pbmclean(1) - Man pages

Pbmclean User Manual(1) General Commands Manual Pbmclean User Manual(1)

NAME
pbmclean - despeckle a PBM image

SYNOPSIS
pbmclean [-minneighbors=N] [-black|-white] [-extended] [pbmfile]

OPTION USAGE
You can use the minimum unique abbreviation of the options. You can use
two hyphens instead of one. You can separate an option name from its
value with white space instead of an equals sign.

DESCRIPTION
This program is part of Netpbm(1).

pbmclean cleans up a PBM image of random specks. It reads a PBM image
as input and outputs a PBM that is the same as the input except with
isolated pixels inverted.

You can use pbmclean to clean up "snow" on bitmap images.

There are two ways pbmclean can define "isolated" pixels: simple and ex-
tended. When you specify -extended, pbmclean uses extended; otherwise
it uses basic.

Basic Mode
In basic mode, pbmclean looks at each pixel individually, and any pixel
that doesn't have at least a minimum number of pixels of the same color
touching it is considered isolated and pbmclean erases it.

The -minneighbors option specifies the minimum number of neighboring
pixels of the same color for a pixel not to be considered isolated.

For example, if -minneighbors is two and there are two contiguous black
pixels in an otherwise white field, each of those pixels is isolated, so
pbmclean erases them - turns both white.

The default minimum 1 pixel - pbmclean flips only completely isolated
pixels.

(A -minneighbors value greater than 8 generates a completely inverted
image (but use pnminvert to do that) -- or a completely white or com-
pletely black image with the -black or -white option).

pbmclean considers the area beyond the edges of the image to be white.
(This matters when you consider pixels right on the edge of the image).

pbmclean does not distinguish between foreground and background; by de-
fault, it flips isolated pixels of either color. But you can specify
-black or -white to have it flip only pixels of one color.

Extended Mode
In extended mode, pbmclean erases all blobs which don't have the speci-
fied minimum number of pixels. A blob is a set of contiguous pixels of
the foreground color. The minimum number of pixels is one plus the
-minneighbors value. You specify the foreground color with -black and
-white (default is black).

For example, if -minneighbors is 2 and the foreground color is black,
and the image contains a straight line 4 pixels long, pbmclean erases
that -- turns all four pixels white. pbmclean also erases 4 pixels in a
square or L-shape.

The default -minneighbors is 4, so a blob must have at least 5 pixels to
escape pbmclean's purge.

Extended mode was new in Netpbm 10.56 (September 2011).

OPTIONS
In addition to the options common to all programs based on libnetpbm
(most notably -quiet, see ]8;;index.html#commonoptions\ Common Options]8;;\ ), pbmclean recognizes the
following command line options:

-black

-white Flip pixels of the specified color. By default, if you specify
neither -black nor -white, pbmclean flips both black and white
pixels which do not have sufficient identical neighbors. If you
specify -black, pbmclean leaves the white pixels alone and just
erases isolated black pixels. Vice versa for -white. You may
specify both -black and -white to get the same as the default be-
havior.

-minneighbors=N
This determines how many pixels must be in a cluster in order for
pbmclean to consider them legitimate and not clean them out of
the image. See ]8;;#description\Description]8;;\ .

Before December 2001, pbmclean accepted -N instead of -minneigh-
bors. Before Netpbm 10.27 (March 2005), -minneighbors was -min-
neighbor.

-extended
pbmclean uses extended, as opposed to basic, isolated pixel de-
tection.

This option was new in Netpbm 10.56 (September 2011).