I've never heard aliasing called a beating artifact. Beating occurs when two
signals at nearly the same frequency add together in phase, then cancel each
other out of phase. Imagine two white picket fences one in front of the
other, both in front of a black background. One fence has 3" wide pickets
spaced every 6", the other has 3.05" wide pickets spaced every 6.1".
Approximately every (3 / 0.1 ) * 6" = 180" the image will change from
showing black between the pickets to showing a solid white area.
Aliasing occurs because if you take a sample every 1.5" of a 3" wide picket
fence space every 6" you will get two white samples then two black samples.
If the pickets are 2" wide spaced every 4" you can still get two white
samples then two black samples when you take a sample every 1.5". --- If
you know that every dimension doesn't have any components less than 3" you
can perfectly reconstruct the image from the samples taken every 1.5".
-jeff
AM radio reception can be ruined by beating because the radio responds to
the slow variation between the peak to peak amplitude - to the overall white
vs black.
Intermodulation can cause beat frequency signals to be created but has
nothing to do with photography but plenty to do with AM radios.
From: "Julian Davies" <julian_davies@xxxxxxxxxxxxxx>
Er...
My fault, in that I was trying to draw a parallel between two entirely
different results which have the same cause!
Quite correct that film doesn't alias. It fogs.
When you hit the limiting frequency, a fixed uniform sample system begins
to
form beating artefacts. Since this is a property of the sampling interface,
the downstream electronics don't know they are artefacts, and can do
nothing
about it.
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