Usage: webpng [-i y|n] [-l] [-t index|none] [-d] [-a] pngname.png
  -i <y|n>   Turns on/off interlace
  -l         Prints the table of color indexes
  -t <index> Set the transparent color to the specified index (0-255 or "none")
  -d         Reports the dimensions and other characteristics of the image
  -a         Prints all alpha channels that are not 100% opaque

If you specify '-' as the input file, stdin/stdout will be used as input/output.