Author Topic: 2019 Solar eclipse from Punta Colorada, Chile  (Read 404 times)

Offline Carlos Milovic

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2019 Solar eclipse from Punta Colorada, Chile
« on: 2019 July 09 15:54:43 »
Dear all,

This is the final version of the 2019 eclipse with my data. HDR composition using 7 bracketed frames (1/8000s to 4s) with a Sigma 150-600mm at 400mm and a Canon 80D camera. Tracking with a CG5 mount. Hope you enjoy it!
Regards,

Carlos Milovic F.
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Offline wvanreeven

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Re: 2019 Solar eclipse from Punta Colorada, Chile
« Reply #1 on: 2019 July 09 22:04:24 »
Very nice! Would you mind sharing some of the secrets of creating the HDR composition with us? Was that all done in PI? If yes, how did you align the subs? Many thanks in advance since I am struggling to combine my own bracketed pics.


Wouter

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Re: 2019 Solar eclipse from Punta Colorada, Chile
« Reply #2 on: 2019 July 09 22:47:38 »
are there any background stars in your image? for the 2017 eclipse many of the brighter stars in leo were visible. regulus was especially apparent so i was able to use DynamicAlignment to hand-align my frames. automatic methods tend to fail (FFTRegistration) since they tend to latch on to the moon's shadow and so you get a moon-aligned image.

carlos, that is a great image. did you have any problem with the overexposed areas in the HDR merge? i had a lot of posterization in my 2017 merge which i think may have been caused by the 14-bit data from the camera not filling up the entire i16 space... in other words similar to the "pink stars" problem you sometimes see with DSLRs. in the end i had to split the channels before doing the HDR merges to prevent the posterization.

rob

Offline Carlos Milovic

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Re: 2019 Solar eclipse from Punta Colorada, Chile
« Reply #3 on: 2019 July 10 07:54:04 »
Wouter,

I don't mind. ;) Yes, everything was done in PixInsight.
For this one, I followed an unorthodox pipeline. Raw files were loaded with in-camera white balance and no back point correction. I substracted the bias from the frames, and then rescaled each channel by the maximum value (I calculated it for the longest frame, and used the same factors for all frames). To avoid SNR issues, I applied a mild TGVDenoise process to the linear data. Then, frames were merged manually, using PixelMath (I was having some artifacts with the HDRCombination tool). The equation I used was: $T*0.17*(1-$T)+$T*im2. The 0.17 factor comes from the time difference between 2 frames (I used more decimals). I worked over the largest exposition, converted to 64bits floating point to avoid losing any data due to rounding. The im2 image was updated each time, to add consecutively shorter frames, one at a time. In the end, I divided by the scaling factors to recover the white balance.
Regarding the alignment of the frames, I didn't do anything. :) Please see my reply to Rob below for more details.

For the HDR compression, I also used an unorthodox method. ;) I combined results using a scale separation approach and the multiscale gradient domain compression tool I wrote a few years ago (with a much lower weight).
The scale separation approach bases its rationale in the same approach as the Homomorphic filter. In general, images are composed of illumination and reflection components. These are multiplicative effects. By taking the logarithm they become additive terms, easier to isolate. Whereas the Homomorphic filters models illumination as the low-frequency components, a multiscale approach uses spatial filters. Instead of wavelets, I used ACDNR to produce a blurred version, with a protected moon-corona boundary. By taking the difference with the log-image I was able to get both large scale (the blurred version) and small scale components. I processed each separately to compress the range of values in the corona/sky background, and to enhance the details (flares, corona, etc). Here wavelets and the Larson-Sekanina filters played a major part.
After the combination of the large and small scale components, I returned to the "linear" range by exponentiating, and then I sed Histogram and curves transforms to fine-tune the appearance. I also increased the color saturation for the solar flares only. Finally, since I got a better result for the appearance of the moon using the gradient domain compression tool, I used a mask to put a stronger contribution from that result in the final image.


Rob,
There where two dim stars. Unfortunately, they were also very soft, and not visible without heavy stretching (and visible only in the longest exposition). I couldn't also use them for PSF estimation, as the PSF was also different between frames.
If I were to merge frames from different sets, I would have used them to align, but this was not the case here. Thanks to the fact I had a decent polar alignment, I didn't have the need to align these particular frames. Due to the wind and maybe the periodic error, I had some movement in other sets. FFTregistration did a fair job with those, although the moon moves a little bit. The Canon 80D camera allows doing 7 bracketed frames automatically, so the movement of the moon if minimized a lot.

