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Messages - marekc

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31
Workshops and Conferences / Re: Advanced Imaging Conference (USA)
« on: 2013 October 12 10:06:00 »
I want to publicly thank Rogelio for his great presentation on PI yesterday, at AIC!

I learned a lot, and a lot of what Rogelio did helped to reinforce things I *thought* I understood about PI workflows, but hadn't been sure about. Seeing a demonstration of the `contour'-based star mask (for star-reduction) was really nice. The demonstration of combining NB and RGB was also great. (There was a simple PixelMath operation that I *should* have known, but seeing RBA demonstrate it was huge.)

Mosaics are one of those things that have always made me think "Oh man, forget that. I have so much to do just to get *single*-frame images to work!" However, after seeing Rogelio demonstrate methods for mosaicking, I am a lot less scared of mosaics.

I should also publicly thank Rogelio, since I probably asked more questions and made more interruptions than anyone else! I owe him a big one for putting up with me :-)

- Marek

32
General / Re: THELI vs PI
« on: 2013 September 26 12:54:03 »
Thanks for posting that comparison, Andres.

Perhaps I'm being too harsh on THELI - which I have never used, I must admit - but when I first saw this thread, I immediately thought "I'll bet it just blurs the image. Ten bucks says those images look less sharp, with less detail and bloat-ier stars." And that's how it looks to me, based on the images you posted.

Again, maybe I'm being unfair, not having done a real comparison myself, but those images seem, to me, to confirm my first knee-jerk guess.

- Marek

33
Image Processing Challenges / Re: HLA images
« on: 2013 September 23 08:04:50 »
Hi Eddy,

I'm woefully unqualified to answer your question, but you've raised some points that I've wondered about, too.

I've seen a number of beautiful-looking images from the Hubble Legacy Archive, which have been processed by amateurs using a variety of tools. From time to time, I've thought `I should go get some of those marvelous HLA images, and process them in PI.' Then I actually look at some of the HLA images, and I'm always a bit shocked by what I see. Despite the large aperture, sensitive detectors, and position in space of the HST, the images are always noisier-looking than I would have suspected, and have a lot more cosmetic defects than I would have suspected.

I guess I had an unrealistic expectation: I envisioned the HST acquisition workflow as being like that of an amateur imager: Shoot lots and lots of subexposures, stack them, and get a resulting image that has an extremely smooth background. And we've all heard of the massive total integration times that went into things like the Deep Field images.

But I think that's not really how a lot of HST data are acquired. I get the impression that the STScI allocates just enough integration time to get the job done, and not to make a dataset that we would find easy to work with.

I might be way off the mark here, but my overall impression is that if we, as amateurs, want to work with data such as that from the HLA, we're faced with a job that's much more like `painting' than like the `documentary school of astrophotography' that the PTeam espouses. PI is very powerful, but as Juan and others have told us, it's not really designed for the more painterly-type touch-up tasks that PS is good at. And, sadly, I'm coming to believe (perhaps wrongly?) that HLA and other `professional' data need an awful lot of painting-type touch-up work, in order to look presentable. Again, I could be approaching this from a state of unfortunate misconception, but I've found my enthusiasm (for working with `pro' datasets) considerably dampened once I actually look at those data. My PI knowledge - modest though it is - just doesn't seem to apply well to them.

- Marek

34
Gallery / Re: NGC7000 - 65H in NSHO with my script SHO_AIP
« on: 2013 September 21 13:54:45 »
That's a good point, Mike. An image like this one - which shows a sufficiently large piece of the sky - really does emphasize that we're seeing one emission-nebula `bubble' with some dust in front, just as you said.

And it's a lovely image!

- Marek

35
topboxman said:

"I have seen many NB images (Sii Ha Oiii mapped to RGB) with RGB stars using Photoshop. Mike is asking how to do this with PixInsight."

I'd love to know how to do this in PI, too.

- Marek

36
Image Processing Challenges / Re: Star Mask Challenge
« on: 2013 September 12 10:25:14 »
Juan, thank you very much for posting your workflow for StarMask-ing this image. I always find that sort of thing very helpful.

I downloaded Chris's Ha image, and I'm trying to follow along with your processing steps for star masking.

I'm having trouble duplicating your result at the HDRMT stage, though. When I apply HDRMT with the same parameters you showed in your example, it doesn't compress the dynamic range in the nebula much at all. It just darkens the background a bit, and creates some dark ringing around the brighter stars. But the nebula remains very bright.

I started the workflow just as you did: I took Chris's linear image, and stretched it with Histogram Transformation. The HT parameters came from an AutoSTF of Chris's image, as in your example.

After that, I set the parameters in HDRMT just as you did: Number of layers = 4, Iterations = 3, Overdrive = 0, Inverted and Median transform UNchecked, Scaling function = B3 Spline, and the three remaining checkboxes UNchecked.

But these settings didn't flatten the nebulosity much, if at all, when I applied HDRMT to the non-linear image.

Had you perhaps made some settings in Midtones Balance that weren't shown in your screenshot? Or maybe I've missed something in the way I'm applying HDRMT.

Thanks,

- Marek

37
General / Re: Thoughts on Star Masks ...
« on: 2013 September 10 12:40:58 »
Hi Tom,

Thanks for posting those screenshots! That sort of thing is really helpful.

