[filmscanners] RE: DSLRs, film scans and color (was: is this about as good asitgets?)

["Paul D. DeRocco" <pderocco@ix.netcom.com>]

> From: michael shaffer
>
>   In the context of scanning film versus DSLRs, you need to define the
> acquired color additionally with respect to "gamut".  That is, you may be
> getting accurate color, but are you acquiring ^all^ the colors.  You could
> use the anology, sRGB versus AdobeRGB ... that is, both are capable of
> delivering accurate color, but AdobeRGB is capable of more colors.
>
>   It is said that film has a much larger gamut of accurate color than does
> any DSLR ... but it begs the question, can this larger gamut be
> scanned, not
> only "accurately", but also completely?

I don't think that film necessarily has a larger gamut than digicams. Any
electronic sensor that has three overlapping bell-curve responses for red,
green and blue, will produce different output for any color of monochromatic
(i.e., laser) light. Since this type of light is by definition the most
saturated (i.e., the widest gamut), such a sensor therefore can capture the
same full range of colors as the eye, if suitable arithmetic is used to
untangle the numbers afterwards. I believe that the sensors in digicams have
this characteristic, although the resulting files are often squeezed into a
narrow gamut because a) very few images actually need the wide gamut, and b)
many people will try to display the images uncorrected on a narrow gamut
monitor.

Film itself may have an equally large gamut, but this isn't necessarily the
case when you put it through a film scanner. Some scanners use three
narrowband sources of light, from LEDs, rather than three broadband
overlapping filters on white light. As long as these narrow bands line up
pretty well with the centers of the bands absorbed by the cyan, magenta and
yellow dyes in the film, they'll do a good job of extracting the full gamut
from the film. But I think different types of film have different absorption
spectra. To the extent that, for instance, the green LED light is affected
by the cyan or yellow dye, and not just the magenta dye, it limits the
gamut. I base this belief on the fact that my Nikon LED-based scanner
requires different profiles for scanning Kodachrome versus E6--if it saw the
slides in the same way that the human eye did, then it would only need one
profile.

--

Ciao,               Paul D. DeRocco
Paul                mailto:pderocco@ix.netcom.com


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