Author Topic: M51 CAHA RGB & HaRGB  (Read 6899 times)

Offline vicent_peris

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M51 CAHA RGB & HaRGB
« on: 2010 June 14 04:25:31 »
Hi all,

altough a bit late, this is the official announcement of our Messier 51 at Calar Alto Observatory. We have made two version. One with embedded H-alpha data:




And a pure RGB image:




This is the credit line: CAHA, Descubre Foundation, DSA, OAUV, Vicent Peris (OAUV/PixInsight), Jack Harvey (SSRO), Steve Mazlin (SSRO), Juan Conejero (PixInsight), Carlos Sonnenstein (Valkanik).

Just to remember, the image has 24 hour exposure time with our new Baader Planetarium filters, and 11 hour with a 7 nm H-alpha filter from the same brand. These filters are the new 65 mm square size. They match perfectly the 50 mm side CCD sensor. And work very well, specially compared to Johnson filters. We have definitely a lot more sensitivity in B band.

Please pay attention to the H-alpha arc to the left of NGC5195; we have not seen any reference to it in scientific research papers.Pay  attention also to the colors of the external halo in the RGB image; specially to the blue arcs at top of the spiral design.


For more information you can visit the CAHA image release:

http://www.caha.es/a-new-look-into-the-whirlpool-image-release.html


Or my own website:

http://astrofoto.es/Galeria/Gal2010_en.html


This image was also APOD on June 11th:

http://apod.nasa.gov/apod/ap100611.html



Best regards,
Vicent.

Offline Harry page

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Re: M51 CAHA RGB & HaRGB
« Reply #1 on: 2010 June 14 10:49:38 »
Hi

You will tell me how you did that Ha  >:D  ,  I can't wait any longer :yell:


Harry
Harry Page

Offline Maxim Usatov

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Re: M51 CAHA RGB & HaRGB
« Reply #2 on: 2010 June 14 12:37:30 »
Hello Vincent,

This is fantastic image of M51, my sincere congratulations and thanks for posting! I would like to ask a question about one particular feature. See bluish loop around M51b core? Is that feature legit? The reason I ask is that the only way I can get this blue loop to appear in other M51 data is to use the HDR wavelet transform on the RGB image. However, no matter how I stretch histograms and boost saturation of the original RGB data (not the Calar Alto data), I can't observe the blue component anywhere. Could it be an HDR artifact? If no, what are the grounds for the blue loop to appear there? (I finally decided to apply HDR on luminance channel only on my own image of M51 that I haven't published anywhere yet - subject to be finalized.) Finally, if you count this as a legit feature, do you observe the blue color at that place in the original non-HDR data?

Thank you!   
Best Regards,
Maxim Usatov | Aries 10" f/15 MCT AP 900GTO QSI 532wsg | Celestron C11-SGT (XLT)
My photos and projects: http://www.bcsatellite.net/bao/

Offline Carlos Milovic

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Re: M51 CAHA RGB & HaRGB
« Reply #3 on: 2010 June 14 15:01:18 »
I believe that this blue "arm" is real. It is clearly visible in the "ultra deep project" data (after hdrwt) too. I can't remember if I saw it on the original data... I'll check that later.
Regards,

Carlos Milovic F.
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Offline Maxim Usatov

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Re: M51 CAHA RGB & HaRGB
« Reply #4 on: 2010 June 14 15:26:47 »
Good evening, Carlos!

I just wanted to make sure we are on the same page. The blue arm extending past through the M51b is indeed real. The object I am discussing is a subtle bluish circular 'loop' that encircles the bright core of M51b. Usually, there is just darkening on that place, however with no blue color added.   
Best Regards,
Maxim Usatov | Aries 10" f/15 MCT AP 900GTO QSI 532wsg | Celestron C11-SGT (XLT)
My photos and projects: http://www.bcsatellite.net/bao/

Offline Carlos Milovic

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Re: M51 CAHA RGB & HaRGB
« Reply #5 on: 2010 June 14 16:07:04 »
oh, ok :) let me take a closer look :D
Regards,

Carlos Milovic F.
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Offline kost973

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Re: M51 CAHA RGB & HaRGB
« Reply #6 on: 2010 June 15 18:42:46 »
just a picture with Stretched levels:)
would like to hear comments about the vast hydrogen clouds around the galaxy
Konstantin

Offline kost973

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Re: M51 CAHA RGB & HaRGB
« Reply #7 on: 2010 June 17 04:15:53 »
no one has any thoughts on this?  :)
like a simple question - it really is, or such treatment?

