Do RGB conversion to XYZ and define color value ?

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I'm working with OpenGL and C. I have RGB input in openGL and need to do computation in CIE XYZ color space. So I do conversion following this color conversion rules.

C++

|X|   |0.412453 0.357580 0.180423 | |R|   
|Y| = |0.212671 0.715160 0.072169 |.|G|   
|Z|   |0.019334 0.119193 0.950227 | |B|

Now, that I have the value in 3D space XYZ colorspace, I want to convert it into 2D space CIE chromaticity diagram. So I normalized the XYZ into xy plane.

C++

x = X/(X+Y+Z)   
y = Y/(X+Y+Z)

Is there anyway I can draw this CIE chromaticity diagram and plot the points using openGL ? I can't find any information related to it.

What I have tried:

Do RGB-CIE XYZ conversion and convert it into 2D plane of xy chromaticity diagram.

Posted 27-Jan-19 16:33pm

lock&_lock

Updated 29-Jan-19 9:58am

v2

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[no name] 29-Jan-19 15:22pm

So you know how to calculate XYZ from sRGB and you know how to calculate xy from XYZ. Is your final problem to show these "xy" values in a "xy" plane by OpenGL?

Btw: This for the math, but I assume you know this allready:www.brucelindbloom[^]

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User 11060979 · Answer 1 · 2019-01-29T09:59:00

Solution 2

I'm not sure what your problem exactly is,
a.) OpenGL?
b.) Calculations?

From your question I see you recognized how to come from 3D- XYZ Space to xy(Y) space.

Anyway:
Here you will find a set of formulas from convert from Spectrum to XYZ on from there to xyY, sRGB, etc. and vice versa (of course excl. 3D back to spectrum):
www.brucelindbloom.com[^]

Here a good article on CP with also a lot of background info:
Color Topics for Programmers[^]

I hope it helps.

[Edit]
Explaining how to calculate(show) the "horse Shoe" in the xy- plane is too much to explain it here ;)

Posted 29-Jan-19 9:59am

User 11060979

Updated 29-Jan-19 10:05am

v3

Comments

lock&_lock 29-Jan-19 16:16pm

Hi, thanks. I was able to convert already. I want to draw confusion line, like this

I know exactly the value of copunctal point (where all the lines converge), but I'm still confused how to specify the value since the copunctal point is not in xy coordinate but in wavelength value. Is there any way I can render this in opengl and C ? I want to see if my calculation was correct or not, I thought it'd make the best sense if I could just draw the graph. As of now, I'll read your recommendation, thanks. Let me know if you have further advice.

[no name] 29-Jan-19 16:22pm

Youe are welcome. Can you explain me what exactly you understand under "confusion line"? The term "confusion line" confuses me a little bit at the moment ;)

And one thing more: I think for a first 2D graphics I would use something more easy like OpenGL unless you are already familiar with OpenGL.

[no name] 29-Jan-19 16:25pm

Or is it maybe "only" the question how to find e.g. 440nm in the xy -plane (which is not trivial but possible to answer)?

lock&_lock 29-Jan-19 16:38pm

hi, 400nm would be 0.16 and 0.009. What I wanted was to draw it with openGL and C, I want to know if it's correct or not. As I said in the previous comment, I found tutorial in phyton but I'm not familiar with phyton. It'd be lovely if I can do it using C. Also unfortunately I've been using glut and OpenGL, not modernOpenGL. I wonder if it's possible. thanks again.

[no name] 29-Jan-19 16:55pm

Quote "400nm would be 0.16 and 0.009":
Are you using 2° or 10° observer?

[no name] 29-Jan-19 17:04pm

My above question we can discuss maybe later.

For me it still looks you know how to calculate all the points, but you don't know how to show them in a grapphics. Is that right?
If yes what dev environement you are using exactly (visual studio, .....)? This would help much more to answer how to show the graphics.

lock&_lock 29-Jan-19 18:25pm

Hi, thanks. Yes, I don't know how to draw the graph in OpenGL with C. Also I'm working in terminal Mac using OpenCV and OpenGL. About the Excel, as of now I just need to check, but I'm afraid I will end-up need to run and show the colored graph in real time anyway, if I need to export the coordinates and import to Excel all the time it'd be so inefficient. Also, all of this time all of this information I got I read from bunch of different sources, web, papers, blog, etc. So I just kind of patch things up together, if you have decent recommendation to read, I'd really appreciate it, since you're also familiar with this topic.

[no name] 29-Jan-19 17:12pm

And if the graphics is only to crosscheck the calculation you can maybe use the help of excel. What I mean: You save either your x/y coordinates into a file or much more easy copy the series to the clipboard to paste them into excel and create the graphics there.

lock&_lock 29-Jan-19 16:40pm

Also confusion line is a series of lines, where all colors along the same line will be perceived as the same color to colorblind people (confuse them), thus confusion line.

[no name] 29-Jan-19 17:34pm

Ok, thank you for this, this is new for me. I'm basically involved in industrial colorimetrics. But this circumstance I need to investigate, thanks again.

Richard MacCutchan · Answer 2 · 2019-01-27T22:33:00

Solution 1

See sRGB - Wikipedia[^].

Posted 27-Jan-19 22:33pm

Richard MacCutchan

Comments

lock&_lock 28-Jan-19 10:14am

Hi thanks, actually I did read before i posted here. Chances are either it's not the easiest thing for me to grasp, or it's not there. It doesn't say anything related to the spectrum on the line nor the conversion to xy plane. So yeah, not the most helpful answer for me.

Richard MacCutchan 28-Jan-19 11:59am

Well this is not a programming question that we can answer for you. You will need to do the research for yourself to find the simplest algorithm to use.

[no name] 29-Jan-19 15:25pm

This is programming question. OP does know how to calculate the values, but seems not able to show them in an OpenGL graphics...

Richard MacCutchan 29-Jan-19 15:33pm

No, he is trying to figure out how to convert one set of values (3D) to another set (2D). Until he knows the formula for that conversion there is not much that can be done in programming terms.

[no name] 29-Jan-19 15:37pm

This 3D to 2D he explained exactly in the right way:
x = X/(X+Y+Z)
y = Y/(X+Y+Z)
It is colorimetrics (my daily job) and he recognizes this part well ;)

lock&_lock 29-Jan-19 16:00pm

Hi, oh.. you're familiar with colorimetry, thank god. yes you're right. I'm trying to normalize CIE XYZ into xy plane.
I want to draw confusion line, like this

I know exactly the value of copunctal point(where all the lines converge), is there any way I can render this in opengl and C ? I thought if I could visualize, I can check if my graph is correct or not. unfortunately I'm not familiar with ModernOpenGL and been using glut and old opengl all this time. I found tutorial with phyton, but I can't risk using too many programming language for just one project. Any advice ?

lock&_lock 28-Jan-19 12:18pm

Hi, thanks ! I finally able to wrap my way around. I will update my question.