[argyllcms] Re: Question about scanner ICC-profiles

From: Hermann-Josef Röser <posts@xxxxxxxxxxxxxxxxxxxxxxxxx>
To: <argyllcms@xxxxxxxxxxxxx>
Date: Fri, 19 Feb 2021 17:06:19 +0100

Hello Roger,

have you considered *how* the profiles will be used?

Regardless of the future use, I would like to understand this behaviour in
the context of how the profiles are created.

Best wishes

Hermann-Josef

--- Begin Message ---

From: <graxx@xxxxxxxxxxxx>

To: <argyllcms@xxxxxxxxxxxxx>

Date: Fri, 19 Feb 2021 16:48:20 +0100

I often hear, in the case of digital photography, that a lower exposure
creates more saturated colors?

True or false? I dont know. But worth testing.

Regardless of exposure, have you considered *how* the profiles will be
used? It may or may not be related to your question but, at least in RelCol
transform, the GS0 patch on the IT8.7/2-1 chart is going to map to Lab =
100,0,0 anyway.

So, regardless of where the white patchs ends, given the change in
exposure, once the profile is used in a conversion, the result will be the
same.

No?

I hope it helps / Roger (MfG)

From: argyllcms-bounce@xxxxxxxxxxxxx <argyllcms-bounce@xxxxxxxxxxxxx> On
Behalf Of Hermann-Josef Röser
Sent: Friday, February 19, 2021 10:26 AM
To: argyllcms@xxxxxxxxxxxxx
Subject: [argyllcms] Question about scanner ICC-profiles

Hello,

may I ask another question?

My scanner can change the exposure time of the scans (analogue gain, AG). It
is recommended to use a dedicated ICC-profile for each setting of the AG. I
created the profiles using colprof and compared the volumes of the gamut
(solid body) of the scanner with AdobeRGB (wire mesh) using viewgam. I
observe the following:

For the standard AG setting of 150 the volume of the scanner gamut does not
extend as far in the L direction as with a lower setting of AG = 100
(relative numbers). Why is that? Here are screenshots to illustrate what I
mean (left AG=150, right AG=100):



Another observation in this direction is the following. I have IT8-targets
from 2 vendors. One seems to be somewhat underexposed with brightest patches
having L = 85, the other has in the brightest patches  L-values of about 93.
For the same AG setting, the profile corresponding to the slightly
underexposed target extends not as far in the L-direction as the better
exposed one. I guess the two observations are related to each other?

With best regards

                Hermann-Josef

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[argyllcms] Re: Question about scanner ICC-profiles

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