Lucky Shot

Star trails and other woes

Even though I want to keep this shot, it didn't go perfectly... so I get to try my hand at reducing unwanted star trails. I set about this task using the GIMP by blending duplicate layers with a darken mode. We start and finish the edit in Darktable, of course.

This video is the second in our faster-edit format. It builds on knowledge from previous videos, running full-tilt through tools and methods to achieve the edit. For fuller explanations, return to the Home Page and scroll down to Topics Discussed or Modules Used on the right-hand bar. Click on any of these, and we assemble a complete playlist of every instance for quick review right here on the site.

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(Banyan Drive, Hilo)
(along 4 Mile Beaches road, Hilo)
(Pahoa shoreline)
(up Mauna Loa, looking toward Mauna Kea)


Welcome to Weekly Edit for Wednesday, February 1, 2017.

So, you're lucky enough to catch a falling star, lucky enough to catch it in an image even -- but: oops! Well, I'll let Harry tell you the story.

(Harry's voice) Oh, boy, did I get lucky.

I got a shooting star right in the middle of Andromeda.

I was doing an image stack.

My idea was to make 150 images of Andromeda and then stack them together to get a beautiful shot of Andromeda.

I don't have much of a long lens: I've got 100mm.

My camera is full frame, so I don't have a lot of magnification there.

Lucky for me, Andromeda is huge.

We were up on the mountain at around 7000 feet (2133 meters) and it was a very clear night, so it looked like things were going to work out pretty well.

But, I blew it.

I did not align my tracker properly, or maybe I bumped my tripod.

I don't know.

I've got these star trails.

Normally, I'd just ditch the whole stack because I messed it up.

But I'm not going to ditch this! I've got a freaking shooting star going through Andromeda! So I need to salvage this.

Let's see what we can do to fix this.

Alright, the first thing I'll do is crop it because I don't want the whole thing.

Let's see: get our aspect ratio and bring in our sides.

Let's fill the frame with the shooting star.

That looks pretty good.

I want to bring out more of Andromeda.

Let's see if we can get a little more by using the Exposure Fusion.

Oh, yeah.

Look at that; that does a great job.

It really brings things out.

That's a good start.

Another place to look is Global Tonemap.

Look at that: now we're starting to see stuff.

We've got a lot of stars; we've got a big Andromeda...

This makes me happy.

I'd like to bring out this area more.

I'll use the Equalizer for that.

I don't want to make the stars brighter, but Andromeda is a different size than the stars.

I can use the size specifications of the Equalizer to enhance Andromeda without making the stars brighter.

I can bring this up a little.

There we go.

Look, it's making it really bright right in the middle, so I'll use this with a Parametric Mask and bring that down a little so the center doesn't get so bright.

The stars are awful bright, though, and we've got some noise.

On the noise, this Non-Local Means works great for night shots, but it's actually stronger than I need.

I'll turn down the Strength down.

Sometimes I can get good results by turning down the Patch Size too.

That seems to be the case this time.

Let's see: move the Patch Size up one or down one.

Yeah, down one is better.

Oh, look at that; there's another shooting star.

There are tons of shooting stars out there.

Another thing I can do is take my Lowpass Filter and make a really small Radius, like a little less than one pixel, and apply a Darken only Blend Mode.

That gets rid of some of this fringing and brings the color into the middle of these stars.

I'll do a couple corrections: Hot Pixels -- Detect by 3 Neighbors is good -- and correct for Chromatic Aberrations.

Then I'll export this into the GIMP to work on the star trails.

I'm exporting it as a TIFF.

TIFF, 16-bit.

I like to work in Adobe.

Here we are in the GIMP.


Lucky Shot.

There's our TIFF.


Now we need a nice big star to work with.

Here we go.

My idea for reducing the star trails is to take a duplicate of this image and bring it down this way so that it overlaps the current image.

That will produce an overlapping area that is just this little ball here.

I'll use the Darken Only Blend Mode so this darker part of the sky over-writes the star trail, leaving me with just this little ball right here.

Let's try that and see how it goes.

Duplicate Layer.

Then change my Opacity and move this down.

See, it creates a little ball right there.

If I bring my Opacity back and go to Darken Only, I've got these nice little balls.

But, now I've got these lines.

