Great work, thanks heaps for this! This'll help me clean up files quickly and easily, as we do the same thing a lot of the time too :)
NB: This works fine on the Windows version of ImageMagick, however if (like me) you want to wrap it in a batch file you must escape the -level command by changing the "60%,91%,0.1" to "60%%,91%%,0.1" or else the batch file will misinterpret it, since %1 refers to variable names (the same as bash scripts). If you don't, you'll just get a black PNG file.
NB: This works fine on the Windows version of ImageMagick, however if (like me) you want to wrap it in a batch file you must escape the -level command by changing the "60%,91%,0.1" to "60%%,91%%,0.1" or else the batch file will misinterpret it, since %1 refers to variable names (the same as bash scripts). If you don't, you'll just get a black PNG file.