Premultiply Alpha is a filter script for the image manipulation program GIMP wich premultiplies the alpha value of each pixel into its color. Images with premultiplied alpha values are used in game development to be able to draw correctly to surfaces.
More on premultiplied alpha und blendmodes can be found at YoYo Games GameMaker Studio Forum.
- Unzip the script to the GIMP script-folder (usually C:/.../User/Username/gimp-2.x/scripts though the gimp-folder might be set to hidden).
- Select the correct layer.
- Apply the layer mask if any exists.
- Open the "Color" menu and select the "Premultiply Alpha" script.
- The original layer will be copied and hidden. A new layer will be created above containing the image with premultiplied alpha.