They can take input either from stdin or from a file specified on the command line. If a filename appears on the command line, stdin will not be checked for input. Filenames must appear before numeric arguments.
Output is directed to stdout and errors to stderr.
Scaling may be specified by a single proportion argument that will scale both axes and preserve aspect ratio, or by independent x and y specifications. RgbascaleB specifies that the unweighted box algorithm will be used to scale the image. RgbascaleF uses a fourier transform to scale the image. The box transform is generally well behaved but can 'fuzz' an image slightly. The fourier transform is better at preserving sharpness of detail, but can 'ring' or 'ripple' slightly around thin, sharp features.