Re: filmscanners: Re: bit depth and dynamic range

[EdHamrick@aol.com]

In a message dated 2/5/2001 3:48:57 PM EST, JPhipps@asf.com writes:

>  So the Nikon scanner
>  scans at 12 bits (12x3=36) and if you want the extra bit depth it stores at
>  16 bits (48 bits). So the file size increases by 100% (if it is a tif for
>  example) while information increases by 50%.

Good software <smile> doesn't store uncompressed tiff files, but
instead has the option to use LZW compression.  The size of the
LZW compressed .tif file only increases 50% when the information
increases 50%.

>  If you had a negative with an extremely high dynamic range (say a child
>  under a tree with a white house in the background in bright sun) and a
>  scanner with low dynamic range you would want to scan the image twice. Once
>  to expose for the child and once to expose for the house.

VueScan already does this, and tests have shown that it works well
with some CCD's but not with others (there's a lot of CCD charge
bleeding into adjacent pixels with the FS 2710 for example).

>  The scanners that use an infrared channel (fourth channel) for surface
>  defect detection typically don't let the user at this channel, so it 
doesn't
>  come into play in the scanner's specifications.

VueScan lets you display this channel by setting the
"Files|TIFF file type" to "16 bit Infrared".

> The scanner uses this
>  information during the scan along with software to remove the effect of
>  dust, scratches, fingerprints, etc. from the output image.

No, the scanner does nothing with this information except return
it to the application.  The application does all the dust removal.
Digital ICE resides entirely in the software in the processor.

>  As many readers on this list know, I'm biased, but I believe the most
>  important feature is the Digital ICE (the surface defect removal), Digital
>  ROC (Color Restoration) and Digital GEM (Grain Management). These tools
>  really make a difference in the quality of scans.

Except that VueScan's dust removal works better than Digital ICE,
VueScan's "Restore colors" works better than Digital ROC, and
VueScan's Clean function works better than Digital GEM.  I'm biased
of course, and people should come to their own conclusions, but
these assertions are simple things to verify by simply trying them.

Regards,
Ed Hamrick