[argyllcms] Re: Making a composite profile, combining ti3 & colprof -r question

  • From: Graeme Gill <graeme@xxxxxxxxxxxxx>
  • To: argyllcms@xxxxxxxxxxxxx
  • Date: Fri, 13 Jun 2014 09:07:06 +1000

Derin Korman wrote:

> For experimenting, I combined two ti3 files (of two different hutchcolor
> targets), simply grabbing the patch data from one, adding a prefix of a
> letter to patch namez (so V1 becomez ZV1 for example) and pasting them on
> the bottom of the others, and updating patch count to match.

        there is no need to change the patch names, just to get
colprof working. They are just used for diagnostics once the
charts have been read.

> This yielded
> much greater delta E but perceptually better profiles I think. I was
> wondering if there is any reason I should not do this.

It's perfectly reasonable. Better to use a larger chart in the first place,
if you are after better characterization though.

The high delta E hints that the process (i.e. print stability, printing process
or measurement process) is not entirely stable.

> What I was trying to
> overcome is channels crossing over each other near highlight/shadows and
> causing casts/noise

Is this CMYK or and "RGB" print path ?

> Secondly, I tried employing the -r parameter with colprof, but trying any
> value from 1 to 30, I could not get the delta e to change even one decimal
> point, does this imply that it does not have any effect?

The values are too high - you have hit the lookup table limit. Normal
ranges would be something like 0.0001 to 5.0 %.

> I also tried the
> -V but that also didn't change delta E (should it?).

No, that's for video display profiles, and works in combination
with the test patch distribution.

> When I enter -r 0,
> that changes things, but I don't own a device that has 0.0 percent error :)

See above.

Graeme Gill.

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