ASCII stereogram

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ASCII stereograms are a form of ASCII art based on stereograms to produce the optical illusion of a three-dimensional image by crossing the eyes appropriately using a single image or a pair of images next to each other.

To obtain the 3D effect (in Figure 1 for instance), it is necessary for the viewer to diverge (unfocus) their eyes such that two adjacent letters in the same row come together. To help in focusing, try to make the two capital Os at the top look like three. Ensure that the image of the central dot is stable and in focus. Once this has been done, look down at the rest of the image and the 3D effect should become apparent. If the Os at the bottom of Figure 1 look like three, then the effect is reversed. It is also possible to obtain opposite 3D effects by crossing the eyes rather than diverging them, although some people find this harder to do.

Figure 1: Near and far distances.

                             O    O
n   n   n   n   n   n   n   n   n   n   n   n   n   n   n   n   n
f    f    f    f    f    f    f    f    f    f    f    f    f    f
e   e   e   e   e   e   e   e   e   e   e   e   e   e   e   e   e
a    a    a    a    a    a    a    a    a    a    a    a    a    a
a   a   a   a   a   a   a   a   a   a   a   a   a   a   a   a   a
r    r    r    r    r    r    r    r    r    r    r    r    r    r
r   r   r   r   r   r   r   r   r   r   r   r   r   r   r   r   r

Figure 2 demonstrates the effect even more dramatically. Once the 3D image effect has been achieved, moving the viewer's head away from the screen increases the stereo effect even more. Moving horizontally and vertically a little also produces interesting effects.

Figure 3 shows a Single Image Random Text Stereogram (SIRTS) based on the same idea as a Single Image Random Dot Stereogram (SIRDS). The word "Hi" in relief can be seen when the image clicks into place.

Some people have included stereograms in their "signature" at the end of electronic mail messages and news articles. Figure 4 is such an example.

Figure 2: A floor, wall and ceiling.

                           O          O
.  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .
 .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .
   .    .    .    .    .    .    .    .    .    .    .    .    .
   .     .     .     .     .     .     .     .     .     .     .
     .      .      .      .      .      .      .      .      .
 .       .       .       .       .       .       .       .       .
      .        .        .        .        .        .        .
   .         .         .         .         .         .         .
.          .          .          .          .          .          .
|          |          |          |          |          |          |
|          |          |          |          |          |          |
|          |          |          |          |          |          |
|          |          |          |          |          |          |
|          |          |          |          |          |          |
|          |          |          |          |          |          |
   .         .         .         .         .         .         .
      .        .        .        .        .        .        .
 .       .       .       .       .       .       .       .       .
     .      .      .      .      .      .      .      .      .
   .     .     .     .     .     .     .     .     .     .     .
   .    .    .    .    .    .    .    .    .    .    .    .    .
 .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .
.  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .

Figure 3: A single image random text stereogram.

                      O              O
OIWEQPOISDFBKJFOIWEQPOISDFBKJFOIWEQPOISDFBKJFOIWEQPOISDFBKJF
EDGHOUIEROUIYWEVDGHOXUIEROIYWEVDGHEOXUIEOIYWEVDGHEOXUIEOIYWE
KJBSVDBOIWERTBAKJBSVEDBOIWRTBAKJBSOVEDBOWRTBAKJBSOVEDBOWRTBA
SFDHNWECTBYUVRGSFDHNYWECTBUVRGSFDHCNYWECBUVRGSFDHCNYWECBUVRG
HNOWFHLSFDGWVRGHNOWFGHLSFDWVRGHNOWSFGHLSDWVRGHNLOWSFGLSDWVRG
YPOWVXTNWFECHRGYPOWVEXTNWFCHRGYPOWNVEXTNFCHRGYPWOWNVETNFCHRG
SVYUWXRGTWVETUISVYUWVXRGTWVETUISVYUWVXRGWVETUISVYUWVXRGWVETU
WVERBYOIAWEYUIVWVERBEYOIAWEYUIVWVERBEYOIWEYUIVWLVERBEOIWEYUI
EUIOETOUINWEBYOEUIOEWTOUINWEBYOEUIOEWTOUNWEBYOETUIOEWOUNWEBY
WFVEWVETN9PUW4TWFVEWPVETN9UW4TWFVETWPVET9UW4TWFBVETWPET9UW4T
NOUWQERFECHIBYWNOUWQXERFECIBYWNOUWFQXERFCIBYWNOFUWFQXRFCIBYW
VEHWETUQECRFVE[VEHWERTUQECFVE[VEHWQERTUQCFVE[VEOHWQERUQCFVE[
UIWTUIRTWUYWQCRUIWTUYIRTWUWQCRUIWTXUYIRTUWQCRUIBWTXUYRTUWQCR
IYPOWOXNPWTHIECIYPOWTOXNPWHIECIYPONWTOXNWHIECIYLPONWTXNWHIEC
R9UHWVETPUNRQYBR9UHWVETPUNRQYBR9UHWVETPUNRQYBR9UHWVETPUNRQYB

Figure 4: A stereogram signature.

 IIIIIIIIIIIIIII   IIIIIIIIIIIIIII  
 H ( )  \|/    H   H   ( )   \|/ H  
 H(   ) -O-    H   H  (   )  -O- H  
 H     )/|\    H   H (     ) /|\ H  
 H======^======H   H======^======H  
 H- |----@-----H   H----| ---@---H  
 H /|\ @\|/ @  H   H   /|\@ \|/@ H 
 H    \|/  \|/ H   H     \|/  \|/H  
 III^IIIIIII^III   III^IIIIIII^III  
Wide eyed stereo  Wide  eyed  stereo

The stereo effect can be used to highlight individual words in a text, as a sort of "secret message". The effect can be disguised when the paragraph is block justified.

Figure 5: Emphasized single words.

According to  the police inspector,   According to  the police inspector,
Edward   John Billings,  there  are   Edward  John  Billings,  there  are
too  many individuals too  close to   too  many individuals too  close to
the case to make an arrest. I asked   the case to make an arrest. I asked
Mary  Smith to comment on the case,   Mary Smith  to comment on the case,
but she declined to comment, on the   but she declined to comment, on the
grounds that she  is engaged to  be   grounds that she is  engaged to  be
married to  Howard Fredericks,  the   married to  Howard Fredericks,  the
victim's  uncle.   Charles  Wilson,   victim's  uncle.   Charles  Wilson,
the victim's brother,  stated  that   the victim's brother,  stated  that
the chaos  was  responsible for  at   the chaos  was responsible  for  at
least  five suicide  attempts  last   least  five suicide  attempts  last
week alone.                           week alone.

Moving animated versions of ASCII stereograms are possible too.

[edit] Acknowledgements

Figures 1, 2, 3 and 4 are due to David B. Thomas, Jonathan Bowen, Charles Durst and Marty Hewes respectively. These four stereograms appeared on the publicly accessible alt.3d USENET newsgroup. Figure 5 was invented on the spot by a Wikipedian.

Originally adapted from an article on ASCII Stereograms by the author of that article (and with his permission).