Re: RPP raw photo processor 64
Re: RPP raw photo processor 64
- Subject: Re: RPP raw photo processor 64
- From: Ben Goren <email@hidden>
- Date: Wed, 05 Jun 2013 13:22:14 -0700
On Jun 5, 2013, at 12:53 PM, Henry Davis <email@hidden> wrote:
> Your response to Ben about white balance on the beach at sunset causes me to ask if there's some "native reference" or starting point for white balance.
Cameras are (essentially) linear devices. This means that you can consider each channel independently and determine what linear multiplier is necessary to ensure that a piece of Spectralon (e.g.) gets rendered, in that channel, as 100%. If you do that for all three channels independently, when you re-combine the channels into an RGB image, both white balance and exposure have been properly normalized.
More here, including pictures and how to simulate the process yourself in Photoshop:
https://trumpetpower.com/photos/Exposure#Normalizing_exposure
You'll notice that, although that's whats going on behind the scenes, only the ``alternative'' raw development applications give you the option to specify those channel multipliers for yourself. Everything else, especially ACR, instead invisibly translates blackbody radiation sliders into those channel multipliers using some secret sauce recipe.
> [T]he camera imposes an inherent error. The colorimetric problem starts there, in the camera. I don't know if a sensor or combination of filters can be made that would make a colorimetric match possible. On the other hand, they sometimes do a pretty good job of matching paint at the paint store.
In practice, especially in controlled (e.g., studio) conditions, you can do at least as good a job as the paint store does, if not much better.
Dr. Roy Berns at RIT has demonstrated that you can overcome the limitations inherent in a camera's color filter array by making multiple exposures taken with and without carefully-selected Wratten filters and combining the resulting images with some high-powered math. I have some ideas for how to get similar (but probably not as good) results with a much less exotic workflow that I'll be testing out once my order for a couple such filters gets fulfilled in ``six to eight weeks'' from a couple weeks ago. Worst case, I'll be able to replicate his results but with his klunky workflow. I'll report on my findings, of course.
Cheers,
b&
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