pamtopbm

pamtopbm [options] [pamfile]

-threshold=number
    Specify the threshold for determining black or white pixels. Pixels with intensity greater than 'number' become white. The default is half of the maximum intensity.

-plain
    Generate a plain (ASCII) PBM output. The default is raw PBM.

pamfile
    The input PAM file. If not specified, reads from standard input.

The pamtopbm command converts a PAM (Portable Arbitrary Map) image to a PBM (Portable Bitmap) image. A PAM image contains pixel data in a general format, allowing for multiple color channels and different bit depths. pamtopbm simplifies this data to a black and white bitmap. It thresholds the input PAM image based on pixel values. By default, any pixel with a total intensity greater than half of the maximum intensity is converted to white in the PBM output, and all others are converted to black. This threshold can be adjusted with command-line options. The command can handle PAM images with multiple color channels by summing them to derive a single intensity value. It is part of the Netpbm suite, a collection of graphics conversion tools widely used on Unix-like systems. pamtopbm is useful when you need a simple black and white representation of an image for further processing with tools that only accept PBM format. This tool is handy to convert portable anymaps to bitmaps for very simple operations or viewers.

The conversion to black and white results in a significant loss of information. Color and grayscale information is discarded. This command might not be suitable for images with subtle variations in intensity that need to be preserved.

pamtopbm is designed to handle PAM images of different depth and color components. However, the more complex the input image, the more information is lost.
For example, for color image first all color components are summed up and then compared with threshold value.

pamtopbm is part of the Netpbm suite, which originated in the late 1980s and early 1990s. It was developed to provide a portable and versatile set of tools for image manipulation and conversion across different platforms. PAM was introduced as a more flexible replacement for the older PGM, PPM formats. Usage has been steady due to the simplicity and wide support of Netpbm across various systems.

pbmtopam(1), pam(5), pbm(5), pamditherbw(1)