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Author Topic: Colour balance for UV/IR  (Read 4877 times)

Neeneko

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Colour balance for UV/IR
« on: May 27, 2012, 10:47:21 pm »

Hello all.

I know this isn't an UV/IR specific forum, but people here seem pretty knowledgeable so I thought I would throw this out here.

I do most of my shooting in ultraviolet and infrared with filters that span various parts of the spectrum.  Colour balance is a constant headache.

When I first started I got a BRNO Balens white balance cap and use the camera's (Canon 35D) built in custom white balance function.  At the time I was not doing any post processing.  Since then I have learned how to use basic post processing tools and am interested in learning how to use other techniques for handling the faux colours in post production rather then depending on the camera's built in support.

I have done some reading about various balance cards (like WhiBal's neutral card) and profile solutions like xrite ColorChecker Passport, but various discussions of those methods only seem to talk about how they work in the visible spectrum.

So I was wondering if anyone here could comment about using things other then white balance caps for UV and IR photography?  Reading about the xrite passport sound especially interesting since it sounds like I could create profiles for each of the various filters rather then recalibrating after every shot, but no idea if it would work that way.

Thanks all.
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jbrembat

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Re: Colour balance for UV/IR
« Reply #1 on: May 28, 2012, 06:52:53 am »

White balance is performed to emulate human visual system.
Human visual system is restricted to visible light.

Jacopo
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Bart_van_der_Wolf

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Re: Colour balance for UV/IR
« Reply #2 on: May 28, 2012, 12:00:32 pm »

I know this isn't an UV/IR specific forum, but people here seem pretty knowledgeable so I thought I would throw this out here.

I do most of my shooting in ultraviolet and infrared with filters that span various parts of the spectrum.  Colour balance is a constant headache.

Hi,

Colour balance is not applicable with partial spectral band light. The only thing you can do is use a lightsource with know emission spectrum, and calibrate your lens+sensor's response for those wavelengths. Then you can assign an arbitrary Look-Up-Table (LUT) to represent different amounts of reflection.

Apparently, Canon cameras are not the best suited for UV photography according to this source.

He also makes other sometimes spectacular looking images but don't forget that this is done by using very special equipment and processing:

Image, courtesy: Dr. Klaus Schmitt

Cheers,
Bart
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== If you do what you did, you'll get what you got. ==

Doug Peterson

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Re: Colour balance for UV/IR
« Reply #3 on: May 28, 2012, 01:13:34 pm »

White balance is performed to emulate human visual system.
Human visual system is restricted to visible light.

Jacopo

+1

One of the joys of IR (for me personally) is to let go of a literal* translation of color and tone. Pick something that is appealing, meaningful, different, or otherwise feels right and don't worry too much about the rest. Of course there is always some challenge if you wish to present a group of images together as a set.

BTW, I think from your note you already know this but for the benefit of other readers: Not all gray cards are neutral throughout the IR and UV spectrum. In other words they may be gray in visible light (evenly bright under each band of the visible spectrum) but have a mild or even severe change in reflectively in IR or UV.

*by literal I mean "what the human eye sees"

Peter_DL

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Re: Colour balance for UV/IR
« Reply #4 on: May 28, 2012, 01:46:49 pm »


He also makes other sometimes spectacular looking images
but don't forget that this is done by using very special equipment and processing:


Wow!
Great image.
Quite sure something like this would not have been possible with any normal photo + digital filters.

--
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Neeneko

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Re: Colour balance for UV/IR
« Reply #5 on: May 28, 2012, 02:56:21 pm »

Colour balance is not applicable with partial spectral band light. The only thing you can do is use a lightsource with know emission spectrum, and calibrate your lens+sensor's response for those wavelengths. Then you can assign an arbitrary Look-Up-Table (LUT) to represent different amounts of reflection.

True.  I realize that colour balance and white balance are not the best way of describing it, but they are the particular methods I have been playing with to get faux colour images.  I know I could make arbitrary lookup tables, but for the moment I do not wish to go that route.

Quote
Apparently, Canon cameras are not the best suited for UV photography according to this source.

Sadly, this is true.  I have chatted with Dr. Schmitt several times on the issue including sending samples and yeah.. even converted to full spectrum, Canon bodies suck at UV.  Unfortunately it is all I have so that is what I am working with.

Quote
He also makes other sometimes spectacular looking images but don't forget that this is done by using very special equipment and processing:

He does indeed have access to equipment that most of us could only dream of, though in his blog he has done a good job demonstrating that using even cheap stuff like old enlarging lenses you can get some pretty good results.
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Neeneko

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Re: Colour balance for UV/IR
« Reply #6 on: May 28, 2012, 02:59:04 pm »

Of course there is always some challenge if you wish to present a group of images together as a set.

Actually one of the challenges is I have been putting together comparisons of how different filters effect IR photography, so I am really interested in having a tool to be as consistent as possible.

Quote
BTW, I think from your note you already know this but for the benefit of other readers: Not all gray cards are neutral throughout the IR and UV spectrum. In other words they may be gray in visible light (evenly bright under each band of the visible spectrum) but have a mild or even severe change in reflectively in IR or UV.

Yep, that is one of my big concerns about trying to use the grey card method.  I only found one site where someone talked about a grey card that was consistent through IR but it was only to plug the card the person made and the site was broken so there was no way to actually order one.
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