ppmcolormask

Create a PBM mask from one or more colors in a PPM image

TLDR

Mask a single color (modern syntax)

$ ppmcolormask -color=[red] [input.ppm] > [mask.pbm]

Mask several colors at once

$ ppmcolormask -color=[red,pink,salmon] [input.ppm] > [mask.pbm]

Use a hex/RGB color

$ ppmcolormask -color=[rgb:ff/00/00] [input.ppm] > [mask.pbm]

Use Berlin-Kay fuzzy color matching

$ ppmcolormask -color=[bk:red,bk:orange] [input.ppm] > [mask.pbm]

Obsolete positional form (single exact color)

$ ppmcolormask [red] [input.ppm] > [mask.pbm]

Feed a non-PPM image via pipe

$ jpegtopnm [photo.jpg] | ppmcolormask -color=[white] > [mask.pbm]

SYNOPSIS

ppmcolormask -color=colorlist [ppmfile_]ppmcolormask color [ppmfile]

ppmcolormask reads a PPM image and writes a PBM bitmap of the same dimensions. In the output, pixels matching any color in the -color list are black; all other pixels are white. The resulting mask is meant to be fed to programs such as pamcomp (as an alpha channel) or used with pnmpaste for region replacement.The Berlin-Kay (`bk:`) form applies a Sugeno-type fuzzy inference over HSV values, so related shades of a named color all match. The positional (non-`-color`) form is retained only for backwards compatibility and supports just one exact color.If ppmfile is omitted, input is read from standard input; output is always written to standard output.

PARAMETERS

-color=colorlist_

Mandatory. Comma-separated list of colors to mask. Each color may be a named color (`red`), a hex/rgb specifier (`rgb:ff/00/00`, `#ff0000`), or a Berlin-Kay fuzzy match prefixed with `bk:`.

-quiet

Common libnetpbm option: suppress informational messages on stderr.

CAVEATS

The non-`bk:` match is exact — small rounding differences from JPEG or scaling can miss pixels. For range or tolerance-based matching, use pambackground (for background selection) or pre-quantize the image with ppmquant.Output is always PBM, so a mask cannot encode partial transparency; convert with pgmtopbm or use `pnmtopng -transparent` if that is what you actually need.

HISTORY

ppmcolormask is part of the Netpbm toolkit originally written by Jef Poskanzer. The `-color` form (accepting a color list and Berlin-Kay matching) superseded the positional-color form in Netpbm 10.32.