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Posted: **Mon Dec 18, 2023 5:05 am**

The Same Color Illusion

Explanation: Are squares A and B the same color? They are! To verify this, either run your cursor over the image or click here to see them connected. The featured illusion, an example of the same color illusion, illustrates that purely human perceptions in science may be ambiguous or inaccurate, even such a seemingly direct perception as relative color. Similar illusions exist on the sky, such as the size of the Moon near the horizon, or the apparent shapes of astronomical objects. The advent of automated, reproducible measuring devices such as CCDs have made science in general and astronomy in particular less prone to, but not free of, human-biased illusions.

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Posted: **Mon Dec 18, 2023 5:31 am**

Even with the cursor-activated bridge, it looks to me that B is lighter than A. It is only when I snip a small area of each and compare that they look the same.

Posted: **Mon Dec 18, 2023 7:40 am**

Just A & B, using paint

Posted: **Mon Dec 18, 2023 7:44 am**

Not Found

The requested URL /apod/image/2312/greyilliusion_wikipedia_960.jpg was not found on this server.

Posted: **Mon Dec 18, 2023 7:48 am**

Iksarfighter wrote: ↑Mon Dec 18, 2023 7:44 am Not Found

The requested URL /apod/image/2312/greyilliusion_wikipedia_960.jpg was not found on this server.

That's just a typo in the link. Try this:
https://apod.nasa.gov/apod/image/2312/g ... ia_960.jpg

Posted: **Mon Dec 18, 2023 12:08 pm**

Ugh! This one gets me every time

Posted: **Mon Dec 18, 2023 1:37 pm**

Rauf wrote: ↑Mon Dec 18, 2023 7:48 am
Iksarfighter wrote: ↑Mon Dec 18, 2023 7:44 am Not Found

The requested URL /apod/image/2312/greyilliusion_wikipedia_960.jpg was not found on this server.
That's just a typo in the link. Try this:
https://apod.nasa.gov/apod/image/2312/g ... ia_960.jpg

FIxed the typo. Sorry!

Posted: **Mon Dec 18, 2023 3:05 pm**

I make a case that the square values are different because of context. To extract the data out of its context, yes, there is a certain raw value that is identical. But to extract the data and proclaim "puzzle solved" is to abandon the context; in effect, this is abandoning data. Basically I'm arguing that a value of a lit area is different from a value of a shaded area, regardless of discovery of certain identical information, because 'lit' and 'shaded' are data. I don't see the influence of perception as discardable.

Posted: **Mon Dec 18, 2023 3:07 pm**

Sorry but they don't look the same color to me, with or without the bridge. Not even close, one is definitely lighter, one darker.

Posted: **Mon Dec 18, 2023 3:09 pm**

what am I missing?

Posted: **Mon Dec 18, 2023 3:13 pm**

JeffW wrote: ↑Mon Dec 18, 2023 3:07 pm Sorry but they don't look the same color to me, with or without the bridge. Not even close, one is definitely lighter, one darker.

Nope. Identical. Which is why we like to use instruments over our own senses in rigorously evaluating nature.

Posted: **Mon Dec 18, 2023 3:53 pm**

JeffW wrote: ↑Mon Dec 18, 2023 3:07 pm Sorry but they don't look the same color to me, with or without the bridge. Not even close, one is definitely lighter, one darker.

Yeah, it's fantastic illusion. Even using the "animate" button at the https://michaelbach.de/ot/lum-adelsonCheckShadow/ link might not convince you. You have to remove everything but those two squares to truly prove to yourself that a "fast one" isn't being pulled!

It even made me wonder whether ALL the squares are actually the same color!

Posted: **Mon Dec 18, 2023 4:00 pm**

Pastorian wrote: ↑Mon Dec 18, 2023 3:05 pm I make a case that the square values are different because of context. To extract the data out of its context, yes, there is a certain raw value that is identical. But to extract the data and proclaim "puzzle solved" is to abandon the context; in effect, this is abandoning data. Basically I'm arguing that a value of a lit area is different from a value of a shaded area, regardless of discovery of certain identical information, because 'lit' and 'shaded' are data. I don't see the influence of perception as discardable.

We're delving into philosophy here, but if two things measured by certain data are identical, what difference does the context make, other than to affect perception (aka, the effect of the whole on human senses)? You're saying that the context is also part of the data? A bullet in a gun is definitely in a different context than a bullet in an ammo box, but it's the same bullet!

Posted: **Mon Dec 18, 2023 4:05 pm**

Pastorian wrote: ↑Mon Dec 18, 2023 3:05 pm I make a case that the square values are different because of context. To extract the data out of its context, yes, there is a certain raw value that is identical. But to extract the data and proclaim "puzzle solved" is to abandon the context; in effect, this is abandoning data. Basically I'm arguing that a value of a lit area is different from a value of a shaded area, regardless of discovery of certain identical information, because 'lit' and 'shaded' are data. I don't see the influence of perception as discardable.

This is about science, and about how our senses can fool us in analyzing an image. Instead of a chessboard, make this a nebula, with two physically identical regions separated spatially, and appearing different to our eyes but measuring instrumentally the same.

