PAM to DJVU Converter

PAM (Portable Arbitrary Map) is a raster image format added to the Netpbm family around the year 2000 by Bryan Henderson, the maintainer of Netpbm, as a generalization that unifies and extends the original PBM, PGM, and PPM formats. Where the classic Netpbm formats each handle a specific image type (PBM for bilevel, PGM for grayscale, PPM for color), PAM provides a single format that can represent any combination of channels, bit depths, and image types through a flexible ASCII header. The PAM header uses keyword-value pairs: WIDTH, HEIGHT, DEPTH (number of channels), MAXVAL (maximum sample value, up to 65535), and TUPLTYPE (a string identifying the image type — BLACKANDWHITE, GRAYSCALE, RGB, GRAYSCALE_ALPHA, RGB_ALPHA, or custom types). After the header, pixel data is stored in binary, with each sample occupying one or two bytes depending on MAXVAL. PAM's key innovation over its predecessors is native alpha channel support: GRAYSCALE_ALPHA (2-channel) and RGB_ALPHA (4-channel) tupletypes provide transparency without requiring a separate mask file, something the original PBM/PGM/PPM formats could not express. One advantage is format unification: a single PAM-reading implementation handles monochrome, grayscale, color, and alpha-augmented images, eliminating the need for separate parsers for each Netpbm variant. The extensible TUPLTYPE mechanism provides another practical strength — custom channel configurations (multispectral, depth + color, or any application-specific arrangement) can be represented and labeled without modifying the format specification. PAM is supported by Netpbm tools, ImageMagick, GIMP, and programming libraries that process the Netpbm family.