# Photoshop Blendmodi in GLSL

I once wrote a texturing tool in which you could paint on a 3D model on multiple layers. These layers were composing the final texture just as you know it from photoshop, complete with alpha, opacity slider and: blend modes. these blend modes are quite simple to implement and it can be useful to use the exact same modes as they are familiar to artists and it’s possible to prototype the final effects in PS (or even write importers and exporters to psd files). The hardest part actually was collecting all the formulas, so this is why I’m collecting them here once again:

I’m assuming the ‘lower’ color is stored in **base** and the ‘upper’ color is stored in **blend**.

**multiply:**result = base * blend;

**screen:**result = vec4(1.0) - ((vec4(1.0) - blend) * (vec4(1.0) - base));

**darken:**result = min( blend, base );

**lighten:**result = max( blend, base );

**difference:**result = abs( base - blend );

**negation:**result = vec4(1.0) - abs( vec4(1.0) - base - blend );

**exclusion:**result = base + blend - (2.0*base*blend);

**overlay:**# per channel: if (base < 0.5) { result = 2.0 * base * blend; } else { result = vec4(1.0) - 2.0 * (vec4(1.0) - blend) * (vec4(1.0) - base); }

**hard light:**# per channel: if (blend < 0.5) { result = 2.0 * base * blend; } else { result = vec4(1.0) - 2.0 * (vec4(1.0) - blend) * (vec4(1.0) - base); }

**soft light:**# per channel: if (blend < 0.5) { result = 2.0 * base * blend + base*base - 2.0 * base*base*blend; } else { result = 2.0 * sqrt(base) * blend - sqrt(base) + 2.0 * base - 2.0 * base*blend; }

**dodge:**result = base / (vec4(1.0) - blend);

**burn:**result = vec4(1.0) - (vec4(1.0) - base) / blend;

OpenGL ES 3.0 this summer? Mac OpenGL capabilities

FWIW, you may find some interest in very comparable work with GLSL, providing various functions (blending, contrast, etc.) :

http://mouaif.wordpress.com/2009/01/05/photoshop-math-with-glsl-shaders/

Nice, thanks for the link, I didn’t know that side.

Incidentally, the wikipedia page for blend modes is a useful tool. It has the math and in-depth explanations for all of the blend modes, if not the exact code for them.

http://en.wikipedia.org/wiki/Blend_modes

Of course, this is still a good resource considering it has actual code instead of just conceptual math. Just thought I’d leave the link here in case anyone else wanted it.

(I know this post is ancient, but it’s on the first page of google still. that’s how I found it.)