Re: Profile verification in PatchTool
Re: Profile verification in PatchTool
- Subject: Re: Profile verification in PatchTool
- From: Marco Ugolini <email@hidden>
- Date: Mon, 05 May 2008 21:40:44 -0700
- Thread-topic: Profile verification in PatchTool
In a message dated 5/5/08 5:11 AM, Roger Breton wrote:
> Hi Marco, Danny,
Hi Roger.
> We get measured Lab that we now have to compare to, to, to, what, the source
> RGB values? No... You know it does not arbeit this way! So, of course, the
> RGB values sent to the monitor have to converted somewhere into some Lab
> values otherwise we'll never be able to calculate deltaEs.
Non, mon ami. No need to *convert* to anything. Simply *assigning* the
monitor profile to the numerical RGB values in the list will provide the
device-independent reference list that will then be compared to the list of
actual values measured by the colorimeter.
> So what does ColorNavigator do (and the others packages)?
>
> They take those test RGB values and process them through the A2B table of
> the monitor profile, to obtain Lab values.
Yes. That is what *assigning* a profile does. It's *not* a conversion (which
would be a full Device 1 [A2B] > PCS > Device 2 [B2A] round).
> What I think PatchTool does is to jump the gun in asking the user, at the
> onset, to choose one of the pre-defined RGB profile to interpret the
> colorimetry of the opened RGB list. So that, the RGB values can readily be
> converted to XYZ (I think that's what Danny indicated), behind the scene,
> and later to Lab, to compute DeltaEs.
Yes, that's one way to generate a reference list of device-independent
colorimetric values. But so is assigning the monitor profile, pure and
simple! I fail to see the need to complicate matters.
> What I think you're asking is why not have the choice of the monitor profile
> itself as the Source, why keep it among the list of predefined RGB profiles
> (sRGB, AdobeRGB, Colormatch, ProPhoto, ...)?
Exactly. It is exactly what puzzles me.
> I guess there is nothing, in principle, that could prevent PatchTool for
> offering the active monitor profile in the list of Source at the time of
> opening an "orphan" list of RGB device values (with no associated Lab
> values), if the user explicitely would prefer to use that for interpreting
> the colorimetry of the RGB list.
Yes. I hope that the choice will be made available in future versions of
PatchTool -- which I must say is a great little program, with a lot of bang
for the buck, in case people believe that I think otherwise. :-)
> But I think the case can be made that, for the purpose of testing the
> performance of monitor profiles, because this is what we want to get to,
> after all, it does not matter as much as we would think it does, what the
> source of the Lab figures is : monitor or independent RGB working space.
Yes, but it would be nice to have a choice to do it either way, and not be
forced to do it in a way that excludes assigning the monitor profile --
which is something that I'm still not clear whether PatchTool's Display
Check can do for *custom* RGB lists.
How's that for confusing? Parbleu... :-)
Marco
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