Are the colored specks I see in very low light similar to camera noise?

Question

In very dark conditions, after my eyes adapt, I sometimes notice faint colored specks or a grainy look. I can also trigger similar effects by pressing on my eyes or staring into darkness. Is this comparable to the high-ISO noise seen in photos, or is it something different about human vision?

user6263 · Answer

The sensor systems are different enough that direct comparison is hard. There are some similarities, but the sensor post processing is exceptionally well tailored to remove undesired artefacts and the maker has not provided a means to turn noise reduction off.

Also, the image is developed by a custom algorithm and the system does not allow access to the RAW data.

Pressing the sensor is cheating and does induce artefacts, as signal can be generated which is sensibly indistinguishable from photon stimulation within the criteria established by the wetware. Pressing the sensor, either through the flexible housing or directly may cause degradation or destruction and is not within the standard operating conditions or guaranteed worst case specs and so is not covered by warranty.

There are two sensor systems whose outputs are combined (something like Fuji's dual site size sensor but totally different).

You'll read things like:

The eye has about 100,000,000 "rods" which are monochrome only sensors. There are about 5 - 10,000,000 "cones" which are colour receptors but less sensitive than the rods. Most of these are in the center of the eye in an area about 0.5mm across (Work that out for sensor cell area !)

To make rubbish of that statement, you'll also read that

there are RGB cones but far fewer blue than R&G and the blue are outside the center but far more sensitive than the R&G so overall the RGB sensitivity is about the same.

Whatever ...

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As light levels drop the cones start to stop working. For my eyes - which seem reasonably standard in this respect (and not others) at 20 lux colour is not too bad. At about 10 lux you can still see colour but notice it starting to suffer. From there it fades away and by 1 lux it's essentially monochrome. Bright moonlight is a few tenths of a lux. Stumbling around a room that is "so dark that you can sort of see doorways so as to get through them" level is somewhere under 0.1 lux so by 0.01 vision per se is largely gone.

BUT and the reason why the above is worth saying at all (maybe) is that the dark adapted eye can detect a single photon. If you are in total darkness you will not see every single photon as there is substantial dead area between the sensors, but if a photon strikes a sensor it will fire and you will see a spot of light. What that spot of light registers as is uncertain. If it fires a rod you'd expect monochrome. Whether it's able to fire a cone may depend on energy level - so if so you'd expect blue flashes to be more common.

Finally, long shot: and this is a maybe, you MAY be able to see secondary emissions from Gamma rays! Gamma ray "telescopes" work by looking for secondary emissions caused by high energy gamma rays striking atoms in the atmosphere and causing a visible photon emission at lower energy. Vanishingly few of the high energy gamma rays make it to earth surface (to contribute to the background count you hear on a Geiger counter) but perhaps a dark adapted eye gets the benefit of a few of these knocking secondary particles off other parts of your eyes! Maybe.