GIMP Stacking Noise Reduction Demo - YouTube

[bobro]

While playing with manual image stacking using GIMP to see the effect on image noise, it occured to me that a short video showing the noise reduction might be interesting to other beginner imagers. (The % layer opacities might not be quite right.) So it's done and can be seen at : 

 

[furrysocks2]

This is a neat wee demonstration, very well presented. Thanks for putting it up!

It interested me and I googled a little - how does the result differ if you use layer opacities (bottom to top) of 100%, 50%, 33%, 25%, 20%, etc..., respectively?

[bobro]

Glad you like the demo. I redid the stacking using a linear opacity progression as you suggested. There is a noticeable improvement in noise reduction with the linear progression. I suppose that's the correct way. It has been a useful learning exercise and helped improve my very basic knowledge of image processing. Attached is an image comparing the two opacity settings (linear on the right) and my 'final' image.

[Steve Ward]

Nice demo , I would highly recommend that you do not use JPEGs for your imaging though , so much data is lost in the compression that it really is a pointless exercise.

Stick to shooting in RAW format all the time , this will preclude GIMP from the operation but as DeepSkyStacker is such a good tool for the stacking the benefits outweigh the negatives.

[bobro]

Thanks for the advice about JPEG files - it really helps when others comment . I have been using DSS but converted the RAW files to JPEGs (using a neat feature of Photo Gallery) for the demo. Sadly GIMP converts DSS TIFF output to 8 bit for processing by GIMP, so potentially losing info that is important when stretching images. Still, I have the original files should a S/W image processing upgrade come along. GIMP still helps with learning and is ok for a brighter image - see my first imaging attempt at the Orion Nebula below (quite a few processing attempts!).

For now the litte tails on stars due to coma are driving me nuts (more mods...) while I'm waiting for clear skies to try and get longer exposures with the newly added guiding. Am I becoming hooked? (I think there's some chromatic aberration on the smiley....)

[wimvb]

Nice demo. It certainly shows the basics of stacking in a clear way. Stacking software will also adjust image rotation and field distortions, which is difficult to do by hand. Also, GIMP doesn't allow for statistical operations such as removing outliers on a pixel basis. But as said, you show the basics in a very educational way.

[DorsetBlue]

Quote

Sadly GIMP converts DSS TIFF output to 8 bit for processing by GIMP, so potentially losing info that is important when stretching images.

Is this the case with the 2.9.x version of GIMP?

[SilverAstro]

1 hour ago, DorsetBlue said:

Is this the case with the 2.9.x version of GIMP?

You are right to raise that,  GIMP 2.9.x can do 8, 16 and 32 bit. It can also do TIFF

RAWs   [ I suppose I should edit this to read  :- most RAWs, if a new camera format comes along then ther may be a little delay before Dave adds it ]    can be converted to TIFF using DCRAW (free)  by Dave Coffin, the 'engine' used by DSS and (most?)  other freeware image tools.

[bobro]

Well spotted! I have been using GIMP 2.8, which is 8 bit. Must download 2.9 and try it out. Certainly makes GIMP even more attractive for astophotography.

[SilverAstro]

3 minutes ago, bobro said:

Well spotted! I have been using GIMP 2.8, which is 8 bit. Must download 2.9 and try it out. Certainly makes GIMP even more attractive for astophotography.

Yes, it was a long wait and GIMP now has a bit of a reputational hazzared because of it !

I believe there is a GIMP plug-in version of DCRAW  floating about ( but it may only fit the 2.8 ? ! I dunno  ) but I use this neat stand-alone small compiled version for Windows :- http://www.centrostudiprogressofotografico.it/en/dcraw/

more info on wiki :- https://en.wikipedia.org/wiki/Dcraw

And I wouldnt be complete if I didnt include a link to the master's home page, but that will only be of interest to geek programers   :- http://www.cybercom.net/~dcoffin/dcraw/

 

[bobro]

Great! It works!  Same Orion RAW files as before, but this time processed (quickly as a test) in GIMP 2.9.5 using the TIFF output from DSS with no need to convert down to 8 bit. Now I just need to capture some decent images to process...

[SilverAstro]

Excellent !

But I am a bit puzzled - why are you stacking in gimp when you have dss, what am I missing ?

[bobro]

The only reason I stacked in GIMP was to show a 'real-time' demo of how stacking reduced noise in images, not to suggest using GIMP for day-day stacking. Just for info/understanding really. Looks like I didn't make that clear enough.

[SilverAstro]

Just now, bobro said:

The only reason I stacked in GIMP was to show a 'real-time' demo of how stacking reduced noise in images, not to suggest using GIMP for day-day stacking. Just for info/understanding really. Looks like I didn't make that clear enough.

Ah I see, yes,, I mean no ! it is just me being dumb !!

anyway, all good practice in gimp for when you do the layering for the core of Orion

(and even more peeps now know about 2.9.x lol! )

 

[furrysocks2]

As a bare bones exploration of the principle, I really enjoyed your demo.

So after aligning and stacking as you've done, can you go ahead and sharpen the stack or is there other magic step that goes on in software like registax?

[SilverAstro]

36 minutes ago, furrysocks2 said:

So after aligning and stacking as you've done, can you go ahead and sharpen the stack or is there other magic step that goes on in software like registax?

There is a wavelets sharpen filter which works quite well on my humble moon pics.

Also a Gaussian blur which can be used to make high and low pass filters. The high pass is handy for removing gradients but is a bit blunt compared to IRIS method (and others) In fact it could be used to remove the vignetting in bobros pleiades if there had only been stars ! but as is would remove all the luvverly nebulosity as well, they being so close in frequency.

 

 

[SilverAstro]

PS  I forgot to add, the Gaussian also works quite well (for a freeby) to separate nebulosity and stars for individual treatments.

[SteveBz]

On 16/01/2017 at 04:35, Steve Ward said:

Nice demo , I would highly recommend that you do not use JPEGs for your imaging though , so much data is lost in the compression that it really is a pointless exercise.

Stick to shooting in RAW format all the time , this will preclude GIMP from the operation but as DeepSkyStacker is such a good tool for the stacking the benefits outweigh the negatives.

Hi Steve,

I'm not sure that I've totally understood this.  My process is to shoot in RAW, convert to 16 bit tiff and then process in whatever tool I choose.  Isn't any 16bit format (like tiff) going to retain detail?  And GIMP 2.9 is now handling 16bit, so I'm still using Gimp, along with ImageMagick or ufraw-batch for the conversion.  You can also use .png with 16bit and lossless.  The Astronomical standard is FITS and DSS handles this along with TIF, although I haven't tried fits with Gimp.

However DSS is now unsupported and long in the tooth, as is Registax.  They both only run under MS Windows unless you are using Wine.  Most of what I do uses OpenCV (which is x-platform) and is hand-rolled in Python.  Here is a beautiful (non-astro) example of OpenCV along with Python and C++ code it's a nice starting point for doing your own thing:

http://www.learnopencv.com/image-alignment-ecc-in-opencv-c-python/

Have I misunderstood something?

What do you think?

Regards

Steve.

[SteveBz]

On 17/01/2017 at 09:34, SilverAstro said:

But I am a bit puzzled - why are you stacking in gimp when you have dss, what am I missing ?

Gimp will also allow you to "add" images week images as layers.  I have about 200 images of Orion that I took with my camera alone, but if you align them and then add them, you can see a detailed wide-field view of the same area of sky:

And then "Added" with Median noise subtraction:

I've seen it done much better, but doing it by hand leads the way to writing a bit of code to do the same thing.

Regards

Steve.