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Specular Difference

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This plugin is for isolating specular light in a scene. It uses two photographs of the scene, one with specular light filtered by a polariser and the other allowing it through. The former is subtracted from the latter to leave mostly specular light.

The plugin does the subtraction using layers, which can be done onto a separate layer if needed. Both images need to be aligned to overlap accurately and their layers can be moved to do this if necessary. Some noise is likely and there's a controller to reduce this, it defaults to 100% and is best left at that. To keep colour distortion to a minimum the photographs should be exposed in the mid to high range, avoiding exposure near white. A brightness control is included to compensate for this.

Getting good results can be tricky, I've put a blog post together which outlines some gotchas and can be found here:

GIMP Version: 
Code License: 


The latest version of this plugin can be found here:

Merci beaucoup!

There was a problem on Windows and Mac where dropping the second image onto a new layer caused it to pick up an alpha channel while the first one didn't. This caused some confusion since the alpha channel needed to be dropped for the plugin to work. It now works without having to do this and I've added a check box giving the option to subtract alpha channels if each layer has one.

There's also a new check box to use layer opacities. This can be used to allow some diffuse light though to the final image.

Have i told you lately that you rock! :)

Thanks again!

I'm on Windows 7 and I installed python.
This isn't a .py file and I can't find anywhere with instructions on how to convert it or install it.
I don't even see Python-fu under filters so I'm thinking it's my software, but I have no idea how to fix it.


and needs to be compiled into an execute file.

Sounds simple enough.
How would I go about doing that?

Someone else would need to compile this for Windows. This isn't something a beginner could do without having a certain degree of skill and know-how. Linux, on the other hand, would only require gimptool to compile it, but you have indicated you are a Windows 7 user.


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