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RE: Shadow Detail and LS2000 Color Management

That's interesting info. I hadn't realized that sRGB wasn't a simple gamma
curve. But anyway, if you take your two test images in Photoshop, and use
Levels to stretch the low end of the scale just to see if the detail's
really there (even though this makes the rest of the picture look like
crap), it's obvious that the scanner color management _is_ clipping off some
of the darkest detail.

As to gamut mapping, you could certainly try selecting different conversion
intents (e.g., absolute colorimetric) just to see if that makes the
conversion any better. But I think that has to do with how extremely
saturated colors are converted, not blacks. But this is black magic...


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

> From: Jerry Lodriguss
> You make a very good point, and I'm sure the accuracy of the profile is
> part of the problem.
> Thor Olson, a color imaging scientist whom I am corresponding with
> privately, also suggested that gamut mapping may be playing a
> part in this
> problem. He told me some very interesting information...
> >Most monitor spaces use an encoding for lightness that has a linear
> >segment near
> >absolute zero, which then splices into a power law curve for the
> >perceptual levels
> >above around 8%.  This is true for both sRGB and L*, and
> probably your other
> >color spaces you tried.  The deep shadow detail near D=3, would all get
> >encoded
> >into a few counts of digital range.
> >
> >A decent film scanner would be loathe to lose this information in this
> >way.  It would
> >probably use an encoding that was more like a power law all the way to
> >zero, spreading
> >the shadow detail across a larger number of counts.
> >
> >Of course when you try to display such an image, it will get
> mapped to the
> >L* or sRGB
> >curve with the linear segment, and the detail will be lost from
> view (but
> >still encoded in
> >the image of course).
> >
> >When you open the image with no profile conversion, PS treats
> the encoded
> >shadows as
> >if they were sRGB (even though the aren't) and the detail becomes
> >visible.  You have
> >told PS to consider those encoded levels as being at a higher luminance
> >than they were
> >originally encoded at.  It will show the shadows, but of course
> the tones
> >(and colors) are
> >not correct.

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