Subject: Random dot stereograms and Single-image stereograms
Date: Sat, 24 Nov 2001 19:45:35 -0500
From: Scott E. Brodie

Dear Alex,

Happy Thanksgiving.

I was looking at your new page which includes mentions of random-dot stereograms, and includes a illustration of a single-image steroegram.

Your abbreviated example blurs the distinction between two aspects of the illusion: the use of random dots to encode stereoscopic disparity is credited to Bela Julesz (then at Bell Labs), and originally was demonstrated with standard stereoscopic viewing, with a complete, separate image presented to each eye simultaneously. This presentation is a "random dot stereogram".

Quite another matter is the "single-image stereogram", where a single quasi-periodic image, creates a stereoscopic illusion when viewed with altered ocular alignment. The quasi-periodic image can be composed of "random dots" (as is your example), or of larger image elements. This presentation is generally credited to Christopher Tyler, of the Smith-Kettlewell Eye Research Institute in San Francisco.

As a co-author of a paper with Julesz, and an acquaintance and vision-research colleague of Tyler, I feel it my duty to point out the distinction. Perhaps it would be a public service for you to point out the distinction, and, if possible, give credit to the original innovators.

Best regards,

Scott.

[Am still trying to see where your construction for doubling the cube breaks the rules!]

Scott E.Brodie New York

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