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Would there be any interest in a series I've been thinking of putting together about all the fantastically counterintuitive ways your eye fools you without you

Would there be any interest in a series I've been thinking of putting together about all the fantastically counterintuitive ways your eye fools you without you even noticing? Example: https://media.giphy.com/media/3o7btPOMufN5FziFWg/giphy.gif https://media.giphy.com/media/3o7btPOMufN5FziFWg/giphy.gif The fact that colors influence colors around them means that there are far more than 256^3 viewable colors: the spatial axis is like a fourth channel. Another fun one: If you take a paper plate and poke a hole in it, then take a toothpick and stick it in front of the hole, from the bottom, pointing upwards.... Then it'll look like it's coming down from the top! It's very hard to explain in words, but basically it's a pinhole camera, so everything appears upside-down. Your brain tries to compensate and flips it right side up, but it can't quite do that with the toothpick-hole scenario. So when you push the toothpick up from the bottom, it looks like it's coming down from the top. Lastly: https://i.imgur.com/epXYhJd.png https://i.imgur.com/epXYhJd.png If you cover up the top half of the image, the bottom looks gray. But the strawberries look red. A fun puzzle is, how do you see an individual pixel? Can you think of any common object that would help you do this? (No magnifying lenses, for example, and using a phone is sort of cheating.) Answer below. ... Answer: pluck a hair out of your head and put it on your screen. The line along the edge of the hair will turn into a stairstep pattern, which is just another way of saying you can see individual pixels.

