed elsewhere as usual.

> When building a
> 'scanner' profile (not a 'camera' profile), 0,0,0 & 255,255,255 (on an
> 8-bit scale) are literally mapped to the darkest and lightest patches
> when I use LPROF to build a profile for my Velvia film using Wolf
> Faust's 35mm targets (288 patches, IT8 chart).

Yes they are, and most often it is done incorrectly. We tried this approach and 
rejected it because of relatively poor results. It is better to add synthetic 
patches in a profiler, or manually add them to the target - either by 
interpolation, or using other considerations.

> Are you not building a
> 'scanner' profile?

Yes, that too.

> I know for 'camera' profiles profiling packages
> don't require the black on the chart to be 0,0,0 from your camera &
> white to be 255,255,255 (in fact, that's really hard to do since
> typically your camera has a much wider dynamic range than that
> possible from imaging a reflective target)

That is why we bracket.

> ... because all it's doing
> is building a 3x3 matrix, no?


> For that matter, how does Wolf Faust even create the IT8 targets on
> positive film?

Using a film recorder, as all such targets are created.

Iliah Borg

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