Colorchecker Passport & Mixed Lighting

[Mike Guilbault]

Should/would you do a custom DNG profile if you're shooting under mixed light - or is that just a WB problem?  For example, shooting an interior which has incandescent light, possibly some halogen and even daylight coming through a window.  

And on the side... how much of the WB target do you really need to get in the frame of your camera to create a WB Preset in camera?  Some places I've read you need to get the whole frame filled, another source says only the central area is needed.  Which is correct?

[Mike Guilbault]

anyone???

[Sheldon N]

I don't think a profile will solve those problems. Usually the issue is that you have different light sources from different directions, in differing intensities across the scene. Add 3 dimensional objects and you get light on different planes of your subject, some of which is mixed from multiple sources and some of which is not (ie. left side tungsten right side window light).  A profile won't solve these issues, and WB adjustment doesn't usually solve them either. 

If you had consistently mixed sources (ie from same direction/distance) then a profile might help.

[digitaldog]

Should/would you do a custom DNG profile if you're shooting under mixed light - or is that just a WB problem?  For example, shooting an interior which has incandescent light, possibly some halogen and even daylight coming through a window.

I’d try to build a dual illuminant profile?

[Sheldon N]

Doesn't a dual illuminant profile work by changing the color profile as you move the WB slider along the Kelvin scale?

I thought if you set the WB for a warm source it biases towards the warm profile and if you set for a cool source it biases towards the cool profile (not 100% on that so please correct me if I'm wrong).  

If that's the case, then it wouldn't really deal with truly mixed lighting sources like Mike was describing (window, plus tungsten overhead, plus halogen lamp in the corner, etc). You'd just get an "average" profile that was slightly wrong for each light source.

[digitaldog]

If that's the case, then it wouldn't really deal with truly mixed lighting sources like Mike was describing (window, plus tungsten overhead, plus halogen lamp in the corner, etc).

No, nothing will automatically (you’ll have to do some fancy selective editing). But it should be a good (better) start.

[Peterretep]

I'll agree with Sheldon saying "I don't think a profile will solve those problems." In capture of an interior space one way to minimize the differences in light sources would be to add more of your own lighting relying less on ambient. In film working on one transparency filters were added over the lens to expose a certain light source while the other lights were turned off. Not as often done now in digital however. With digital you can do a few different raw conversions in which you vary the WB and carefully blend the resulting layers in PS, that is a technique I often do in conjunction with relying less on ambient.

Peter

[Anders_HK]

ExpoDisc is a good tool for a good departure point of WB in mixed lighting; http://www.expoimaging.com/product-detail.php?cat_id=1&product_id=2&keywords=ExpoDisc_Neutral

Got mine on Ebay.

Best regards,
Anders

[ErikKaffehr]

Hi,

My take is that a custom DNG profile is most useful for:

1) Calibrating a given camera for a given set of conditions

2) Calibrating for difficult light

Once calibration is done I don't see any reason to use anything but setting white balance.

The Adobe DNG profile editor can also tweak colors, so it may be slightly more useful than the Xrite DNG profiler, may be worth a try.

Another observation. I have the impression that the color checker has very benign spectral characteristics. An illumination with uneven spectral characteristic may work well with the color checker but have problems with pigments/surfaces/color having an uneven reflection spectrum.

Best regards
Erik

Should/would you do a custom DNG profile if you're shooting under mixed light - or is that just a WB problem?  For example, shooting an interior which has incandescent light, possibly some halogen and even daylight coming through a window.  

And on the side... how much of the WB target do you really need to get in the frame of your camera to create a WB Preset in camera?  Some places I've read you need to get the whole frame filled, another source says only the central area is needed.  Which is correct?

[Mike Guilbault]

With digital you can do a few different raw conversions in which you vary the WB and carefully blend the resulting layers in PS, that is a technique I often do in conjunction with relying less on ambient.

Peter

That's an excellent idea Peter. I've blended exposures before, but hadn't thought of doing it in these instances.

I guess I'm still trying to get my head wrapped around the difference between using the Colour Checker Passport for a DNG Profile and White Balance.

[madmanchan]

The dual illuminant aspect of a DNG profile is to deal with separate images with different lighting conditions (e.g., you have a shot taken in daylight, and another shot taken under incandescent).  It doesn't deal with spatially-varying illumination within a single shot.