On 09.10.2013 at 03:20 P.M., Elle Stone wrote:

The topic of Documentation came up recently. It occurred to me that existing and future Gimp developers might find documentation on color spaces and ICC profiles helpful. So I wrote up a "Completely Painless Programmer's Guide to XYZ, RGB, ICC, xyY, and TRCs", which is posted on my website at http://ninedegreesbelow.com/temp/xyz-rgb.html.

Indeed, it's very useful. It might surely take me some time to work through it, but thank you very much for your efforts to share your knowledge!

If there's an interest, I'll put together Part 2, which would cover:

* CieLAB (how it relates to XYZ and why it's useful for image editing) * CMY(K) (how it relates to RGB and XYZ) * YCbCr, YUV, HSL, and HSV (how these derivative color spaces are connected to their parent RGB color space) * LCMS2 (how it links working space profiles with monitor, camera, and printer profiles)

Yes, there is interest in it (at least from me).

Kind regards,

Sven

Hi Elle,

On 09.10.2013 15:20, Elle Stone wrote:

The topic of Documentation came up recently. It occurred to me that existing and future Gimp developers might find documentation on color spaces and ICC profiles helpful. So I wrote up a "Completely Painless Programmer's Guide to XYZ, RGB, ICC, xyY, and TRCs", which is posted on my website at http://ninedegreesbelow.com/temp/xyz-rgb.html.

I am not a developer, but this is the best text I found about this stuff up to now. Very well written.

If my Guide seems useful to developers, I'll put the content under an applicable license so it can be hosted elsewhere and modified by other people.

Please do that! I'll make a video from it (well, parts of it, as usual with the books also.... ;-) )

Rolf http://meetthegimp.org

On Wed, 2013-10-09 at 16:32 -0400, Elle Stone wrote:

perhaps I should move the Guide out of the "temp" folder (which is for temporary posts) and over to the "photography" folder, with appropriate license information at the bottom and with the reference to Gimp from git and Cairo in Figure 6 removed.

If you do that, please add a redirect, since the URL has now been posted on a public list.

What you've written is incredibly useful, thank you!

A couple of minor suggestions - * make references to figures and tables be links within the document * consider using HTML abbreviation/acronym/initialism markup, or just span elements with title attributes, for the abbreviations and jargon, throughout the document (yay for search and replace) or at least the first occurrence in any paragraph.

Yes, keep up the good work with a part 2 :-)

Liam

Liam Quin - XML Activity Lead, W3C, http://www.w3.org/People/Quin/
Pictures from old books: http://fromoldbooks.org/
Ankh: irc.sorcery.net irc.gnome.org freenode/#xml

On 09.10.2013 22:32, Elle Stone wrote:

On 10/9/13, Rolf Steinort wrote:

On 09.10.2013 15:20, Elle Stone wrote:

If my Guide seems useful to developers, I'll put the content under an applicable license so it can be hosted elsewhere and modified by other people.

Please do that! I'll make a video from it (well, parts of it, as usual with the books also.... ;-) )

Rolf, can you suggest an appropriate license?

I release all my stuff under Creative Commons.

I think CC is the best suited license for texts and images. Which flavour to take depends on what rights you want to keep for yourself.

CC-0 - the same as public domain in the US, everybody can do what they want with the text.

CC-BY - everybody can do what they want with the text as long they mention the license and your name. I am so full of myself to use that one. ;-)

Then there are the more restrictive licenses with "Share Alike", "No Derivates" and "No Commercial use". http://creativecommons.org/choose/ has a questionaire for making that decision.

CC-BY-SA is about the same as GPL, I think. I used that for some time but dropped the "SA".

Rolf
http://meetthegimp.org

Hi Elle,

I hope you agree that I added a link to your documentation in our developer wiki:
http://wiki.gimp.org/index.php/Users:Beginner_Developer%27s_FAQ

Kind regards,

Sven

Elle Stone (l.elle.stone@gmail.com) wrote:

In the meantime, if anyone would like to read it and give feedback, corrections, suggestions, I'll edit the Guide to make it more clear, more useful, etc (if nobody is interested, that's OK too!).

I think it is very helpful. I've been dabbeling with colors some time ago (trying to improve the color reproduction of a network camera) but did not dive into the "profiling" area.

Some remarks:

In section B3 I had trouble following, because having five XYZ coordinates to specify a RGB cube (with - as you claim - additive light) seems over-determined. It is not clear how RGB(1,1,1) - i.e. additive RGB(1,0,0) + RGB(0,1,0) + RGB(0,0,1) results in the specified white point. The same problem is there with the black point. *if* this stuff is additive, then black always will be the absence of R, G, B, i.e. a pitch black XYZ(0,0,0). So there is a dragon lurking when claiming additivety.

Another (slightly philosophical) issue for me is, that you never explain what you mean by color. You write that "every real color (that is, every color out there in the world, that humans can see) has a unique location".

It might be worth noting, that this is different from looking at color as "a specific intensity-distribution of wavelengths". There are different intensity-distributions that map to the same XYZ coordinate. While a person with normal eye-sight perceives these two "intensity-distributions" as the same color (and for these purposes XYZ is perfectly OK) a person with a color vision deficiency might be able to keep them apart -
see e.g. http://en.wikipedia.org/wiki/Colorblindness#cite_note-5

I am not sure if mentioning this helps or if it confuses stuff... :)

Bye, Simon

simon@budig.de              http://simon.budig.de/

Reading through this thread, could this mean that we can see CMYK in GIMP soon? (natively)

On 9 October 2013 23:00, Simon Budig wrote:

Elle Stone (l.elle.stone@gmail.com) wrote:

In the meantime, if anyone would like to read it and give feedback, corrections, suggestions, I'll edit the Guide to make it more clear, more useful, etc (if nobody is interested, that's OK too!).

