pbmnoise

Updated: 18 December 2021
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NAME

pbmnoise - create a PBM image made up of white noise

SYNOPSIS

pbmnoise width height [-ratio=M/N] [-pack] [-randomseed=integer] [-endian=]{big|little|native|swap}]

Minimum unique abbreviations of option are acceptable. You may use double 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.

pbmnoise creates a PBM image with random pixels. You specify the probability 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 arguments.

OPTIONS

In addition to the options common to all programs based on libnetpbm (most notably -quiet, see Common Options), 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 proportion 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 fractional pixels at row ends by default. When this option is specified, the unused pixels are carried over to the next row, eliminating 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 invocations.

By default, pbmnoise uses a seed derived from the time of day and process ID, which gives you fairly uncorrelated results in multiple 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 results 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 machines. 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 colored 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 efficient. 


  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

SEE ALSO

pbm pgmnoise pgmtopbm

HISTORY

pbmnoise was new in Netpbm 10.97 (December 2021).

In Netpbm before that, you can use pgmnoise.

AUTHOR

Akira F Urushibata wrote this program and contributed it to the public domain in December 2021.

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