Author Topic: ML functions combo in low flux imaging  (Read 8679 times)

SpcCb

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ML functions combo in low flux imaging
« on: October 06, 2014, 05:49:33 PM »
Modules & functions w/ ML:
• Long exposure (Bulb) with mirror pre lock-up @600s
• Dual ISO @1600-100
• ADTG/DFE Gain: -23 w/ e-gain @0
• Black offset level: 256 ADU
• White clipping level: 16383 ADU

Setup:
• 5D2 w/ cooling capability, device off (passive mode), sensor temperature @12°C (end of exposure)
• Optic: 400f/2.8L mod. working @f/2.6
• Filters: RGB composite with Hα - OIII - Hβ, 1x600s per wavelength
• Astronomical mount for sideral tracking w/ pseudo random dithering between exposures


North America Nebula (NGC7000)

Post:
• CR2->DNG w/ cr2hdr-20bit v.0eabcb0 - 2014-08-29
• FPN reduction w/ full resolution master made with 301 samples
• Multi-spectral AMaZE demosaicing w/ 100 pass per wavelength
• Bin2 on each wavelength
• Dynamic compression, same on each wavelength
• Richardson-Lucy deconvolution w/ 49 pass per wavelength
• 1000px resampling in PS

Divers:
• No dark frames or noise reduction
• Made in Vexin Regional Natural Park (France), September 2014.

Audionut

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Re: ML functions combo in low flux imaging
« Reply #1 on: October 06, 2014, 11:39:54 PM »
Very nice.

Levas

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Re: ML functions combo in low flux imaging
« Reply #2 on: October 07, 2014, 12:36:30 AM »
 :o wonderfull result.

Did I read it correct that this is essentially one single exposure of 600 seconds ?

Few things I have never heard of:

• Multi-spectral AMaZE demosaicing w/ 100 pass per wavelength   (Edit: I do know the AMaZE demosaicing part of this line)
• Bin2 on each wavelength                                                          (Edit: Probably some pixelbinning ?)
• Dynamic compression, same on each wavelength
• Richardson-Lucy deconvolution w/ 49 pass per wavelength

What are these functions and what software did you use to get it done ?

SpcCb

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Re: ML functions combo in low flux imaging
« Reply #3 on: October 07, 2014, 01:32:57 AM »
Indeed Levas, only one frame of 600s per wavelength.

Multi-spectral AMaZE demosaicing is a kind of AMaZE demosaicing _like we can find in last dcraw versions or RawTherapee_ with multiple levels analysis computed from the energy distribution across different spectral bands in a discreet cosine transform (DCT) block, to get better results. Specially with N&B frames what we get in this case with narrow band filters.
Bin2 is a regular pixel binning, by 2x2. It makes a 2x2 pixels matrix to become 1 pixel by summing signal levels in the matrix. It means we get SNR~4x.
Dynamic compression is also a regular operation to visually get more details on discreet areas. I used a HDR Multiscale Transformation (HDRMT), made by Vicent Peris.
Richardson-Lucy deconvolution is a special operation to enhance spacial informations.

Pixel binning, dynamic compression and Richardson-Lucy deconvolution can be done with common astronomical softwares like PixInsight or Iris.
Multi-spectral AMaZE demosaicing is an home made stuff, with MIDAS.

Levas

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Re: ML functions combo in low flux imaging
« Reply #4 on: October 07, 2014, 10:30:02 AM »
Thanks for the detailed explanation, lot's of post processing going on there  ;)
And now I noticed the wavelength filters: Hα - OIII - Hβ (must read better next time  :P )
So 3 wavelengths and the rest of the light is blocked out.