Offline vicent_peris

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Re: M51 CAHA RGB & HaRGB
« Reply #8 on: 2010 June 17 06:44:24 »
Hi,

you should know that it is completely normal to have a hydrogen halo around a galaxy. Our H-alpha frames were superflattened, so there are no background gradients.

Here is a pic of the denoised H-alpha channel, highly stretched:



The frame is cropped because we had two problems with it. The first is a star just on the CCD bezel that caused a bright reflection on the bottom. The second was a large dust donut that appeared during the night and caused a large artifact; as this dust spot was not flattened, we cropped the frame the upper part of the image.

I've registered the RGB image, so you can do a blink between them:



The H-alpha was added to the R channel when both images were linear. H-alpha was multiplied by 4 (R_channel + [Halpha_image * 4]). So the H-alpha halo is visible in the areas where the broadband halo gets fainter.


Vicent.

Offline vicent_peris

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Re: M51 CAHA RGB & HaRGB
« Reply #9 on: 2010 June 17 10:03:20 »
Hello Vincent,

This is fantastic image of M51, my sincere congratulations and thanks for posting! I would like to ask a question about one particular feature. See bluish loop around M51b core? Is that feature legit? The reason I ask is that the only way I can get this blue loop to appear in other M51 data is to use the HDR wavelet transform on the RGB image. However, no matter how I stretch histograms and boost saturation of the original RGB data (not the Calar Alto data), I can't observe the blue component anywhere. Could it be an HDR artifact? If no, what are the grounds for the blue loop to appear there? (I finally decided to apply HDR on luminance channel only on my own image of M51 that I haven't published anywhere yet - subject to be finalized.) Finally, if you count this as a legit feature, do you observe the blue color at that place in the original non-HDR data?

Thank you!   

Hi Maxim, thanks you,

that's an interesting question. To me it's very important to have a multiscale perspective on color. Imagine you're looking at a completely red apple. But now I put a green glass between you and the apple: your apple is transformed from red to orange.

From the multiscale, and more precisely from the HDRWT algorithm perspective, pixel color is relative to the hue of local structures. This makes sense in astronomy, because you are looking at integrated light from unresolved objects. Even more, in the case of nebulas, you are looking at gaseous structures inside larger structures. In other words, HDRWT is removing the effect of the green glass over the apple, turning it redder.

In the case of M51, HDRWT helps to differentiate between stellar populations. It remove the large yellow structures around the galaxy cores and lets you look inside the galaxy body. To better understand, I've made an animation. It comprises three images:

- The GALEX UV image of M51:




- Our image with midtones adjustment and a color saturation curve:




- The same image as above, but putting an HDRWT process between midtones adjustment and color saturation curve:




And here is the animation:




As you can see, the HDRWT algorithm gives a better separation of hues (=better differentiation between stellar populations). See that there isn't any artifact or "new structure" at all.

As I said above, it's important not only to know what color equilibrium to find (=color calibration), but to know that a structure color is relative to its environment.



More at the Adler. ;-)
Best regards,
V.

Offline Maxim Usatov

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Re: M51 CAHA RGB & HaRGB
« Reply #10 on: 2010 June 17 15:35:47 »
Hi Vincent,

Thank you for your reply. So there is an assumption NGC 5195 features a young star population strip surrounding the bulge, then followed again by older stars? I suspect this is a brave assumption if it is based solely on how the HDRWT algorithm treats the environment, i.e. supposing dark features are actually blue if the environment is yellow. If there was a slight hint of blue component in the original image, I would give up at this stage right away.

