Manual: pamsistoaglyph

Pamsistoaglyph User Manual(1)			   General Commands Manual		       Pamsistoaglyph User Manual(1)

NAME
       pamsistoaglyph - convert a single-image stereogram to a red/cyan anaglyphic image

SYNOPSIS
       pamsistoaglyph [--invert] [--sep=number] [--minsep=number] [--gray=number] [in_netpbmfile

       All  options can be abbreviated to their shortest unique prefix. You may use either white space or an equals sign be‐
       tween an option name and its value.

DESCRIPTION
       This program is part of Netpbm(1).

       pamsistoaglyph reads a Netpbm image as input and produces a Netpbm image as output.

       pamsistoaglyph takes a single-image stereogram (SIS) such as those produced by pamstereogram(1) and converts it to  a
       red/cyan	 anaglyphic image such as those produced by ppm3d(1).  Many people have trouble tricking their eyes into fo‐
       cusing beyond the image in front of them and are therefore unable to perceive the 3-D shape hidden within  a  single-
       image  stereogram.   Anaglyphic stereograms are easier to perceive in 3-D but require a pair of red/cyan glasses such
       as those often used to watch 3-D movies. The goal of pamsistoaglyph is to help people who have trouble  viewing	sin‐
       gle-image stereograms see the intriguing 3-D effect.

       pamsistoaglyph  can  convert  single-image random-dot stereograms (SIRDS), wallpaper stereograms, and even dual-image
       stereograms to anaglyphic images.

OPTIONS
       In addition to the options common to all programs based on libnetpbm (most notably  -quiet,  see	  Common Options  ),
       pamsistoaglyph recognizes the following command line options:

       For most images, no command-line options need to be specified.  The following options are available, however, for un‐
       usual circumstances.

       --invert
	      Swap the left- and right-eye
		  images. pamsistoaglyph assumes that its input
		  represents a wall-eyed stereogram and generates the anaglyphic
		  image accordingly. If the generated image appears to recede into
		  the page where it should pop out of the page (and vice versa),
		  this typically implies that the input image represents a
		  cross-eyed stereogram. Use --invert to correct
		  the image depth.

       --sep=number
	      Specify the distance in pixels between the left- and right-eye
		  images. Essentially, this corresponds to the distance between
		  repetitions of the background pattern.  The --sep
		  option should rarely be necessary
		  as pamsistoaglyph is fairly good at determining
		  automatically the eye-separation distance.

       --minsep=number
	      This option is similar to --sep but
		  constrains pamsistoaglyph only to
		  a minimum eye-separation distance. Any distance larger
		  than number is acceptable.  The --minsep
		  option should rarely be necessary
		  as pamsistoaglyph is fairly good at determining
		  automatically the eye-separation distance.  The default value for
		  the minimum eye-separation distance is 10% of the image width;
		  this value seems to work well in practice.

       --gray=number
	      Limit the number of gray levels to use when searching for the
		  optimal eye-separation
		  distance.  Because pamsistoaglyph looks for
		  repeated patterns, it is vulnerable to being confused by slight
		  variations in color.	By reducing the input image to grayscale and
		  capping the number of gray levels,
		  pamsistoaglyph ameliorates the effects of
		  unintentional color variations (such as those caused by conversion
		  from a low-quality JPEG image, for example). The default of 63
		  seems to work well so the --gray option should
		  rarely be necessary.

NOTES
       The  registration  algorithm used by pamsistoaglyph was developed specifically for this program. As far as the author
       knows, there are no existing algorithms for converting stereograms to anaglyphs.	 The algorithm works as follows:

       •      Convert the image to grayscale to increase the ability to identify
		  matches.

       •      Count the number of pixels that match N pixels ahead in the
		  image for all N in [1, width/2].

       •      Maintain a running mean (mu) and standard deviation (sigma) of
		  the number of matched pixels.

       •      Store the N corresponding to each spike in the number of
		  matched pixels. A spike is defined as a tally that exceeds the
		  mean plus one, two, or three standard deviations. Only the first
		  spike of a given standard-deviation multiplier is stored.

       •      If a tally greater than mu+3sigma was encountered, return the
		  corresponding N. If not, then if a tally greater than
		  mu+2sigma was encountered, return the
		  corresponding N. If not, then if a tally greater than
		  mu+sigma was encountered, return the
		  corresponding N. If not, then return the N that
		  produces the minimum average distance between matched pixels
		  (i.e., #matches divided by #pixels). If no
		  such N exceeds the minimum allowable eye-separation value,
		  return zero to indicate failure.

       •      If the algorithm returned zero, rerun the algorithm independently
		  on each row of the input image and return the median of
		  all N that exceed the minimum allowable eye-separation
		  value. If no such N exists, abort with an error
		  message.

HISTORY
       Scott Pakin wrote pamsistoaglyph in April 2009.	It first appeared in Netpbm in Release 10.47 (June 2009).

AUTHOR
       Copyright (C) 2009 Scott Pakin, scott+pbm@pakin.org

SEE ALSO
       •      pamstereogram(1)

       •      ppm3d(1),

       •      http://en.wikipedia.org/wiki/Stereogram

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/pamsistoaglyph.html

netpbm documentation					05 April 2009			       Pamsistoaglyph User Manual(1)