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Messages - drmikevt

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46
General / Re: Combining NB with RGB in a galaxy
« on: 2017 October 16 07:29:27 »
John

It is quite a bite to chew on, but here is Vincent's approach (one of the authors of many of PI's tools) to combining Ha and LRGB data.  Take some time with it - it is advanced, but should give superior results to other methods.  Good luck!

http://pixinsight.com/tutorials/narrowband/

In reference to your mask question - I'm not sure what you are asking.  What are you talking about when you say, 'the masked result'?  You can not permanently save an image with a mask applied, if that is what you are asking, but I'm not sure why'd want to do that anyway.  Depending on what you are trying to do, there is almost certainly a work around, however.

Mike

47
General / Re: Looking for Tone Mapping presentation
« on: 2017 October 13 09:07:01 »
Here is another little tutorial on removing stars in PI.  http://trappedphotons.com/blog/?p=731

Sorry, I don't have the presentation you are looking for, but he uses PS, not PI to remove stars, I believe.

I have found that the tutorial that you link to above works best to remove stars with minimal artifact - much better than the one that I posted, at least for me.  The key, however, is a very, very good star mask that fits both large and small stars well.  For this, it is almost always the case that 2 or more star masks need to be combined (at least for me).  To remove stars, my current best approach is to mask and then apply MMT with the first 6 layers deleted, and then again with the first 3 layers deleted. I find that Morph. Transformation makes a bigger mess that is harder to clean up.  Then, I use TVGD in both the linear and non-linear states to try to knock the artifacts from star removal into submission.

If anyone has a different and better approach to star removal, please post!

Good luck!
Mike

48
General / Re: masks dont show in color
« on: 2017 October 12 18:28:20 »
You had managed to hide the mask, somehow.  On a mac, this is done with command-k.  Or, you can right click the image, go to the mask option and choose 'show mask'.  Or, you can click the little 'show mask' icon in the top button bar.  Most people, I think, hide the mask once applied so that you can better see what you are doing to your image. 

If you want a manual, consider buying Warren Keller's book, Inside Pixinsight.

Mike

49
General / Re: Local Normalization and set of LRGB images
« on: 2017 October 11 15:31:13 »

LocalNormalization must already be making the reference and target subs statistically compatible before comparing them, so I don't think this is an issue.  An integration will have better SNR than an individual sub but that seems like an advantage rather than a problem.  The idea of using an integration came from Juan in one of his early posts about LN, so I'm pretty sure it is sound  ;)

But this is my point - (and again, I am very open to the idea that I am not thinking about this correctly) - if LN is adjusting the frames to be more similar (statistically compatible), it must be using a reference for that adjustment, which I would assume is the reference image.  If so, I guess it comes down to:  what is the most important aspect of the reference to achieve the best resulting image?  SNR? (probably not), Noise?, Median/Background level?.  If it is background level then I still think that an integrated image *could* have an unnecessarily high background, depending on the data set.  You said earlier that SNR doesn't really matter.  If noise determines the best reference frame then, certainly, the integration is the best.  Since Juan suggested to use an integrated image, I'm sure that that is what we should do - I just want to understand the process better to know how to pick the best reference. 

Mike

50
General / Re: Local Normalization and set of LRGB images
« on: 2017 October 10 20:12:40 »
Yes, my apologies - I should have said that the reference needs to be inspected and DBE'd. 

But I have a question about using an integration - it would seem that, since you are using a stack of varying quality, with many of the frames being of a higher background than the frame you would choose as a reference (if you were choosing a reference that way), that the resulting integration would be of a higher-than-optimal background level due to the influence of the frames that would be most heavily normalized by LN.  This would mean (if I'm making any sense) that if your data is varied and you use an integration as the reference than the resulting, normalized integration would not have an optimal SNR due to a higher than necessary background....No?  I don't know if I'm thinking about this correctly or not, but its something I've been thinking about.  So far, for me, 'my' method (using a chosen sub) has been working well to improve the quality of the final integration over not using LN. 

Also, while we're on the topic, do you (Rick) tend to experiment with the scale parameter for difference images or do you leave it at the default of 128? 

Thanks
Mike

51
General / Re: Local Normalization and set of LRGB images
« on: 2017 October 10 12:22:13 »
Again, we are waiting for instruction, but I think the whole point of LN is to normalize your image stack to a single image.  I used the best SNR frame (also taking into account FWHM and eccentricity) from the total 48 images. 

52
General / Re: Local Normalization and set of LRGB images
« on: 2017 October 10 07:49:49 »
And the corrected, normalized images....

