I don’t feel this is much of an illusion. I think you just can’t see the movement of gray on black. Or maybe this is what illusions are in a very simple form?
Somewhere in between, there are shades of gray where the smooth movement of the pigeons is visible. And there are shades of gray where your brain can't separate it from the underlying black motion. That's interesting, no?
That's what makes all optical illusions interesting - exploring the thresholds where our brain's perceptual machinery takes shortcuts.
I've noticed there's a tendency, especially among smart people, to be dismissive of optical illusions. 'I didn't fall for it' - because to a certain personality, it's important to feel like your mind can understand things and you can't be 'fooled'.
But good optical illusions aren't fooling you. You don't need to feel defensive about whether you were 'tricked'. They're hacks that exploit edge cases in your visual cortex, and cause your brain to be fed erroneous data. They're interesting and useful because they help you calibrate the instruments your brain uses to collect data!
For the record: the illusion still works for me if I slide the color all the way to black. One eye, both eyes, it always works for me.
On the third hand, movement is an illusion in all cases: what's really happening is that static pixels are changing color and brightness (the pixels may jitter slightly in changing color, but that's not the motion we perceive.)
All these views seem to me to be reasonable, they are just different perspectives.
As a pixelated image, I dunno: our insistence on viewing groups of pixels as shapes is an illusion to start with.
There really is an image there when viewed at the intended scale.
In the digital version, if a group of pixels appears to be part of some object, that's as good a reason as any to argue it is part of that object (though strictly speaking, it's a meaningless question since it's just a bunch of pixels).
One is an illusion, or the set of all illusions, and the other is the set of all images generated by pixels.
Not all images generated by pixels are an illusion. Otherwise you would say that all images generated by, say, acrylic paint, are an illusion because they're made of molecules.
An illusion is not an illusion if what you perceive is what is actually happening.
The whole point of the "pigeon neck" illusion is that it tricks the eye into perceiving areas as growing that we know are incapable of growing. If the areas are inelastic matter, that's a cool effect: we know that a printed image on a transparency sheet cannot truly grow just by sliding it around a table.
If the areas are pixels... it's less significant. Nothing is actually moving to start with. It's all neighboring lights flashing on and off. If a group of those lights is part of an object, it's only to the extent that the viewer perceives it as such.
Note that this is not the case with other digital illusions. This one in particular is ruined because it relies on a strip of pixels 'belonging' to one of the two (perceived) objects that sandwiches it.
There is, objectively, data being presented, which we perceive.
You're glossing over the importance of a particular scale, the scale at which humans operate in on a daily basis, and making the assumption that reality is what's happening at a smaller scale.
This is incomplete.
If we want to talk about the image, the underlying components become progressively less important as the scale decreases. When we view a painting, or an image on a screen, when are less interested in up quarks, down quarks, and electrons, and more interested in the image and the medium.
Black text going in front of a black background doesn't have that effect. My knowledge of what I'm seeing agrees with what I see. My knowledge is "there is black text in front of that black text", and my visual cortex says "sure, I can't see it but that's perfectly plausible". This pigeon video does have that effect. My knowledge says that the pigeon image is moving smoothly, but I can clearly see its head bobbing; there's a disagreement.
Do other people define "illusion" differently? Or perceive something differently?
This just relies on poor contrast.