Sometimes I make time lapses of the night sky, with maximum exposure times of 15 seconds (I don't have a tracking mount...)
I live nearby a big city, so lot's of sodium street lights over here.
Do you think I can benefit from a clip in (clicks in DSLR in front of the mirror) type of this filter ?
http://www.astronomik.com/en/visual-filters/uhc-e-filter.html
Of course I don't expect a filter like that too give results like the photo you posted  :P (For that I need a tracking mount and lot's of knowledge in post processing astro pictures)

Did try to capture the summer milky way a few months ago:
https://drive.google.com/folderview?id=0B1BxGc3dfMDaSkNlZ0ZtaHN4Ym8&usp=sharing

Although not bad, it could use a lot more contrast(and I already added a lot contrast in Lightroom in this example).

a1ex

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Re: ML functions combo in low flux imaging
« Reply #5 on: October 07, 2014, 10:31:39 AM »
• Long exposure (Bulb) with mirror pre lock-up @600s
• Dual ISO @1600-100

You have used Dual ISO on a such a long exposure? It worked?! Can you share a CR2?

Greg

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Re: ML functions combo in low flux imaging
« Reply #6 on: October 07, 2014, 02:40:26 PM »
Great picture!   :o

SpcCb

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Re: ML functions combo in low flux imaging
« Reply #7 on: October 07, 2014, 03:00:08 PM »
Quote from: Levas
Thanks for the detailed explanation, lot's of post processing going on there  ;)
And now I noticed the wavelength filters: Hα - OIII - Hβ (must read better next time  :P )
So 3 wavelengths and the rest of the light is blocked out.
Indeed, inferential narrow band filter was used; light pass for 7~8nm around the frequency, all is block out.
Plus the 5D2 used is also modified, the internal IR-cut filter is not the original one; replaced by a full spectrum Astrodon filter (400~700nm):

This is better if you want to use special filters because the original Canon IR-cut block more or less some wavelength, so you loose a lot of _interesting_ informations.

Quote from: Levas
Sometimes I make time lapses of the night sky, with maximum exposure times of 15 seconds (I don't have a tracking mount...)
I live nearby a big city, so lot's of sodium street lights over here.
Do you think I can benefit from a clip in (clicks in DSLR in front of the mirror) type of this filter ?
http://www.astronomik.com/en/visual-filters/uhc-e-filter.html
Of course I don't expect a filter like that too give results like the photo you posted  :P (For that I need a tracking mount and lot's of knowledge in post processing astro pictures)
EOS clip filters are very interesting; you can use them with a lot of optics/lens (specific astronomical filters are design to be used only with astronomical optics because of the angular light flux issue). But I never used EOS XL clip filter for full frames camera yet (I see you use a 6D). It should be done next months. It looks tricky, because of the mirror (block in up position?).

The UHC-E filter is adapted if you have a very polluted sky, it gives very good results. All sodium (high and low pressure lamps) emissions are blocked.
But if the sky is moderately polluted, IDAS LPS gives better results because this filter preserve a kind of spectrum continuum (for RVB imaging in one shot) but some sodium emissions are not blocked.
In images:

Left to right: no filter, LPS, UHC

Quote from: Levas
Did try to capture the summer milky way a few months ago:
https://drive.google.com/folderview?id=0B1BxGc3dfMDaSkNlZ0ZtaHN4Ym8&usp=sharing

Although not bad, it could use a lot more contrast(and I already added a lot contrast in Lightroom in this example).
Not bad! We can see NGC7000 Nebula, like in the image top of this thread ;)
Your sky doesn't look so polluted in fact. If you are in Europe I know good pollution maps, if you need to have a idea.

Quote from: a1ex
You have used Dual ISO on a such a long exposure? It worked?! Can you share a CR2?
Yes, I did. :D
There's a lot of hot pixels without cooling, and we can't use the cr2hdr hot pixels removing in this case (because of stars) so it's a bit tricky, but it works. With a good cooling it works better, of course (it's better than in regular photography actually).
But the major issue is the spacial resolution loose, important in astrophotography.
Here it was not a problem because it was not for an high end imaging, just for filter tests (we can see horrible reflections in OIII band) and I planned to bin + resample since the beginning, so..
I'll see to PM you CR2 ASAP (I'm not front of my home computer for couple of days).

Beside, the most important stuff in my eyes is the ADTG/DFE Gain + black offset + white clipping definition, drive the Canon sensor like a specialized/scientific/astronomical camera is enormous. I'm thinking to make a ML module with special tweaks for astronomy (and some specialized functions like FWHM map assist in liveview), just need to find time to do a public friendly version.