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: Steve Upton <email@hidden>
- Date: Mon, 13 Apr 2015 10:56:38 -0700
> 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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