Images are converted by scaling them to fill the guaranteed reproduceable area on a default page. Each RGB pixel p is converted to greyscale according to:
where %r, %g, and %b default to 30, 59, and 11, respectively. Greyscale images are passed through a high pass filter and dithered to a bilevel image. The resultant images are written as a TIFF Class F document.
pr * %r + pg * %g + pb * %b
By default, output has a horizontal resolution of 204 dpi and a vertical resolution of 98 lines/inch. The vertical resolution can be doubled with the -m option. The -l option specifies the default, 98 lpi, resolution.
The -r, -g, and -b options can be used to specify alternate percentages to use in converting color values to greyscale.
By default, sgi2fax will write the output to a file named sgi.fax. An alternate name can be specified with the -o option.
By default, the output image is encoded using Group 3 1D encoding. 1D or 2D encoding can be specified with the -1 and -2 options, respectively.
A non-default page size can be specified with the -s option.