gemtopbm

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$ tldr gemtopnm

gemtopbm [gemfile]

gemfile
    The path to the input GEM Paint .img file. If omitted, gemtopbm reads the image data from standard input.

gemtopbm is a utility from the Netpbm tools suite. It is designed to convert image files in the GEM Paint .img format into the Netpbm monochrome Portable Bitmap (PBM) format. The GEM Paint format was commonly used on systems like the Atari ST and early IBM PCs running the GEM (Graphical Environment Manager) desktop.

gemtopbm reads the GEM .img file, processes its pixel data, and outputs a corresponding PBM image to standard output. PBM is a very simple, raw bitmap format representing black and white pixels. This command is particularly useful for working with legacy image data from GEM-based applications or for archiving and converting old graphics files into a more universally accessible format within the Netpbm ecosystem. As GEM .img files are inherently monochrome, gemtopbm ensures a direct translation to PBM.

gemtopbm specifically handles the monochrome GEM Paint .img file format. It may not correctly process other GEM image formats or colored GEM files. The output is always a PBM (Portable Bitmap), which is monochrome, meaning any color information in a non-monochrome GEM file (if passed to it, though typically GEM Paint .img files are monochrome) would be lost or misinterpreted. This command is primarily for legacy file conversion.

gemtopbm reads its input GEM image from the file specified on the command line or from standard input if no file is given. The converted PBM image is always written to standard output. This allows for piping its output to other Netpbm utilities or redirecting it to a file. For example: gemtopbm input.img > output.pbm or cat input.img | gemtopbm > output.pbm.

The GEM Paint .img format is a monochrome bitmap format used by the GEM Paint application. gemtopbm expects this specific structure. The output PBM format is a simple, plain text or raw binary representation of a monochrome image, where each pixel is either black or white.

gemtopbm is a component of the Netpbm project, a comprehensive suite of graphics file format conversion tools. The Netpbm package evolved from programs initially developed by Jef Poskanzer in the late 1980s and early 1990s. As GEM was a significant graphical environment during that era, tools like gemtopbm were created to facilitate the conversion and interoperability of image data from such platforms into more standardized formats like PBM, PGM, and PPM, which form the core of the Netpbm suite. Its inclusion reflects the need to support legacy graphics formats popular in the early PC and Atari ST computing environments.

pbm(5), netpbm(1)