Re: DNG Profile Editor question.
Re: DNG Profile Editor question.
- Subject: Re: DNG Profile Editor question.
- From: Ben Goren <email@hidden>
- Date: Wed, 16 Mar 2016 09:30:13 -0700
On Mar 16, 2016, at 9:09 AM, Ethan Hansen <email@hidden> wrote:
> Camera sensors are imperfect, the range of colors captured in profiling shot(s) limited, light sources neither characterized fully nor matching an assumed model, etc. And those are only first-order effects - further complications include whether the sensor satisfies the Luther condition (aka Maxwell-Ives criterion).
That's an accurate summary of the biggest challenges in camera profiling...but they're all addressable or not as bad as one might fear.
One of the biggest considerations is the scene illuminant, and whether you want to faithfully reproduce its appearance or make the scene appear as if it had been shot under some other illuminant, presumably a standard such as D50. The latter especially requires knowing the scene illuminant...but you can either measure it directly with a spectrometer or do a surprisingly good job of estimating it if you've a good idea what it was. For example, if you know that the scene is outdoors or lit by something incandescent and you have a known sample in the image (such as a chart, but could be anything you've measured), you can use that to determine the actual color temperature and thus the actual illuminant. This, of course, also gets you correct white balance -- something not achievable with an eyedropper unless the sample is spectrally flat. It also gets you a perfectly normalized exposure.
Colors near the spectral locus are going to be problematic, and you may do your profiling a disservice by attempting to force it to deal with them. On the other hand, no output device can even come close to representing them, either, so there's no practical point in even trying. Even if you succeeded, you're not going to see the colors on your monitor, let alone in a print. That leaves some sort of objective analysis as the only reason you might want something like that...and digital cameras are so far from being the right tool for that sort of thing it's not funny.
(And, though sensors aren't perfect, they're shockingly good. Non-linearity comes almost entirely from optical artifacts, especially lens flare but sometimes also internal reflections in the camera's mirror box. Get the lighting and geometry right for reproduction work and none of that is a factor.)
> Most scenes containing color gradations ended up having visually jarring, ugly transitions.
That's an indicator of a poorly-constructed profile. But good profiles, especially ones meaningfully encompassing a significant gamut, are difficult to construct....
Cheers,
b&
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