[Leica] How digital noise is different from film grain (my best description)

[abridge at gmail.com (Adam Bridge)]

Today I was spotting some black and white scans and the difference
between digital noise and film's grain leaped out at me.

In film, as you move into the blacks, they become denser and denser as
the grains converge. So blacks are black.

But in digital the noise happens IN the blacks - adding speckles of
light where there should be black or at least very dark. The worse the
noise the higher up the luminance values the effect becomes. So at 100
you see nothing in the very dark areas but by, say 400 there are
subtle flecks of brightness creeping while while at 1600 these effects
are moving well up into the mid-tones.

So when you look at a digital image or a film image there is a
definite quality difference between the way noise and grain operate in
the dark tones.

Adam