Noise as seen by the human eye

About noise... I realized the other day that even with the human eye... in the dark there's a good amount of noise that you can actually see through your own eyes... if you look around right now even in daylight (or office light), there's still "noise" that you see... the lenses of your eyes are not perfectly crystal clear, so why expect that of a camera?

I'm not sure I follow that because I notice none especially in daylight. It might be the Rods & Cones of the eye that you are noticing - but I think that would be difficult - except in very low light.

Reign wrote in post #6175060
About noise... I realized the other day that even with the human eye... in the dark there's a good amount of noise that you can actually see through your own eyes...

Time to upgrade to a 1D 'body'.....

digital camera noise is caused by the sensor, not the lens. what you see when it's dark or you close your eyes is called "retina noise"

i read somewhere that the human eye is the equiv of ISO800 in terms of sensitivity

What your eyes sees and what the camera sees are two entirely different things.

What people "see" is largely made up of what the brain combines out of the constantly changing input from the eye - the eye only sees a small amount of what you think it does (there's many focusing and aperture changes going on at any one time). Also, the human eye only sees a very small amount, the rest of the scene (as you see it) is filled in by the brain according to it's experience and expectations (look at how optical illusions work to fool you into seeing what's not actually there).

I hate to seem argumentative (okay, that's a lie, I love it) but I couldn't resist replying to this. I think the general idea is right, but the details aren't.

Pete wrote in post #6180400
What your eyes sees and what the camera sees are two entirely different things.

I disagree. What your eye sees and what the camera sees are basically the same. Identical, even. What your mind chooses to focus on in a scene is a subset of the scene. So your conscious awareness of the scene at any given moment is a subset of the scene. This is different than the whole scene, and hence different than the image captured by the camera. But your eye did capture the entire scene, you just chose to ignore most of it. Of course the spatial resolution of your peripheral vision is lower than the point where you are focusing. But you are still constantly being fed this information from your eyes.

Pete wrote in post #6180400
What people "see" is largely made up of what the brain combines out of the constantly changing input from the eye - the eye only sees a small amount of what you think it does (there's many focusing and aperture changes going on at any one time).

No, it sees mostly what you think it does. Your retina/brain process this data a lot to extract features (edges, faces, color, movement, etc) but all of that is based on data from the eyes.

Pete wrote in post #6180400
Also, the human eye only sees a very small amount, the rest of the scene (as you see it) is filled in by the brain according to it's experience and expectations (look at how optical illusions work to fool you into seeing what's not actually there).

The human eye collects data from your entire field of view, all of the time. Ever notice how something moving in your peripheral vision catches your attention? A spider climbing along the wall or a distant airplane can cause you to look immediately as it enters your field of view. Why? Even though you aren't consciously paying attention to the periphery, your brain is still processing that information. It is particularly good at detecting motion, and lets you know about it.

But you are partially right about optical illusions. A study was done (sorry, can't cite it from memory) where some psychologists showed various optical illusions to people from some remote, non-industrial sort of tribe. Some of the illusions didn't work on them. The interpretation was that they aren't surrounded by straight lines, right angles, perfect circles, etc. So they didn't make the same assumptions about the images they were being shown. So experience plays a roll in some cases, but not all. Some illusions work by tricking the image processing in your brain, and are independent of experience or knowledge. There are similar illusions for hearing and touch as well. Anyway, it's not accurate to say that the brain fills in most or even much of what we see. It makes assumptions while performing image processing tasks, but it is using all of the data you eye supplies.

Or at least that's what I learned in grad school getting a PhD in neuroscience. Maybe an article in a photography magazine contradicts that.

Oh, Man; you guys are making my brain hurt. It's sure interesting though.

Reign wrote in post #6175060
About noise... I realized the other day that even with the human eye... in the dark there's a good amount of noise that you can actually see through your own eyes... if you look around right now even in daylight (or office light), there's still "noise" that you see... the lenses of your eyes are not perfectly crystal clear, so why expect that of a camera?

Time to see an opthalmologist.

Bobster wrote in post #6180381
i read somewhere that the human eye is the equiv of ISO800 in terms of sensitivity

With no evidence other than having spent hours in a darkroom, I'd like to say that mine are closer to ISO 10,000,000 and I'd bet most people's are too. Every time my camera is set to ISO 3200 at f/1.8 and is still whining for the flash or a tripod, I can see just fine with my eye's natural shutter speed of however fast my neurons fire.

I found a few relevant numbers on the inside front cover of my old vision psychophysics book. The typical ambient luminance level of starlight is about 10^-3 cd/m^2. (don't mind the units, just the 10^-3) Sunlight is 10^5. So that's an 8 order of magnitude (100,000,000 fold) range of brightness your eye can detect. Although your eye takes a few minute to adjust to the really low light, and obviously can't distinguish details in dark shadows in direct sunlight. In a typical, well-lit scene your eye has a dynamic range closer to 1000. So the brightest object you can see (without blown, overexposed highlights) can be about 1000x brighter (as measured in cd/m^2) than the darkest areas of a shadow where you can still see some contrast.

Also, just for fun since the numbers are there... the area of the retina is 5 cm x 5cm and the number of cones (the photoreceptors you use in bright lighting) is about 5 million (packed into just 1.5mm in the middle of the retina, mostly). There are 100 million rods per eye (mostly outside the fovea, or middle part of the retina). [edit: but remember that you only use these rods in very low-light conditions. sorta like adding an extra 98 megapixels when you crank you 5D up to ISO 3200]

Also, just for fun. About 10 photon (yes, just 10) can cause a rod to tell your brain that is saw light. (a single photon being absorbed causes a measurable electrical change in the rod, but not enough for it to signal a ganglion cell that it has 'seen' something) I'm not sure how that compares to your favorite CMOS sensors. Pretty favorably, i bet.

But then there's the color range the eye can see as compared to what your camera can record and your monitor can display. But that's a whole other topic. (lucky you!)

HankScorpio wrote in post #6198427
I can see just fine with my eye's natural shutter speed of however fast my neurons fire.

rods are really slow. In low ambient light the fastest temporal frequency your eyes can detect is 40Hz. Anything faster gets blurred together. So that would mean a 1/40th second exposure time would be pretty blurry (for a camera analogy) but not totally indistinguishable. Luckily your eyes carry around a bipod all the time. Although, your brain is a lot better than a Digic IV chip, so that helps, too.