tbabb 9y ago
Perhaps a nitpick, but 256^3 doesn't really represent anything about human perception-- it's just how we store colors in computer memory. The human eye can perceive a far wider range of colors than any screen can (currently) represent. It's just as valid (and probably more accurate) to use floating point to store color (rather than bytes), and in many high-fidelity applications this is actually how it's done. The bit about colors "looking different" in different contexts also isn't really an "extra axis". The example you give is just your brain (attempting to) separate out the illumination from the scene colors. The range of actual colors you can perceive isn't increased by this. Fundamentally human color perception is three-dimensional, because humans have three classes of color receptors on their retinas. There are also rods in the retina (the cells that are color-insensitive and detect only brightness), and in principle they could inform color perception, but this does not seem to be the case-- the intensity of light only shifts things around in the original three-dimensional space. There are also a very, very few people (women only) with genetic mutations that give them four different color receptors in their retina. However, there is no evidence that their brains can take advantage of this extra information and allow them to perceive an extra "axis" of color. It is much more likely that the "mutant" receptors are lumped in with the stimulus of one of the others, which will shift their perception of color, but not expand it. In short: There are three axes of color perception. Optical illusions don't change that.
- sillysaurus3 9y ago
  Optical illusions reveal that we have more than three axes of color perception. The first gif and the last photo are examples of this, and the renaissance artists had a firm appreciation of it. (See DaVinci's journals, specifically the chapters on color.) Part of the reason I want to put together this series is to rekindle this knowledge. It seems very much "lost": your comment represents the status quo of color science, but if you were an ambitious artist in 1450, you'd run experiments and determine that much of what we take as fact is actually quite a lot more complicated in practice. The eye, and especially our perception of colors, is so complicated that entire tomes barely scratch the surface. And Munsell's discoveries were only made in 1900, barely over a hundred years ago. There's still a lot more to discover. To be clear: it's true that our three receptors imply three axes of color perception. But when you assemble an image as a whole, the entire portrait results in an experience quite different than any individual color. EDIT: That the perception of color is influenced by surrounding colors is true, but that this adds a "fourth channel" is [citation needed]. One of the most important aspects of color science is that you have to be willing to believe the possibility that some strange ideas are true. In this case, I can dispel that illusion, but only if you're open minded to it: Consider a painting. Why choose a certain shade of yellow? To produce an effect. The above images demonstrate that where you put that shade of yellow causes a very different effect. Now, if you accept as an axiom that the only reason to choose a color is to produce an effect, then that means all three primary colors (red, green, blue) are different axes in your ability to cause an effect. But the fact that the arrangement of colors causes different effects means that the spatial arrangement is a fourth "lever" that you can use to change the experience. That implies it's accurate to call this phenomenon a fourth channel. (I'd post this edit as a reply, but HN isn't having it right now.) One interesting area of science to investigate is the frequency spectrum of natural images. Our brains are tuned to see certain frequencies more than others, e.g. blades of grass. And the reason colors produce different effects depending on where they are in relation to each other is to help us resolve different shapes in an image. http://web.mit.edu/torralba/www/ne3302.pdf http://web.mit.edu/torralba/www/ne3302.pdf https://www.cs.cmu.edu/~efros/courses/LBMV07/presentations/0208Gist.pdf https://www.cs.cmu.edu/~efros/courses/LBMV07/presentations/0...
  - 9y ago
danblick 9y ago
There is a book called "Vision Science" (by Stephen Palmer) that is full of interesting stuff about how the brain interprets visual information. One thing I liked (there were lots): you probably know that your eyes move around with jerky motions called saccades. But if our eyes move in jerks, why don't we observe motion blur (like a camera would have) while our eyes are moving? It's not that our eyes aren't affected by motion blur: the answer is that our brains are wired so that when our eyes are moving, we don't really see anything at all. You just kind of discard the input you get while your eyes are jumping around. https://en.wikipedia.org/wiki/Saccadic_masking https://en.wikipedia.org/wiki/Saccadic_masking
sjcsjc 9y ago
"Would there be any interest in a series I've been thinking of putting together about all the fantastically counterintuitive ways your eye fools you without you even noticing?" Yes
dghf 9y ago
> there are far more than 256^3 viewable colors This is trivially true: the gamut of sRGB does not cover all possible colours. See this diagram: https://en.wikipedia.org/wiki/SRGB#/media/File:Cie_Chart_with_sRGB_gamut_by_spigget.png https://en.wikipedia.org/wiki/SRGB#/media/File:Cie_Chart_wit.... As examples, you can't accurately represent true (spectral) violet or darker/deeper but fully saturated yellows in sRGB. > Lastly: https://i.imgur.com/epXYhJd.png https://i.imgur.com/epXYhJd.png If you cover up the top half of the image, the bottom looks gray. But the strawberries look red. To me, the strawberries look red, the plate is a desaturated cyan, and the meringue is a very desaturated yellow, whether I cover the top half of the image or not.
kyberias 9y ago
>Lastly: https://i.imgur.com/epXYhJd.png https://i.imgur.com/epXYhJd.png If you cover up the top half of the image, the bottom looks gray. But the strawberries look red. For me covering the BOTTOM half makes the bottom look grey. Otherwise it looks slightly red.
mcshicks 9y ago
Several years ago I went to a James Turrell exhibit at the LA County Museum of Art. He had this one piece called "dark spaces" that is kind of like the experiment where you go sit an a dark (i.e. lightproof) room for like 10 or 15 minutes and then you start to see this 'blob' in front of your eyes where he's leaked in a really small amount of light. Anyway if you like weird things with light he has a lot of them. Since he uses light as his medium you can't get too much of a sense of them from a photo, you kind of have to see them in person. http://jamesturrell.com/work/type/dark-space/ http://jamesturrell.com/work/type/dark-space/ http://www.lacma.org/art/exhibition/james-turrell-retrospective http://www.lacma.org/art/exhibition/james-turrell-retrospect...
tzs 9y ago
> Lastly: https://i.imgur.com/epXYhJd.png https://i.imgur.com/epXYhJd.png If you cover up the top half of the image, the bottom looks gray. But the strawberries look red. The strawberries even look reddish to me if I crop the image down to just one of the red-appearing parts of one strawberry and zoom that to a reasonable size. Looking at the RGB values, I see that the exact gray (128,128,128) parts of the strawberries are surrounded by areas that are slightly different, usually in that they have a slightly smaller red component and maybe a little more green and blue, e.g., something like (118, 129, 129). If I zoom in enough that I don't see those very slightly less red regions, the strawberries seem gray with no hint of red. This works even when 80% of the visible image is pure gray in the central, with edge areas having slightly reduced red or slightly increased blue or green. I wonder why it works that way, instead of the other way around, which would be that the large central gray would be seen as gray, with the edges seen as being bluish/greenish? I wonder if it has something to do with the distribution of colors in nature? Offhand, I can't think of many natural things that are a pure gray, so maybe we favor an interpretation that has the whole image having some color over one that has a large, unnatural gray area?
heavenlyblue 9y ago
> fantastically counterintuitive ways your eye fools you without you even noticing It does not have to be "fooling" when if fact it's just part of the processing pipeline. > The fact that colors influence colors around them means that there are far more than 256^3 viewable colors: the spatial axis is like a fourth channel. No it's not: it may as well be that the function applied to the perceived colours, while takes neighbours as an input - still outputs the same 256^3 colours.
- dkersten 9y ago
  > No it's not: it may as well be that the function applied to the perceived colours, while takes neighbours as an input - still outputs the same 256^3 colours. Kinda like those post-processing shader effects (like blur etc) that look at neighbouring pixels to output a 256^3 colour value for the center pixel. The pixel value never leaves the 256^3 range, but its value is adjusted based on what surrounds it.
visarga 9y ago
So the brain has its own adversarial examples, it's not just GANs that can be fooled.

