pamtopnm

Convert a PAM image to an equivalent PNM image, i.e. a PBM, PGM, or PPM image

$ pamtopnm [path/to/image.pam] > [path/to/output.pbm|pgm|ppm]

$ pamtopnm [[-v|-version]]

pamtopnm [-ppm|-pgm|-pbm|-pbmalpha] [-plain] [-alphaout={alphaPamFile|-}] [-bgcolor=color] [pamfile]

-ppm
    Force PPM (Portable Pixmap) output, even for grayscale or mono images.

-pgm
    Force PGM (Portable Graymap) output, quantizing color to grayscale.

-pbm
    Force PBM (Portable Bitmap) output using Floyd-Steinberg dithering.

-pbmalpha
    Force PBM output with alpha channel dithered to two bit planes (opaque/transparent planes).

-plain
    Produce plain (human-readable ASCII) PNM instead of raw binary.

-alphaout=alphaPamFile|-
    Write alpha channel to separate PAM file (or stdout with '-').

-bgcolor=color
    Composite transparent pixels over specified color (Netpbm quadruplet, e.g., 'white' or '0,0,0,255').

pamtopnm is a command-line tool from the Netpbm graphics suite that reads a Netpbm PAM (Portable AnyMap) image and converts it to a standard PNM (Portable aNyMap) format, such as PPM (color), PGM (grayscale), or PBM (monochrome). PAM is a superset of PNM, supporting advanced features like alpha channels, arbitrary tuple sizes, and color spaces, making pamtopnm essential for pipelines needing PNM compatibility.

By default, it auto-detects the optimal PNM type: PPM for RGB or CMYK images, PGM for grayscale, and PBM for black-and-white with dithering. Output uses maxval 255, scaling if necessary. Alpha transparency can be handled by outputting to a separate PAM file or compositing over a background color.

Forcing formats overrides auto-detection: -ppm for full color, -pbm applies Floyd-Steinberg dithering for bitonal output. Plain (ASCII) PNM is available via -plain. It reads from stdin or a file and writes to stdout, integrating seamlessly with tools like pnmtopng or display. Widely used in batch processing, scripting, and legacy format conversions on Unix-like systems.

Auto-selects PPM/PGM/PBM based on image tuples; scales maxval to 255; writes raw PNM to stdout.

pamtopnm image.pam > image.ppm
pamtopnm -pbm -plain grayscale.pam
pamtopnm -alphaout=alpha.pam -bgcolor=white transparent.pam

Developed as part of the Netpbm project by Jef Poskanzer starting in 1988; PAM format introduced in 2000 to extend PNM capabilities. pamtopnm added shortly after for backward compatibility, now maintained by Netpbm community.

pnmtopam(1), pamtomp(1), ppmtopam(1), pnm(5), pam(5)