We would never claim the regions are different simply because of a perceptual failure. We would deliberately discard our perception and accept the instrumental measurements.

Posted: **Mon Dec 18, 2023 4:13 pm**

My favorite illusion is seeing a color that monitors cannot reproduce, that rarely exists in nature, and that some folks' eyes simply cannot see: true cyan.
I do wonder if our beautiful Neptune is close to true cyan. I remember watching "Neptune All Night" on tv in the late 1980s, and wondering if it was somewhat close.

There are many sites that present it. Here is one:

https://www.thesun.co.uk/tech/17536709/ ... true-cyan/

Posted: **Mon Dec 18, 2023 4:18 pm**

Hi Chris, I was wondering: that cylinder has to be there for a reason. If the cylinder was removed, would the chess board suddenly appear as a mono-color surface?

Posted: **Mon Dec 18, 2023 4:25 pm**

zendae1 wrote: ↑Mon Dec 18, 2023 4:18 pm Hi Chris, I was wondering: that cylinder has to be there for a reason. If the cylinder was removed, would the chess board suddenly appear as a mono-color surface?

I'm not Chris, but presumably it's the shadow the cylinder casts that makes the squares the same color. If you remove the cylinder, you could either remove its shadow as well or keep it. I'd guess that if the shadow remains, so does the illusion.

Posted: **Mon Dec 18, 2023 4:26 pm**

zendae1 wrote: ↑Mon Dec 18, 2023 4:18 pm Hi Chris, I was wondering: that cylinder has to be there for a reason. If the cylinder was removed, would the chess board suddenly appear as a mono-color surface?

I don't think the cylinder serves any purpose other than informing us that the shadowed area is, in fact, a shadow. Without the cylinder we'd likely interpret it as a stain.

Posted: **Mon Dec 18, 2023 4:43 pm**

Hey, there are actually 6 squares with tops all matching the colors of A and B! I used Windows PowerToys' Color Picker to verify that. The color is rgb(120, 120, 120), or hex 0x787878:

Posted: **Mon Dec 18, 2023 4:44 pm**

Chris Peterson wrote: ↑Mon Dec 18, 2023 4:26 pm
zendae1 wrote: ↑Mon Dec 18, 2023 4:18 pm Hi Chris, I was wondering: that cylinder has to be there for a reason. If the cylinder was removed, would the chess board suddenly appear as a mono-color surface?
I don't think the cylinder serves any purpose other than informing us that the shadowed area is, in fact, a shadow. Without the cylinder we'd likely interpret it as a stain.

But would that affect the illusion at all? I'd guess the illusion would remain.

Posted: **Mon Dec 18, 2023 4:57 pm**

Thank you johnnydeep and Chris.

Posted: **Mon Dec 18, 2023 5:07 pm**

johnnydeep wrote: ↑Mon Dec 18, 2023 4:44 pm
Chris Peterson wrote: ↑Mon Dec 18, 2023 4:26 pm
zendae1 wrote: ↑Mon Dec 18, 2023 4:18 pm Hi Chris, I was wondering: that cylinder has to be there for a reason. If the cylinder was removed, would the chess board suddenly appear as a mono-color surface?
I don't think the cylinder serves any purpose other than informing us that the shadowed area is, in fact, a shadow. Without the cylinder we'd likely interpret it as a stain.
But would that affect the illusion at all? I'd guess the illusion would remain.

So it would seem.
_

Posted: **Mon Dec 18, 2023 6:37 pm**

Chris Peterson wrote: ↑Mon Dec 18, 2023 5:07 pm
johnnydeep wrote: ↑Mon Dec 18, 2023 4:44 pm
Chris Peterson wrote: ↑Mon Dec 18, 2023 4:26 pm

I don't think the cylinder serves any purpose other than informing us that the shadowed area is, in fact, a shadow. Without the cylinder we'd likely interpret it as a stain.
But would that affect the illusion at all? I'd guess the illusion would remain.
So it would seem.
_

greyillusion_wikipedia_960_nocyl.jpg

Thanks - and indeed it does! Now remove the shadow.

Posted: **Mon Dec 18, 2023 8:49 pm**

johnnydeep wrote: ↑Mon Dec 18, 2023 4:43 pm Hey, there are actually 6 squares with tops all matching the colors of A and B! I used Windows PowerToys' Color Picker to verify that. The color is rgb(120, 120, 120), or hex 0x787878

I used Color Picker online. (I saved the image locally then uploaded it to the site.)

Posted: **Mon Dec 18, 2023 8:59 pm**

Confused wrote: ↑Mon Dec 18, 2023 8:49 pm
johnnydeep wrote: ↑Mon Dec 18, 2023 4:43 pm Hey, there are actually 6 squares with tops all matching the colors of A and B! I used Windows PowerToys' Color Picker to verify that. The color is rgb(120, 120, 120), or hex 0x787878
I used Color Picker online. (I saved the image locally then uploaded it to the site.)

Yup, that also works. I've used it before myself.

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