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Astrophotography and Sketching >> Beginning and Intermediate Imaging

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joelimite
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Re: Processing Messier 33 in PixInsight - A Tutorial new [Re: Raginar]
      #6069886 - 09/08/13 04:42 PM

Excellent tutorial, Madratter! I'm extremely new to deep-sky astrophotography and have only used DeepSkyStacker and Photoshop. I'm intrigued by your tutorial, though, and now want to try PixInsight.

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Jeff2011
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Re: Processing Messier 33 in PixInsight - A Tutorial new [Re: Raginar]
      #6069997 - 09/08/13 05:48 PM

So far it all makes sense to me. I can can correlate the PI operations to what I do in StarTools. However, I am beginning to see some differences. Good stuff. Looking forward to the combining process.

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Madratter
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Re: Processing Messier 33 in PixInsight - A Tutorial new [Re: Jeff2011]
      #6070197 - 09/08/13 08:27 PM Attachment (17 downloads)

Hi Joel. Thanks for the kind words. Even if you don't end up using PixInsight the concepts will still apply with other processing techniques. That goes hand in hand with what Jeff is saying about StarTools (which I also own).

Deconvolution is a way of tightening up the detail in your image. It can make stars smaller, and it can bring out detail in your images.

Perhaps the way to start is to show what happens if you actually use the defaults on an image. It is usually pretty dreadful, and will illustrate why we go to the trouble of all the steps that are about to occur.

If you have followed along, you might want to save your current results. I called mine L_dbe. I save as a 32 bit fit file. I actually save after every operation. There is actually a history explorer, but that won't help if the electric goes out.

Bring up that image and use either [ctrl]a or STF (ScreenTransferFunction) to stretch it so you can see what is happening. Next we want to define a preview. This can be done by pressing [alt]n. Move the cursor to where you want to start. Then press and hold the left mouse button and drag to where you want the preview to end.

Previews are very useful in PixInsight and we will be using them from time to time for a number of purposes.

If successful, you will end up with something like this:

Edited by Madratter (09/08/13 08:42 PM)


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Madratter
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Re: Processing Messier 33 in PixInsight - A Tutorial new [Re: Madratter]
      #6070205 - 09/08/13 08:30 PM Attachment (10 downloads)

If you left click on the tab down the left side of the image that says Preview01, you should now see this:

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Madratter
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Re: Processing Messier 33 in PixInsight - A Tutorial new [Re: Madratter]
      #6070210 - 09/08/13 08:35 PM Attachment (12 downloads)

Notice I made my preview large enough that it does not all fit, when showing it at scale 1:1. (You can change the scale by using your middle mouse scroll wheel). However, we really want this at 1:1. We can either live with it this way, or using common windows methodology, we can grab the end of the frames and enlarge the window.

Now one of the things that makes previews useful, is that because they are not as big as the full image, computationally expensive processing can be tried out before committing the settings to the entire image.

Bring up the deconvolution tool. I have opened mine up to also show the deringing parameters. We aren't currently using them but we will.


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Madratter
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Re: Processing Messier 33 in PixInsight - A Tutorial new [Re: Madratter]
      #6070217 - 09/08/13 08:38 PM Attachment (13 downloads)

Now with the preview tab showing, drag the triangle in the lower left of the deconvolution parameters box over the preview image. This will apply those settings to the preview.

The result is this:


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Madratter
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Re: Processing Messier 33 in PixInsight - A Tutorial new [Re: Madratter]
      #6070221 - 09/08/13 08:40 PM Attachment (21 downloads)

I think it is pretty obvious the result of using the defaults is horrid. There are now black rings around the stars. The bright stars have a bright ring around a brighter middle, and the noise in the image has been intensified.

You can get rid of these bad results by using [crtl][shift]z. Actually that will toggle the results so you can look at the before and after. Get rid of the bad results.

Do NOT try and get rid of the by hitting the back button in PixInsight. That will NOT accomplish what you want.