53
General / Re: Local Normalization and set of LRGB images
« on: 2017 October 10 07:49:02 »
My experience shows that this works very well (assuming the same target and position angle). 

Although we don't know all the ins and outs of LN yet, we might argue that this is exactly what the process is for - normalizing images taken under varying sky conditions. 

In fact, attached is a little gif I made of a Blink slide show before and after applying LN.  The data is 48 Sii images taken in 2 groups, about 2 month apart.  I'll have to post the other one in a separate post for size reasons.

This one is no LN applied

54
General / Re: Drizzle and Dynamic Crop in PixInsight 1.8.5
« on: 2017 October 10 05:52:54 »
Yes, it is assumed that you have registered before running Image Integration. 

You don't *have* to use Linear fit - I just like it because sometime the 'slope' rejection frame makes it easier to see what needs to be cropped. 

And - it is important to note that you can not move images/files around once you start the registration process.  Leave everything in place until you finish your final drizzle image.

And - the above process is not mine, it is recommended by David Ault and you can read about it in more detail here:  http://trappedphotons.com/blog/?p=693.  He does not cover drizzle, but you would just add it to the end of his tutorial. 

55
General / Re: Drizzle and Dynamic Crop in PixInsight 1.8.5
« on: 2017 October 09 21:37:38 »
Igor

Obviously, you can not do what you are doing.  Do this instead:
 - Choose a reference image and run Image Integration on your images using Linear fit rejection
 - Use the resulting slope, dark and light rejection maps to create your crop.  I start with the slope - apply Dynamic crop to it, adjust the sides and then save an instance to the work area (drag the triangle to a blank space on the work area).  Apply that new instance to each reference frame and make sure the bad areas are cropped.  Apply it to the integration frame and make sure it looks like you want, including rotation. 
 - When it is how you want, apply your crop - your image should be in it's final configuration - and rename that image 'registration_ref' or something.
 - Use that image to register all your images, including the ones you used to make the image.  This will crop, rotate and register your images all in one step. 
 - Now, you can integrate and drizzle as you like.

Good luck!
Mike

56
General / Re: Red Continuum Filter, star mask, eccentricity fix
« on: 2017 October 09 21:23:01 »
I'll take a stab and post some thoughts - take with a grain of salt...

First of all, you have to realize that a really bad eccentricity (or even a kind of bad one) will have effects across the entire image, not just the stars.  So, whatever you are imaging will also be fuzzier and this will affect the final image.  In general, it is best to discard bad FWHM and Eccentricity frames - you can't really correct for those image capture errors.  How bad?  That is up to you and how much of your data you can trash. 

If you are going to improve things, it would be with the Deconvolution tool, but you need some really good SNR for it to work well and not make things worse.  There are a few good tutorials on youtube.  It can only do so much, though. 

If all you want is better stars then you can also try replacing the stars in the image with the ones from the RC filter through a very good star mask using Pixelmath.  Make sure the backgrounds are very, very close. But, this does not solve the issue of the effect of bad frames on your target.

My advice would be to trash the bad frames - this will solve many issues before they occur, but at the expense of SNR.  As you move forward, you will 1) learn how to capture more consistent frames and 2) build the overhead into your workflow, knowing you need to capture 8 hrs to get 5 good hours (or whatever). 

My .02
Mike

57
General / Re: Photometric colour calibration tooooo Blue
« on: 2017 September 19 09:31:07 »
Juan

I understand all of that.  But then, why have the other white reference options?  Having those options present implies that a different setting may be best for a specific image.  Others have 'complained' about images being too blue and have found different/better results with different white references - this is the basis for the advice above.  Are you saying that if the spiral galaxy reference does not work well, then the operator is doing something wrong?  Your comment seems to say that trying different white references is not the way forward when the image colors are perceived as 'off', but assuming correct usage of the process, what other means are recommended?

Mike

58
General / Re: Photometric colour calibration tooooo Blue
« on: 2017 September 19 08:12:20 »
It sounds like you need to experiment with the white reference setting.  As M42 is not an 'average spiral galaxy', this default setting may not be optimal for that object.  The issue is - with about 50 choices, which star reference will give the best results?  Maybe try researching some of the larger stars in image and use the setting associated with those...?  As you know, it early days with this process, which means a lot of trial and error....

Also - are you using a background reference preview?  This may help a lot.

Mike

59
Gallery / Re: StarAlignment vs FFTRegistration?
« on: 2017 September 18 12:59:24 »
Thanks, and sorry for posting in the wrong directory.  :-[

60
Gallery / StarAlignment vs FFTRegistration?
« on: 2017 September 18 12:15:54 »
Can someone please discuss why we might want to use one over the other to register images? 

Thank you!
Mike

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