De-hazing Pictures

Gyro_Kai

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near Frankfurt, Germany
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(pictures can be enlarged by clicking)
Often, when the flying is good, the visibility is not. When the air is calm, we often have an inversion layer, i.e. fog or even Smog close to the ground. Therefore the pictures usually don’t turn out too well.

However, there is a way to reduce the haze somewhat with most image processing software. My choice of software is Gimp, a public domain program free of charge.

Our object for improvement is the following picture:
2011_10_02_19_13_35.jpg

If you load this into Gimp you can choose in the menu Colors-Levels
gimp1.jpg

You get the following picture:
gimp2.jpg


This picture shows you the full range of availably brightness from Black at the left to White at the right.

The curve in the middle shows you, how much the photo is actually using from this range. In this case it looses a lot of dark options, and some bright as well. In other words it has very little contrast and most pixels are rather gray.
gimp3.jpg

A photo with more contrast looks like this:
2011_01_08_15_38_43.jpg
gimp4.jpg
 

Gyro_Kai

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near Frankfurt, Germany
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MT-03, Calidus (rent)
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Here comes the trick
Back to our picture, we now use the two markers on the outside, and pull them in, in order to reduce the available range, thus stretching the used range from min to max.
gimp5.jpg

Already the picture now looks much better. Additionally you can change the overall brighness by moving the center marker left or right.

Press OK and you are done and can save the picture.

And here is the final result and once more the original picture

2011_10_02_19_13_35.jpg 2011_10_02_19_13_35-corr.jpg

Other programs like Photo-Plus or Photoshop have this function called Histogram.

I hope this helps, feel free to ask me if you need help.

Kai.
 

GyroDoug

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Layton, UT.
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Kai,

That's really cool that you can make a picture better than the original. Thanks for sharing this technique with us. Perhaps some of us will even learn how to do this ourselves.
 

choppergabor

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I'd like to submit my version that had been altered by using saturation control and areal burning to bring the colors out and removing the red lens flare :) They are both very useful tools. The Hue control needs to be used carefully as it can alter the colors and turn them into unnatural at times. Good job Kai :)
 
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Gyro_Kai

Senior Member
Joined
Nov 29, 2006
Messages
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Location
near Frankfurt, Germany
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MT-03, Calidus (rent)
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about 150
Yes using those blanket tools make sense, for tweaking. My method sometimes return a too blue picture, then those general tools work well. But as you can see very well, the flying pink pig is gone :).

Kai.
 

aerobatic

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Drummondville, Qc, Canada
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If you want to get better contrast in Photoshop with the «Levels» or «Curves» functions (they both perform about the same things) and don't want your colors to be phased out, you could convert your RGB pictures to Lab color space before.

Once the adjustments done, bring back the file to RGB space (or CYMK space if you intend to print it).

Maher
 

James

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Gallatin, TN 37066
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Gyro_Kai, I have 4 different photo programs and I have done some good things with them, but it can be complicated. I have 2 internal hard drives, one for operating, one to store pictures. Never heard of Gimp, is it pretty easy to use?

James Lee - TN
 

Gyro_Kai

Senior Member
Joined
Nov 29, 2006
Messages
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Location
near Frankfurt, Germany
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MT-03, Calidus (rent)
Total Flight Time
about 150
Hello,

The Histogram function described above is available in all photomanipulating programs as far as I know. I chose Gimp because it is free. Gimp is often considered the closest rival to Photoshop, however not as easy to use.

Kai
 

Joe Pires

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Jan 16, 2006
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Geneva FL FD92
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That is very cool. I have always wondered what that histogram thing was. I remember the term from statistics, but as soon as I think of statistics I start to shake.
 
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