Help with M31

[Anthonyexmouth]

Pixinsight is a bit of a love hate thing for me. My fault for not processing more often. I get the hang of something then forget what I've done. Now I'm having one of my can't remember days and can't get M31 right. Getting too much cyan in the outer region and blown out core. Anyone wanna give me a poke in the right direction. 

Here's my problem image in tiff format, I'll post the raw stack and alt version in the next post because of file size limits. 

M31 too cyan.tif

[Anthonyexmouth]

Here's the raw stack. 

M31 stack.xisf

[ONIKKINEN]

What did you do to make it so cyan? Have you tried colour calibrating with SPCC, it churns out a well balanced image every time.

Unfortunately my PI trial ran out and my bank account balance disagrees on the importance of buying the software so cant run it through now, but i am sure SPCC would not make it so cyan. The problem there is that the colour palette becomes quite boring and you'll have to selectively boost the blues quite a bit in case you wanted a typical neutral looking core and blue outer regions with red Ha poking out here and there. In that case you dont want to apply saturation globally, you want to avoid adding much yellow/orange saturation or the core becomes deep fried but instead apply saturation to the bluer and redder (Ha) parts of the image.

On a side note, the image is way too big at 8k pixels in the wider axis which is also why the file size is ridiculous. You can safely at least bin x2, probably more, and lose nothing of value. Also helps a lot with your noise (only noise seems to exist in single pixel level detail).

[Anthonyexmouth]

5 minutes ago, ONIKKINEN said:

What did you do to make it so cyan? Have you tried colour calibrating with SPCC, it churns out a well balanced image every time.

Unfortunately my PI trial ran out and my bank account balance disagrees on the importance of buying the software so cant run it through now, but i am sure SPCC would not make it so cyan. The problem there is that the colour palette becomes quite boring and you'll have to selectively boost the blues quite a bit in case you wanted a typical neutral looking core and blue outer regions with red Ha poking out here and there. In that case you dont want to apply saturation globally, you want to avoid adding much yellow/orange saturation or the core becomes deep fried but instead apply saturation to the bluer and redder (Ha) parts of the image.

On a side note, the image is way too big at 8k pixels in the wider axis which is also why the file size is ridiculous. You can safely at least bin x2, probably more, and lose nothing of value. Also helps a lot with your noise (only noise seems to exist in single pixel level detail).

All i've done is a SPCC calibration, stretch and slight curves. 

[ONIKKINEN]

2 hours ago, Anthonyexmouth said:

All i've done is a SPCC calibration, stretch and slight curves. 

What kind of curves and what does the image look like if you dont do the curves but just do a simple stretch after SPCC?

[Anthonyexmouth]

37 minutes ago, ONIKKINEN said:

What kind of curves and what does the image look like if you dont do the curves but just do a simple stretch after SPCC?

I'll post it tomorrow. 

[Simon Pepper]

Hope you do not mind I had a quick go at this. See below and steps I just took. I think it could have done with a little more DBE but I like it! 

• SCNR removed green
• Inverted image and repeated SCNR green
• Range masked the core and pulled down the curve 
• Range selection again more aggressive in the core pulled down curve
• NoiseXterminator 0.4 and 0.1
• Histogram transformation on each colour channel to balance them out this knocked out a lot of the blue

This  is good data and the core of M31 is bright as we know is it even possible to not blow it out to an extent? Oh and I 180 flipped it as any other way I see it as upside down which is stupid as there is no up in space  

 

[Anthonyexmouth]

10 minutes ago, Simon Pepper said:

Hope you do not mind I had a quick go at this. See below and steps I just took. I think it could have done with a little more DBE but I like it! 

• SCNR removed green
• Inverted image and repeated SCNR green
• Range masked the core and pulled down the curve 
• Range selection again more aggressive in the core pulled down curve
• NoiseXterminator 0.4 and 0.1
• Histogram transformation on each colour channel to balance them out this knocked out a lot of the blue

This  is good data and the core of M31 is bright as we know is it even possible to not blow it out to an extent? Oh and I 180 flipped it as any other way I see it as upside down which is stupid as there is no up in space  

 

Well that's looking better. It's only about 7 hours data. 144x3min I've got another 13 hours sitting on the NAS waiting in 60s and 240s subs. 

So you adjusted the core before stretching? 

[Simon Pepper]

5 minutes ago, Anthonyexmouth said:

Well that's looking better. It's only about 7 hours data. 144x3min I've got another 13 hours sitting on the NAS waiting in 60s and 240s subs. 

So you adjusted the core before stretching? 

I didn't stretch anything I literally loaded your TIF in and completed the above steps. I did a range mask on the core, but you could extract the lum then blur it or use the GAME script to create a mask and then used curves on RGB and Lum and just pulled the curve down to remove some of that brightness, but you have to be a little careful doing it this way. Looking again I think its still a little blue so probably needs another curves or histogram on the blue channel to knock a little more out. 

