[argyllcms] Re: Problem chartread: "Need reflection spot, strip.......instrument doesn't support it"

  • From: Per Nordlund <nordlund.per@xxxxxxxxx>
  • To: argyllcms@xxxxxxxxxxxxx
  • Date: Wed, 4 Mar 2015 20:40:44 +0100

Hi,

Thank you for all your help!

I don't quite understand this. In some papers there are a lot of FWA (OBA)
such as most RC-papers. These papers are often rather good papers such as
the SIHL Masterclass Lustre Paper that cost ½ to 1/3 of better OBA-free
papers. Their longivety is often as good (sometimes better). As I
understand they absorb UV-light and emit it as visible light and so they
can fool the meter. Is what you mean that when I look at these pictures in
an UV poor environment the profile will be wrong as it is made in what it
sees as visible light in an UV-invironment? i think I want my pictures to
be viewed in something like a D50 environment?! It should have been much
better if the papers didn't have this OBA-content then I think they could
be viewed in all environments! I have made two pictures on the above SIHL
paper with an own profile one with the -f D50M2 argument and one without
the -f argument. It's evening here so I cant compare them in daylight but
in incandescent warm light they do look about the same. In a "black"
UV-light the one with the -f D50M2 is warmer (I can see more red in a
portrait) than the one without. Could this be true?

I haven't used the -i argument as I don't understand how to use it. I can't
measure the OBA-content in a specific paper but maybe I can use one of the
reference files? I guess it's one of the D50_.sp-files but which one to use
for different papers with OBA? Where to start? I think Ernst Dinklas
measurements could be to some help? Should I put the .sp file in the bin
directory or does Argyll find the reference files by itself?

For my "better" pictures I will mainly use papers with less or none FWA.
For example the Canson Platine Fibre Rag is without and the Canson Baryta
Photographique seems to have rather little. I can confirm this in UV-light.
There is a big difference between these two papers and the RC-paper! I
don't think it's necessary to make any FWA-compensation with the Canson
Baryta and if so very little. What compensaton to use if I want to?

I'm impressed with what Argyll is capable of and I have got good profiles
with 720 patches on an A4 sheet. I tried also to use the "preprofiling
option" with one of the Canson own profiles but Argyll couldn't open the
file. I did put the profile in the bin directory and put in the name of the
file in the command. How to do this if I make my own pre profile with a
couple of hundred patches? Can Argyll open it if I let it stay in the bin
directory?

Best regards,

Per



2015-03-03 0:58 GMT+01:00 Graeme Gill <graeme@xxxxxxxxxxxxx>:

> Per Nordlund wrote:
>
> > I used -f D50M2 as
> > FWA compensation. Is there any difference using only M2?
>
> Hi,
>     FWA compensation works by adjusting your profile measurements
> to match your viewing conditions, so by choosing an M2 condition,
> you are assuming that your viewing environment is UV poor.
>
> There shouldn't be a difference between -f D50M2 and -f M2,
> but note that neither of these options are accurate in
> calculating a good visual result - they are just there to allow
> comparison to other measurements made under M2 conditions.
> This is because the measurements are D50M2 but the XYZ
> calculation uses D50, a situation not perfectly consistent with
> the real world.
>
> If your viewing environment is UV poor, then it is better
> to use -f -i D50M2, so that both the measurement and XYZ
> calculation use the same illuminant.
>
> In practice I guess there may not be a huge difference between
> -f M2 and -f -i M2, but they are different.
>
> Graeme Gill.
>
>
>

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