XaoS online help - Random dot stereogram
Description: XaoS, realtime, fractal, zoomer

# Random dot stereogram

Fractal images are good as a base for random dot stereograms. In case you don't know what these are, please point your browser to Google or another search engine and find some articles about such images, because learning to read such images takes some effort. They make it possible to generate three dimensional images on a normal monitor without any additional hardware, by exploiting bugs in the human brain (although you need two working eyes, and some people never learn to see them; they can simply ignore this feature).

XaoS is able to generate these images in animations, so you may use all normal XaoS functions (except palette changing and palette rotation, which makes no sense applied to a stereogram). To make the animation yet more exciting, XaoS emulates "falling" into the set; while you zoom in, your distance from the set drops and drops--but you never hit it; when the set reaches the level of your monitor, the distance is changed again so you are far away.

To make this work right, XaoS needs to know the exact size of your monitor. Because most platforms have no way to determine this, you need to use command line options to tune it. If it's not set or is wrong, the stereograms will probably be impossible to see (if your monitor is too big or resolution too low), or the images will seem to be shallow (if your monitor is too small or resolution too high).

By default XaoS expects my 15" monitor (29.0cm x 21.5 cm). Another cause of problems is the virtual screen supported by some windowed environments (like some X servers) that makes a program think that the resolution is higher than it actually is, and you see only part of this extra-large screen.

The worst thing you could possibly do is to run full-screen XaoS in some graphical windowing system (OS/2 on top of Windows or Wine on top of Linux, perhaps) where XaoS can't tell the real size of its window at all. In such cases, it's normally better (not to mention faster) to run XaoS natively, rather than under such an emulation layer.

The following command line options are provided to specify sizes:

`-screenwidth`, `-screenheight`
  Lets you specify the size of your screen in centimeters. Note that you need to specify the size of the visible image on the monitor, not the size with edge borders, or the size of the tube. The simplistic `my monitor is 17", just turn 17" into centimeters' doesn't work; that 17" is a marketing figure and has only a vague connection to reality. Get out a ruler and measure it.
`-pixelwidth`, `-pixelheight`
  Lets you specify the exact size of a single pixel, if XaoS cannot determine this for itself from your screen size.

These options are used by some other parts of XaoS as well, so you should use them even when you don't want to see stereograms. You should probably write a small starting script (or alias, or shortcut; whatever your environment uses) that passes the correct parameters to XaoS.

If the window is smaller than 8cm in any direction, you will probably be unable to see anything; make the window bigger. The correct way to see XaoS stereograms is:

1
  Start XaoS with options specifying the exact size of your screen or one pixel on it
2
  Sit 60cm away from monitor
3
  If you use a windowed environment, resize XaoS's window to make it wider than, say, 15 cm.
4
  Enable the filter (by pressing `E`)
5
  focus on a point far away from the monitor (try to use your own reflection, if your monitor's not antireflective); the random blurring should eventually fall into the pattern of a Mandelbrot set.
6
  Carefully use your mouse to zoom into interesting areas (it is easy to lose concentration when you are not trained; but you can use the autopilot...)
7
  Enjoy animation :)

If you still can't see the stereograms, it could be that the fractal, or your eye, is deformed. A deformed fractal can be caused by your specifying your monitor size wrongly. Visual problems that damage depth perception, as well as problems like astigmatism, can make it impossible to see stereograms at all.

More information about filters

Available as: menu item, command line option