Combine Cycles passes in way compatible with photoshop I'm trying to take my Cycles render passes into photoshop and combine them there. The purpose of this is to be able to manipulate the passes individually with various photoshop tools. However, photoshop does not support the way that Cycles passes are usually combined.

Normally, you have ((Diffuse Direct + Diffuse Indirect) * Diffuse Color) + ((Gloss Direct + Indirect) * Gloss Color). However, Photoshop does not have the Add blend mode.

So to do this, I need a different way to combine passes that does not rely on the Add blend mode. Is there another way that will be reasonably accurate?
According to this, Linear Dodge is the same as Add in Blender. However, if you are working with 8 or 16bit jpg/png/tga, Photoshop by default will works in display-referred space (i.e. everything is gamma corrected and non-linear), so the results of adding multiple render layers together in a non-linear space will be WRONG.

The only way to work in a linear space, which is absolutely critical, is to use 32bit EXR, that's the only way Photoshop will operate in linear space, and follow this workaround.

In short, don't use Photoshop. It's really not designed for linear values and will give you wrong results  unless you specifically configure it to work in linear space.