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Pamsistoaglyph User Manual(0)					    Pamsistoaglyph User Manual(0)

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 between 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	pamstere-
       ogram(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 focusing beyond the image in  front  of  them
       and  are  therefore  unable  to perceive the 3-D shape hidden within a single-image stere-
       ogram.  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 single-image stereograms see the intriguing 3-D
       effect.

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

OPTIONS
       For most images, no command-line options need to be specified. The following  options  are
       available, however, for unusual 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 pro-
       gram. As far as the author knows, there are no existing algorithms for  converting  stere-
       ograms to anaglyphs.  The algorithm works as follows:

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

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

       o      Maintain a running mean (μ) and standard deviation (σ) of
		  the number of matched pixels.

       o      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.

       o      If a tally greater than μ+3σ was encountered, return the
		  corresponding N. If not, then if a tally greater than
		  μ+2σ was encountered, return the
		  corresponding N. If not, then if a tally greater than
		  μ+σ 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.

       o      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
       o

	      pamstereogram(1)

       o

	      ppm3d(1) ,

       o

	      http://en.wikipedia.org/wiki/Stereogram <http://en.wikipedia.org/wiki/Stereogram>

netpbm documentation			   5 April 2009 	    Pamsistoaglyph User Manual(0)
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