gemtopbm

View documentation for the current command

$ tldr gemtopnm

gemtopbm [-verbose] [gemfile]

-verbose
    Prints processing information, such as image dimensions, to standard error

The gemtopbm command is a utility from the Netpbm graphics package that converts bitmap images in the GEM (Graphics Environment Manager) format to the portable bitmap (PBM) format.

GEM format was used by Digital Research's GEM desktop environment and Ventura Publisher for raster images, often containing multiple resolutions of the same image. gemtopbm reads a GEM file and extracts the largest available bitmap, outputting it as a plain PBM (black-and-white) image to standard output.

This tool is ideal for legacy image conversion in Unix-like environments. It supports GEM bitmap version 2 files. If no input file is specified, it reads from standard input, allowing piping from other tools.

Output PBM images can be further processed with other Netpbm utilities like pbmtoxxx for conversion to PNG, JPEG, or other formats. The command is efficient for batch processing old GEM archives.

Installation is typically via the netpbm package on Linux distributions. Usage integrates well in scripts for image migration or archival workflows.

Reads GEM bitmap v2 files from gemfile or stdin. Extracts largest bitmap if multiple resolutions present; ignores vector data.

gemtopbm image.gem > image.pbm
cat image.gem | gemtopbm -verbose | pnmtopng > image.png

Part of Netpbm suite, originally developed by Jef Poskanzer starting 1988; gemtopbm added in early 1990s to support legacy GEM/ Ventura formats from Digital Research (1984). Maintained in Netpbm releases up to current versions.

pbmtogem(1), pbm(5), netpbm(1)