Removing star paths due to camera motion

[cinclodes]

During a recent sea trip to the Arctic, we had the most colorful auroras I have ever seen. Although the ship was moving, I set up a Nikon Z6ii with a 20 mm lens on a tripod to get some photos. They came out better than expected, but stars appear as complex orbits due to the motion of the ship. An example is attached. Would it be possible to remove such star tracks with Photoshop? I will give it a try if this is the kind of thing that it can handle.

 

[Babine]

Try with PS Filter/Dust & Scratches/ Radius 4 pixels and Threshold 0 Level on a duplicate and apply, via a mask, using a brush opacity at whatever you prefer.
I also added back noise.

 

[Rich54]

Try with PS Filter/Dust & Scratches/ Radius 4 pixels and Threshold 0 Level

@Babine ,
Did you reduce the size of the OP's original image before you used the Dust & Scratches filter? The reason I ask is because the D&S filter worked very nicely when I tried it, but for me, the settings need to be Radius = 21 and Threshold = 4.

I have a very old version of Photoshop. I suppose it's possible that the D&S filter has changed, but somehow I don't think that's the issue here.

 

[cinclodes]

Thanks so much, Babine and Rich54. Would you please post your version, Rich54? I have never used Photoshop, but I'm going to get it on the basis of this result. The terms Radius and Threshold don't mean anything to me, but I will have to start climbing the learning curve!

 

[Rich54]

Here it is. The technique and final result is the same as Babine's, but I kept your at the original large size.

 

[cinclodes]

Those are beautiful results! I'm sold on Photoshop. Is it hard to learn how to do this?

 

[cinclodes]

I purchased Photoshop, and, thanks to the expertise offered here, was able to do the other photos myself. Thanks so much for the guidance!

 

[Babine]

@Babine ,
Did you reduce the size of the OP's original image before you used the Dust & Scratches filter? The reason I ask is because the D&S filter worked very nicely when I tried it, but for me, the settings need to be Radius = 21 and Threshold = 4.

I have a very old version of Photoshop. I suppose it's possible that the D&S filter has changed, but somehow I don't think that's the issue here.

I applied the filter to a full sized duplicate (my usual routine) with the settings that I've shown (using a up-to-date version of PS) and applied with a mask to keep some of the stars visible. I resized it for the web.

 

[Rich54]

I applied the filter to a full sized duplicate (my usual routine) with the settings that I've shown (using a up-to-date version of PS) and applied with a mask to keep some of the stars visible. I resized it for the web.

That's very interesting. In my old CS5, I first tried using your recommended settings and it did nothing. I needed to crank it up to 21 and 4.
I may soon need to stop giving out Photoshop advice because my version is so out of date.

 

[cinclodes]

That's very interesting. In my old CS5, I first tried using your recommended settings and it did nothing. I needed to crank it up to 21 and 4.
I may soon need to stop giving out Photoshop advice because my version is so out of date.

Those parameters worked well in the version of Photoshop (26.3.0) that I just purchased. All of the corrected aurora images (as well as some that were taken on land and thus didn't have star trails) are now posted here.

 

[Rich54]

Those parameters worked well in the version of Photoshop (26.3.0) that I just purchased. All of the corrected aurora images (as well as some that were taken on land and thus didn't have star trails) are now posted here.

All of your sky images are soft-focus, which makes the Dust & Scratch filter very appropriate and fairly easy. For other images where the surrounding areas are sharp and need to retain detail, it can be trickier. Here is a general guideline for how to use the D&S filter:

• Always use it on a new duplicate layer, in case you ever need to refer back to what you originally started with.
• When you first open the filter, set both the Radius and Threshold sliders all the way to the left.
• Now very slowly increase the Radius setting until your dust and scratches—or in your case the star trails—are blurred away and disappear. Keep the radius as low as possible while still getting the job done.
• Next, go to the Threshold slider. The more you slide it to the right, the more it "undoes" the blurring you just did with the radius slider. The trick here is that you want the Threshold setting to be as large as possible so that it restores the sharpness of all the other "good" parts of the image, while still keeping the blur on the actual dust and scratches so that they're not visible.

On some images, this balance is not easily achieved. In that case, use the filter to get rid of the dust and scratches as best you can, and then apply a layer mask to this layer. Fill the mask with black, and then use the brush tool with white to paint away individual dust & scratches. (At this point you probably don't yet know what a layer mask is, so just save this tip for later.)

 

[cinclodes]

The images that were obtained at sea are indeed soft-focus due to the motion of the camera. The images that were obtained with the Nikon on land don't have this problem. However, some of them do show the tracks of aircraft, but I wouldn't try to filter those out. Thanks for the detailed information on using the filter. As a mathematician, I would have thought that this type of filter would be based on recognizing a 1-D scratch or a 0-D speck of dust embedded in a 2-D image and using the information in the pixels surrounding the scratch or speck of dust to fill it in. Thanks again for the help! I have been on four Arctic sea trips, but I might not get another chance. It meant a lot to me to be able to salvage these photos!