Ha test with poor r...
 
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Ha test with poor results  

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(@1cm69)
Neutron Star Customer
Joined: 2 years ago
Posts: 132
March 4, 2019 16:42  
Posted by: Mabula Haverkamp - Admin

Hi Kirk @1cm69,

I have found the issue with your data yesterday. Another APP user, @andersstange, also experienced difficulties with star analysis and registration and his issue was directly related. It turned out that hot pixels were detected as stars and not the stars. To solve this issue, I have added a new algorithm in the star analysis module that is capable of better discrimination between hot pixels and stars 😉

So the good news is that APP 1.072 will have the solution to this problem. All the testdata that I have including the data of you both work now robustly (without problems).

https://www.astropixelprocessor.com/community/release-information/astro-pixel-processor-1-072-preparing-next-release/

at the bottom:

  • FIXED, IMPROVED, STAR ANALYSIS, star detection has been further improved by adding an algorithm that better discrimates between hot pixels/small FWHM stars/big FWHM stars. Some users experienced difficulties because hot pixels were detected as stars. The added algorithm studies the star size/FWHM distribution initially found. The details of the distribution are very usefull to make the discrimination between hot pixels/small FWHM stars/big FWHM stars.

I will try to release APP 1.072 within 1-2 days now 😉

Kind regards,

Mabula

Excellent, thank you Mabula. 

Kirk


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(@1cm69)
Neutron Star Customer
Joined: 2 years ago
Posts: 132
March 14, 2019 12:02  

Hi Mabula @mabula-admin

I have just downloaded APP v1.072 and this did indeed solve the Registration issue, thanks for that fix.

I still seem to be having major issues with my Flats though and I do not know whether this is due to my use of a H-alpha NB filter on a colour DSLR.

I will try to explain in detail.

Firstly here is an integration of 2 sessions totaling 7 x 1200s ISO800 Light frames of B33 & calibrated using 10 x 1200s ISO800 Darks, 20 x 2.5s ISO800 Flats, 100 x ISO800 MB plus BPM with astro modded DSLR through Baader 7nm H-alpha filter.

S1 n S2 Integration

 

Even after cropping away the 2 session stacking edges I am seeing a lot of noise where the vignette normally is.

 

For a more obvious & in-depth look here is an image in H-alpha of the Whale Galaxy using the same equipment as I did for my B33 capture, although this is only over a single session 

INTEGRATION HA

Please forgive the overall quality as this is an ongoing project & currently only consists of 4 x 900s ISO800 Light frames & calibrated using 8 x 900s ISO800 Dark, 10 x 2.5s ISO800 Flats, 100 x ISO800 MB plus BPM

It is very obvious in this image to see the light areas where the vignette is located, particularly along the bottom edge as well as a curved structure at the right hand edge.

I am using the H-alpha algorithm in 'TAB 0' for these Integrations but below I will show how a single Flat & the Master Flat appear in both H-alpha & normal Airy Disc in APP.

SINGLE FLAT Airy Disc

SINGLE F RGB

SINGLE FLAT H-alpha

SINGLE F HA

MASTER FLAT Airy Disc

MF RGB

MASTER FLAT H-alpha

MF HA

 

In my single Flat (Airy Disc) the RED channel is already showing that a small part of the data is at the right hand edge of the histogram, so it would be impossible for me capture a longer exposure and the (H-alpha) version of the same Flat shows a very good histogram.

Now this is a different story with the Master Flat as this is quite obviously showing clipping to the left hand side of the histogram in both (Airy Disc) & (H-alpha) versions but in a very small section of the RED channel for the (Airy Disc) version of the Master Flat, this is touching the right hand side of the histogram.

I cannot see a way to rectify my Flats issue.

I have read in various forums that although the vignette been light seems like it is over correcting, it is actually the case that Flat frames are under exposed which causes the lightness.

I only seem to be seeing this problem since attempting H-alpha narrowband imaging using my DSLR. I am pretty sure that I have not seen this when capturing regular broadband images, especially since Mabula helped me out a while ago understanding capturing Flats correctly.

I capture my Flats using a light panel with my optical train and focus left in exactly the same position as when capturing my Light frames.

The excessive looking vignette at the bottom of my Flats is the shadow of the prism of my OAG.

Regards..,

Kirk


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(@1cm69)
Neutron Star Customer
Joined: 2 years ago
Posts: 132
March 14, 2019 12:34  

I have just found this thread on CN: https://www.cloudynights.com/topic/570669-optimizing-flats-from-osc-camera-using-nb-filters/

and I am attempting to get my head around the answer in post 2 and how to implement this in APP to give it a try.


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(@1cm69)
Neutron Star Customer
Joined: 2 years ago
Posts: 132
March 15, 2019 17:47  

OK, I have done a little more investigation on this and following the post: https://www.cloudynights.com/topic/570669-optimizing-flats-from-osc-camera-using-nb-filters/#entry7775470 from the same thread as my last post, I attempted to use the SuperPixel algorithm in APP.

All seemed to be going OK, I loaded all my files and it Integrated & I could easily load the Linear Integration but as soon as I changed the viewer drop-down option to calibrated I got this error message:

Error Loading Calibrated SuperPixel Frame In Viewer

I then decided to just choose the 'Split Channels' option in the Calibration Tab & save the calibrated frames, that's when this error appeared:

Error When Trying To Save Calibrated Frames In SuperPixel Mode

So I went back to the drawing board and ran all my data once again with the algorithm set as Hydrogen-Alpha, here is the result and I have purposely not cropped the image, leaving the stacking artifacts intact:

Using HA From Start

Now I cleared everything out of APP, set the algorithm to Adaptive Airy Disc, loaded all my files ran calibration, chose the 'Split Channels' option and saved the calibrated frames.

