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Messages - Bobinius

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1
General / Re: Masked stretch and big star appearance
« on: 2019 September 20 09:09:36 »
Hi,

Have you tried "ArcsinhStretch"  I do a small stretch and then a larger stretch and then finish with a tweak of the HistogramTransform.

space is not black
John

Hi John,

Yes, and it looks very promising! Actually I tried it at first but it was a bit difficult to balance the Ha and the S and O with ArcsinhStretch and I was not please with the nebulosity. Now that you've mentioned it, I gave it another shot and the stars are really good, I managed to balance the channels before combining them using HT.

All best

Bogdan

2
General / Re: Masked stretch and big star appearance
« on: 2019 September 19 04:44:29 »
You can try this:

MaskedStretch and Stars Cores

Greetings,

Enzo.

I tried it but it works only on RGB images, so you can eventually repair the narrowband after recombination in linear. I was combining them in non-linear after the stretch, so it is not adequate for this strategy. I finally decided to try a different stretching strategy not Masked in order to preserve the stars.

3
General / Re: Masked stretch and big star appearance
« on: 2019 September 18 10:32:45 »
You can try this:

MaskedStretch and Stars Cores

Greetings,

Enzo.

Many thanx! Looks promising. I attached an image of my Ha star artefact.

4
General / Re: Masked stretch and big star appearance
« on: 2019 September 18 10:14:32 »
Depending on how much you are trying to stretch and the saturation of the stars during capture this artifact may be unavoidable.  When this happens to me, I make a mask of the larger stars and apply a very mild Convolution to the cores to smooth them back out again.  It works quite well. 

Mike

Thanx that was my plan too. I tried to masked them when I do the Masked stretch but this creates some weird artifacts around the edges of the masked core (I don't if it is doable or my masks are not adapted).

5
General / Re: Masked stretch and big star appearance
« on: 2019 September 18 05:26:46 »
I am already using 100 or higher, does not seem to depend on this parameter. I'll try to post an image when I get home, the center of the big stars is saturated (uniform white) and round.

6
General / Masked stretch and big star appearance
« on: 2019 September 18 02:39:11 »
Hi everyone,

I am working on a narrowband project and the best stretching method for obtaining nebular detail and equilibrium (O3 is really faint) in this cas was Masked Stretch. However the bigger stars in the image have completely saturated circular white core with a net separation from the rest of the star (similar to the deconvolution artefact when the stars are not masked). Is this a known artefact of masked stretch on big stars and are there any setting for obtaining a more gradual tapering of the signal from the center of the star?

Thanx.

Bogdan

7
Ok, I managed to found the PI link (the download link was modified I guess) and it works very well in Pixinsight.

However when I restart PI the module is no longer there and has to be reinstalled! Is this a known bug? I have the latest PI version.

8
Hi Nikita,

I am not able to install the module, I used the link that you provided for the PI module but Pixinsight does not detect any new module in the directory when I tried to install it. Am I missing something? The zip file seems to be containing the same files as the .exe version of starnet.

Many thanks

Bogdan

9
Gallery / Re: M16 Eagle Nebula
« on: 2019 August 13 13:41:25 »
You have to focus... Use a Bahtinov mask for example.

10
General / Re: The problem of green in narrowband SHO palette
« on: 2019 August 06 13:26:58 »
Your 'local' colour is based on your optical equipment, your local conditions, and your sky conditions as photons pass through to your OTA. So, yes, you - as the imager - have to choose how you want to represent the wavelegths of the incoming light.

You will always err in favour of 'what looks good to you'.

You're right Niall and I agree that there are multiple physical factors that are between the object and the final xisf or fits. However, not everything is subjective and while I agree that the colour assignment for the specific emission lines are arbitrary, once this step is completed, you have to represent correctly those photons that arrived on your sensor. It is not their fault if more of them are Ha and therefore green. When you delete them you are deleting data. I am just trying to understand how to keep my workflow as accurate as I can in order to represent the Universe as it is, not as I would like it to be. (once I assigned the false colours...) I mean, why use Colour calibration for LRGB data if "anything goes"? Why should the Pixinsight team develop new Photometric colour calibration tools if "all is in the eye of the beholder"?

11
General / Re: The problem of green in narrowband SHO palette
« on: 2019 August 06 11:01:32 »
As Niall indicated above as we didn't start with colour in the first place it is totally down to you how much red you remove, it all depends on what looks pleasing to you
Well actually we do start with colour: Ha is a deep red, SII is a deeper red and OIII is blue-green (teal). Just an idle remark.

Yes, if you try to respect the spectral lines. But the same data when using the natural colours has very low contrast. I think that's what justified the SHO palette in the first place. And of course it would be close to impossible to visually distinguish a Ha emission zone from a S2 emission zone.

12
General / Re: The problem of green in narrowband SHO palette
« on: 2019 August 06 10:55:28 »
Dave,

Probably you are right with the histogram, I usually look what's going on and indeed there is a difference between the intensity transformation (the green pixel value is less but not zero) and a clip (which would totally delete the pixel).

For example, do you know if there is a standard protocol at Hubble for producing the images - I mean I hope that the M66 aspect that Hubble produces does not depend if Sandra from NASA who did the post-processing Saturday really loves pink hues or not. Hopefully there are some objective rules for treating the image.

 ;D she usually makes good choices.

I think it is down to the processing team, i.e. Sandra LOL

13
General / Re: The problem of green in narrowband SHO palette
« on: 2019 August 06 02:22:45 »
Dave,

Probably you are right with the histogram, I usually look what's going on and indeed there is a difference between the intensity transformation (the green pixel value is less but not zero) and a clip (which would totally delete the pixel).

For example, do you know if there is a standard protocol at Hubble for producing the images - I mean I hope that the M66 aspect that Hubble produces does not depend if Sandra from NASA who did the post-processing Saturday really loves pink hues or not. Hopefully there are some objective rules for treating the image.

14
General / Re: The problem of green in narrowband SHO palette
« on: 2019 August 05 08:08:39 »
Any method you choose to create your final colour image from your NB data is perfectly valid.

After all, you didn't start with 'colour' in the first place.

You are free to use any processing steps you wish to get the image you desire - and there are no requirements to 'fill the Green channel' with data whatsoever.

Food for thought?
h
I agree that the color assignment is arbitrary and the SHO palette is there mainly for contrast reasons. Once you assign Ha to green, the Ha data is Green ( I was talking specifically about the SHO palette). If I am trying to take a real picture of a celestial object, that's representative, am I not going to lose data and misrepresent that object if I clip the green data? Should this difference in intensity be compensated by longer total exposure for O3 and S2 for example?

15
General / Re: The problem of green in narrowband SHO palette
« on: 2019 August 05 08:03:49 »
The green should not actually be there or is required, however, it is the way the different channels react.....its very complicated, Vincent Peris did explain it to me with lots of diagrams but it was 5 years ago and I have forgotten, basically you should not have any green in a narrowband image, unless, of course you want some.....that's all up to you.

To remove red use color masks then curves on the red channel.

Thanx for the video, very useful as I did not use this mask technique for processing. Probably the mask is more flexible than SCNR. SCNR is really fast for removing the magenta around the stars (due usually to the O3 filter bloating): you just invert the image and apply a SCNR at 1, that's it.

The idea with the red is that we usually do not decrease the reds for example in a HOO image (or do you?) It would be analogous to decreasing green in SHO. How do you know IF it should be removed or HOW MUCH to remove? (other than esthetic criteria, "I like it more this way" kind of justification).

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