OptiPNG return the same exit code if the operation sucess or if do not (errorlevel=1).
The MS-DOS estandar is return exit code = 0 if the program finish OK.
Return exit code -1 if the program finish with error.
In addicion the program can return several exit codes for comunicate several error status, but retur 0 if sucesfull and -1 if terminate with error are the minimal.
It is very importan for control the aplication in batch archive or for call it from grafical interface.
Can you add this change.