# maybe a stupid question - noise and human eyes



## ULFULFSEN (Sep 9, 2014)

i know there are grave differences between a CMOS or CCD sensor and our eyes.

but can someone explain why we don´t see noise?
i guess our eyes the rod cells, cone cells and stuff have to fight noise too.

i guess our brain is filtering out the noise. but how?


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## AcutancePhotography (Sep 9, 2014)

ULFULFSEN said:


> i know there are grave differences between a CMOS or CCD sensor and our eyes.
> 
> but can someone explain why we don´t see noise?
> i guess our eyes the rod cells, cone cells and stuff have to fight noise too.
> ...



1. Our eyes do not collect one image, but a constantly changing set of input signals (almost like video). This helps with the SNR We also do not see with only one apature (pupil) but a constantly changing pupil. 
2. There is an incredably large amount of image processing that goes on in our brains. 

But our eyes are not perfect. If you go into a dark room, with just the right amount of light, you can see the noise.

There is was an interesting discussion on this topic at

http://arstechnica.com/civis/viewtopic.php?f=6&t=59638&sid=f302819d0bf865bc25186893c67722fb


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## Maximilian (Sep 9, 2014)

ULFULFSEN said:


> i know there are grave differences between a CMOS or CCD sensor and our eyes.
> 
> but can someone explain why we don´t see noise?


our brain is too smart and erases everything distracting.



> i guess our eyes the rod cells, cone cells and stuff have to fight noise too.
> 
> i guess our brain is filtering out the noise. but how?


Of course they do. But I don't know how the brain does it, sorry.

But in real dark situations when the visual center is too distracted by not recognizing anything usefull to focus on, you - at least I - can see some "noise", e.g. when you wake up in the middle of the night in your dark sleeping room.


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## tolusina (Sep 9, 2014)

look in the bokeh, it's right there......... :


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## Marsu42 (Sep 9, 2014)

Maximilian said:


> our brain is too smart and erases everything distracting.



I'm not sure if I would call this behavior smart 



ULFULFSEN said:


> i guess our brain is filtering out the noise. but how?



Noise can be perceived as detail (as people around here always point out, noise *is* detail). A noisy image can thus appear crisper and sharper, that's why the good ol' blocky jpeg compression is so efficient while "smoother" and more modern wavelet or deblocked approaches can look blurry. For the same reason, applying synthetic "film" noise to a blurry digital video makes it more watchable.


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## Maximilian (Sep 9, 2014)

Marsu42 said:


> Maximilian said:
> 
> 
> > our brain is too smart and erases everything distracting.
> ...


Try prgramming some image processing source code doing something comparable and try to find a processor capable to interpolate everything inbetween with that mass of data. 

I call that smart. Maybe not intelligent, maybe not wise but smart.


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## Marsu42 (Sep 9, 2014)

Maximilian said:


> I call that smart. Maybe not intelligent, maybe not wise but smart.



Right, we can settle on this, evolution proves it *has* to be smart :->. As far as I remember the eye even has a better healing brush than Lightroom or Photoshop and seamlessly replaces the missing data in the eye's white spot. It's just that over the years I trust my eyes less and less, esp. when comparing "objective" digital photography with what reality I see for myself.


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## m (Sep 9, 2014)

ULFULFSEN said:


> but can someone explain why we don´t see noise?



Ever noticed the reduced saturation of colors when looking in the dark?
Those two image sensors in your head have different types of pixels, some good for color, some good for low light.

It's not like "hey, our sensor has a lot of noise" but instead "hey, our sensor goes monochrome above ISO 6400*, because the color pixels stop working"
Quite a leica-esque feature if you ask me. 

*not your actual ISO rating


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## Marsu42 (Sep 9, 2014)

m said:


> It's not like "hey, our sensor has a lot of noise" but instead "hey, our sensor goes monochrome above ISO 6400*, because the color pixels stop working"



To be precise, even in good light the color pixels only work in the center of the image, but it's no problem as long as the image processor doesn't realize it


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## ULFULFSEN (Sep 9, 2014)

m said:


> ULFULFSEN said:
> 
> 
> > but can someone explain why we don´t see noise?
> ...



i know that, rod cells. 

but even when we only see monochrom there should be luminance noise.
but when im out with my dogs in the dark, i don´t see (notice) the noise.

actually thats why i ask, last night was full moon and i thought why it looks so clean, even the darkest shadows, for human eyes. 

i wonder how our brain is filtering and cleaning the signal.


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## ajperk (Sep 9, 2014)

Some people do see the equivalent of noise in their vision. The phenomenon is often referred to as "visual snow." I actually have this problem, myself. It's as if everything is covered by a fine layer of static, particularly noticeable on large plain surfaces, and in the dark. It's gotten worse as I've gotten older. I went to a neuro-opthalmogist at one point to try and identify a cause for it. Nothing could be found, even after a battery of visual tests and a cranial MRI to look at my optic nerves. The doctor I saw said he gets four to five patients a year describing this particular problem. As far as I have read they aren't sure how many people exhibit it or what causes it. I wonder if it is perhaps the failure of some particular part of the brain's visual processing, maybe "applying" to much gain to the signal coming from the eyes?


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## lo lite (Sep 9, 2014)

ULFULFSEN said:


> i know there are grave differences between a CMOS or CCD sensor and our eyes.
> 
> but can someone explain why we don´t see noise?
> i guess our eyes the rod cells, cone cells and stuff have to fight noise too.
> ...



When I hold the palms of my hands in front of my face I see quite some noise. Also at night in the total darkness (under the blanket). Don't you see that?


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## Maximilian (Sep 10, 2014)

Marsu42 said:


> It's just that over the years I trust my eyes less and less, esp. when comparing "objective" digital photography with what reality I see for myself.


Maybe this comes with experience, maybe this comes with the aging of your and my eyes, especially when we work a lot in front of a display or do too much pp


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