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Dark adaptation - more than meets the eye?


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large.Capture.JPG.2ff0371f80a6169d2555989129dcdd4f.JPGImages are interpreted and made sense of by the brain so I think your answer is yes the brain must surely be involved. There are many  examples of "optical illusions" which show how the brain can be fooled in its interpretation of grey scale and colour pending on the adjacent colour or contrast. In the image above the two squares A, and B are actually the same shade; something is clearly happening in the brain!  All that said I would hazard a guess though that the greater part of dark adaptation takes pace in the physiology of the retina. 

Jim 

 

https://en.wikipedia.org/wiki/Checker_shadow_illusion

 

Edited by saac
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On 19/08/2020 at 19:15, saac said:

. In the image above the two squares A, and B are actually the same shade; something is clearly happening in the brain!

I think that is a cheat- this is the one from Wikipedia page and they are different shades!

892C8894-F0E3-4F2B-8EBF-12F09A309C9B.jpeg

 

Or can it be possible that the optical illusion not only fools our brains but my iphone camera too? They are quite different shades in the photo I took of the illusion on my PC screen!

 

checkerboard 3 difference.jpg

Edited by markse68
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I doubt very much that it is a "cheat" rather a well documented affect.  Our ability to see colour and shade is very much influenced by the surrounding colour and shade.  Take for example the "black" pixels projected onto a screen by a projector - exactly how does a beam of light produce black?  It is the surrounding pixels which make it appear black to our eyes/brain. 

Jim 

 

 

Edited by saac
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9 minutes ago, saac said:

I doubt very much that it is a "cheat" rather a well documented affect.  Our ability to see colour and shade is very much influence by the surrounding colour and shade.  Take for example the "black" pixels projected onto a screen by a projector - exactly how does a beam of light produce black.  It is the surrounding pixels which make it appear black to our eyes/brain. 

Jim 

 

 

Yes I understand that and indeed if i download the image and put it into gimp using ink dropper tool the shades are identical. But why when i take a photo with my phone of the pc screen and do the same thing in gimp are the shades not the same at all? 🤷‍♂️

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15 minutes ago, markse68 said:

Yes I understand that and indeed if i download the image and put it into gimp using ink dropper tool the shades are identical. But why when i take a photo with my phone of the pc screen and do the same thing in gimp are the shades not the same at all? 🤷‍♂️

Im really not sure, but screens do need to be colour calibrated  before a proper visual comparison can be made . The ambient light may also alter the colour you perceive on the screen. 

When you cut and paste direct from the photograph as it is displayed on the screen the computer  transfers a faithful  copy of the hex colour code of the two squares.  When you take a photograph of the screen the mobile phone camera will make its own interpretation based on its sensor , software and ambient light.  So I guess if the two squares were indeed originally the same shade they may not end up being recorded as such in the photograph on your camera. 

Jim 

Edited by saac
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Mark how do you use that ink dropper tool in Gimp to look at the colour code?  I must admit when I look at the chequerboard photo I don't like it !   My senses are telling me that the two squares are different shades; I agree, it is impossible to believe they are same !  I always find optical illusions really unnerving :) 

 

Ps - It's ok Mark I found it  - Shift and the Ink Dropper together - wow they do indeed show as the same code!  So it must be a perception thing - the brain making a judgement and influencing perception.  These illusions can be so disorientating.

Jim 

Edited by saac
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32 minutes ago, saac said:

Ps - It's ok Mark I found it  - Shift and the Ink Dropper together - wow they do indeed show as the same code!  So it must be a perception thing - the brain making a judgement and influencing perception.  These illusions can be so disorientating.

Jim 

I find it slightly amusing that it fools cameras too 😂

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On 21/08/2020 at 19:35, markse68 said:

Yes I understand that and indeed if i download the image and put it into gimp using ink dropper tool the shades are identical. But why when i take a photo with my phone of the pc screen and do the same thing in gimp are the shades not the same at all? 🤷‍♂️

It's probably adjusting the image to strecth the dynamic range, is it on an HDR setting?

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50 minutes ago, Stub Mandrel said:

It's probably adjusting the image to strecth the dynamic range, is it on an HDR setting?

No i never use HDR. You’d think a camera sensor would measure the values as being the same but I guess there’s processing involved that like you say adjusting the dynamic range. Interesting though

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