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colour shift in photographs

Community Veteran
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Registered: 24-09-2008

colour shift in photographs


I was out taking a few photographs last night of the Aurora, what the eye sees, the camera interprets as something different.
What I saw was white tinged with blue white, yet with various time exposures I get green tinged with red.
The photograph below was given a 20 second exposure (10 second makes the green a bit darker, 30 second makes the green lighter.)
The Green is just not real, Can anyone explain?
15 REPLIES
Community Veteran
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Re: colour shift in photographs

What camera are you using? And is the original in RAW format or jpg? If it's RAW you can manipulate the white balance to a better value using the RAW software that was supplied with the camera (or Photoshop).
The colour shift is possibly something to do with using auto white balance on the camera. You should if possible set the white balance manually, or you will get some strange effects...
http://www.astropix.com/HTML/I_ASTROP/CUSTOMWB.HTM
You've got a meteor in that pic too!  Very nice. Where in the UK was this taken?
EDIT: Could you post the exposure etc. settings for this pic please?
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Re: colour shift in photographs

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Community Veteran
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Re: colour shift in photographs

OK.
Unfortunately there's no white balance info so I assume it's auto. Second, it looks as though it's a direct jpg shot as opposed to RAW converted to jpg. If it was also shot in RAW try tweaking the white balance in Photoshop. If you're shooting in jpg you could do far worse than shooting in RAW. Gives you far more processing options.
Nice pic though. 
magnetism2772
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Registered: 06-06-2010

Re: colour shift in photographs

your photo of a green aurora is showing the correct colour
ie solar winds colliding with oxygen in earths atmosphere is what is giving off this green light
however the eye is seeing it as white
take florescent tubed light its actually green in colour ( i think the camera does show it in green light too)
but as we know it looks white
hmmmm
Community Veteran
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Re: colour shift in photographs

The colour of the display depends on which atom in the atmosphere is struck by the solar wind....
Green - oxygen, up to 150 miles in altitude
Red - oxygen, above 150 miles in altitude
Blue - nitrogen, up to 60 miles in altitude
Purple/violet - nitrogen, above 60 miles in altitude
It's entirely possible for there to be a white/blue display, and it's also possible for the photographed colour to be shifted by a white balance error.
Community Veteran
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Re: colour shift in photographs

[quote="giro"]take florescent tubed light its actually green in colour ...
but as we know it looks white
the use of "actually" and "looks" in that sentence is ... um ... a bit debatable, and I won't even begin to start on "know" ...
magnetism2772
Grafter
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Registered: 06-06-2010

Re: colour shift in photographs

perhaps the taken picture was  shot in the dark using an ultra violet light source , ie using the cameras electronic flash?
see the fury of the sun as hot compressed helium gas flows to the surface of the sun
under ulra violet camera  view
pierre_pierre
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Re: colour shift in photographs

you could google it, copy, paste without having a clue about the science of colour
I always use a daylight colour balance light when doing hobby work,  DMC make 430 different colour threads
magnetism2772
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Re: colour shift in photographs

well my qualifications should assure most readers
i personally have a modern digital camera that has a flash ,
a work area lit by fluorescent lighting that one might see in a workshop
I've recently put in time to study  photography using varying light sources
and the last time that i used my camera was yesterday  Cool
pierre_pierre
Grafter
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Re: colour shift in photographs

 
the visible spectrum is the parabola on the graph


Digital Photography

In digital photography, color temperature is sometimes used interchangeably with white balance, which allow a remapping of color values to simulate variations in ambient color temperature. Most digital cameras and RAW image software provide presets simulating specific ambient values (e.g., sunny, cloudy, tungsten, etc.) while others allow explicit entry of white balance values in Kelvin. These settings vary color values along the blue–yellow axis, while some software includes additional controls (sometimes labeled tint) adding the magenta–green axis.
looking at the top picture Ultra violet is the blue part at the bottom left, it is nowhere near the green bit of the graph
magnetism2772
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Re: colour shift in photographs

looks like this topic will have to be expanded further
The Sun is essentially all colors mixed together, which appear to our eyes as white.
When we see the Sun at sunrise or sunset, it may appear yellow, orange, or red.
But that is only because of its light rays being "bent" through the Earth's atmosphere
So why are the solar images sometimes green, or blue, or red, or orange?
Actually, all forms of light and energy are part of the same phenomena: the electromagnetic spectrum.
Our eyes can detect only a small amount of this energy, that portion we call "visible light."
we know from seeing a picture of a neon green or bright red Sun that the image was actually taken in some non see-able version of light such as extreme ultraviolet
below is a  pictorial view of the electromagnetic spectrum.
showing how sun rays can look green in ultra violet light
Sometimes the display color of the Sun is culturally determined ie red sun = japan
yellow sun = childs sun
but in spite of the Japanese or  how children see the sun
the sun is actually white

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Re: colour shift in photographs

Quote from: nozzer

You've got a meteor in that pic too!  Very nice. Where in the UK was this taken?
EDIT: Could you post the exposure etc. settings for this pic please?

@Strat, thanks for posting details, only get onto the Internet every few days, so cannot readily respond.
@Nozzer: Thanks for all the information, will digest. Photograph was taken from a valley just north of Eyjafjallajökull, (61.710919N  19.733747W), photo looks North by North West, timed at 00:30 approx local time, clouded over by 02:00, have been working in Iceland (not the supermarket) since 1st week in July. Thanks for the meteor pointer, colleague pointed out the big dipper in the image. It was taken as a Jpeg, not raw, was using a Nikon, didn't keep track of the time exposures but think this was 20 seconds at full aperture, I had to switch cards as my 'point and click' couldn't cope
@giro and Pierre, thanks for the details on colour, still is very different from what the eye sees, the eye sees white and tinged blue. Read somewhere the colour relates to the 'altitude'?, but it was a non-scientific journal article.
Lurker
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Re: colour shift in photographs

I think its more likely to be the space station than a meteor.
You can check for sure sighting in the future on this site: http://spaceflight1.nasa.gov/realdata/sightings/cities/view.cgi?country=United_Kingdom&region=Englan...
Presumably there will be a way to check retrospectively too.
pierre_pierre
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Re: colour shift in photographs

@journeys
if you open up your jpeg in Irfan view and click on Image - Infoo - Exif it will give you the info you want
as below, one from this morning