Camera profiling with ICC et al
Camera profiling with ICC et al
- Subject: Camera profiling with ICC et al
- From: email@hidden
- Date: Thu, 11 Sep 2008 11:07:42 EDT
Chris, Edmund, Uli, Eric, and others,
Forgive me for coming into this thread late. I've been very remote and will
be again till next week. A couple comments:
1) I have the new camSpecs monochromator from Image Engineering designed
specifically for profiling by measuring camera spectral sensitivities out to the
near IR. Compared to lab-grade monos, its fast, inexpensive, repeatably, and
easy. I have no financial affiliation with IE except that I am a happy customer
and helped design it. I have measured all my cameras, compared the results to
lab-grade monos, and obtained very similar results. I've not seen near IR
issues with any recent cameras.
2) Once the camera spectral sensitivities, linearity, training data, etc. are
known then it is a simple and very accurate matter to determine the optimal
profile for any given illumination.
3) However, an ICC profile can only handle one illumination condition at a
time, though this does not preclude mixed (though not spatially varying in terms
of SPD) illumination if it is adequately characterized. This is a limitation
of ICC, though it is easily circumvented by building and embedding profiles
on-the-fly based on the scene illumination metadata or precomputing and storing
multiple profiles.
4) In my understanding, fundamentally, it is the latter approach that
underpins and is an advantage of Adobe's method compared with a
single-illumination-only ICC profile. Though Adobe doesn't use the ICC-wrapper, the Adobe profile
data itself is fundamentally similar (and probably not incompatible with some
massaging) to using multiple well-constructed ICC profiles. Adobe should be
commended for their approach, not berated.
5) Assuming that rendering from scene-referred to output-referred is turned
off (frequently not an easy assumption to check) it takes a very carefully
designed, controlled, and executed experiment to objectively evaluate the profile,
Adobe, ICC or otherwise. Much of what I have seen described here is simply
inadequate for validating profile quality.
Thanks,
Eric Walowit
Tahoe
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