Do optical WB filters improve RAW color latititude?

Started Aug 26, 2012 | Discussions thread
John Sheehy
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Re: Do optical WB filters improve RAW color latititude?
In reply to Vitruvius, Aug 27, 2012

Vitruvius wrote:

I know this might get really technical, but I am wondering if an optical color correction filter can enhance a digital RAW file. I know the RAW file is “what the camera sees” without correction. So you can shoot RAW and then you allow the camera to adjust White Balance or you do it yourself later on the computer. The question really is; do you lose more image color information by shifting the post exposure digital image later or by filtering the incoming light with an optical color filter during exposure? I have FL-D and blue filters for incandescent light from the film days. I guess I should do some trials but I wouldn’t know where to start with the technical comparisons.

I am thinking that digital RAW files would have more color latitude if they were pre-white-balanced during exposure by a color correction filter. Not sure though. Thanks in anvance.

You can use optical color filters to get various effects, but for the two situations of which you speak - old-style flourescent and incandescent, filtration can be counter-productive, unless you are doing long exposures at base ISO. If you are using a high ISO because of a needed shutter speed, you will need an even higher ISO with the filter. So, if you use the blue filter for incandescent, you will create slightly more noise in the blue channel, and even more noise in the green and red channels which you will weaken further. If, however, you are shooting at base ISO on a tripod, then yes, you can reduce the noise in the blue channel by using the correction.

BTW, what you are suggesting filters the scene to be treated by daylight, which seems logical, but daylight is not the native WB of digital cameras! The vast majority of them create white in the RAW data when red is twice as strong as green, and blue is 1.4x as strong as green, IOW, the native WB is a pinkish-magenta. You will get a minimum of chromatic noise and a maximal DR of full-color when the lighting is magenta. When the lighting is greenish, you get the maximal DR with monochrome extended highlights and shadows, but minimal full-color DR.

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John

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