The Optical Illusions Thread

blessmycottonsocks

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The photo below is black and white.
Coloured gridlines, noticeable when you zoom in, have been added to the greyscale image and your mind fills in the colour.

colour.JPG
 

RaM

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Is there a way of testing that? I can see the grid lines but cant convince
the grey cells that it is black and white.
 

ChasFink

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The photo below is black and white.
Coloured gridlines, noticeable when you zoom in, have been added to the greyscale image and your mind fills in the colour.

View attachment 43434

Perhaps similar to this one; All the balls are the same colour.
I don't understand the premise here. The first image is not black and white, it's colorized. The fact that the colorization is done with colored grids and not a more solid tinting doesn't change that. The balls in the second image are the same background color, but have different colored stripes; therefore they're not the same color, any more than higher-numbered billiard balls are the same color because they're all white with different colored bands. These are no more "optical illusions" than halftone printing or a TV screen.
 

PeteByrdie

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I don't understand the premise here. The first image is not black and white, it's colorized. The fact that the colorization is done with colored grids and not a more solid tinting doesn't change that. The balls in the second image are the same background color, but have different colored stripes; therefore they're not the same color, any more than higher-numbered billiard balls are the same color because they're all white with different colored bands. These are no more "optical illusions" than halftone printing or a TV screen.
Very accurate, but not a very succinct way of saying it. The point is, people wouldn't expect their vision to be so deceived. Saying it the way it was stated, that the image is black and white with coloured grid lines over it, explains it in a way people can understand and will cause them to say, 'Wow! My whole understanding of vision has been turned on its head.'
 

Floyd1

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I don't understand the premise here. The first image is not black and white, it's colorized. The fact that the colorization is done with colored grids and not a more solid tinting doesn't change that. The balls in the second image are the same background color, but have different colored stripes; therefore they're not the same color, any more than higher-numbered billiard balls are the same color because they're all white with different colored bands. These are no more "optical illusions" than halftone printing or a TV screen.
I suppose it's the same principal/trick that rug-makers have used for years. By using only 3 or 4 colours, depending on which colour goes next to another colour, they can give the illusion that many more colours were used than actually were.
 

Floyd1

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I don't understand the premise here. The first image is not black and white, it's colorized. The fact that the colorization is done with colored grids and not a more solid tinting doesn't change that. The balls in the second image are the same background color, but have different colored stripes; therefore they're not the same color, any more than higher-numbered billiard balls are the same color because they're all white with different colored bands. These are no more "optical illusions" than halftone printing or a TV screen.
Is this any better?
Checker Shadow Illusion By Original: Edward H. Adelson, vectorized by Pbroks13. - Own work, CC BY-SA 4.0, https://commons.wikimedia.org/w/index.php?curid=75000950
 

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ChasFink

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Is this any better?
Checker Shadow Illusion By Original: Edward H. Adelson, vectorized by Pbroks13. - Own work, CC BY-SA 4.0, https://commons.wikimedia.org/w/index.php?curid=75000950
Yes, it is.

The statement that goes with that one is "Squares A and B in this illustration are the same color. And they're not squares, but 2D representations of squares in 3D space." That's an optical illusion.

The statement isn't "The cylinder is not all green, but only appears that way because of the balance of individual pixels on your computer screen," which, while true, is not as much an optical illusion as it is a statement of how computer screens work.
 

Floyd1

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Yes, it is.

The statement that goes with that one is "Squares A and B in this illustration are the same color. And they're not squares, but 2D representations of squares in 3D space." That's an optical illusion.

The statement isn't "The cylinder is not all green, but only appears that way because of the balance of individual pixels on your computer screen," which, while true, is not as much an optical illusion as it is a statement of how computer screens work.
Whenever I see your avatar I want to go and find the steps in Los Angeles where L&H filmed the famous piano scene. I'm off to do just that now.
 

blessmycottonsocks

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Today's Monday puzzle in The Guardian, featured "The magic of the Borromean rings".

Quite apart from the puzzle, I was intrigued by the motif of the rings themselves.
They date back to at least the 13th century and have the curious property that when any one of the rings is removed, the other two will no longer be linked.

Even more weird is that, rather like Escher's famous tri-bar, this looks at first glance like a rational object but, on closer scrutiny, you can see that it would be impossible to make a physical version of it using undistorted rings.

Borromean.JPG
 

Floyd1

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After staring at the cross in the center of this image for 20 seconds or so, you will start to see either a green dot running around the circle or a green dot circling around, seeming to erase the magenta dots on the grey background. If you shift your eyes, the magenta dots will appear again.
The lilac chaser, otherwise known as the “pac-man” illusion, is primarily the effect of “negative retinal afterimage,” which occurs when our perceptual system adapts to fill in the gap left by the “afterimage” of complementary hues on a neutral background. In this case, the disappearance of lilac dots produces the appearance of afterimages of the complementary color (green).
And the Gestalt effect contributes to the visual phenomenon of a flying green disk. After a while, the brain starts to integrate the successive afterimages and perceive a single flying object instead.
 

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escargot

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After staring at the cross in the center of this image for 20 seconds or so, you will start to see either a green dot running around the circle or a green dot circling around, seeming to erase the magenta dots on the grey background. If you shift your eyes, the magenta dots will appear again.
The lilac chaser, otherwise known as the “pac-man” illusion, is primarily the effect of “negative retinal afterimage,” which occurs when our perceptual system adapts to fill in the gap left by the “afterimage” of complementary hues on a neutral background. In this case, the disappearance of lilac dots produces the appearance of afterimages of the complementary color (green).
And the Gestalt effect contributes to the visual phenomenon of a flying green disk. After a while, the brain starts to integrate the successive afterimages and perceive a single flying object instead.
When I click on that the effect began right away! :D
 

Floyd1

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When I click on that the effect began right away! :D
Yes it did with me also, but only on the bigger version. Without clicking and enlarging this one I posted, if I stare at the cross, the magenta circles just disappear and it becomes a blank page.
 

escargot

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Yes it did with me also, but only on the bigger version. Without clicking and enlarging this one I posted, if I stare at the cross, the magenta circles just disappear and it becomes a blank page.
I saw the bloody thing everywhere.
 
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