1. Got a little question regarding the addition of colors in different colorspaces.

Colors from the RGB colorspace are additive and can be added by adding there individual color components.
When c1 and c2 are colors then the addition is c3 with c3.r = c1.r+c2.r, c1.g+c2.g and c1.b+c2.b (with the r, g, b postfix being resp the red, green and blue components of the colors). c3 is then the resulting color when we shine 2 lights with color c1 and c2 towards the same spot.

When we describe the same colors by a different colorspace (XY for example), is the resulting color c3 (in XY) also obtained by simply adding the individual components? Like c3.x = c2.x + c1.x and c3.y = c2.y + c1.y

Might be a stupid question, but I just want to know how do you add 2 colors (I mean like in the lights example) when the colors are described by another colorspace.
Simply converting to RGB and back seems quite incorrect as XY covers a much broader range of colors.

Hope I'm clear enough.
S.

2.

3. You've lost me at 'induvidual color components'... but then again; color study is not my thing xP

4. I found this for you (PDF): COLOR PROCESSING FOR MULTI-PRIMARY
DISPLAY DEVICES
.

Will this help?

"In chromatics, XYZ usually indicate colors. Generally speaking, XZ are not used to represent color space. XZ are converted into the form of xy first, and the xy are used to indicate the color space.

x=X/(X+Y+Z) (1)

y=Y/(X+Y+Z) (2)

The XYZ coordinates may be quickly converted into xy coordinates according to formulas (1) and (2)."

5. (by individual color components I meant primary color components, srr for that)

What I see in what you posted is that I always have to convert and back, which I find hard to believe. I mean isn't there a common 'formula to compute addition of colors in any given colorspace? I guess I wasn't clear enough :?

Anyway I reformulate my question:

In RGB we have:
cRGB3 = cRGB1 + cRGB2
(with cRGB3 the resulting color of the light when we shine 2 lights... see first post).

let's assume we have a colorspace CP (undefined) and a mapping from the RGB colorspace to the CP colorspace MRGBtoCP.

with
cCP3 = MRGBtoCP(cRGB3)
cCP2 = MRGBtoCP(cRGB2)
cCP1 = MRGBtoCP(cRGB1)

does in this case
cCP3 = cCP1 + cCP2 hold for any colorspace CP?

6. I think this may belong more in the Math forum than the Physics forum, but anyway...

The simple answer is, no, there's no universal formula for addition of colors. (RGB is a nice colorspace because it has a simple formula for that. Other colorspaces are used for other reasons.) To see why, consider the HSV colorspace. Two colors with the same saturation/value will have a sum with the same saturation/value. Google HSV converter of you want to play around with the numbers.

7. Ok, I see now.

Srr for being in the wrong forum. I thougth colortheory was a physics subject.

S.

8. Well, it could be, depending on which direction you approach it from. (It could even end up in the computer science section, since that's where it's most often used.)

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