I don't have extensive knowledge on galaxies, however I have a hard time finding a similar galaxy, and I've never seen any non-irregular galaxy demonstrating similar structures. Indeed, the darkening region whereby the HDRWT puts the 'blue loop' is surrounded by 'yellow' bulge with older stars, however, to my view. this is simply not enough to give HDRWT carte blanche on revealing stellar populations. I look at the animation you presented and I don't see any intensity peaks in the GALEX UV image at the place the 'blue loop' appears. If there's indeed a strip of young stars, that should have appeared in the UV image as increased intensity - white, and not black, isn't it? Or probably I don't understand the goal of your animation presentation. Please clarify.

There is NGC 6782, at the other hand:
http://antwrp.gsfc.nasa.gov/apod/ap011121.html

However, the image above is UV, and not RGB, so the data is there. I have browsed a few papers on the structure of NGC 5195, however they are all a bit too much for my head. Any galactic morphologists around?  

PS: What's Adler? :-)

PPS: Sorry to be pain in the rear. However, as this forum says - criticism is welcomed. If I'm over the top - just let me know.
Best Regards,
Maxim Usatov | Aries 10" f/15 MCT AP 900GTO QSI 532wsg | Celestron C11-SGT (XLT)
My photos and projects: http://www.bcsatellite.net/bao/

Offline vicent_peris

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Re: M51 CAHA RGB & HaRGB
« Reply #11 on: 2010 June 17 16:42:14 »
Quote
Thank you for your reply. So there is an assumption NGC 5195 features a young star population strip surrounding the bulge, then followed again by older stars? I suspect this is a brave assumption if it is based solely on how the HDRWT algorithm treats the environment, i.e. supposing dark features are actually blue if the environment is yellow. If there was a slight hint of blue component in the original image, I would give up at this stage right away.

Hi,

this is NOT an assumption based only on how HDRWT works, but on the correspondence between our processed B channel and the UV image. Really you don't see any correpondence between them??? You don't see the two small arcs to the left of the nucleus in both images???


V.

Offline Niall Saunders

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Re: M51 CAHA RGB & HaRGB
« Reply #12 on: 2010 June 17 23:47:46 »
Hi Maxim,

Quote
PS: What's Adler? :-)

Vincent will be holding a Seminar at Adler Planetarium, where he will be discussing the PixInsight approach to image processing. See the "Announcements" section of the Forum for full details.

And, no, I do not consider your questioning to be 'over the top'. It is exactly questioning like this that causes people to re-think their strategies, making sure that they really are using a valid approach, before they come back to explain their reasons. OK, so it might be 'over my head' (not difficult :(), but it is not 'over the top'.

Cheers,
Cheers,
Niall Saunders
Clinterty Observatories
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Offline Maxim Usatov

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Re: M51 CAHA RGB & HaRGB
« Reply #13 on: 2010 June 18 00:42:46 »
I finally got it now. The blue loop actually appears closer to the core, and this is evident at high magnification. There is a darkening, however it actually surrounds the loop, so the blue loop and darkening features do not coincide. (I have erroneously thought they do as they look more superimposed on the M51 data I am processing.) The loop indeed matches arcs on the UV images. Vincent, now this all suddenly makes sense to me.   
Best Regards,
Maxim Usatov | Aries 10" f/15 MCT AP 900GTO QSI 532wsg | Celestron C11-SGT (XLT)
My photos and projects: http://www.bcsatellite.net/bao/

Offline vicent_peris

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Re: M51 CAHA RGB & HaRGB
« Reply #14 on: 2010 June 18 01:00:11 »
Hi,

ok, an À Trous Wavelet decomposition of the image without HDRWT shows this clearly:

8 pixel scale:





16 pixel scale:





32 pixel scale:





64 pixel scale:




And by raising color saturation of the 64 pixel scale, we can see better the yellow envelope:




The difference between À Trous and HDRW is that the latter is local illumination level independent.


Regards,
Vicent.