>: I recall seeing a blocky image of Lincoln in an issue of Byte some years
>: ago, the intent of the article being to report on how little information is
>: needed to present a recognizable image.
>Not really an answer to your question, but there is a quite amusing painting
>by Salvador Dali based on that image. It's one of his more famous ones,
>and should be pretty easy to find in a library or bookshop.
Actually, the effect of these blocky images demonstrates a more important
aspect of the human visual system. Namely, that we find edges by following
the local edge energy upward in frequency until it dead-ends. If the blocky
images are too close we see just blocks because the block edges dominate
perception. If we stand back or blur the projector etc. we are low-pass filtering
the image. Then our visual system dead-ends on the lower frequency edges
associated with an underlying pattern.
Dali takes this one step further. His painting looks like one thing close
and another thing far because there is structure within the blocks. The
original painting is in the Guggenheim in NY.
William C. Snyder
University of California Santa Barbara
CRSEO: Center for Remote Sensing and Environmental Optics