re: scanners ,gamuts and urban myths
re: scanners ,gamuts and urban myths
- Subject: re: scanners ,gamuts and urban myths
- From: email@hidden
- Date: Tue, 26 Nov 2002 18:48:27 EST
Tom,
Right on! You bring up a couple examples that make me wonder... So, a couple
of questions:
<<Cameras and scanners with such wide span sensitivities can sometime clip
due to incorrect exposure or fluorescence in the original scene>>
1) Doesn't this limit the camera/scanner input device gamut? If the device
clips (for whatever reason) colors (e.g. very high or low luminance or high
chroma) that were otherwise discriminable in the original scene/image, to a
reduced value, then hasn't the device limited the gamut? Maybe its a dynamic
range limitation, but doesn't it manifest itself as reduced device gamut?
<<A drum scanner, or negative film scanner, can be completely different>>
2) This is the extreme case I alluded to earlier. Such a device is intended
for estimating colorant amounts for traditional separation, so the idea of
estimating the colorimetry of any original, has only very limited utility. If
you try to use such a device as a general input device (obviously not
advised), there will be some colors whose reflectance falls largely in a
range where the device may have little or no sensitivity. Consequently, the
device can't see the color well (or at all). So, in this context, wouldn't we
say that its gamut is limited (which isn't necessarily a bad thing if its
used for what it was designed)? If its gamut is limited, that becomes a good
argument to dissuade those from using such a device for color management
inappropriately. I ask this because there are less extreme cases where the
device may have somewhat broader sensitivities with less than ideal overlap.
Where the sensitivity is low and device perhaps noisy, the device might not
be able to discriminate well and perhaps clip. Doesn't this also effectively
somewhat limit the gamut?
<< Correctness of Colorfulness from subject to reproduction >>
3) You remind us of this often overlooked yet critically important fact.
Colorfulness is not chroma or saturation. It seems there is too much emphasis
placed on reproducing and mapping chroma and saturation, ignoring the fact
that what we really care about here is colorfulness which depends on factors
such as scene brightness (among others), that current workflow solutions
poorly address...
Thanks for sharing your knowledge and experience in this area with us.
Eric Walowit
Tahoe
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