pam_filter

pamfilter filterprogram [ filterprogram_arguments ]

filterprogram
    The name of the program to use as a filter. pamfilter executes this program as a child process.

filterprogram_arguments
    Optional arguments to pass to the filterprogram.

pamfilter is a versatile Netpbm utility that reads a PAM (Portable Arbitrary Map) image from standard input, applies a specified filter operation to it, and writes the filtered PAM image to standard output.

The filter operation is defined by a separate program which pamfilter executes as a child process. pamfilter forwards the input image data to the program's standard input, and then reads the program's standard output as the filtered image.

This command is very useful for image manipulation tasks such as adding effects, altering pixel values, or performing other image transformations using custom logic encoded within the filter program.

It supports a wide range of PAM image types including grayscale, color, and transparency.

The filterprogram must be executable and correctly handle PAM image data on standard input and standard output.
pamfilter offers no means of verifying if the output of the filterprogram is a valid PAM image.
The user is responsible for ensuring the security and correctness of the filterprogram.

To blur an image using a fictional filter program named blurfilter:
cat input.pam | pamfilter blurfilter 10 > output.pam

Here, blurfilter is the name of the program that performs the blur, and 10 is an argument passed to blurfilter, potentially representing the blur radius.

pamfilter is part of the Netpbm suite. The Netpbm suite has been developed and maintained since the 1980s. pamfilter was likely developed to provide a flexible framework for extending the image processing capabilities of Netpbm through external programs. Its design emphasizes modularity, allowing users to create specialized image filters without modifying core Netpbm tools. It allows custom programs to interact with Netpbm.

pamditherbw(1), pamtopnm(1), ppmtopam(1)