`etc1tool` is a command line utility that lets you encode PNG
images to the [ETC1](https://registry.khronos.org/OpenGL/extensions/OES/OES_compressed_ETC1_RGB8_texture.txt) 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]
```

This table lists the command options:

| 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*. This option is 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`). |