[Octave-bug-tracker] [bug #50429] image package: xyz2lab changed slightly in Matlab (and other color conversion functions)

[Hartmut]

URL:
  <http://savannah.gnu.org/bugs/?50429>

                 Summary: image package: xyz2lab changed slightly in Matlab
(and other color conversion functions)
                 Project: GNU Octave
            Submitted by: hardy
            Submitted on: Wed 01 Mar 2017 07:31:14 PM UTC
                Category: Octave Forge Package
                Severity: 3 - Normal
                Priority: 5 - Normal
              Item Group: Matlab Compatibility
                  Status: None
             Assigned to: None
         Originator Name: 
        Originator Email: 
             Open/Closed: Open
         Discussion Lock: Any
                 Release: 4.2.1
        Operating System: Any

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Details:

quoting the original issue reporter:

Octave - image - xyz2lab

For a research project, I was comparing the results between the built-in
Matlab function and the implementation on
http://www.brucelindbloom.com/index.html?Eqn_XYZ_to_Lab.html . In these
calculations it turns out that Matlab does use "D65 = [0.95047, 1, 1.08883];",
despite of the truncation in the whitepoint function.This means that the
comment on line 58 can be changed.

I also have another remark: the sourcing on Wikipedia for the white point is
pretty poor. I found an Excel file on the website of the CIE, from which it
should be possible to calculate the D65. I haven't implemented this, as that
is way more precision than I need, but it would improve the rigor. I might
write something on Wikipedia, but I won't promise. I copied the Excel file
download link to the way back machine, so it can safely be cited:
https://web.archive.org/web/20170131100357/http://files.cie.co.at/204.xls

Best regard,
R. W.




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