See these lines? There's a line here too.

It's because I didn't cover it up exactly when I moved it.

I don't think there's a way to cover it up exactly, so I'll do it twice.

One will be just a tiny bit to that side and one a tiny bit to this side.

Then I can get the two sides.

These pixels are really big.

In order to do that maneuver, I'll need to re-sample it first to make it bigger.

So, let's start over again.

First I'll re-sample this layer.

Scale Image, and let's make it 5000px.

Where did our big star go? Let's find it.

There it is.

Now we can see what we're doing.

Now we've got more to work with.

First I'll make a Duplicate Layer of this and store it down here.

I'll use that later.

I'll show you why later on.

Then I'll make another Duplicate Layer of this one and change its Opacity so I can see what I'm doing.

Then I'll do what I did before: move it down here to make this little ball area, but I'll move it just a tiny bit to the left this time.

Then I'll turn that off.

I'll make another Duplicate Layer and do the same thing again: change the Opacity and move it down.

But this time I'll move it just a tiny bit to the right.

Then the area where all three come together will be my star area.

Change its Opacity back.

Take this one: Blend Mode -- Darken Only.

And this one: Blend Mode -- Darken Only.

Okay, that turned out better.

We still have a little edge here, and it looks like we're not going to get it perfect, but I think things are looking much better.

EXCEPT we've lost our shooting star.

See that? Now, if we move our last Duplicate that we made to the top and turn it on, we have our shooting star.

So, I can make this one have a Layer Mask.

Then I can Paint.

We want this to show up.

Let's put it on the bottom.

Merge Down this one.

Merge Down this one.

I've got the Layer Mask on the wrong part.

Let's see: Delete Layer Mask.

We'll put the Layer Mask on this one, and then Paint through right here on my shooting star, and maybe on Andromeda-- we'll see.

I'll make my Pencil a little larger and paint down the shooting star.

Now let's see what our original Andromeda looks like versus the one with the Darken Only Blend Modes applied.

That's the original, and this is the one with the Darken Blend Modes.

I like the original better, so I'll paint that area too.

This time I'll use the Paintbrush so we have feathered edges.

I'll turn down my Hardness, turn my Size up, and turn my Opacity down and do a couple passes.

Let's see what our Layer Mask looks like.

Okay; I want to fill this in a little better.

Right in here we've got a better Andromeda, but we've got smeared-out stars.

Now I need to come in with the Eraser Tool and do some fine-tuning.

I'll turn my size down...

...oh, down further than that, and just a little smaller.

Then we can get each of these little stars right here.

Then we can come back with a Paintbrush and fix any last ones we need to.

It's a little tedious, but it goes quickly.

That's starting to look better.

I've got a little edge right here where it was darker.

I will go back to my Paint tool and bring back that one.

That looks good.

Now I can see some star trails along the shooting star, so I'll go along that edge with the Eraser Tool and knock down some of those.

There we go.

I can't get them all, but I can get a lot of them.

We've still got some leftovers where things didn't line up quite right, and we've lost some of the stars, but I think overall we've got a massive improvement.

Let's look at our original.

Yeah, that is a big improvement.

We'll merge these two down and we'll Save this.

Now we can open it in Darktable and finish up this edit.

We've got smaller stars now.

But, I want to bring out the stars more now.

(laughing) There are a couple ways to do that.

We can use the Equalizer to bring up the size of the stars that we want, like this.

And maybe not the bigger ones.

And we can change this to Lighten only.

Hey, we got some stars back: nice.

And I want to bring back Andromeda.

Once again, we're running into this problem where, when it's too bright, it's just too much.

We'll use a Parametric Mask to bring that down a little so it doesn't affect the brighter areas as much.

And I think we can bring out a little more detail in Andromeda.

Let's try doing that with a Lowpass Filter.

Turn our Saturation all the way down; bring our Radius down so we can see some details in here.

There we go: we can see some dark and light areas now.

Maybe just a little less? Yeah, right around there, and I'll use a Softlight Blend Mode.

I can bring that down a little bit, like that.

I want to bring up some of this lighter area with a Tone Curve.

This looks like a bit much too.

It looks burned-in.

Once again, let's use the Lowpass, give it a small Radius -- enough to make it look better, like that -- then I'll use the Darken only Blend Mode.

