This program generates a “Single Image Random Dot Stereogram”, or SIRDS, from a Macintosh PICT file or a portable grey-map file that describes a 3D scene. A SIRDS is an image which, when viewed in the appropriate way, appears to the brain as a 3D scene. The image is a stereogram composed of seemingly random dots. The program incorporates a new, simple, and symmetric algorithm for generating such images from a solid model. It improves on previous algorithms in several ways: it is symmetric and hence free from directional left-to-right or right-to-left bias, it corrects a slight distortion in the rendering of depth, it removes hidden parts of surfaces, and it also eliminates a type of artifact that we call an “echo.”
The program is described in Working Paper 1993/2 of the Department of Computer Science, University of Waikato, Hamilton, New Zealand. (This report can be obtained from ftp.cs.waikato.ac.nz.)
Using SIRDS
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SIRDS reads and writes PICT files and 256 level PGM files. A level of 0 (black), corresponds to a z-level of 0.0 (the far plane) through to level 255 (white) corresponding to a z-level of 1.0 (the near plane).
To see your first Single Image Random Dot Stereogram, use the ‘Open’ menu item to select a PICT or a PGM file. A few examples come with the distribution, mainly the examples given in our paper.
As soon as you have selected a file, the program will automatically generate a SIRDS based on our symmetric algorithm -- with hidden line removal. This mode is termed the ‘linked (h/s)’ approach in our paper.This Macintosh program only generates stereograms with hidden lines removed.
‘mu’ is the distance that the near plane is closer to the eyes than the far plane. By default this value is 0.33 (~= 1/3) This Macintosh program does not allow you to change ‘mu’.
You can save the SIRDS as a PICT file and you can print it.
Shimmering is approximated by choosing the ‘Shimmer’ menu choice. This will take the gray scale SIRDS and animate the palette. This only works if your display is set for 256 colors. {An IBM-PC program is also available, this only demonstrates the SHIMMERing effect and is called “shimmer.zip”, available at the above site}
How to See SIRDS
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This program generates stereograms to be viewed while going wall-eyed (or boss-eyed), this is where you focus twice past the screen (look for the reflection of your nose...). The two dots at bottom of the window aid in viewing the object.
Looking at the two dots, try and focus past the screen; you will initially see 4 dots, if you look further away these dots will converge into 3. As you stare at the centre dot an object will slowly appear (The time required for this step varies on the person, from 1 second to 10 minutes). {If you are equally short-sighted in both eyes, removal of your glasses may help…}
I find that Cup and Hemisphere are the easiest files for a first time viewer to see.
The ‘Shimmering’ option also helps to ‘lock onto’ the image, as the cycling colours do not allow you to focus on the plane of the screen.
About This Macintosh Program
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This program is by David Phillip Oster. Since it is based on work placed in the open literature by Harold W. Thimbleby, Stuart Inglis, & Ian H. Witten, the source code is available for any use with only the following restriction:
you may use this source code any way you like, but you may not forbid anyone else from also using the source code.
The source is available at: ftp://ftp.netcom.com/~ftp/pub/os/oster/SIRDS
This program compiles under THINK C 7, and Metrowerks.
This program is a fat binary, so it runs at full speed on 68000 and PowerPC based Macintoshs. It has Balloon Help. This program runs best if you set your display to ‘Millions of Colors’ or to ‘256 colors’. Shimmering only works in 256 colors.
Fiction about SIRDS
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I recommend the novel “Snow Crash” by Neal Stephenson, Bantam Books, 1992, a cyberpunk novel about a cyberspace designed according to the Macintosh User Inteface Guidelines. The plot involves patterns that look to the uninitiated like mere white noise, but the trained mind finds meaning so compelling in the patterns, that the human mind actually crashes, becomes incapable of doing anything else, after perceiving the meaning in the patterns.