Then I once again cleared all data from APP and only loaded the RED channel frames that were split and continued to Integration with just these, here is the result:

Airy Disc Red Only

Right, straight away the output from using the HA algorithm is brighter but it is also a whole lot noisier especially around the central bottom area of the image where the vast majority of my vignette/prism shadow appears.

Could be my eyes deceiving me though.

Kirk 


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(@mabula-admin)
Quasar Admin
Joined: 2 years ago
Posts: 2127
March 19, 2019 23:20  
Posted by: 1CM69

Hi Mabula @mabula-admin

...

 

In my single Flat (Airy Disc) the RED channel is already showing that a small part of the data is at the right hand edge of the histogram, so it would be impossible for me capture a longer exposure and the (H-alpha) version of the same Flat shows a very good histogram.

Now this is a different story with the Master Flat as this is quite obviously showing clipping to the left hand side of the histogram in both (Airy Disc) & (H-alpha) versions but in a very small section of the RED channel for the (Airy Disc) version of the Master Flat, this is touching the right hand side of the histogram.

Hi Kirk @1cm69,

No, this conclusion is not correct. The clipping that you see in the histogram of the masterflat is actually the dslr's sensor raw border 😉

APP uses the whole sensor to calibrate the data. After calibration these raw borders are always cropped away from the calibrated light frame. So if you look at the MasterFlat, you actually see the whole sensor, please check the image dimensions and zoom in on the raw borders, you can see these in the masters.

I think there should be nothing wrong here, the red channel looks well illuminated and green and blue are 100% irrelevant since you are using a H-alpha filter.

Kind regards,

Mabula

 

Main developer of Astro Pixel Processor and owner of Aries Productions


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(@mabula-admin)
Quasar Admin
Joined: 2 years ago
Posts: 2127
March 19, 2019 23:42  
Posted by: 1CM69

OK, I have done a little more investigation on this and following the post: https://www.cloudynights.com/topic/570669-optimizing-flats-from-osc-camera-using-nb-filters/#entry7775470 from the same thread as my last post, I attempted to use the SuperPixel algorithm in APP.

All seemed to be going OK, I loaded all my files and it Integrated & I could easily load the Linear Integration but as soon as I changed the viewer drop-down option to calibrated I got this error message:

Error Loading Calibrated SuperPixel Frame In Viewer

I then decided to just choose the 'Split Channels' option in the Calibration Tab & save the calibrated frames, that's when this error appeared:

Error When Trying To Save Calibrated Frames In SuperPixel Mode

Hi Kirk @1cm69,

The Super Pixel debayer algorithm was broken, it is fixed in APP 1.073 😉

To be clear, I can think of no good reason to process data with the Super Pixel algorithm. It will have a serious bad effect on registration precision and you throw away half of your resolution. Using Super Pixel and then extracting the red channel is really an inferior processing workflow compared to the H-a debayer algorithm.

Having said this, whatever demosaic algorithm you choose, it has 0% influence on data calibration, at least in APP. Calibration is done on the Bayer CFA pixels before debayering/demosaicing is done 😉

So I went back to the drawing board and ran all my data once again with the algorithm set as Hydrogen-Alpha, here is the result and I have purposely not cropped the image, leaving the stacking artifacts intact:

Using HA From Start

Now I cleared everything out of APP, set the algorithm to Adaptive Airy Disc, loaded all my files ran calibration, chose the 'Split Channels' option and saved the calibrated frames.

Then I once again cleared all data from APP and only loaded the RED channel frames that were split and continued to Integration with just these, here is the result:

Airy Disc Red Only

Right, straight away the output from using the HA algorithm is brighter but it is also a whole lot noisier especially around the central bottom area of the image where the vast majority of my vignette/prism shadow appears.

Could be my eyes deceiving me though.

Kirk 

So if you see differences between Adaptive Airy Disc and H-alpha debayer it has to do with the actual stretching of the data. The H-a debayered data is monochrome and thus the stretch parameters will only be based on this single channel. On the Adaptive Airy disc data, the stretch parameters are based on 3 channels, the red channel with your H-a data and 2 channels (G,B) with mostly noise, this has the effect that the stretch parameters are reduced, which might give you the impression that there is less noise, where in fact, there is more in 2 channels which you don't need I think. So you need to take into account how the data is stretched.

Please let me know if this is clear 😉

I would really think that your horsehead result is a good start and I am sure that If you add more data it will improve significantly! You have only 7 frames of 1200 seconds with a 7nm filter in front of a bayer cfa sensor, really, what you have now, is not bad at all to start with I would think. Realise that with only 7nm, very little light is reaching the sensor, off course the H-alpha nebula will get better contrast when compared to a shooting with a broader filter, but the remaining sky background will still be very black and will be dominated by noise. More data and perhaps even longer exposures will surely help.

Cheers,

Mabula

This post was modified 6 months ago by Mabula Haverkamp - Admin

Main developer of Astro Pixel Processor and owner of Aries Productions


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(@1cm69)
Neutron Star Customer
Joined: 2 years ago
Posts: 132
March 19, 2019 23:48  

Thanks for your detailed responses Mabula. 

I will keep plugging away getting more data as and when I can to add to the mix. 

Kind regards..,

Kirk


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