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01-06-2011, 02:51 AM   #1
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White balance for discontinous spectrum?

Hi. I recently got a K5 and so far I am extremely happy with its low-light facilities. However, I had some trouble shouting pictures by night in streets with sodium vapor lamps.
I tried several manual white balance settings (changed color temperature etc.) but I was not really satisfied. Most of the time it appeared too orange in comparision to my personal impression!
Is there another way to deal with such light sources of discontinous spectra?

Thanks!

01-06-2011, 05:19 AM   #2
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This is pretty tough due to the spectrum of sodium lights as you point out. I am not sure there is a real solution without doing a ton of work in a photo editor

Although not a solution, since sodium lighting essentially renders your vision to B&W ( with colors being shades of grey) why not process as a B&W shot ?

You could select specific colored lights to remain but convert the rest of the image to B&W and use the splashes of color as accents
01-06-2011, 06:15 AM   #3
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Hi, if I remember Sodium produces 2 yellow wavelengths.
You would need to filter those specifically.

Astronomical Light pollution filters are designed to remove Sodium and Mercury
wavelengths. But these leave ordinary whites as green/crimsons.
Even if they did work in sizes over 2" their costs are also astronomical!

Sorry but not much help here.........
01-06-2011, 07:26 AM   #4
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Did you try setting to daylight (~5500-6000K) explicitly? Something close to that should give a result reasonable close to perception I guess.

01-06-2011, 11:04 AM   #5
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Sylvania (the creator of sodium vapor lighting) developed a filter to use with vapor sodium lighting for photographic purpose. I don't know if they still manufacture that filter and where you could find it.
01-10-2011, 05:43 AM   #6
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B&W helps with sodium vapor lamps

Thanks for your comments.
The hint to use B&W proved to be particularly helpful. The problem with sodium vapor street lamps really is that their light only contains one color (two very close yellow lines). So in the abscence of other similarly strong light sources the picture automatically gets quasi black-and-yellow which looks very unnatural but can be turned into black-white... which nicely avoids the original problem!
01-10-2011, 01:42 PM   #7
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Remember 'if you can't beat them join them'

If you set the WB to CTE, the camera will try to show you the colors in the scene, not the ones that your brain was trying to see It should emphasize the mood much more then rendering things neutral.

- Itai
01-10-2011, 03:57 PM   #8
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QuoteOriginally posted by FH_le Quote
Thanks for your comments.
The hint to use B&W proved to be particularly helpful. The problem with sodium vapor street lamps really is that their light only contains one color (two very close yellow lines). So in the abscence of other similarly strong light sources the picture automatically gets quasi black-and-yellow which looks very unnatural but can be turned into black-white... which nicely avoids the original problem!
Glad I could help. Was not sure if B&W was the direction you wanted to go but as you say the monochromatic nature of the light led me that direction

01-10-2011, 09:28 PM   #9
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There are 2 kinds of sodium vapor lights in use. High pressure and low pressure. As pointed out low pressure sodium vapor lights produce light in only 1 band that is basically just monochrome yellow. If a scene is only illuminated in a monochrome light then you can only get that one color. So if you only have yellow you canít get red or blue or even green. It is just not an issue of balancing for the other colors to make something that is normally white look white. White is going to just look yellow. Even if you convert it to B&W it could still look strange as the other colors have a gray value that will not be the same if you only have yellow. This is why in B&W you use color filters to change these gray values to make the photo look more interesting. So with low pressure sodium vapor lights you are just about out of luck. Astronomers like low pressure sodium vapor lights because they can use a filter that blocks most of the light and see all the other colors in the sky. If you use this filter with a scene only illuminated by a low pressure sodium vapor light you just get black. So astronomers have made a big push for all outside light to be low pressure sodium vapor light. This has for the most part been a dismal failure. People donít like the way low pressure sodium vapor lights look so only some stretches of road have them.

This is bad for astronomers but good for photographers as most of the yellow streetlights you see are high pressure sodium vapor lights. High pressure sodium vapor lights produce more colors then just yellow, it is still not a good white but it still give you something to work on. The first thing you have to realize is this light doesnít resemble a black body so trying to change the CB by changing the temperature is not going to work. But this is OK as there is an easy way (so easy that it may become your preferred way to set CB) in PP. You will want to do this with a RAW photo (or a RAW converted to 16 bit TIFF), as you will need as much color information as you can get. Most PP software has a way to set your CB and in that is usually an advanced setting that you can use to set a white point. This white point doesnít have to be white but is really a gray point. Gray is just a darker white. You donít want a point were any of the color channels may has been exceed so a light gray is better then white. When you use this the software will move all the colors independently to make this point white (gray) not just shift them as if you are setting it by temperature. So to use this all you have to know is what in you photo is white (gray). If you think about it you will realize there are usually something in a scene you can use like oh say concrete. Most concrete can be used (just not new as it looks green) but you may have to use a spot that is not to close to the light or to far. A little trial and error maybe needed.

DAZ
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