tbabb 9y ago

Perhaps a nitpick, but 256^3 doesn't really represent anything about human perception-- it's just how we store colors in computer memory. The human eye can perceive a far wider range of colors than any screen can (currently) represent. It's just as valid (and probably more accurate) to use floating point to store color (rather than bytes), and in many high-fidelity applications this is actually how it's done. The bit about colors "looking different" in different contexts also isn't really an "extra axis". The example you give is just your brain (attempting to) separate out the illumination from the scene colors. The range of actual colors you can perceive isn't increased by this. Fundamentally human color perception is three-dimensional, because humans have three classes of color receptors on their retinas. There are also rods in the retina (the cells that are color-insensitive and detect only brightness), and in principle they could inform color perception, but this does not seem to be the case-- the intensity of light only shifts things around in the original three-dimensional space. There are also a very, very few people (women only) with genetic mutations that give them four different color receptors in their retina. However, there is no evidence that their brains can take advantage of this extra information and allow them to perceive an extra "axis" of color. It is much more likely that the "mutant" receptors are lumped in with the stimulus of one of the others, which will shift their perception of color, but not expand it. In short: There are three axes of color perception. Optical illusions don't change that.

sillysaurus3 9y ago
Optical illusions reveal that we have more than three axes of color perception. The first gif and the last photo are examples of this, and the renaissance artists had a firm appreciation of it. (See DaVinci's journals, specifically the chapters on color.) Part of the reason I want to put together this series is to rekindle this knowledge. It seems very much "lost": your comment represents the status quo of color science, but if you were an ambitious artist in 1450, you'd run experiments and determine that much of what we take as fact is actually quite a lot more complicated in practice. The eye, and especially our perception of colors, is so complicated that entire tomes barely scratch the surface. And Munsell's discoveries were only made in 1900, barely over a hundred years ago. There's still a lot more to discover. To be clear: it's true that our three receptors imply three axes of color perception. But when you assemble an image as a whole, the entire portrait results in an experience quite different than any individual color. EDIT: That the perception of color is influenced by surrounding colors is true, but that this adds a "fourth channel" is [citation needed]. One of the most important aspects of color science is that you have to be willing to believe the possibility that some strange ideas are true. In this case, I can dispel that illusion, but only if you're open minded to it: Consider a painting. Why choose a certain shade of yellow? To produce an effect. The above images demonstrate that where you put that shade of yellow causes a very different effect. Now, if you accept as an axiom that the only reason to choose a color is to produce an effect, then that means all three primary colors (red, green, blue) are different axes in your ability to cause an effect. But the fact that the arrangement of colors causes different effects means that the spatial arrangement is a fourth "lever" that you can use to change the experience. That implies it's accurate to call this phenomenon a fourth channel. (I'd post this edit as a reply, but HN isn't having it right now.) One interesting area of science to investigate is the frequency spectrum of natural images. Our brains are tuned to see certain frequencies more than others, e.g. blades of grass. And the reason colors produce different effects depending on where they are in relation to each other is to help us resolve different shapes in an image. http://web.mit.edu/torralba/www/ne3302.pdf http://web.mit.edu/torralba/www/ne3302.pdf https://www.cs.cmu.edu/~efros/courses/LBMV07/presentations/0208Gist.pdf https://www.cs.cmu.edu/~efros/courses/LBMV07/presentations/0...
- 9y ago

