Transparency: additive color blending

Hi,

Matlab seems to use the classical way to handle alpha channels, so that transparency works in a way 'subtractively', like layers of translucent fabric. If you pile up patches set with FaceAlpha = 0.5, say, you'll eventually end up with a dark zone.

I'd like to generate an additive mix, corresponding to the superposition of several light sources. Piling up enough of these patches would eventually lead to a white zone. If you code in OpenGL you can play with different modes of alpha blending, but I haven't found a similar way to do it in Matlab.

Thanks for any clue!

P.

[Walter Roberson]

For any one layer, would your coefficient still be in opacity (i.e., 0 = transparent, 1 = opaque), or would you be using a transmittivity coefficient? Or, I suppose, an emistivity coefficient of some sort. A brightness even? (A bright red light plus a dull blue light is going to look mostly bright red rather than the result being additive purely on wavelength.)

[Pierre]

I basically thought of adding alpha-premultiplied color channels (works only on a black background). Said otherwise: not multiplying the destination color by (1-alpha_src).

There may be smarter ways to do this. Please suggest them! Nevertheless 1) I'd like the color mix to be symmetrical; 2) it must be codable in Matlab!

[Richard Voigt]

I just went looking for pretty much exactly the same thing. Have a couple answers which are "close" but still not achieving symmetry.

http://stackoverflow.com/q/17790817/103167