Re: Primer on photographic exposure, etc.
Re: Primer on photographic exposure, etc.
- Subject: Re: Primer on photographic exposure, etc.
- From: Lars Borg <email@hidden>
- Date: Mon, 20 May 2013 21:46:53 -1000
BTW, shooting targets filling the frame with the target may be not
the best approach.
No, don't do that. (flare, vignetting...)
Or establish the light distribution by also shooting a gray card
overlaying the chart, then normalize the light.
Profiles (especially matrix) can be multiplied.
That's probably not accurate for narrow spectra, but may work OK for
very smooth spectra.
Actual light is an extremely interesting question, I do not feel
like I can do better with actual light than just measuring it with
some portable spectrophotometer.
Right, but then you have to redo the spectral math to get the matrix.
Noise.
Noise can be averaged, by adding more pixels, multiple chart shots.
In-camera flare and lens flare.
Yes. That's a challenge.
While you may be able to subtract much flare from the camera data
during calibration, that doesn't help in actual color management as
the flare is not removed from images before conversion.
As an alternative add estimated flare to your reference data,
matching how the chart looks to the camera, not how it measures.
Another yet connected thing is that RGB about 30 (on 0..255 scale,
gamma 2.2) is too "light" for what cameras can do now.
Don't quite follow you. Yes, the sRGB tone curve has a limited
dynamic range and shadow resolution.
For comparison, digital cinema projection uses 12-bit with gamma 2.6.
Supposedly that's enough to not show any artifacts for a 2000 : 1 DR
at 48 nits.
Lars
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