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Re: [photo-3d] Kodachrome demise, digital rise


  • From: "John A. Rupkalvis" <stereoscope@xxxxxxxxxxxxx>
  • Subject: Re: [photo-3d] Kodachrome demise, digital rise
  • Date: Mon, 30 Apr 2001 10:38:04 -0700


> Perhaps there is some chemical aspect of kodachrome 25 that accentuates
> the edge effects, which is what Paul is responding to.
>
> .r.

The structure of Kodachrome is quite different from most other films, and
gives the impression of greater edge delineation or acuity, giving the
visual impression of being "sharper" even though the actual resolution is
not very different from other current color films.  Resolution and sharpness
are two different things.  With sharpness, we think we see more detail,
although from an absolute standpoint we do not.  Resolution can be
quantitatively measured, sharpness is an edge characteristic that yields a
visual impression that can only be qualitatively measured.

This might be easier to understand if applied to a video image.  A video
image of fixed resolution can be made to look sharper by enhancing the "edge
peaking".  Losses normal to the video process tend to make edges look
softer, resulting in a "fuzzy" appearance.  A square wave imaged on the
video would have rounded corners on the oscilloscope.  The peaking adds a
"spike" to the square wave to compensate.  This makes the video picture look
sharper, even though it exhibits no more lines of resolution.  Some TV's
even have a control  labeled "sharpness", which is really just a peaking
coil.  As you turn it down, the picture looks soft, or fuzzy.  As you turn
it up the picture looks sharper, but starts to look artificial, as edges
become overdelineated and the image starts to look posterized, with black
outlines like a cartoon.  The picture usually looks best somewhere
inbetween.  Exactly where is a matter of personal preference.

The same thing is true of film.  Some people prefer a "sharper" look, others
a "softer" look.  Some subjects look better on sharper films, some subjects
look better on softer films.

JR


 

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