Nuke merge not working

[pbxos]

When you convert a image say of a live action plate on blue screen bg to b&w and then subtract it from the original image you get a really black and blue image, then add it to the original again and you get a hires super saturated image, If you do it in Photoshop it works perfectly when I do the same thing in Nuke nothing happens but ever so slightly more saturated but no where near the same even the subtracted image looks lighter in nuke. any ideas

[fbrandst]

Can you show an example of your images, as this is working for me. I can imagine that this has something to do with the values in your plate. Nuke calculates everything in 32bit floating point whereas PS does work in 8 or 16bit as well. So math operations look completely different in 8bit, when values are clamped at 0 or 1...keep that in mind.

[pbxos]

http://imageshack.us/photo/my-images/821/83343414.jpg/

RAW FILE: http://uploading.com/files/85b4f9bb/ccm436.b2.1.exr/

I apologize about the size but I assume you want the raw file.

[nathanfx]

Did you set your read nodes to out put the right color profile for the footage? If you don\'t your math operations will be incorrect and give you unexpected results like the one you are mentioning.

[colton]

Did you set your read nodes to out put the right color profile for the footage? If you don\'t your math operations will be incorrect and give you unexpected results like the one you are mentioning.

Very true, also Photoshop does all of its math in sRGB, while Nuke does its own in linear. In theory throwing a linear->sRGB before your color ops, and then going back sRGB->linear afterwards should give you the same thing you see in Photoshop. Photoshop\'s layer blending modes are a bit esoteric though, and don\'t perform exactly like those in Nuke....

[pbxos]

Seemed to be the problem thanks