How to Remove Light Pollution Using GIMP

How to Remove Light Pollution Using GIMP

Have you ever taken a picture of the night sky and been disappointed because the light pollution has washed all the stars away or covered your picture with a distracting orange glow. This post contains a step-by-step video guide to removing light pollution from your images. It uses the free to download GIMP software. This software allows you to manipulate your photos. 

Read on to learn how to turn a picture like this:

Light polluted image of the night sky

Into a picture like this, in a few easy steps:

Orion Taurus Jupiter.tif

Click the image to enlarge and see in higher quality.

How to Remove the Light Pollution

The video below will show you how to use the despeckle filter in GIMP. The despeckle filter settings should be set to uncheck adaptive then slide the radius slider all the way to the right. The black and white sliders are then set to -1 and 256 respectively. The clone tool is then used to smooth out any nebulae or bright stars. The despeckled layer is then subtracted from the original image to remove the sky glow. This may sound complicated but the video below shows each step and makes it an easy process to follow. 

If you are unable to play the video then follow the instructions below:

1. File > Open  to open the image into GIMP

2. In the Layer dialog box (Cmd+L on a Mac), right click the image and click duplicate layer.

3. Filters > enhance > despeckle

4. Uncheck adpative and make sure recursive is not ticked

5. Set radius to 30

6. Set Black to -1

7. Set White to 256, and click OK.

8. In the layer box make sure the despeckled layer is still selected, then click on mode and select subtract.

9. Image > Flatten Image 

10. Enjoy the light pollution free image

If after you despeckle the image you can see nebulae, galaxies, planets or bright stars still present in the image you can remove them using the clone tool. 

Foreground Elements

If your picture has foreground elements, like the trees in this example, you will need to cut them out before you remove the light pollution. The foreground can then be pasted back on top after the light pollution is removed. Here is a post  to demonstrate how to remove foreground elements like trees using GIMP and how to paste them back on after you have removed the sky glow from your picture.

Enjoy your new found clear skies images.

Related Posts: Full length, Astrophotography

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