Perhaps the question is really about discrete versus continuos? Because
the digital sensor output is digitized, it has discrete levels of
output, so we think of it as discrete in nature while we think of film
or the eye as continuos or analog. However, the digital camera sensor
itself is not any more discrete than the eye or film, and given enough
bits in the A/D converter, digital could distinguish an arbitrary level
of color resolution.
That being said, light is photons and are discrete. If a sensor is
capable of detecting individual photons there is potentially no
difference between the eye, film, or digital. The question then becomes
"what is the quantum efficiency of the sensor medium?" Film may be more
efficient than a CCD, and the eye more than film, I'm not sure. The
difference in perceived quality may have more to do with the noise
nature of the sensor, distortion, RGB filter shape, etc.
In the end, the difference is in the display medium. We all share
photos online, limited by our 8 bit monitors. Nothing quite like a good
photographic print in the hand. But digital is analog at the sensor
level, and all sensors are discrete at the photon level. Efficiency of
conversion can differ but the output medium is where the photo hits the
road.
In the analogy of audio, digital output can be made indistinguishable
from analog, however with analog, you never get exactly the same
output. So the nature of the noise, distortion, and randomness may be
the real distinguishing characteristics. Film has a non-linear response
curve, digital sensors a more linear response with sharp clipping, and
I don't know what the eye does. So the analogy may be like the color
and bokeh of a lens.
For all practical purposes, todays digital cameras, with enough light,
are just as capable as film in distinguishing color. But none are
capable of distinguishing a good photo from a bad one. For that, we
need Walt.
Wayne
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