Re: Comparing L*a*b* measurement scales: Photoshop vs Xrite
Re: Comparing L*a*b* measurement scales: Photoshop vs Xrite
- Subject: Re: Comparing L*a*b* measurement scales: Photoshop vs Xrite
- From: Mike Pucher <email@hidden>
- Date: Mon, 13 Apr 2015 16:35:11 -0700
Thanks for the input, everyone.
It is clear to me now that I was confused by the data export options in
i1Profiler, and that no correction to the data is needed. I misunderstood
the output scale of "0.0-1.0" or "0.0-100.0" as a proprietary handing for
L*a*b*, when that option only applies to exporting spectral data. (Learned
that from Robin off the list, can't take any credit for figuring that one
out on my own.)
On Mon, Apr 13, 2015 at 10:56 AM, Steve Upton <email@hidden> wrote:
>
> > On Apr 9, 2015, at 11:26 AM, Mike Pucher <
> email@hidden> wrote:
> >
> > I have a set of L*a*b* measurements of color charts that I created with a
> > i1Pro2 spectrophotometer. The Xrite software exports L*a*b* values on a
> > scale of L*:0-100 and *a*b*: -100 to +100*.
> >
> > I've written a script for Photoshop to automate the calculation of
> specific
> > metrics of captures of those charts, but there's one snag: Photoshop
> > displays L*a*b* values on a scale of L*:0-100 and *a*b*: -128 to +127*.
> >
> > I assume, but I haven't been able to find confirmation, that it is a
> > mathematically linear conversion (mapping) from the *-100 to +100 a*b*
> > scale* to the *-128 to +127 a*b* scale.* Can anyone verify this? Or point
> > me in the direction of the proper way to map the values between the two
> > scales?
>
> Hi Mike,
>
> How do you know the range from the “X-Rite Software” is -100 to +100 for
> a* and b*?
>
> I see no reason to believe that you should scale anything. I would think
> you are safer thinking of your -100->100 data as simply range limited and
> you should encode it to the same values in Photoshop
>
> regards,
>
> Steve
>
>
>
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--
*Mike Pucher*
*Sr. Image Capture Specialist*
*Animation Research Library*
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