Re: Primer on photographic exposure, etc.
Re: Primer on photographic exposure, etc.
- Subject: Re: Primer on photographic exposure, etc.
- From: Iliah Borg <email@hidden>
- Date: Wed, 15 May 2013 18:53:30 -0400
Hi Lars,
> Still, with such a target you're calibrating only for reflective colors.
That is indeed so.
> Shouldn't you include more colors near the spectrum locus?
Myself, I do profiling using a monochromator. Tried different approaches over the years, including LEDs and filters over flash and halogen lamps, similar to what IE are doing. Monochromator turns to be the best approach.
> Sure there are target tolerances for the same SKU.
I measured up to 6 deltaE2000, used Spectrolino. Within one batch, up to 4 deltaE2000.
> Are these tolerances bigger than the color inaccuracy of the camera system itself (which is maybe 10 dE over a large set of colors after calibration)?
Cameras serial numbers and lenses especially make a lot of difference, I'm afraid canned profiles are not exactly what a picky repro photographer would like given he has an option of custom profiling his cameras with his own lenses. Polarizing filters are adding a lot of variations too, depending on the angle of rotation and lighting factors.
Using monochromator to shine the light onto the "bare" sensor and through different lenses one can see how certain wavelengths are getting attenuated heavily. Most of the canned profiles I built for RPP are "no lens" profiles. It helps for metameric failure issues as far as I can see.
Monochromators are quite within the reach these days, Edmund Optics and other resellers have a good selection.
The greatest and often overlooked problem is that profiles depend on exposure, especially for saturated darker colours. It is a good idea to make "bracketed" profiles, like for white patch exposed to 248 for normal exposure and -2 EV, -3 EV, -4 EV profiles.
Possibly a better approach is to combine data from monochromator and from actual target shots, I'm working on it currently, looks promising.
--
Best regards,
Iliah Borg
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