Probably GIMP. Last time tried to use GIMP, I spend about an hour trying to work out how to remove an alpha channel without also applying it. I could clearly s

Probably GIMP. Last time tried to use GIMP, I spend about an hour trying to work out how to remove an alpha channel without also applying it. I could clearly see the image I wanted in the red, green and blue channels. But because the alpha channel was filled with full transparent, all I could see outside of individual color channel mode was the checkered background. Deleting the alpha channel or converting the image format from RGBA to RGB just erased the entire image to black. I eventually found the solution in the eraser tool, which had an erase alpha mode. I had to set it to a really large size and go over the entire image. Would probably have been faster to just write a script in python.