etc1tool is a command line utility that lets you encode PNG images to the ETC1 compression standard and decode ETC1 compressed images back to PNG.

The usage for etc1tool is:

etc1tool infile [--help | --encode | --encodeNoHeader | --decode] [--showDifference
diff-file] [-o outfile]
Option Description
infile The input file to compress
--help Print usage information
--encode Create an ETC1 file from a PNG file. This is the default mode for the tool if nothing is specified.
--encodeNoHeader Create a raw ETC1 data file (without a header) from a PNG file.
--decode Create a PNG file from an ETC1 file
--showDifference diff-file Write the difference between the original and encoded image to diff-file (only valid when encoding).
-o outfile Specify the name of the output file. If outfile is not specified, the output file is constructed from the input filename with the appropriate suffix (.pkm or .png).