Author Topic: Cygnus 36 piece mosiac  (Read 65 times)

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MarkS

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Cygnus 36 piece mosiac
« on: Jun 11, 2019, 01:00:52 »
Finally(!) I'm now at the preview stage of my magnum opus from last September in France:



It's a 6x6 pane mosaic of the Cygnus region.  The most difficult thing I've ever processed!  My aim was to produce an image with colours as natural as possible given that the camera is modified. Star colours were used as the guide for this and then the nebulosity has to take care of itself.  This is also a trial run for a new full-colour processing sequence that results in colours as true to the original data as possible.

Acquistion

Data shot in France in September 2018 over 3 nights using my H-alpha modified Sony A7S on a Takahashi Epsilon 180ED telescope: 500mm focal length at f/2.8

36 mosaic panes were shot, with plenty of overlap. Each pane is a stack of 20 dithered exposures of 30sec each at ISO 10000 i.e. 10 minutes total per pane. So the whole image is a total of 360min i.e. 6 hours exposure.

Processing Sequence

1) Each pane was stacked in PixInsight (using bias, flats and darks with dark optimisation) with sigma rejection.
2) PhotometricColorCalibration was then used to set the white balance by matching the stars in the image against an online database of stars. G2V (i.e. solar white) was used as the reference white for this image but there are plenty of other choices.
3) A crude background subtraction was done on each pane so the background brightness of the overlapping panes more or less matched.
4) AstroPixelProcessor was then used to merge the mosaic (it's much easer in APP than in PixInsight). APP uses star alignment to perform the merge to subpixel accuracy and then blends each pane of the mosaic together.
5) Back into PixInsight to perform the Sony A7S camera correction matrix relevant for the Adobe RGB colour space.
6) PixInsight DBE (dynamic background extraction) was then used to subtract the residual light pollution. This is the really critical part of the processing and is done while the data are still linear. It's a trial and error iterative process.
7) Once I was happy with the background subtraction, the 2.2 gamma relevant for the Adobe RGB colour space was applied. Only now does the true colour emerge from the data.
8 ) This was followed by a small amount of colour preserving stretch using ArcsinhStretch.  The stretch factor (i.e. the brightening factor) was only 2.5 in this case because applying the colour space gamma has done most of the "heavy lifting" in stretching the data.
9) Noise reduction was done in Photoshop CC. The noise reduction in the camera raw filter on the Filters menu is by far the easiest and most effective noise reduction I know of.
10) The ragged edges of the mosaic were then cropped off.
11) I haven't applied any further colour saturation in this version but I might do so later.

Here's a link to the 8500x5600 version, which is still only half size:
http://www.markshelley.co.uk/Astronomy/2019/CygnusMosaicHalfSize201909_preview.jpg

I'm very happy to receive any constructive feedback.

Mark

P.S. The embedded ICC colour profile used in those image files is Adobe RGB.  This should display correctly in most modern colour managed browsers.  The colours should look like this version which I've converted to the sRGB colour space, so it will definitely display correctly:



If the colours in the other images don't look the same as this one then your browser (or whatever you are using to view the image) is not doing proper colour management.



« Last Edit: Jun 11, 2019, 06:33:30 by MarkS »

Apophis

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Re: Cygnus 36 piece mosiac
« Reply #1 on: Jun 11, 2019, 07:22:56 »
Great result,  i would like to have a go but probably wont be able to as will not be getting Pixinsight anytime soon.
Lovely image.
Roger
Watch the skies.................

Carole

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Re: Cygnus 36 piece mosiac
« Reply #2 on: Jun 11, 2019, 08:32:35 »
Excellent work as usual Mark and what a lot of work to combine and refine this resulting image.  I really enjoyed browsing through the linked huge image. 

All the stars are perfect throughout and a huge amount of effort has gone into this to refine the true colour.

I spotted the following DS objects - maybe there are more and I have missed some:
The Crescent
Propeller
Space Shuttle Nebula
at least 1 globular cluster and another cluster
Butterfly nebula
NGC6914
Pelican Nebula
NA Nebula

Carole


NoelC

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Re: Cygnus 36 piece mosiac
« Reply #3 on: Jun 11, 2019, 09:10:55 »
Just stunning Mark
Like taking a journey through the galaxy!
Can't spot the joins (obviously) but the level of detail is amazing.
Noel
Synta mount, a bunch of telescopes and a shed (on wheels).

Apophis

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Re: Cygnus 36 piece mosiac
« Reply #4 on: Jun 11, 2019, 14:18:03 »
NB
This is way ahead of any i have seen win awards, it blows them all away.
Awesome.
Is it ok if i share with family and friends giving you full credit of course.

Roger
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RobertM

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Re: Cygnus 36 piece mosiac
« Reply #5 on: Jun 11, 2019, 18:58:35 »
That’s really excellent Mark, especially for a preview.  I can’t wait to see the final image.

I do have one big problem with it - I can only enjoy bits of it at full res at a time :(  Did you do this on an 8k monitor or did you suffer doing it on a lesser screen ?

Robert

MarkS

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Re: Cygnus 36 piece mosiac
« Reply #6 on: Jun 11, 2019, 19:01:29 »
Quote from: Apophis

Is it ok if i share with family and friends giving you full credit of course.


Go ahead - the final version will not be much different.

Quote from: RobertM
I do have one big problem with it - I can only enjoy bits of it at full res at a time :(  Did you do this on an 8k monitor or did you suffer doing it on a lesser screen ?

I did it all on a small screen :(  Two 1920x1080 monitors in fact.

Mark

The Thing

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Re: Cygnus 36 piece mosiac
« Reply #7 on: Jun 11, 2019, 19:40:44 »
Golly gosh. I keep looking at it and seeing small areas I would like to image. Fantastic job Mark.

julian

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Re: Cygnus 36 piece mosiac
« Reply #8 on: Jun 11, 2019, 20:33:32 »
That's fantastic image Mark
I save it to desk top and viewed it via windows photo viewer, with black back ground.
I think you are going to need a bigger piece of paper next time. :lol:

 

MarkS

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Re: Cygnus 36 piece mosiac
« Reply #9 on: Jun 11, 2019, 21:33:23 »
Quote from: Carole
Excellent work as usual Mark and what a lot of work to combine and refine this resulting image.  I really enjoyed browsing through the linked huge image. 

All the stars are perfect throughout and a huge amount of effort has gone into this to refine the true colour.

I spotted the following DS objects - maybe there are more and I have missed some:
The Crescent
Propeller
Space Shuttle Nebula
at least 1 globular cluster and another cluster
Butterfly nebula
NGC6914
Pelican Nebula
NA Nebula

Carole

You're right - it's amazing how many recognisable objects there are in there.  I'm now thinking I must extend it out to include the Veil Nebula :)

Mark

Roberto

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Re: Cygnus 36 piece mosiac
« Reply #10 on: Jun 12, 2019, 09:28:53 »
This is a fantastic image Mark  8) So much going on; one really needs to spend time going through it in detail.
Thanks for sharing.

Roberto