I was having some posterization effects in my earliest attempts. I figured that the reason was a slight mistmatch between the linear factors that was calculated by HDRCombination and the theoretical ones, and also the fact that it uses a monocrome mask. To minimize these problems, I did it manually as described to Wouter. Instead of a strong mask, I preferred to use the same data to mask the incorporation of the shorter frames. Since they had been already denoised, it did not degrade the data in a significant way.
To deal with the "pink stars" effect I introduced the scaling factors in the pipeline. But, the problem was not only that. The saturated region varied in size between the channels. A single monochrome mask cannot do the job here.



Thank you both for your compliments!


Regards,

Carlos Milovic F.
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PixInsight Project Developer
http://www.pixinsight.com

Offline wvanreeven

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Re: 2019 Solar eclipse from Punta Colorada, Chile
« Reply #4 on: 2019 July 10 08:02:37 »
Great workflow Carlos and I am afraid it is way out of my league. In the end I managed to create decent HDR images using Photomatix Pro. The images have been posted on my Facebook page ;-)

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Re: 2019 Solar eclipse from Punta Colorada, Chile
« Reply #5 on: 2019 July 10 10:26:22 »
OK i'm glad to hear that the trouble i had wasn't "just me".

the large scale/small scale stuff seems very important. in my own images there is a huge low-frequency "halo" around the sun that i had trouble removing. when you look at images from druckmuller, these large-scale components are entirely gone. but i understand he and his team have developed lots of code for processing eclipse images so i am not surprised.

in my own efforts i also ended up with a sort of ringing artifact around the moon which was undoubtedly caused by HDR compression, but my efforts to supress it were not successful. i have been meaning to go back and try again but frankly it is a lot of work!

rob

Offline Carlos Milovic

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Re: 2019 Solar eclipse from Punta Colorada, Chile
« Reply #6 on: 2019 July 10 14:32:38 »
Hey Wouter, you got a very nice result there, especially for the moon's surface. You may want to try the Larson-Sekanina filter to try to bring a bit more of the details in the corona.


Rob, there are also a few other problems I didn't mention. For example, I have a very noticeable ringing-like artifact on the surface of the moon. I believe that it might be some interference pattern coming from the actual PSF given by the limited aperture of the lenses. That is one of the reasons I kept the moon so dark. :)

Yes, the scale separation stuff is very important (and powerful!). You may take a look at a paper we made (https://doi.org/10.1179/1743131X15Y.0000000028) where we compared a few HDR alternatives. Those based on scale separation performed very well. And we have been doing starless+stars decompositions for processing for a long time now, with great success.
Druckmuller's results are amazing. I followed some pages and found a paper where a method is described. I will try to read it soon, but I'm afraid I don't have much time to implement something along these lines.

A trick I found processing 2010's eclipse data was to actually replace the moon with a "bright extrapolation" of the corona. I used DBE to extrapolate the brightness profile and replaced the moon with it. This way HDR algorithms work much better, without external ringing or other artifacts. I didn't try this trick for this new data, though. Now I'm a bit overloaded again with work at the university, so I will disappear soon. ;)
Regards,

Carlos Milovic F.
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PixInsight Project Developer
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Re: 2019 Solar eclipse from Punta Colorada, Chile
« Reply #7 on: 2019 July 10 15:43:54 »
i will take a look at that paper. i did actually do something like what you are describing - filling in the moon with the color of the corona right behind the moon. maybe making the whole moon a single value was a mistake. it did reduce the dark ringing but i still ended up with bright ringing right at the edge of the moon. although, if i remember right this may have come from the processing i did on the moon itself, which might have benefitted from the same trick.

rob



Offline wvanreeven

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Re: 2019 Solar eclipse from Punta Colorada, Chile
« Reply #8 on: 2019 July 11 02:11:07 »
you got a very nice result there, especially for the moon's surface.

Thanks!

You may want to try the Larson-Sekanina filter to try to bring a bit more of the details in the corona.

Thanks for the suggestion of the Larson-Sekanina filter! I applied it quickly to my images and indeed much more details become visible in the corona. However, the Moon gets very much distorted so I will need to fix that afterwards. In any case I'll need to investigate the options of the filter in order to get the best results.


Wouter

Offline Carlos Milovic

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Re: 2019 Solar eclipse from Punta Colorada, Chile
« Reply #9 on: 2019 July 11 11:36:34 »
Wouter,
Make sure to enter the coordinates of the center of the moon in the X-center and Y-center parameters. Play with the radial and angular increments to get the desired result (in terms of the scales affected by the filter... I used zero for the radial one, and 0.5 or 1 for the angular one). Then modulate it with the amount. The deringing algorithm is pretty naive, but it helps to prevent dark artifacts.
To protect the moon just extract the luminance, and use it as a mask. You may fine-tune it using curves, etc. :)


Rob,
I think that a gradient inside the moon will decrease these bright artifacts because you will be transforming a sharp edge into a steep continuous gradient. Worth a try. ;)
Regards,

Carlos Milovic F.
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PixInsight Project Developer
http://www.pixinsight.com