GIMP advice, first ever stack

[miguel87]

Need some basic advice.

Took 75x30s exposures at iso 1600 last night. Stacked them in DSS, all going well so far, opened the image in GIMP and it looked OK just very dim (I had been warned that this would be the case).

Followed some online advice about processing in GIMP because I havent got a clue!

It suggested I go to Colour, levels, all channels, auto input levels.

This made the image totally white! Bright white!

So my image out of DSS is just ok (the individual 30s exposures are better) but they have stacked together neatly.

Any tips appreciated.

It may just be the limitations of my cheap setup. If that's the case I dont mind and will stick with visual. BUT the individual photos look pretty good so I thought stacking them would improve things, not make it worse!

 

Edited May 2, 2020 by miguel87

[miguel87]

Ok so I tried again with the original exposures. The only thing I did different was not ticking an option about making a black value 0 or something.

Anyway, considerably better results and I am very happy for my first ever stack and first process.

Please tell me where I could do better tho. The colour levels confused me because the sliders were not doing what I wanted, I set them where I though was least terrible then went onto use the black dropper thing.

After doing that I went back to the sliders and they were having a much better effect??

Anyway, my first ever stack, an odd target of 56 Ursae Majoris (a friend had this star 'named' after them as a present) and picked up NGC3675 in the top corner.

200P, EQ5, RA motor, unguided, pentax K-r

Edited May 2, 2020 by miguel87

[CloudMagnet]

The easiest way to use the sliders in levels is to first use the grey slider (in the middle underneath your histogram) and move that left but stop before you hit the peak of the histogram. This will make the image a lot brighter but dont worry. Press OK to close and then reopen levels again. This time, pull the black slider to the right until you get a nice darker image. You can keep doing this as often as you want, and you find a nice balance.

The more you compress the sliders together, the more detail you will bring out but at a cost of bringing out noise and gradients- so keep this in mind.

[bottletopburly]

You could give Startools a go free to try for as long as you like and reasonably priced if you want to buy license certainly less effort required to produce an image  https://www.startools.org/

[ollypenrice]

The 'Levels and Curves' routine is common to all processing packages and lies at the heart of astrophotography. Give it a Google!

Olly

[miguel87]

Thanks I will google the term. And I guess fiddling around is the best way to get better. Interested to try a bright target next, perhaps m13 or Bode's.

✌

[NGC 2419]

I just came across this GIMP astrophotography tutorial today. It should give you some ideas.

 

Clear skies!

[happy-kat]

I used budgetastro.net Doug uses Photoshop but I followed nearly all of it using paintshoppro so GIMP should do very similar as well.

[miguel87]

4 hours ago, NGC 2419 said:

I just came across this GIMP astrophotography tutorial today. It should give you some ideas.

 

Clear skies!

Brilliant thanks I will give it a watch

[JonCarleton]

M3 is a good target this time of year.  Very bright.

And in GIMP, you do most of  your heavy lifting with Colors->Levels using the sliders as mentioned.  I use the "Move-center-slider-left, then move-left-slider right." approach.  The press OK and repeat as needed.  Don't slide past/into the histogram curve area, or you will be removing data.  The curve is recalculated based on your slider settings each time after you hit OK, so taking multiple "small bites" is better than trying to do everything in one shot.

I also spend a lot of time in Colors->Hue-Saturation after I get image density that I can live with.  I prefer it to Colors>-Curves, though it accomplishes the same thing in the end.

After that, you can do things with color selection masks and things, but if you did a good job stacking with darks, flats and bios integration, you reallly don't need to do so much of that.  It is easy to get caught up in over-processing.

Edited May 4, 2020 by JonCarleton

[miguel87]

19 minutes ago, JonCarleton said:

M3 is a good target this time of year.  Very bright.

And in GIMP, you do most of  your heavy lifting with Colors->Levels using the sliders as mentioned.  I use the "Move-center-slider-left, then move-left-slider right." approach.  The press OK and repeat as needed.  Don't slide past/into the histogram curve area, or you will be removing data.  The curve is recalculated based on your slider settings each time after you hit OK, so taking multiple "small bites" is better than trying to do everything in one shot.

I also spend a lot of time in Colors->Hue-Saturation after I get image density that I can live with.  I prefer it to Colors>-Curves, though it accomplishes the same thing in the end.

After that, you can do things with color selection masks and things, but if you did a good job stacking with darks, flats and bios integration, you reallly don't need to do so much of that.  It is easy to get caught up in over-processing.

Thanks Jon, that's really helpful. Just need practice on multiple images. Hard to know how well I have done with the particular area of sky I targeted as there is not alot going on.

Mike

[JonCarleton]

1 hour ago, miguel87 said:

Thanks Jon, that's really helpful. Just need practice on multiple images. Hard to know how well I have done with the particular area of sky I targeted as there is not alot going on.

Mike

I'm just a newbie, but I learned how to cheat early on.  Moon first, then wake up early (May 2020) and get Mars, Saturn and Jupiter.  All easy targets for single image photography.  Then you can play with stacking and see the value of additional depth and clarity.  Then globular clusters.  They are all over the place and very easy (very bright).  Once again, single image will give you something to hold in your hand for starters, then you can work with stacking once you have focus, pointing and tracking working.  Only trouble is (and my newbie is showing here) all globular clusters look pretty much alike.

You have a 200P and mine is basically a 250P, so very similar scopes.  You should be able to get good results.  Are you using a Dobsonian or Equatorial mount?

 

 

Edited May 4, 2020 by JonCarleton

[miguel87]

18 minutes ago, JonCarleton said:

 

You have a 200P and mine is basically a 250P, so very similar scopes.  You should be able to get good results.  Are you using a Dobsonian or Equatorial mount?

 

 

I am using an EQ5 mount just with the cheap motor drive. But I spent time setting up for this image and was impressed that there was no visible change in the frame over 72 exposures of 30 seconds each.

Looking forward to trying some globulars and waiting for a nice bright nebula to come round!

[JonCarleton]

I will never forget the first time I saw Orion Nebula through the camera.  At first all I got was an eyepiece-like smudge, then I just barely touched the gain and nearly fell out of my chair.