Monday, July 1, 2013

How To Remove Haze With GIMP?


I am sure some experts in the use of GIMP can tell me how to remove haze and generally make a picture like this look better.  Contrast alone isn't enough; use of the Curves filter doesn't seem to do it.

5 comments:

Mauser said...

You can't really create data that isn't there. I'm not sure about in Gimp, but even in Photoshop, I'd be hard pressed to improve that image.

Okay, I've taken a crack at it, I did the best I could adjusting the levels on the Red Green and Blue independently, but there isn't a lot of dynamic range to work with. The individual histograms are maybe 33% wide.

On the other hand, it was very educational to mess with it, especially when the sky turned yellow and the trees orange at various points in the process.

Let me know what you think!

Josh said...

Histogram Equalization is the entry-level option for this sort of thing -- in GIMP, Colors → Auto → Equalize -- but it's pretty limited in what it can do, and a very hazy image like that will often get pretty serious noise issues.

Alternatively, a duplicate layer set to a Blend Mode of Multiply will do something similar but weaker, but less likely to cause noise.

Practically speaking, a physical filter is the best option for those sort of pictures.

J Greely said...

Levels followed by Curves should help. You need to correct the two stops of underexposure before you try to increase the contrast; your pixels are clustered in the 0-127 range instead of spread across 0-255.

-j

Doug said...

I'm not a GIMP user but the image was fixable to a fair degree in Nikon Capture NX2. Levels & Curves selectively applied along with some "color control points" and contrast brings the image out. The sky falls apart (banding) then and has to be fixed with some blurring. I wouldn't normally push an image so far but sometimes a fair image is better than none at all.

I can e-mail you my rework of the image if you wish.

Mauser said...

It might be interesting to see if he were to put up and compare our various cracks at it.