Archived posting to the Leica Users Group, 2011/01/08

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Subject: [Leica] Optical Illusion
From: dennis at (Dennis)
Date: Fri, 07 Jan 2011 22:28:15 -1000
References: <>

Previously, on the LUG:

-------- Original Message --------
Subject: Re: [Leica] OT:  optical illusion
Date: Sat, 05 Nov 2005 20:18:07 +0100
From: Didier Ludwig <rangefinder at>
Reply-To: Leica Users Group <lug at>
To: Leica Users Group <lug at>
References: <229pm115rc5matisq7skleq8vjup7d3pgj at>

The main thing is, our visual perception system is perfectioned for
"movie mode", not "stills mode". Our retina can be cheatened very easy
with optical tricks like that. I use a similar animation in my classes
at the Lucerne Art school to explain how our eyes/retina/nerves/brain

The retina has cells that can send color informations, and others can
send brightness/darkness informations, and the brain puts it together to
an image. There are millions of cells overlayered, but each cell has a
certain delay time after it has send an information, until it's ready
for the next one. If, for a certain time which can vary from a few
seconds to a minute or longer, one cell gets the same color/brightness
value to communicate, it starts to compensate it with sending the
inverse value (complementary color) in this interval time (called the

To come back on this sample: It's an animation with 12 frames. On each
of the frame, there is one pink dot missing, clockwise. Now, if your
eyes follow the rotation movement, you see the "missing dot" turning
round. That's what really happens. That's not an illusion.

Now to the illusions: If you focus on the cross in the middle, you start
to see a green dot where the the missing pink dot, or better said, the
grey background, should be seen. Why? It's the complementary color
afterimage mentioned above. Make a red dot on a white paper, look at it
for 10 seconds, then look at a white surface, and you'll see what I mean
(or better said a a cyan dot).

Then, if you look longer at the cross, even the pink dots do disappear
and you see only the green one rotating on a grey ground. Why this?
That's because the pink (normal image) and green (afterimage)
impressions are neutralizing theirself, making it grey like the
background. Try it with other colors here:


Tina Manley wrote:
> LUG:
> We're discussing eyesight on another list and somebody sent this link:
> <>That's
> the weirdest thing I've ever seen!
> Tina

In reply to: Message from images at (Tina Manley) ([Leica] Optical Illusion)