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

2017-12-04 Thread Christoph Schäfer
 
 

Gesendet: Montag, 04. Dezember 2017 um 09:11 Uhr
Von: "Jan-Peter Homann" 
An: "Christoph Schäfer" 
Cc: "Eric Soder" , "everd...@freiefarbe.de" , "Peter Jäger" 
Betreff: CxF- colour plattes (e.g. from freie Farbe) in Open Source applications



Hi Christoph,
Thank you for your engagement with the Scribus team. I have some more questions, which probably need to be dicussed with the english speaking open source / prepress community:

1) Handling spectral CxF data in open source applications:
--
- Do you know any existing open source libraries, which are converting spectral-data to Lab ?
- If yes, it is possible to combine this library with littleCMS (e.g. to make it easy for applications using littleCMS to convert spectral-data to Lab and use in littleCMS ?)
- if yes, do you think it makes sense to intergrate CxF support into this library ?

2) CxF as universal XML-based dataformat for colour palettes in color critical open source applications ?
CxF ist is quite powerful dataformat to describe colour palettes. I supports not only spectral data, but also Lab-based colour palettes as also device specific color palettes (e.g. RGB or CMYK for a specified profile)
So far as I know, is CxF the only data format, which can be used to describe colour palettes and which is ISO standardized.

So it may makes sense to discuss the handling of colour palettes not only Scribus related but in general for open source applications. It is e.g. possible to create a a CxF colour palette which contains:
- spectral data
- Lab-data for defined lightning condition (e.g. D50)
- sRGB data

- specialized applications could use the spectral-data,
- ICC aware applicatons with LCMS support could use the Lab D50 data
- all other applications could use the sRGB-data

3) Coordinate Scribus CxF Support with other Open Source projects ?
Do you think, that that it makes sense to coordinate the CxF support in Scribus with other open source projects, to e.g. create a library for CxF support with e.g. following functionality:
- extract RGB colour palettes for applications without LCMS support
- extract Lab- colout palettes for applications with LCMS support
- convert spectral data to Lab for applications with LCMS support, if no Lab-data is available ?

Use cases would e.g. be:
- use CxF palettes in othe applications like e.g. Inkscape
- visualize a CxF color palette in 2D or 3D based on RGB-values

Regards
Jan-Peter
 

-- 
Homann colormanagementtel: +49 30 611 075 18
Jan-Peter Homann  mob: +49 171 54 70 358
Herzbergstr. 55   www.colormanagement.de
10365 Berlinmailto:hom...@colormanagement.de





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

2017-12-04 Thread Alexandre Prokoudine
On Mon, Dec 4, 2017 at 1:06 PM "Christoph Schäfer" wrote:

> 1) Handling spectral CxF data in open source applications:
>
> --
> - Do you know any existing open source libraries, which are converting
> spectral-data to Lab ?
> - If yes, it is possible to combine this library with littleCMS (e.g. to
> make it easy for applications using littleCMS to convert spectral-data to
> Lab and use in littleCMS ?)
> - if yes, do you think it makes sense to intergrate CxF support into this
> library ?
>

I only know of SpecEd. It's an abandoned little Qt (afaik) app that
translates wavelength into CIE XYZ and sRGB.

The website doesn't work anymore, but both the page and the source code are
available via Web Archive:

http://web.archive.org/web/20150801195457/http://malat.biz/view/Projects/SpecEd

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

2017-12-05 Thread Tobias Ellinghaus
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.

[...]

Tobias

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

2018-06-29 Thread Øyvind Kolås
On Tue, Dec 5, 2017 at 11:57 AM, Tobias Ellinghaus  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
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