[Elbasso]

5 hours ago, Anthonyexmouth said:

Pixinsight is a bit of a love hate thing for me. My fault for not processing more often. I get the hang of something then forget what I've done. Now I'm having one of my can't remember days and can't get M31 right. Getting too much cyan in the outer region and blown out core. Anyone wanna give me a poke in the right direction. 

Here's my problem image in tiff format, I'll post the raw stack and alt version in the next post because of file size limits. 

M31 too cyan.tif 505.83 MB · 2 downloads

That is some quality data you've got there!

Could you share a few details on the gear you've used? 

[Anthonyexmouth]

12 hours ago, Elbasso said:

That is some quality data you've got there!

Could you share a few details on the gear you've used? 

Stellar Mira 90 triplet , 294mc and a skytech l pro max filter

[ONIKKINEN]

3 hours ago, Anthonyexmouth said:

Stellar Mira 90 triplet , 294mc and a skytech l pro max filter

You should have mentioned that filter as the first thing of the post. See the spectrum:

Blue and cyan is passed, deep green-yellow-orange is mostly blocked. So the colour palette will be skewed, as the input data was skewed. You might want to just tweak the levels manually to get the palette you are looking for.

[Elbasso]

5 hours ago, Anthonyexmouth said:

Stellar Mira 90 triplet , 294mc and a skytech l pro max filter

Thanks. Data Quality makes good sense now 😂

[Anthonyexmouth]

Had another play and came up with these 2. Still not happy and got a headache overloading on youtube tutorials. 

 

[Elbasso]

I think both look great. In the end, it's just a subjective thing. Personally, I would reduce the stars in the second image a bit to let M 31 take center stage. Again, there's no right or wrong in my opinion (with these 2 variations) 

[Xilman]

First thing I always look for in images of M31 is the clarity of the stars. The first star is generally AE And, which is a LBV (luminous blue variable) star in the galaxy. It has been on my observing program for years and so can spot the region at a glance. Another LBV, AF And is also on the program.

By this metric the lower image is superior but both are good.

Here are the locations of the two variables on your image, with a zoom factor of 4 so that individual pixels can be seen. Note that AE And is markedly fainter than AF And, which is in line with my recent measurements. AE And was at V=17.52 and AF And at V=16.14 on 2023-01-24.0.  I guess your limiting magnitude is around 18.0 to 18.2.

 

AE And:              AF And:   

 

 

[Anthonyexmouth]

4 minutes ago, Xilman said:

First thing I always look for in images of M31 is the clarity of the stars. The first star is generally AE And, which is a LBV (luminous blue variable) star in the galaxy. It has been on my observing program for years and so can spot the region at a glance. Another LBV, AF And is also on the program.

By this metric the lower image is superior but both are good.

Here are the locations of the two variables on your image, with a zoom factor of 4 so that individual pixels can be seen. Note that AE And is markedly fainter than AF And, which is in line with my recent measurements. AE And was at V=17.52 and AF And at V=16.14 on 2023-01-24.0.  I guess your limiting magnitude is around 18.0 to 18.2.

 

AE And:              AF And:   

 

 

This is data from around Oct last year if that makes a difference. 

[Xilman]

It will make a difference but I guess only a little one.  I can (and will find out) but these are enormous blue supergiant stars and are extremely luminous --- somewhere between 50K and 500K times as bright as the Sun.  As such, they take a long time (weeks or months or more) to change in brightness other than in exceptional circumstances. The first is when they go supernova, which they haven't yet but will inevitably do so quite soon - in the next few million years. The second is if they are eclipsed or gravitationally lensed by another fainter star. There are no reports in the literature but I may have, just, picked up an eclipse though much more careful analysis is required.

Since I have been following them, AE And has faded by about a magnitude, which means it is now only 40% of its earlier luminosity.

Incidentally, please measure objects in your images and submit your results. You can certainly do valuable scientific research while also producing attractive images. If you, or anyone else for that matter, would like assistance I would be happy to oblige. As you have demonstrated, you can produce measurable images of individual stars in nearby external galaxies such as M31 and M33. Stars in our galaxy are easy by comparison!

 

 

[Xilman]

Incidentally, close inspection (and I mean close, I have only just noticed it) the stars show a slight colour gradient, being generally bluer at the top and redder at the bottom.

No idea what may be the cause, but it may be atmospheric dispersion or imperfect stacking of the subs.

[Xilman]

14 minutes ago, Xilman said:

It will make a difference but I guess only a little one.  I can (and will find out) but ...

My observations from 2022-10-31.0 show AE And at V=17.22 ± 0.05 and AF And at V=16.39 ± 0.02  so a change, but not very much.