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How to remove brown spots
Tom Mann
Guru
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Is the reason that you want to reduce the color and tonality differences in these areas because you think they are not real and some sort of artifact that needs to be removed, or because even if they actually were real, you just don't like them?
I ask because it is well known that the true colors of auroras can not be seen by the naked eye, and only be seen using sensitive detectors like those in modern DSLRs (see the 1st article referenced below). Auroras often have many colors besides the usual yellow-green, but reds, purples, and other colors around the edges of the brightest areas, but at lower intensities. These are due to emissions from other chemical species and other excited states of the main nitrogen emitters. These occur because of differences in excitation and collisional energy relaxation processes at different altitudes. To be honest, that's what these colors look like to me.
You might want to take a look at articles like these before you try to remove these areas:
Why Only Photographs Reveal the Northern Lights' True Colors:
http://www.space.com/23707-only-photos-reveal-aurora-true-color.html
What makes the color of the aurora:
http://odin.gi.alaska.edu/FAQ/#color
Both of the above articles are on highly respected scientific websites: space.com, and The Geophysical Institute of the University of Alaska.
Also, please look at the colors in my tweaked version (ie, Post #14 of this thread). Be sure to click on the in-line preview to view it at full size. You will see that there is not just one color in the areas you outlined, but include weak reds, oranges, and purples, exactly like discussed in the articles I cited, the only difference being that the version you observed did not have quite so much intensity in these colors as the examples in the articles, so your was predominantly yellow-green.
HTH,
Tom M
PS - Also, I'm curious - - At what latitude did you photograph this aurora? It might have simply been a weak one, but if you weren't further north than about 50 or 55 degrees north, even on strong auroras, it can be very hard to all but the most prominent color.
PPS - FWIW, I suspect that the small areas of haze directly above the ice field are also real, possibly an advection fog formed because of the clear sky conditions.
I ask because it is well known that the true colors of auroras can not be seen by the naked eye, and only be seen using sensitive detectors like those in modern DSLRs (see the 1st article referenced below). Auroras often have many colors besides the usual yellow-green, but reds, purples, and other colors around the edges of the brightest areas, but at lower intensities. These are due to emissions from other chemical species and other excited states of the main nitrogen emitters. These occur because of differences in excitation and collisional energy relaxation processes at different altitudes. To be honest, that's what these colors look like to me.
You might want to take a look at articles like these before you try to remove these areas:
Why Only Photographs Reveal the Northern Lights' True Colors:
http://www.space.com/23707-only-photos-reveal-aurora-true-color.html
What makes the color of the aurora:
http://odin.gi.alaska.edu/FAQ/#color
Both of the above articles are on highly respected scientific websites: space.com, and The Geophysical Institute of the University of Alaska.
Also, please look at the colors in my tweaked version (ie, Post #14 of this thread). Be sure to click on the in-line preview to view it at full size. You will see that there is not just one color in the areas you outlined, but include weak reds, oranges, and purples, exactly like discussed in the articles I cited, the only difference being that the version you observed did not have quite so much intensity in these colors as the examples in the articles, so your was predominantly yellow-green.
HTH,
Tom M
PS - Also, I'm curious - - At what latitude did you photograph this aurora? It might have simply been a weak one, but if you weren't further north than about 50 or 55 degrees north, even on strong auroras, it can be very hard to all but the most prominent color.
PPS - FWIW, I suspect that the small areas of haze directly above the ice field are also real, possibly an advection fog formed because of the clear sky conditions.
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Thank You Tom for the detailed answer!
This photo is taken in Iceland, Jökulsarlon lagoon.
Now I think that You are right that these brown areas are caused by aurora itself. Then I should leave this photo as it is.
I took many photos from different places around this lagoon and those other pictures have clear colors.
One sample is here:
This photo is taken in Iceland, Jökulsarlon lagoon.
Now I think that You are right that these brown areas are caused by aurora itself. Then I should leave this photo as it is.
I took many photos from different places around this lagoon and those other pictures have clear colors.
One sample is here:
Last edited by a moderator: