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[filmscanners] Re: Scene brightness and CCDs



Todd writes:

> What kind of luminance range have we the right to
> expect from the better digicams?

Poor ... but not because of any limitation of CCDs.

CCDs, under the best conditions, can handle a dynamic range of 17 stops or
more.  However, compressing seventeen stops into the 8-bit range of a
typical digicam output file would result in a photograph containing
virtually no contrast, in most cases, so digicams adjust the output from the
CCD to improve contrast by discarding or attenuating the extremes of range
(film, incidentally, is also designed to do exactly this--it's built into
the emulsion).  Unfortunately, a consequence of this is that highlights tend
to blow out, and shadows tend to block.

> Will legions of photos with blown out highlights
> be the legacy of the new technology ...

Probably.  The fact that digital is doing well at all is proof that some
aspects of image quality are simply unimportant to many image consumers.

> Okay, these are provocative questions... let me
> not get in a rant... but seriously, how will these
> devices compare to our beloved films?

CCDs themselve compare extremely well indeed, if they are very large, and
refrigerated, and have a great many pixels.  But CCDs in most digicams do
not meet any of these criteria, and image processing within the camera
software only makes things worse.

> It's clear they can't handle the luminance that
> neg films can...not by a long shot...but can they
> even match the worst of transparencies?

CCDs can do both, but digicams cannot.  The CCD isn't necessarily the
weakest link.

> Are these blown highlights the result of poor
> processing algorithms ...

Yes, but it's not really poor processing so much as a compromise in
processing.

Unprocessed data from a CCD with maximal dynamic range would look very bland
and low-contrast on most displays or paper, just as Wide Gamut RGB normally
looks dull on a monitor, even though it has just about the largest gamut of
any color space around.



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