Re: [APML] 7331 (again!)

[Joe Pedit <pedit@email.unc.edu>]

> Joe:
> to answer your question, I would simply stay away from film.  I spoke with a
> Harvard astrophysicist, who was contemplating using film for the last solar
> eclipse.  The nonlinear response, made calibration far too messy.  All
> astronomy has gone to CCD (linear response), for ease of analysis.  I think
> any attempts to do any quanitative analysis for film, is a waste of time.
> CCD has far greater dynamic range, negative film is limited at ~ 7 f-stops.
>

Joe D.,

Thank you for your comments and advice regarding the switch to CCD. 
Like many APML subscribers, I too would like to own a large array CCD
camera.  Unfortunately, I can't afford such a camera nor the laptop that
would be necessary to operate it -- heck, I can't even afford a computer
for the home.

I have been working on an article on "noise" in scanned photographic
images for my club's newsletter.  I have been looking at the problem
with the tools I have available -- a camera, a couple of films, and a
scanner.  One could easily argue that these tools are inadequate for the
task, however, these are the only tools I and most APML subscribers have
at our disposal.  I have been using the concepts of spatial random
fields (SRF) to quantify noise in scans from a color (PJ400) and a black
and white (tech pan) film.  I have also looked at how averaging images
and smoothing images alters statistical measures of image noise.

As you would expect, the variogram sills for the scanned tech pan images
are much lower than the variogram sills from the PJ400 images. 
Surprisingly, the variogram ranges are very similar for the two films. 
Averaging images affects the variograms in the manner predicted by
theory (i.e., a reduction in the variogram sills, but no change in the
variogram ranges).  Smoothing images also change the variograms in the
expected manner (i.e., a reduction in the variograms sills, but an
increase in the variogram ranges).  The ideal method for reducing
"noise" as measured with variograms would reduce the sill and the
range.  With your background in image science, could you recommend a
procedure that would accomplish this?

Is my analysis full of flaws?  You bet -- that is why the tentative
title for the article is "An esoteric look at noise in images from
scanned negatives".

Joe P.

--  APML Archives at <http://astro.umsystem.edu/apml/>  ---
             Unsubscribe at <majordomo@seds.org>