[CREATE] Fw: CxF- colour plattes (e.g. from freie Farbe) in Open Source applications

[Øyvind Kolås]

On Tue, Dec 5, 2017 at 11:57 AM, Tobias Ellinghaus <houz at gmx.de> wrote:
> Am Montag, 4. Dezember 2017, 11:03:29 CET schrieb Christoph Schäfer:
> [...]
>
>> -- - Do you know any existing open source libraries, which are converting
>> spectral-data to Lab ?
>
> How do these values look like? How many samples per patch are given? I don't
> know of such a library, but I know people who deal with these things and I
> might be able to get sample code to turn into a small library.

I've recently made a new project that aims to deal with this by
continuing workon other spectral color processing code. Coloritto is
now a protoype CxF viewer/editor, that includes computing CIE XYZ from
reflectance spectra in cxf files. My plan is towards supporting
ISO17972 CxF-4 spectral characterization with tint ramps on black and
white substrates - for custom spectral separation and
simulation/proofing see https://gitlab.gnome.org/ok/coloritto/ for
further information.

The color hue match in the Freie Farbe data set is good, good enough
that one can spot many errors that seem to be due to shuffling of
colors or rows of colors during measurement, one such color is
selected in the following screenshot :
http://pippin.gimp.org/tmp/freie-farbe-bug.png  and text file dump:
http://pippin.gimp.org/tmp/freie-farbe.txt this screen shot uses an
orthogonal projection along the L axis, the straighter the spokes the
better the exact hue has been matched.

PS: I plan to implement  interpolation based reconstructinon of
spectrum from CIE XYZ using the freie-farbe dataset as ground
reference lookup table, and thus should be able to generate a new
synthethic dataset based on the existing HLC_EPV_M0_V2-3.cxf that
yields exact CIE Lab/lch/HCL based on these representative spectra.

/Øyvind Kolås