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Author Topic: Creating a Custom Camera Profile - White Balance - before or after  (Read 8786 times)
RFPhotography
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« Reply #20 on: September 08, 2011, 02:52:43 PM »
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That's not WB though, Peter.  If you've got a colour correction filter on the front of the lens (e.g., warming, cooling) then that is going to impact the colour captured at the sensor and it would completely throw off the software.

ETTR really plays no part in the creation of a camera profile using something like the ColorChecker Passport.  It simply needs a good, correct exposure.
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Peter_DL
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« Reply #21 on: September 09, 2011, 10:24:02 AM »
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That's not WB though, Peter.  If you've got a colour correction filter on the front of the lens (e.g., warming, cooling) then that is going to impact the colour captured at the sensor and it would completely throw off the software.

It is, Bob,
it is indeed as simple:

+/-EV camera exposure = global linear scaling of the Raw RGB data, >/< 1 (except for possible clipping issues and noise of course).
Colour correction filter on the front of the lens = linear scaling of the Raw RGB data with different weighting per R/G/B channel = White Balance.

Another question might be, if this is really supported by the Raw conversion software.

Peter


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« Last Edit: September 09, 2011, 10:32:14 AM by Peter_DL » Logged
RFPhotography
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« Reply #22 on: September 12, 2011, 01:05:17 PM »
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Right.  And if the weighting of the light captured is altered at the sensor level then reversing it or altering it after the fact wouldn't be possible.  Or at least would be much more difficult.  The choice of in camera white balance doesn't affect the exposure or light captured.  A colour filter on the lens would affect both.  I don't think I have any colour filters tucked away in the deep, dark recesses of my office (I'm actually kind of afraid to look for fear of what else might be in there - who knows, I might find Jimmy Hoffa) so I can't experiment but I think I might have some old shots in my library so let me see what I can find.

OK, here's an example.  One shot has no filter on the lens.  The other, of essentially the same scene, has a Cokin 007 which is a very deep red/quasi-IR filter.  Both have the same White Balance of 4100.  The information captured at the sensor is altered with the filtered image.  There's no way this could be corrected for in a RAW converter.  Using a warming, cooling or other colour filter on the lens would cause the same type of alteration of information captured at the sensor level to a lesser degree.  The filtered images have a 'white balance', really a colour cast that's locked in and can't be altered so it can't be stripped out by the profiling software.  Whereas if the WB is just in the metadata and isn't locked in via a colour cast, it can be stripped out.  This is why you can't create a camera profile from a JPEG file, the WB is locked in and impacts the colours in the image.
« Last Edit: September 12, 2011, 01:28:20 PM by BobFisher » Logged
madmanchan
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« Reply #23 on: September 14, 2011, 03:52:27 PM »
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The main thing that color filters (e.g., placed in front of a lens) will "throw off" is the mapping of white balance gains (or, equivalently, "camera neutral values") to temperature/tint values. In other words, the relationship between the adopted white point of the scene and the raw values will be thrown off if using a normal color profile that was built without the filter. So using WB presets like "Daylight" or "Cloudy" in the raw conversion software won't work properly. As Shot WB will almost certainly also not work properly. On the other hand, a click-WB will usually continue to work fine.
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ErikKaffehr
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« Reply #24 on: December 13, 2011, 12:03:36 AM »
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Hi,

That's extreme filtering, It has nothing to do with spectral balance.

I would suggest to use DNG profiler without filter and use the normal gray balance tool using a grey card (CC, WhiBal etc) to set color balance. If you are using some light balancing filter all the time you may as well build your profile with it.

Best regards
Erik



Right.  And if the weighting of the light captured is altered at the sensor level then reversing it or altering it after the fact wouldn't be possible.  Or at least would be much more difficult.  The choice of in camera white balance doesn't affect the exposure or light captured.  A colour filter on the lens would affect both.  I don't think I have any colour filters tucked away in the deep, dark recesses of my office (I'm actually kind of afraid to look for fear of what else might be in there - who knows, I might find Jimmy Hoffa) so I can't experiment but I think I might have some old shots in my library so let me see what I can find.

OK, here's an example.  One shot has no filter on the lens.  The other, of essentially the same scene, has a Cokin 007 which is a very deep red/quasi-IR filter.  Both have the same White Balance of 4100.  The information captured at the sensor is altered with the filtered image.  There's no way this could be corrected for in a RAW converter.  Using a warming, cooling or other colour filter on the lens would cause the same type of alteration of information captured at the sensor level to a lesser degree.  The filtered images have a 'white balance', really a colour cast that's locked in and can't be altered so it can't be stripped out by the profiling software.  Whereas if the WB is just in the metadata and isn't locked in via a colour cast, it can be stripped out.  This is why you can't create a camera profile from a JPEG file, the WB is locked in and impacts the colours in the image.
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