pbmnoise(1) - Man pages

Pbmnoise User Manual(1) General Commands Manual Pbmnoise User Manual(1)

NAME
pbmnoise - create a PBM image made up of white noise

SYNOPSIS
pbmnoise width height

[-ratio=M/N] [-pack] [-randomseed=integer] [-endian=]{big|little|na-
tive|swap}]

Minimum unique abbreviations of option are acceptable. You may use dou-
ble hyphens instead of single hyphen to denote options. You may use
white space in place of the equals sign to separate an option name from
its value.

DESCRIPTION
This program is part of Netpbm(1).

pbmnoise creates a PBM image with random pixels. You specify the proba-
bility each pixel will be black or white (essentially, the proportion of
black to white pixels in the image).

You specify the dimensions of the image with the width and height argu-
ments.

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

-ratio=M/N
The proportion of black pixels in the generated image.

To be precise, this is the probability that any given pixel will
be black. By the law of large numbers, we can expect the propor-
tion of black pixels in a reasonably large image to be close to
this fraction.

The option value is a fraction. The denominator must be 1 or an
integer power of 2 up to 65536. the numerator must be 0 or a
positive integer not exceeding denominator.

The default is 1/2, meaning the output image has essentially the
same number of black and white pixels.

If the ratio is 0 the output image is entirely white. If 1, the
output is entirely black.

-pack The program generates pixels in 32-bit units discarding any frac-
tional pixels at row ends by default. When this option is speci-
fied, the unused pixels are carried over to the next row, elimi-
nating waste in exchange for some overhead cost.

Using this option improves performance when the image width is
small.

-randomseed=integer
This is the seed for the random number generator that generates
the pixels.

Use this to ensure you get the same image on separate invoca-
tions.

By default, pbmnoise uses a seed derived from the time of day and
process ID, which gives you fairly uncorrelated results in multi-
ple invocations.

-endian=mode
pbmnoise internally generates random 32-bit integers and uses the
machine's binary encoding of those integers as strings of pixels.
Because the integers are random, it doesn't normally matter what
binaary encoding is used for them, but if you need consistent re-
sults between machines using the same random number generator, it
matters. For that reason (mainly for testing the program), this
option lets you control that encoding, between big-endian and
little-endian.

mode is one of the following:

big Force big-endian output by rearranging bytes on little-endian ma-
chines. No effect on big-endian machines.

little Likewise, force little-endian output.

native Do not rearrange anything. This is the default.

swap Always swap regardless of system endianness.

EXAMPLES
This generates a random PBM image with roughly one-third of pixels col-
ored black:
pbmnoise -ratio=11/32 1200 1200 > random.pbm

The following is an alternate method for generating a random PBM image
which uses pgmnoise and pgmtopbm instead of pbmnoise. It is less effi-
cient.
pgmnoise -maxval=100 1200 1200 | \
pgmtopbm -threshold -value=0.333 > random.pbm

This generates a random PPM image, maxval 1:
pbmnoise 600 400 > red.pbm
pbmnoise 600 400 > green.pbm
pbmnoise 600 400 > blue.pbm
rgb3topbm red.pbm green.pbm blue.pbm > random.ppm