danblick 9y ago

There is a book called "Vision Science" (by Stephen Palmer) that is full of interesting stuff about how the brain interprets visual information. One thing I liked (there were lots): you probably know that your eyes move around with jerky motions called saccades. But if our eyes move in jerks, why don't we observe motion blur (like a camera would have) while our eyes are moving? It's not that our eyes aren't affected by motion blur: the answer is that our brains are wired so that when our eyes are moving, we don't really see anything at all. You just kind of discard the input you get while your eyes are jumping around. https://en.wikipedia.org/wiki/Saccadic_masking https://en.wikipedia.org/wiki/Saccadic_masking

sjcsjc 9y ago

"Would there be any interest in a series I've been thinking of putting together about all the fantastically counterintuitive ways your eye fools you without you even noticing?" Yes

dghf 9y ago

> there are far more than 256^3 viewable colors This is trivially true: the gamut of sRGB does not cover all possible colours. See this diagram: https://en.wikipedia.org/wiki/SRGB#/media/File:Cie_Chart_with_sRGB_gamut_by_spigget.png https://en.wikipedia.org/wiki/SRGB#/media/File:Cie_Chart_wit.... As examples, you can't accurately represent true (spectral) violet or darker/deeper but fully saturated yellows in sRGB. > Lastly: https://i.imgur.com/epXYhJd.png https://i.imgur.com/epXYhJd.png If you cover up the top half of the image, the bottom looks gray. But the strawberries look red. To me, the strawberries look red, the plate is a desaturated cyan, and the meringue is a very desaturated yellow, whether I cover the top half of the image or not.

kyberias 9y ago

>Lastly: https://i.imgur.com/epXYhJd.png https://i.imgur.com/epXYhJd.png If you cover up the top half of the image, the bottom looks gray. But the strawberries look red. For me covering the BOTTOM half makes the bottom look grey. Otherwise it looks slightly red.

mcshicks 9y ago

Several years ago I went to a James Turrell exhibit at the LA County Museum of Art. He had this one piece called "dark spaces" that is kind of like the experiment where you go sit an a dark (i.e. lightproof) room for like 10 or 15 minutes and then you start to see this 'blob' in front of your eyes where he's leaked in a really small amount of light. Anyway if you like weird things with light he has a lot of them. Since he uses light as his medium you can't get too much of a sense of them from a photo, you kind of have to see them in person. http://jamesturrell.com/work/type/dark-space/ http://jamesturrell.com/work/type/dark-space/ http://www.lacma.org/art/exhibition/james-turrell-retrospective http://www.lacma.org/art/exhibition/james-turrell-retrospect...

tzs 9y ago

> Lastly: https://i.imgur.com/epXYhJd.png https://i.imgur.com/epXYhJd.png If you cover up the top half of the image, the bottom looks gray. But the strawberries look red. The strawberries even look reddish to me if I crop the image down to just one of the red-appearing parts of one strawberry and zoom that to a reasonable size. Looking at the RGB values, I see that the exact gray (128,128,128) parts of the strawberries are surrounded by areas that are slightly different, usually in that they have a slightly smaller red component and maybe a little more green and blue, e.g., something like (118, 129, 129). If I zoom in enough that I don't see those very slightly less red regions, the strawberries seem gray with no hint of red. This works even when 80% of the visible image is pure gray in the central, with edge areas having slightly reduced red or slightly increased blue or green. I wonder why it works that way, instead of the other way around, which would be that the large central gray would be seen as gray, with the edges seen as being bluish/greenish? I wonder if it has something to do with the distribution of colors in nature? Offhand, I can't think of many natural things that are a pure gray, so maybe we favor an interpretation that has the whole image having some color over one that has a large, unnatural gray area?

heavenlyblue 9y ago

> fantastically counterintuitive ways your eye fools you without you even noticing It does not have to be "fooling" when if fact it's just part of the processing pipeline. > The fact that colors influence colors around them means that there are far more than 256^3 viewable colors: the spatial axis is like a fourth channel. No it's not: it may as well be that the function applied to the perceived colours, while takes neighbours as an input - still outputs the same 256^3 colours.

dkersten 9y ago
> No it's not: it may as well be that the function applied to the perceived colours, while takes neighbours as an input - still outputs the same 256^3 colours. Kinda like those post-processing shader effects (like blur etc) that look at neighbouring pixels to output a 256^3 colour value for the center pixel. The pixel value never leaves the 256^3 range, but its value is adjusted based on what surrounds it.

visarga 9y ago

So the brain has its own adversarial examples, it's not just GANs that can be fooled.