How to take this shot or make this image?

blackstar

Senior Member
This is a screenshot from the National Geographic site. Just wonder how the image is photoed or processed?

Screen Shot 2020-11-17 at 10.13.34 PM-s.jpg
 

hark

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You can either take one long exposure or multiple shorter exposures that get combined. Steve Perry has this option for the latter and explains he takes multiple images to help cut down on noise. But you can also accomplish it by taking one long exposure.

 

blackstar

Senior Member
Thanks, Fred and Cindy. Know all about star_trail photographing. But the image shows both northern lights and star trail scenes. Here is another screenshot image taken at the same place: Yellowknife and Great Slave Lake, Canada.
Only northern lights are the main scene and no star trails.
Screen Shot 2020-11-18 at 10.44.57 AM-s.jpg
 
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blackstar

Senior Member
Thanks, sparky. I also thought it's some sort of composite image. Just wonder if it's a composite from one northern-lights image and one star-trails image? If so, how?
 

480sparky

Senior Member
I would use two layers in GIMP. The aurora in the top layer. Set that layer mode to "Screen" and adjust the contrast and brightness.
 

hark

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I would use two layers in GIMP. The aurora in the top layer. Set that layer mode to "Screen" and adjust the contrast and brightness.

I agree with Sparky. It can be done as more than one image combined together.
 

BF Hammer

Senior Member
I see the star trails in front of the aurora, which is actually just weird to my eye. So he took a long exposure which I presume brought out the ground level exposure and minimized ISO noise. It could be 1 very long exposure or a layer-stack with many exposures. The aurora appear to be more noisy, so a shorter exposure at a higher ISO setting. He then layered them and combined. But again, the trails in front of the aurora look weird to me and I would have either layered different or thrown out the whole project.
 

hark

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I see the star trails in front of the aurora, which is actually just weird to my eye. So he took a long exposure which I presume brought out the ground level exposure and minimized ISO noise. It could be 1 very long exposure or a layer-stack with many exposures. The aurora appear to be more noisy, so a shorter exposure at a higher ISO setting. He then layered them and combined. But again, the trails in front of the aurora look weird to me and I would have either layered different or thrown out the whole project.

That's a really good observation, BF Hammer. :)
 

480sparky

Senior Member
I see the star trails in front of the aurora, which is actually just weird to my eye. .......

The aurora aren't clouds, however. Since they're merely a reaction by molecules high in the atmosphere reacting to a magnetic field, they can't occlude any light source behind them.
 

blackstar

Senior Member
Thanks all.
Here is an example I tried in Gimp using "Lighten only" blending mode with two layers. Remark: BF is correct about the flaw of star trails in front due to gimp's (maybe PS too) blending mechanism, but sparky's point (aurora isn't cloud) could also be true. In my example, there are enough objects behind star trails, they should be in front...
2020-08-08_12-32-12-s.jpg

StarStaX_2020-08-09_21-19-28-2020-08-09_21-45-15_gap_filling-comet-s.jpg

2020-08-08_12-32-12-blending-lightenonly-s.jpg
 

blackstar

Senior Member
Gimp does Brighten Only as commutative, i.e., the layer order doesn't matter -- white pixels always come on top! (in my example, I think the small cloud is whiter than star trails and thus leave star trails behind)
 

hark

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Thanks all.
Here is an example I tried in Gimp using "Lighten only" blending mode with two layers. Remark: BF is correct about the flaw of star trails in front due to gimp's (maybe PS too) blending mechanism, but sparky's point (aurora isn't cloud) could also be true. In my example, there are enough objects behind star trails, they should be in front...

When blending 2 (or more) images in Photoshop, if there is any problem with stars showing up in front of trees or other closer subjects, you'd have the option to use a layer mask. With that, you'd brush over the stars to hide them making all the stars appear behind the closer objects.

I never used Gimp to know whether or not that is an option. Glad you were able to give the process a try!
 

blackstar

Senior Member
When blending 2 (or more) images in Photoshop, if there is any problem with stars showing up in front of trees or other closer subjects, you'd have the option to use a layer mask. With that, you'd brush over the stars to hide them making all the stars appear behind the closer objects.

I never used Gimp to know whether or not that is an option. Glad you were able to give the process a try!

There are ways to use mask layers in Gimp for various purposes too. Thanks for your tip, Cindy.
 

BF Hammer

Senior Member
When blending 2 (or more) images in Photoshop, if there is any problem with stars showing up in front of trees or other closer subjects, you'd have the option to use a layer mask. With that, you'd brush over the stars to hide them making all the stars appear behind the closer objects.

I never used Gimp to know whether or not that is an option. Glad you were able to give the process a try!

Yes GIMP has layers and layer-masking. I use them often.

NFL5sI9.jpg
 
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