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Old 14th Sep 2018, 9:55 pm   #50
kalee20
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Join Date: Feb 2007
Location: Lynton, N. Devon, UK.
Posts: 7,061
Default Re: The Persistence of Analogue

Quote:
Originally Posted by Phil G4SPZ View Post
Cameras are a good example. We all know that the resolution of a good quality fine-grained 'analogue' photograph can exceed that of an indifferent digital image. I am frequently amazed at the quality of some very old monochrome photographs. But we'd surely miss digital tools like Photoshop for removing the creases and stains!
Ah. But is photographic film analogue? For simplicity, thinking black and white only, I have generally believed that it contains many many microscopic crystals of silver halide. When irradiated by photons, a few atoms are converted to metallic silver; developing causes the whole crystal to become silver; fixing removes the unconverted crystals. Because the crystals are so minute, and distributed through the emulsion, and because photons are discrete, there is a probability that a particular crystal will encounter a photon, approximately proportional to the exposure to light.

Thus, ultimately, each crystal is either 'off' or 'on' and it's only because there are so many of them that it appears continuous, both space-wise and darkness-wise.

Same goes for our eyes - retinas are covered with discrete sensors, each sensor generating an output or not (I recall reading that a retinal rod cell registers an output if hit by more than 50 photons in a millisecond, which is pretty awesome). So resolution of our eyes is not infinite, but is 'good enough' to appear so; and with the minute scanning movements that eyes make, there's even a bit of 'dither' allowing interpolation to maybe an extra couple of bits, spatially! My personal conclusion is that God exists, and He is a design engineer...

I suppose the exposure and focussing mechanisms are also semi digital - they are activated by muscles which are composed of discrete cells, but the contraction of each muscle cell is dependent on how often it gets a triggering impulse - and as time is (as far as we know) not quantised, the strength of a muscle's contraction can be varied by nerve impulses with a truly infinite mark:space ratio!
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