I think it is very helpful. I've been dabbeling with colors some time ago (trying to improve the color reproduction of a network camera) but did not dive into the "profiling" area.

Some remarks:

In section B3 I had trouble following, because having five XYZ coordinates to specify a RGB cube (with - as you claim - additive light) seems over-determined. It is not clear how RGB(1,1,1) - i.e. additive RGB(1,0,0) + RGB(0,1,0) + RGB(0,0,1) results in the specified white point. The same problem is there with the black point. *if* this stuff is additive, then black always will be the absence of R, G, B, i.e. a pitch black XYZ(0,0,0). So there is a dragon lurking when claiming additivety.

Another (slightly philosophical) issue for me is, that you never explain what you mean by color. You write that "every real color (that is, every color out there in the world, that humans can see) has a unique location".

It might be worth noting, that this is different from looking at color as "a specific intensity-distribution of wavelengths". There are different intensity-distributions that map to the same XYZ coordinate. While a person with normal eye-sight perceives these two "intensity-distributions" as the same color (and for these purposes XYZ is perfectly OK) a person with a color vision deficiency might be able to keep them apart -
see e.g. http://en.wikipedia.org/wiki/Colorblindness#cite_note-5

I am not sure if mentioning this helps or if it confuses stuff... :)

Bye, Simon

--
simon@budig.de http://simon.budig.de/ _______________________________________________ gimp-developer-list mailing list
List address: gimp-developer-list@gnome.org List membership:
https://mail.gnome.org/mailman/listinfo/gimp-developer-list

On Wed, Oct 9, 2013 at 10:32 PM, Elle Stone wrote:

On 10/9/13, Rolf Steinort wrote:

On 09.10.2013 15:20, Elle Stone wrote:

If my Guide seems useful to developers, I'll put the content under an applicable license so it can be hosted elsewhere and modified by other people.

Please do that! I'll make a video from it (well, parts of it, as usual with the books also.... ;-) )

I'm sure "adding documentation" is like "adding code" - it doesn't happen automagically. But if anyone wants to put (all or portions) of the Guide somewhere in Gimp documentation, I can supply a PDF or a latex file, or plain text, or whatever is convenient. And if having the Guide also on my website presents a conflict of some sort (I don't know how these things are supposed to work), I can remove the Guide from my website altogether.

You are a skilled writer; you've got some home turf advantage though. Combined with your color knowledge you are be much more well suited to clarify what the babl format strings we keep using in GIMP mean, as well as how it fits into our overall scheme of things in current and future GIMP. What you do not understand; we might not quite understand ourselves yet either.

The babl README/website, our lowest level of developer documentation relevant to this hasn't seen much improvement during the last half decade or so. This is generated from some static html in the docs directory of the source code in git. One could almost start with a link to your current write-up. I see no problem in the content our alternate versions of the content being used different places.

I haven't considered the license of the documentation of babl/gegl separately from the project code itself before. But do not see a problem with including self-contained bits/chapters under a create-commons license; or some other compatible license on their websites.

yvind --

On Thu, Oct 10, 2013 at 3:58 AM, Jorge Tijerina wrote:

Reading through this thread, could this mean that we can see CMYK in GIMP soon? (natively)

It's unrelated :)

Alexandre

Elle Stone (l.elle.stone@gmail.com) wrote:

On 10/9/13, Simon Budig wrote:

Another (slightly philosophical) issue for me is, that you never explain what you mean by color.

I added a one-paragraph summary of color: http://ninedegreesbelow.com/photography/xyz-rgb.html What do you think? Will my one-paragraph summary work?

Yeah, I like it.

I am not sure if mentioning this helps or if it confuses stuff... :)

Based on your input I rewrote the explanation of imaginary colors, hopefully clarified what a "real" color really is, and touched on the subject of nonstandard color perception. Metamerism, though very important, might be more distracting than helpful?

Yeah, Metamerism probably is distracting.

For my mental model of color the spectral distribution of the light is quite important and I wonder if it would help a color-newbie to have more of this "tangible" stuff in the text. But this certainly also is a question of personal preference and I don't want to impress my views onto your text :)

To look at the weaknesses/hypothetical problems of the XYZ model there are two things worth noting:

a) two distinct spectral distributions might end up at the same XYZ coordinates.
b) there are XYZ coordinates in the first octant, which can not be mapped back to a spectral distribution.

(put in mathematical terms: XYZ is neither injective nor surjective)

And I'd explain it by looking at the monochromatic light (visible to the "average human"), which has a very specific position at the border of the horseshoe.

By adding up more wavelengths you'll always end up inside the horseshoe, (and there is more than one way to add up monochromatic light to end up at a certain XYZ coordinate). On the other hand, creating an actual light source with XYZ coordinates *outside* the horseshoe is an impossibility, even for rocket scientists, unless we assign XYZ coordinates for invisible wavelengths or allow for "negative" light sources...

The human aspect of XYZ is visible in two aspects: first the limited spectrum we consider and then the weird shape of the horseshoe, which is determined by the response curves of the "average" cones in the human eye. But only the first one has an effect on the "reality" vs. "imaginarity" of a XYZ coordinate IMHO.

However, adding tons of more diagrams with spectral distributions, X/Y/Z response curves etc. would at some point destroy your intentions with your text, so I won't complain... :)

Bye, Simon

simon@budig.de              http://simon.budig.de/

On 10/10/2013 06:10 AM, Elle Stone wrote:

I added a one-paragraph summary of color: http://ninedegreesbelow.com/photography/xyz-rgb.html What do you think? Will my one-paragraph summary work?

That one paragraph, with its descending tree of links, appears to me to provide a path to a post-graduate color perception/management course.

Beautiful!

-- Burnie