NAME

       pamshuffle - Shuffle pixels of a Netpbm image

SYNOPSIS

       pamshuffle [-column [-randomseed integer]] [pamfile]

       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(1).

       pamshuffle  reads  a  Netpbm  image  as  input and produces an output file with the pixels
       shuffled.  The operation  only  changes  the  location  of  existing  pixels;  nothing  is
       discarded or added.

       By  default,  pixels change location within rows independently, but it is also possible to
       perform the same shuffle on every row, meaning the program is shuffling  vertical  columns
       of  pixels.   Either way, there is no vertical rearrangement; this means images consisting
       entirely of horizontal stripes, such as the national  banners  of  Germany,  Thailand  and
       Ukraine, will be unchanged.

       To  shuffle  vertically,  or  to perform a complete scramble, use pamshuffle together with
       pamflip.  See examples below.

       Input is from Standard Input if you don't specify the input file pamfile.

       Output is to Standard Output.

       pamshuffle works on a multi-image stream.   It  operates  on  each  image  in  the  stream
       independently and produces a multi-image stream output.

       The shuffling algorithm is the widely known
        Fisher-Yates method ⟨https://en.wikipedia.org/wiki/Fisher%E2%80%93Yates_shuffle⟩ .

OPTIONS

       In addition to the options common to all programs based on libnetpbm (most notably -quiet,
       see
        Common Options ⟨index.html#commonoptions⟩ ), pamshuffle recognizes the following  command
       line options:

       -column
              Shuffle vertical columns, i.e. perform the same movement on all rows.  Without this
              option, the program shuffles each row independently.

       -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, pamshuffle uses a seed derived from the time of  day  and  process  ID,
              which gives you quite uncorrelated results in multiple invocations.

EXAMPLES

       In  the  following  example,  output is to Standard Output.  You will probably want to add
       redirection to somewhere useful.

       •

              pamshuffle is useful when you  want  to  randomize  the  orderly  output  of  image
              generators such as pamseq and pgmramp.

              Produce five permutations of integers 0 to 15:

              pgmramp -lr -maxval=15 16 5 | pamshuffle -plain

       •      Shuffle columns:

              pamshuffle -column image.ppm

       •      Shuffle rows:

              pamflip -cw image.ppm | pamshuffle | pamflip -ccw

       •      Perform complete shuffle:

              pamflip -cw image.ppm | pamshuffle | pamflip -ccw | pamshuffle

SEE ALSO

       pamseq(1), pgmramp(1), pamflip(1), ppmshift(1), ppmspread(1), pam(1)

HISTORY

       pamshuffle was new in Netpbm 10.99 (June 2022).

AUTHOR

       By Akira F. Urushibata.  Contributed to the public domain by the author.

DOCUMENT SOURCE

       This  manual page was generated by the Netpbm tool 'makeman' from HTML source.  The master
       documentation is at

              http://netpbm.sourceforge.net/doc/pamshuffle.html