re:Digital vs Analog (might be backwards!)

[P3D Gregory J. Wageman <gjw@xxxxxxxxxx>]

Mike K. writes:

>In a digital camera, *each* pixel can be not only black or white, but
>in most cases least 254 brightness values inbetween, which seems a lot
>higher tonality than a singular minimum-sized silver spec.  And as such, 
>it takes an area of the film to provide the tonal range that an equivalent 
>digital-camera pixel has.  This is why it seems that the silver specs are 
>acting like dithered/halftoned binary representation of the image.  One then
>can conclude that silver-based film is more digital than a digital camera 
>because on the microscopic scale, each pixel in a digital camera *is*
>roughly ananalog representation, while each "pixel" of silver film is
>roughly binary.

This can't be right (about film, I mean).  In order for film to behave
as you say (with light-darkened silver halide crystals acting like a
halftone), then adjacent crystals would have to have knowledge of what
their neighbor is doing (i.e., "this area is supposed to be 50% grey,
and my neighbor is on, so I should be off").  In the digital halftoning
world, this knowledge is present in the computer program which is
approximating a true grayscale value by turning on and off a certain
ratio of pixels in a given area.

But film emulsion has no way to "know" that some of these crystals need
to be black and some need to be transparent in order to approximate a
grey tone over an area.  I believe the way it works is that the individual
crystals do indeed react to incident photons in an analog manner, becoming
progressively more opaque the more light that strikes them.  The micrographs
you saw probably looked the way they did because the image they recorded
had a stippled texture, not because the emulsion was behaving like a
halftone.

>This view of the film also explains and makes reasonable data I've seen
>in recent news stories talking about digital images that claim that the
>equivalent resolution of 35mm film is 3 million pixels, not the much larger
>numbers put forth in this forum.

Like digital imaging companies don't have a vested interest in convincing
a skeptical photographic community that film resolution really isn't as high
as it is?  A reasonable estimate of the resolving power of film is 100 line
pairs per millimeter.  These numbers come from the film companies themselves.
By simple math, this is 200 lines/mm, giving a 33mmx23mm 35mm film chip
the equivalent of about 6600x4600 pixels, which is a little over 30
million pixels.  I'm sure they'd love you to believe it's only a tenth
of that.

        -Greg W.


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