[HarHarVeryFunny]

But we can differentiate grey from red, so there'd have to be something more to a specific grey blob to make us see it as red rather than grey (which is how we'd normally see a grey blob).

It doesn't have to be a strawberry (or rather a strawberry as part of a consistently lit scene), but it has to be something that makes our brain predict it is red.

The phenomena behind the illusion is "color constancy" - they way we (learn to?) see objects as being of a consistent color regardless of how they are illuminated.

[mwcz]

If I blur the strawberry image enough that all the objects are unrecognizable, reducing everything to blobby abstract shapes, how would color constancy apply? The areas that used to be strawberries still look reddish. Is the suggestion that certain amorphous blob shapes trigger our brain to predict they are red, and all the strawberries in the image, when blurred, are members of that set of shapes?

[mwcz]

Really interesting. If I reproduce the same colors (plate, strawberry lit, strawberry shadow) but with simple squares, the colors that were associated with strawberries do still look a little bit red to my eyes. The more I stare at it, the more red it looks, I would assume because there's so much green and blue, saturating those cones, and causing the relatively neutral "lit strawberry" color to appear red by contrast (like the negative afterimage effect). But even more interesting is that if I glance back and forth at the strawberry image, my "lit strawberry" square starts to look a _lot_ more red.

The strawberry illusion is really cool, thanks for sharing.

[HarHarVeryFunny]

I guess the way to test that would be to sample all the colors in the illusion scene, and use them to randomly color squares in, say, a square grid, and see if any look red, and if so whether it's the same color(s) that looked red in the original illusion.

I believe color constancy is partially based on adjacency of colors as well as whole scene and lighting.

Depending on how you blobbified the image, it may still recall a plateful of something, and the same colors will still be adjacent to each other, so doing the randomized grid test would tell you if it's just the mix of colors or are the other hints coming to play.

It's possible it is just the mix of colors - same way if you wear color tinted glasses (or ski goggles) and the color of everything changes, but in a consistent way, and (maybe after a few min adaptation) you can still discern the colors reliably.

Edit: On second thought that colored goggles example doesn't prove it's just mix of colors - that's just general color constancy more like the strawberry illusion itself.

[mwcz]

Yeah, I think you're right. I replied to my other comment describing the effect on my perception of using squares. The blobs did retain an association with the original image, either because I'd just looked at it, or that the shapes were still ever-so-remotely still strawberryish. Since all I did was severely blur the image, the effects of the original lighting would still be very present.