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Autostereograms
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  If you have visited any poster shop in your high street recently
you *may* have seen what appears to be posters of random dots and you
would be right in thinking that is what you had seen.  These posters
are dubbed autostereograms, being so because you can get a three
dimensional image out of those seemingly pointless patterns.  You may
have noticed that the images had a repeating pattern on the top. 
This is repeated at different focal lengths to produce the 3D image:

A *           *
B *                *

  Imagine that the first dot is part of the pattern, and the second
in each case is the same dot in the repeat.  In A the dot is closer,
but in B is repeated further away.  This results in B looking further
away.  Note: the 3D image is in no way connected to the visual
pattern!  To see the pictures you have to double the focal length of
your eyes.  Guess now how far you are from your monitor/TV.  Now
double it and image you are looking at something that far away.  It
is sometimes helpful to focus on your reflection (which will be twice
as far as you are from the screen :-)).

  If this doesn't work, then try this with A above.  Cross your eyes
until you see 4 stars.  Try and bend the image so that two of the
stars touch, leaving you with 3 stars.  That is how you see the
image.  For this method, you have to know the repeat length of the
picture you are looking at.

  By now I guess you may want to see a real 3D image.  Unfortunately,
due to the randomness of the dots, ArcFS cannot compact the resulting
sprites, and they have to be BIG to appreciate the effect.  Therefore
we have decided not to include an image with the article.  I have
created images with my own software.  I would have released it, but a
much better version appeared (tres similar to mine) called Wowpix by
'Garrard', get it from Arcade BBS.  It worked by using a MODE 12
sprite with different colours representing different focal lengths. 
A random pattern was plotted at the left, then copied so many pixels
to the right for each y position all the way up the screen, then for
each x pixel.

  It does take time to get the images the first time, but once you
have the knack, they appear in a second.  You can get hooked - just
visit your local Athena and watch peoples eyes bend and contort.  By
the way, the stuff about the images "expanding your mind" is a load
of bollox.

  Here is a special treat for you.  When you go back to a menu, look
at your reflection in the TV/monitor, making sure you focus on the
reflection of your eyes.  The stars appear to become true 3D; great eh!

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