usage: /usr/bin/djpeg [switches] [inputfile]
Switches (names may be abbreviated):
  -colors N      Reduce image to no more than N colors [legacy feature]
  -fast          Low-quality processing [legacy feature]
  -grayscale     Force grayscale output
  -rgb           Force RGB output
  -rgb565        Force RGB565 output
  -scale M/N     Scale output image by fraction M/N, eg, 1/8
  -bmp           Select BMP output format (Windows style)
  -gif           Select GIF output format (LZW-compressed) [legacy feature]
  -gif0          Select GIF output format (uncompressed) [legacy feature]
  -os2           Select BMP output format (OS/2 style) [legacy feature]
  -png           Select PNG output format
  -pnm           Select PBMPLUS (PPM/PGM) output format (default)
  -targa         Select Targa output format [legacy feature]
Switches for advanced users:
  -precision 12  Force 12-bit-per-sample output [useful for shadow recovery]
  -dct int       Use accurate integer DCT method (default)
  -dct fast      Use less accurate integer DCT method [legacy feature]
  -dct float     Use floating-point DCT method [legacy feature]
  -dither fs     Use Floyd-Steinberg dithering when quantizing colors (default)
                 [legacy feature]
  -dither none   Don't use dithering when quantizing colors [legacy feature]
  -dither ordered  Use ordered dithering when quantizing colors
                   [legacy feature]
  -icc FILE      Extract ICC profile to FILE
  -noicc         Do not transfer ICC profile to PNG output file
  -map FILE      Quantize to colors used in named image file [legacy feature]
  -nosmooth      Use faster, lower-quality upsampling
  -onepass       Use 1-pass color quantization (low quality) [legacy feature]
  -maxmemory N   Maximum memory to use (in kbytes)
  -maxscans N    Maximum number of scans to allow in input file
  -outfile name  Specify name for output file
  -nooverwrite   Don't overwrite output file if it exists
  -memsrc        Load input file into memory before decompressing
  -report        Report decompression progress
  -skip Y0,Y1    Decompress all rows except those between Y0 and Y1 (inclusive)
  -crop WxH+X+Y  Decompress only a rectangular subregion of the image
                 [requires PNG, PBMPLUS (PPM/PGM), Targa, or GIF output format]
  -strict        Treat all warnings as fatal
  -verbose  or  -debug   Emit debug output
  -version       Print version information and exit