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Author Topic: Using color filters for color balance with digital  (Read 1459 times)

michaelnotar

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Using color filters for color balance with digital
« on: May 02, 2009, 02:54:50 pm »

Quote from: cmi
Hi gang,

Im photographing landscape and now I have some motives where I want to go again and re-shoot it in the highes possible quality. For one of these pictures my blue channel is really... horrible... so Im looking for optimisations naturally. I have read somewhere (cant find it!) that if you use colored filters for whitebalance, the quality of usually noisy channels like blue (quite often more noise), is enhanced. Is this complete nonsense or is it true? If yes, anyone has experience with this? What additional equipment I would need and how would I do it? (For one part I think it cant be true because then it would be a common advice.)

Also on a sidenote, why is it that the blue channel often gets more noise? I figure because of the different distributed wavelenghts in the particular spectrum, and if a channel is low it simply gets noise. But I dont know and I wonder if anyone could explain it with more detail.

Now I could just buy some filters and try for myself, and will probably just do that, but Im curious!

Regards,


Christian


i saw this in another section, thought i would repost here. i am curious to hear from Doug of CI hopefully and other technical specialists on this technique vs. color correction in C1 etc.
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Doug Peterson

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Using color filters for color balance with digital
« Reply #1 on: May 02, 2009, 05:51:53 pm »

Quote from: michaelnotar
i saw this in another section, thought i would repost here. i am curious to hear from Doug of CI hopefully and other technical specialists on this technique vs. color correction in C1 etc.

From iPhone...

If your goal is the highest possible quality then correct by lens filter wheneve practical. Keep in mind the lens filter cuts light and therefore makes it harder to focus/compose/hand-hold; sometimes it's just not practical. Also there are many situations in which you don't want to "correct" away warmth; a neutral sunset kinds misses the point!

You shoot landscape so tungsten doesn't come up for you very often, but I'm going to use tungsten as my main example because it's where the question most commonly comes up with our clients.

Setting the white balance away from the sensor's native daylight range inherently means pushing one channel and pulling another. So if your light source is warm (low kelvin; e.g. Tungstun) and you want to produce neutral tones in the final image then without a lens filter you will be pushing the blue channel and therefore increasing blue channel  noise and decreasing it's shadow detail while decreasing highlight detail on red subjects (which makes for terrible skin tones).

The extent to which this meaningfully reduce image quality depends on
1) how much you are shifting the white balance (e.g. 500 or 2000 degrees)
2) the dynamic range of your system
3) how well exposed and what ISO the image (which establishes the baseline of noise)
4) whether your camera has a profile specific to the light source e.g. Phase produces a tungsten color profile (not the same as a tungsten white balance) for each of its digital backs.

So a modern digital back can "recover" from uncorrected  tungstun light much better than a entry level dSLR.

This is why it's often said that digital backs deal with mixed lighting much better than other options; with more fidelity per pixel more dramtic local color changes can be made without introducing excessive noise.

Doug
Captureintegration.com
« Last Edit: May 02, 2009, 05:58:33 pm by dougpetersonci »
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CBarrett

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Using color filters for color balance with digital
« Reply #2 on: May 02, 2009, 06:09:38 pm »

That's pretty damn interesting, Doug.  But even though (or maybe because) I've shot thousands of sheets of chrome with an 80D10M behind the lens.... I cringe at the idea of putting a piece of gelatin in between a Digital Rodenstock and a P45+.  Eeew.... filters.  I am so done with those damn things.... LOL

It does make me want to test the process, though... wonder if I have any 80A's still hangin around....

-cb
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michaelnotar

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Using color filters for color balance with digital
« Reply #3 on: May 02, 2009, 06:14:16 pm »

its interesting too. but i like not having CC filters these days. i just correct light sources. i just keep any digital camera/back on daylight or auto WB and that seems to be just fine.
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Graham Mitchell

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Using color filters for color balance with digital
« Reply #4 on: May 02, 2009, 06:39:43 pm »

Doug pretty much explained it all. Most mild WB shifts are acceptable but extreme lighting requires filtration for acceptable results.
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marcmccalmont

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Using color filters for color balance with digital
« Reply #5 on: May 02, 2009, 10:05:55 pm »

With the high pixel density sensors today I have found any filter even a clear protection filter noticeably degrades sharpness so its a trade off, is it a wide dynamic range scene and clipping of one channel  is costing me the shadow detail or is a tack sharp shot more important? For me sunset/sunrises are where I would use a filter to limit the one channel that is clipping and sharpness is secondary, for most daylight landscape scenes I would not erode sharpness with a filter. just food for thought
Marc
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Marc McCalmont
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