pnmtoddif - Convert a PNM image to DDIF format
pnmtoddif [-resolution x y] [pnmfile [ddiffile]]
This program is part of Netpbm(1).
pnmtoddif takes a PNM image and converts it into a DDIF image file.
pnmtoddif writes PBM format (bitmap) data as a 1 bit DDIF, PGM format data (grayscale) as an 8 bit grayscale DDIF, and PPM format (color) data as an 8,8,8 bit color DDIF. pnmtoddif writes any DDIF image file uncompressed. The data plane organization is interleaved by pixel.
In addition to the number of pixels in the width and height dimension, DDIF images also carry information about the size that the image should have, that is, the physical space that a pixel occupies. Netpbm images do not carry this information, hence you have to supply it externally. The default of 78 dpi has the beneficial property of not causing a resize on most Digital Equipment Corporation color monitors.
Burkhard Neidecker-Lutz, Digital Equipment Corporation, CEC Karlsruhe email@example.com