This option (short: -m) can be used to limit the number of mip levels generated. Using -m 1 allows to use mipgen as a cheap-ish image converter.
mipgen
mipgen generates mipmaps for an image down to the 1x1 level.
Usage
$ mipgen [options] <input_file> <output_pattern>
Run mipgen --help for more information about available options.