I can't figure out how to compress PNGs losslessly into WebP.

These are the options it gives:

    Usage:
     cwebp [-preset <...>] [options] in_file [-o out_file]

    If input size (-s) for an image is not specified, it is assumed to be a PNG or JPEG file.
    Windows builds can take as input any of the files handled by WIC
    options:
      -h / -help  ............ short help
      -H / -longhelp  ........ long help
      -q <float> ............. quality factor (0:small..100:big)
      -preset <string> ....... Preset setting, one of:
                                default, photo, picture,
                                drawing, icon, text
         -preset must come first, as it overwrites other parameters.
      -m <int> ............... compression method (0=fast, 6=slowest)
      -segments <int> ........ number of segments to use (1..4)
      -size <int> ............ Target size (in bytes)
      -psnr <float> .......... Target PSNR (in dB. typically: 42)

      -s <int> <int> ......... Input size (width x height) for YUV
      -sns <int> ............. Spatial Noise Shaping (0:off, 100:max)
      -f <int> ............... filter strength (0=off..100)
      -sharpness <int> ....... filter sharpness (0:most .. 7:least sharp)
      -strong ................ use strong filter instead of simple.
      -partition_limit <int> . limit quality to fit the 512k limit on
                               the first partition (0=no degradation ... 100=full)
      -pass <int> ............ analysis pass number (1..10)
      -crop <x> <y> <w> <h> .. crop picture with the given rectangle
      -resize <w> <h> ........ resize picture (after any cropping)
      -map <int> ............. print map of extra info.
      -d <file.pgm> .......... dump the compressed output (PGM file).

      -short ................. condense printed message
      -quiet ................. don't print anything.
      -version ............... print version number and exit.
      -noasm ................. disable all assembly optimizations.
      -v ..................... verbose, e.g. print encoding/decoding times

    Experimental Options:
      -af .................... auto-adjust filter strength.
      -pre <int> ............. pre-processing filter