That fills in the inside of this a little.

I don't want that everywhere because I'm actually knocking down my stars with it too much, so I'll Paint that on.

We'll give it a little Mask Blur.

That's looking better.

This is catching my eye, up here, so I'll Crop that out.

I don't want it to be distracting.

There we go.

Okay, I want more color.

We'll steepen our channels a little.

Let's see what color Andromeda is.

A little bit to the magenta here.

And a little bit to the yellow.

Alright, now I've got a little more color.

We've got too much green and red color noise in here.

Look at that.

I want to get rid of that some.We'll try a couple different methods to see what's best.

We'll try Wavelets.

We'll go down here to HSV Color and move this over to Wavelets.

We still have some blotches here, even if I bring this up.

I have to bring this all the way up to really knock it down, and it still isn't knocked down all the way.

That's not too bad, though, and Andromeda is looking pretty good.

Another way we can do this is with Equalizers.

So, let's open another instance of the Equalizer and go to the color.

We'll bring up the noise reduction side.

That gives us some results.

We can also do it by bringing down the contrast side.

Now, these blotchy areas are bigger than the stars, so we can actually leave the smaller one and just work on these larger sizes of color.

There we go.

So, reducing color contrast in the larger sizes.

is our best bet.

There we go.

This side of the image is a little darker than this side.

I wonder if that had to do with my lens.

I'll bring that up just a little.

Oh, it came up quite a bit.

Then I want to get all the stars to pop a little more.

I'll use the Highpass Filter.

We'll go down and get the size of the stars we want.

This will give them nice round edges too, instead of all that noise from my star trail subtraction.

There we go.

Then I'll use an Overlay Blend Mode for this.

That makes our stars a little brighter and the sky a little darker.

We don't need 100%; we'll do it right around 50% When we first started, this end of the tail was much lighter and this end of the tail was darker.

Let's look at that.

See? We seem to have lost some of that with all of our work.

I want to bring it back to finish up.

We'll use a Tone Curve.

First, we'll Paint the area we want to work on.

Then I'll combine it with a gradient.

Let's turn on our indicator.

We need to use our Mask Manager.

Here we are: Tone Group.

Go to the first one, set it to Union; go to the second one and set it to Intersection.

Okay, now it has more of an effect as it goes out.

We've got these sharp edges, so I want to Mask Blur those.

There we go.

Turn off our Mask Indicator.

Then we can take down our highlights and get closer to the original.

It looks like we've got a lot of noise and it's pretty bright on this side.

I want to take a quick stab at that and then export this and set my Blackpoint.

That looks like the right thing to do.

that matches a little better.

There is a lot of color over there too.

This whole side of the image has a lot of color.

Final adjustments.

There we go.

Now, I'm going to export this and set my Blackpoint, do a little final sharpening, and that should do it.

Alright: Blackpoint.

Down we come.

Nice, that looks better.

And bring that up a little.

And a little final sharpening.

I'm not sure what I can do about all that.

Maybe I can use a Parametric Mask with a Gaussian Blur and just pick the darker parts.

A tiny bit of a Mask Blur there.

I've got little halos everywhere now.


Bring my Brightness down? Ah, there we go; that cleaned things up.

I want to exclude this area because I don't see how that's helping things.

Oh, one last thing: I've still got this little bit up here.

Okay, (laughing) there we go.

Alright everybody.

Hey, have a great week.

I'll see you next week.


(Mouse's voice) Darktable and the GIMP: powerful allies in the fight against star trails! Well, that falling star wasn't the only lucky thing about our week.

We got a new patron! Thank you Michael, for supporting us on Patreon! We now have four patrons.

Thank you to all of you.

You are inspiring and encouraging us to keep making Weekly Edits.

'But how do I get to Patreon?' you might ask.

Well, let me show you.

We have a link right here on our home page.

If you scroll down past Recent Posts to Resources, here, hidden in there is Patreon Support.

You see the cute picture of our puppy and click right through to our Patreon page where it is super-easy to become a patron.

Choose a reward or choose your own amount, and just click the Continue button.

Everyone, thanks for watching; thanks for being with us.

I hope you enjoy your week.

Until next week, a hui hou.

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