Can underexposed aurora photos be recovered from JPEG, or do I need the RAW files?
Asked 7/11/2014
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I photographed the aurora on a trip to Norway, but the images came out almost black. When I adjust the histogram, I can reveal the aurora, but the result is extremely noisy and grainy. Is there any realistic way to recover these photos from the JPEGs, or would I need the original RAW files?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
12y ago
2 Answers
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If you open the image with any editor, you can see in the histogram (below) that it only uses (in a significant proportion) 12 of the 255 available brightness levels. This means that it only has 12 shades to represent the image that it captured.

Switching to the logarithmic histogram,

you can see that actually there is more, but the most significant part, representing more than 99.9% of the image, is between levels 0 and 16 of each channel and 99.8 of the absolute greyscale.
(The red part on the right of the histogram is just the date/timestamp)
You can still do something to "push" the exposure and get an idea of the picture:

But unfortunately it can't get much better, since the information is simply not there.
Originally by user7984. Source · Licensed CC BY-SA 4.0
user7984
12y ago
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Only to a limited extent. Your JPEG appears to be severely underexposed, with most of the image data packed into the darkest few brightness levels. When you brighten it, you’re stretching a tiny amount of tonal information across the full range, which makes noise and banding/grain very obvious.
So yes, you can push the exposure in an editor and reveal the aurora somewhat, but it won’t become clean or detailed because that information was never properly recorded in the JPEG.
If you have the RAW files, use those instead. RAW retains far more tonal levels than JPEG, so lifting the shadows can give a noticeably better result, though it may still be noisy if the original exposure was very dark.
If you only have JPEGs, the best you can do is carefully brighten them, accept a gritty look, and apply moderate noise reduction. But there is no full recovery if the capture was grossly underexposed.
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