- Marek

38
Gallery / Re: M33
« on: 2013 September 08 12:34:34 »
Nice image!

M33 is a bit of an obsession of mine; oh how I dream of getting a good image of it someday. Yours is very good.

This is going to sound like a weird way to compliment an image, but one of the things I like about the colors in this image is that the remind me a bit of Ektachrome 200, such as in Jim Cormier's wide-field Milky Way images. I know that's a strange way to compliment an image, but I think it's something that looks cool! :-)

- Marek

39
Gallery / Re: Corona Australis region
« on: 2013 September 02 20:40:16 »
Talk about "making the most of a bad situation"! The amount of dust and nebulosity that you got with only 2 hours of data is quite remarkable!

- Marek

40
Gallery / Re: Dark clouds of NGC7000 (Ha) : special PI process...
« on: 2013 September 02 10:42:22 »
Wow! That's a stunner! Your hard work and long integration time really paid off.

- Marek

41
Gallery / Re: M31
« on: 2013 September 01 16:00:53 »
Ah, cool! The fixed-position camera made for an extra challenge, and I think the image came out great.

I suppose it could (in theory) be mosaicked, but I'll bet that would require at least a 4-panel mosaic. Yikes, probably not practical. I like your solution.

- Marek

42
Gallery / Re: M31
« on: 2013 September 01 11:50:52 »
Hi Albert,

I'm an idiot. I didn't look at your image closely enough. Both the "M31 axis" and the "M32-NGC205 axis" are oriented pretty symmetrically, relative to the long and short axes of the frame.

That'll teach me to shoot my mouth off before closely examining the image! I should have looked at it more carefully before writing my post.

- Marek

43
Gallery / Re: M31
« on: 2013 September 01 11:48:02 »
Oooh, that's a very nice M31, Albert!

The image is nice and deep, and that's something I really enjoy seeing in galaxy images. I get a particular enjoyment from seeing a galaxy image that not only resolves nice details in the spiral arms, but includes a lot of the faint outer halo. And when that halo is reasonably smooth, with a decent SNR... well, one doesn't see that too often. That's a very nice aspect of your image.

I have a question about the framing, because it reminds me of my own efforts to shoot M31 (such as this: http://bit.ly/15qRjF4). I noticed that in your image, the long axis of the galaxy runs roughly from one corner of the image to the other, but it's closer to being along the short dimension of the frame than along the long dimension of the frame. When I was making my first efforts to shoot M31, I didn't realize there was a difference. I just thought "Well, I've oriented my camera such that M31 runs from one corner to another, and the line connecting M32 and NGC 205 will run along the other diagonal." I hadn't set it up quite right, though. The M31 axis should have been closer to the long axis of the frame, and the M32-NGC205 axis should have been closer to the short axis of the frame. That wasn't the case, so I had to start over.

I feel somewhat bad posing this question, because it sounds like I'm saying "hey, did you make a mistake?", and that's rather rude. I guess I'm just curious to find out if any of these ideas were part of how you composed the image. My experience with M31 made me realize how complicated the framing of an image can be, and so I'm always interested to learn about how people framed their images.

Thanks, and very nice image!
- Marek

44
General / Re: Thoughts on Star Masks ...
« on: 2013 August 31 03:58:45 »
I've always found star masks to be, far and away, the hardest thing about Pixinsight. They're streets ahead of everything else, when it comes to difficulty and complexity, IMO.

Two main things make them hard for me:

1) Lots and lots of controls. The idea of 'experimenting' or 'iterating' is pretty difficult, when there are so many things to adjust.

2) The names and descriptions of the controls make very little sense to me. The best way I can describe them is that they strike me as "non-physical". Reading the name or description of a control almost never gives me a clear idea of what the control does.

Something like real-time previews, or even just pictorial depictions of what the controls do, would be a godsend for me.

In fact, here is how I envision the ideal, user-friendly StarMask tool:  You have your image, and you click on several of the smallest, dimmest stars that you'd like to see masked. Then you click on several of the largest, bloat-y-est stars you'd like to see masked. Maybe even a few stars in between. The tool would take it from there.

It's a bit like autoguiding. Imagine you're about to start an autoguider calibration routine, in a program like PHD or Maxim. You have the option to click on a star, in order to tell the program "*This* is the star I'd like to use for the calibration." You don't use a series of sliders and fill-in boxes in order to specify the star you're interested in. You click on it. Done and done. Clicking on representative stars is, in my dreams, the ideal way to interact with StarMask. I'd much rather see this implemented (if it's even possible) than any number of new sharpening or denoising tools, however marvelous they may be.

Another example of the kind of thing I envision: When you're using PEMPro, there's a Calibration Wizard, which figures out your plate scale, your position angle, which axis is RA, etc..  The program takes an unguided 20-second exposure, and you click on the beginnings and ends of several star trails in the resulting image. Done and done.

I realize that StarMask is doing things that are much more complicated than the examples I've given above, but I can't help fantasizing about a more user-friendly way of using the tool.

- Marek

45
Wish List / Re: Documentation Tools
« on: 2013 August 26 11:46:38 »
+1

Marek

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