Re: filmscanners: Infrared dust removal accuracy

[RogerMillerPhoto@aol.com]

In a message dated 6/25/2001 3:11:15 PM Pacific Daylight Time, 
wilksd@home.com writes:


> I have some vague idea of how infrared scanning is used to remove dust and
> scratches from film scans on scanners that have this capability. Is there
> any possibility that this method could mistake elements of the actual image
> on the film for the undesirable dust or scratch and thereby "remove" parts
> of the photographic image? Has anyone had observations or done any testing
> in this regard? Perhaps photographinq a high contrast texture or the white
> fluff from poplar trees floating in the air aqainst a dark background and
> then surgically placing lint on one half the film to be scanned for
> comparison? I am currently "stuck" with an Artixscan 4000T which, of course,
> does not have this capability as far as I know.
> If my vague knowledge of this subject has caused me to ask an rtfm type
> question I apologize in advance. I will infer my thickheadedness from any
> polite responses, no need to say it out loud. :-) Thanks.
>
> Darrell


Darrell, no part of your image will be accidentally removed.  The film is 
transparent to the IR beam but the dust particles block it and it's very easy 
for the hardware/software system to tell the difference.  I've read on this 
list that some people say the dust removal system can soften the image, 
probably because the software replaces parts of the image where the dust 
particles were by sampling the area immediately around them and it's 
obviously not able to accurately and perfectly select the correct colors and 
densities for those parts of the image blocked by the dust particles. 

Silver based black and white film won't pass IR, so there's no way to use IR 
dust removal with it.  And I've read here that Kodachrome doesn't do a good 
job of passing IR, so, while some people report success with IR dust removal 
on Kodachrome, there's no way to guarantee that it will always work.  

But you should have no concern about part of your image being accidentally 
lost because the IR beam gives a very high contrast between actual dust and 
the image itself.  In fact, I believe that I read on this list that Vuscan 
can display the mask showing where the dust spots have been detected, so you 
could verify visually as to what it has detected as dust.