Can you solve this puzzle about background noise?

[AstroMuni]

1 hour ago, Lee_P said:

This is a fully edited version with 24 hours of integration time.

Looks awesome

[AstroNebulee]

3 hours ago, Lee_P said:

Nice pics! Back when I started with my camera I did some tests, and found that Darks + Flats gave me the best results. I might try again though, as I'm learning a lot about how to make proper comparisons

Hi Lee

Yes it's all about experimenting and what works for you and your set up. I also have only just started my astrophotography journey properly, I hope it all gets sorted for you. 

Clear skies 

[Lee_P]

6 hours ago, vlaiv said:

Sure, it is rather easy to do. There are several ways, but I'll show you easiest one.

- Either drag&drop your fits onto ImageJ bar (I do it below toolbar - onto status bar - but it will show words drag & drop as soon as you drag fits anywhere on that window) or go File / Open ... and select your fits

- make sure you are working with 32bit fits - if not, convert it to 32 bit (just click on menu option to switch data type - it is Image / Type menu)

- If your fits is color one - you'll get "stack" (this is ImageJ terminology - not actual astronomy stacked image we call stack) of three separate images - each channel) - move bottom scroll bar onto middle one (being green) and then right click anywhere on the image, you'll get menu:

Marked are scroll bar and menu option - duplicate. Once you hit that - it will ask you if you want to duplicate "stack" (several slices) or just one slice:

Leave "Duplicate stack" unchecked and this will create new image - copy of just green channel.

Close original stack of three channels as we will be working just on green for the time being.

- Hit Analyze / Measure menu option

You should get stats for your image and Median value should be there (it's not show on screen shot as it is far right but Mean value is shown).

If you by any chance don't have median in results - you need to customize your measurements. It is done via Analyze / Set measurements menu:

There are quite a few options that you can use - just check Median and make sure you have enough decimal places for precision.

Now you can repeat measurement via Analyze / Measure and you should have Median value included.

- Note down median value (in my case - it is 0.05964.... ) and do Process / Math / Subtract

- After that - you can do another measurement to confirm results:

Here we go - old and new value

- In the end - File / Save as / Fits ...

Repeat with other files ...

 

Ok, I followed your thorough instructions with a few modifications that may have messed things up -- I saved as TIFFs so I could put them into Photoshop. Then once I'd adjusted the levels, I saved as 16bit so I could export as JPEG for the GIF. This is my result. I don't see the noise level going down appreciably, but I do see an increased gradient.

Here are the FITS files. If you've got the time, I'd be very interested to see my experiment done properly!

24.fit22.fit20.fit18.fit16.fit14.fit12.fit10.fit8.fit6.fit4.fit2.fit

 

Thanks,

-Lee

[Lee_P]

5 hours ago, AstroMuni said:

Your image is beautiful btw. I am probably class 6 and I have street lights around 40ft away from where I park my scope.

You could check here: https://www.lightpollutionmap.info/

I'd have guessed you'd have darker skies than Bortle 6 to get that much detail in just 8 minutes!

[AstroMuni]

On 14/05/2021 at 20:18, Lee_P said:

You could check here: https://www.lightpollutionmap.info/

I'd have guessed you'd have darker skies than Bortle 6 to get that much detail in just 8 minutes!

Thats where I got my guess from. Its somewhere between 5 & 6 I think, closer to 6.

[Lee_P]

On 14/05/2021 at 20:14, Lee_P said:

Ok, I followed your thorough instructions with a few modifications that may have messed things up -- I saved as TIFFs so I could put them into Photoshop. Then once I'd adjusted the levels, I saved as 16bit so I could export as JPEG for the GIF. This is my result. I don't see the noise level going down appreciably, but I do see an increased gradient.

Here are the FITS files. If you've got the time, I'd be very interested to see my experiment done properly!

24.fit 3.04 MB · 2 downloads 22.fit 2.98 MB · 2 downloads 20.fit 2.93 MB · 2 downloads 18.fit 2.87 MB · 2 downloads 16.fit 2.82 MB · 2 downloads 14.fit 2.76 MB · 2 downloads 12.fit 2.71 MB · 2 downloads 10.fit 2.65 MB · 3 downloads 8.fit 2.6 MB · 2 downloads 6.fit 2.54 MB · 2 downloads 4.fit 2.49 MB · 2 downloads 2.fit 2.44 MB · 2 downloads

 

Thanks,

-Lee

Hi @vlaiv, have you been able to make a fair comparison with these FITS files? I'm interested to see the results when done properly, and not bodged like I've done 😅

[vlaiv]

Just now, Lee_P said:

Hi @vlaiv, have you been able to make a fair comparison with these FITS files? I'm interested to see the results when done properly, and not bodged like I've done 😅

Hi, sorry, I totally missed the part where you asked me to do it.

Will do it and post results.

[vlaiv]

8 minutes ago, Lee_P said:

Hi @vlaiv, have you been able to make a fair comparison with these FITS files? I'm interested to see the results when done properly, and not bodged like I've done 😅

In fact - I didn't miss that - I just saw that I downloaded .fits - but forgot to do it. Again, sorry about that.

Here is animated gif (I did not put in numbers of hours - but it is visible when right side changes):

[Lee_P]

8 hours ago, vlaiv said:

In fact - I didn't miss that - I just saw that I downloaded .fits - but forgot to do it. Again, sorry about that.

Here is animated gif (I did not put in numbers of hours - but it is visible when right side changes):

Thanks vlaiv, this is great! You're my hero!