Joe Gwinn wrote:
<> The question that nagged me while I was reading was simple: Given that film
grain is totally random, why would scanning (sampling at some number of pixels per
inch) cause grain to be affected more than anything else in the image? Random is
random, so the scanner pitch (number of pixels per inch) shouldn't matter one bit.
And the grain is far too fine for even the pro scanners to resolve. Yet, it seems to
matter. Why?
What size is film grain? Some of you folks know!
<> Film granularity (grain clumping)
And what size is the granularity?
<> Now, we can see where the grain aliasing comes from. First of all, it's
really granularity aliasing; the grains are too small for any non-research scanner to
see. And (unlike the grain) the granularity has a built-in characteristic distance,
the average spacing between granules, and if the scanner's sampling pitch is about
the same as the average spacing between clumps, the effect of the granularity will be
greatly enhanced, and may become wierd as well.
Is wierd weider than weird?
What to do? Films designed to be scanned will have somehow abolished the
peak, so there is no characteristic average distance, or moved the
characteristic distance well away from typical scanner pitches, probably by
making the characteristic distance far smaller the the scanner pitch.
So a film 'optimized' for scanning would be optimized for scanning at a
particular optical dpi. This might explain the recent post about how
scanning optimized film performed worse for one listee's particular
scanner than another 'normal' film. It might also explain the
differences in results between listees with the same films, different
scanners. Any theory on the likely effects of coherence of the scanner
light on this phenomenon?
Would changing the 'clump size' affect edge characteristics, and thus
apparent sharpness? When people talk about finer grained films with less
apparent sharpness, are they talking grain or granularity?
If one has existing film to be scanned, the only solution is to change the scanner pitch (optical, not interpolated) to avoid the peak.
So it is possible that a relatively lower dpi scanner, possbily with a
low coherence light source, would likely have success with a higher
percentage of random existing film images?
If my theory is correct, making the scanner optical pitch larger or smaller will work equally well, though one's instinct is to go for finer. It will all depend on the actual probability density versus distance function, which may not have just one peak. Cheaper to buy a couple of scanner, maybe 2700 and 4000dpi than a non-existant variable optical pitch scanner?
Moose
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