I can do that. Is it only GIMP that can remove the alpha channel though? Or can SAI or Krita do it? I'd hate to have to download a completely new program just for map making. :/ Also; where do I put the image files when I'm done?
SAI unfortunately does not have the ability to make height maps because it does not support gray scale. :c Photoshop and GIMP are the most popular applications used I believe. I don't know which specific other applications are able to remove it but Photoshop should be able to.
When you are done with a height map export it as Kerriki stated to FeralHeart > media > terrains.