Arcane University:Gimp for Skyrim
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GIMP (GNU Image Manipulation Program) is a free image editor, with functionality similar to Photoshop. It can be used for digital painting, color correction, layering, masking, and scripted functions. For Skyrim, this is a great free alternative to Photoshop to combine the specular and normal map. While GIMP does have basic support for some DDS files, it is recommended to use another program for final export, as GIMP's compressor is inferior to most others.