pamsistoaglyph(1)

SECCIÓN: 1 - Comandos de usuario

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

NAME

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

anaglyphic image

SYNOPSIS

pamsistoaglyph [--invert] [--sep=number] [--minsep=number] [--gray=num‐

ber] [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 im‐

age as output.

pamsistoaglyph takes a single-image stereogram (SIS) such as those pro‐

duced by pamstereogram(1) and converts it to a red/cyan anaglyphic im‐

age 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 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 single-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 ⟨index.html#commonoptions⟩ ), 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 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 be‐

tween

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 con‐

version

from a low-quality JPEG image, for example). The default of

seems to work well so the --gray option should

rarely be necessary.

NOTES

The registration algorithm used by pamsistoaglyph was developed specif‐

ically for this program. As far as the author knows, there are no ex‐

isting algorithms for converting stereograms to anaglyphs. The algo‐

rithm works as follows:

• Convert the image to grayscale to increase the ability to iden‐

tify

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 indepen‐

dently

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

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)

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