We can avoid some of the ringing artifacts by playing with the deringing parameters. Try these settings:



Edited by Madratter (09/08/13 08:51 PM)


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Madratter
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Re: Processing Messier 33 in PixInsight - A Tutorial new [Re: Madratter]
      #6070237 - 09/08/13 08:53 PM Attachment (14 downloads)

If you apply those parameters, you will get something like this:

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Madratter
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Re: Processing Messier 33 in PixInsight - A Tutorial new [Re: Madratter]
      #6070245 - 09/08/13 08:57 PM

Again, this is no good but at least we have gotten rid of the dark rings around the stars. But now there are all the unsightly bright lumps around stars and other places in the image. You can try to control them with the Global Bright Deringing parameter (try .01) but the results will still be worse than the original.

OK, that should give you some insight into why we are going to go through the steps that follow. To do Deconvolution properly, we are going to need three things first:

1) A Point Spread Function for stars in the image.
2) A star mask to help protect the brightest star from ringing artifacts.
3) A mask to protect the background areas in the image from being touched and made more noisy.


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Madratter
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Re: Processing Messier 33 in PixInsight - A Tutorial new [Re: Madratter]
      #6070252 - 09/08/13 09:02 PM Attachment (11 downloads)

First we need to get a Point Spread Function (PSF) for the stars in the image. Bring up the DynamicPSF tool.

Use of this tool is anything but obvious.


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Madratter
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Re: Processing Messier 33 in PixInsight - A Tutorial new [Re: Madratter]
      #6070265 - 09/08/13 09:10 PM Attachment (9 downloads)

Go back to your image (click the tab on the left on the window). Mine is named L_dbe. Depending on what you have been doing, yours may be named differently.

Now click on stars within the image. They need to be distributed across the image. Take care to avoid ones that are real bright or real faint. It is very important to avoid stars that are saturated (overexposed). Also avoid stars that are real close together. As you click, the results will be added to the DynamicPSF window.

You'll end up with something that looks like this:


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Madratter
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Re: Processing Messier 33 in PixInsight - A Tutorial new [Re: Madratter]
      #6070268 - 09/08/13 09:13 PM Attachment (10 downloads)

Here is a view of the DynamicPSF window with parameters filled in:

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Madratter
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Re: Processing Messier 33 in PixInsight - A Tutorial new [Re: Madratter]
      #6070272 - 09/08/13 09:16 PM Attachment (8 downloads)

Scroll through the entries in the DynamicPSF window and look for any that say something other than Moffat.

Any such entries are not good for modeling the PSF we need for deconvolution.


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Madratter
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Re: Processing Messier 33 in PixInsight - A Tutorial new [Re: Madratter]
      #6070275 - 09/08/13 09:18 PM Attachment (8 downloads)

Those entries can and should be eliminated by selecting them and then clicking the red "-" icon in the DynamicPSF window.

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Madratter
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Re: Processing Messier 33 in PixInsight - A Tutorial new [Re: Madratter]
      #6070283 - 09/08/13 09:24 PM Attachment (7 downloads)

It is now time to export the PSF as an image to be used when doing the deconvolution. Select all the entries in the window [ctrl]a (yes that is confusing since it is the same key sequence used to auto-stretch the data). It is very important to select them all or the PSF you export will be for only the star or stars selected. This is a easy mistake to make.

Once all the entries are selected, click the icon that looks a bit like a camera.


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Madratter
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Re: Processing Messier 33 in PixInsight - A Tutorial new [Re: Madratter]
      #6070286 - 09/08/13 09:26 PM Attachment (6 downloads)

If done correctly, you should now have an image that is your average PSF of those stars. I save that image as a fit file (I called it PSF). After you have the PSF image, get rid of the DynamicPSF window (click the X). Keeping it around will just confuse things later.

Edited by Madratter (09/08/13 09:35 PM)


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Madratter
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Re: Processing Messier 33 in PixInsight - A Tutorial new [Re: Madratter]
      #6070295 - 09/08/13 09:32 PM Attachment (8 downloads)

Next up is creating a star mask. Fortunately there is a handy tool for this purpose called, wait for it, StarMask (those clever developers). If they were really Unix gurus, they would have called it something like Spot because that was the name of their dog (or biff). OK, enough of the deep inside jokes.

Bring up the StarMask Tool.


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Madratter
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Re: Processing Messier 33 in PixInsight - A Tutorial new [Re: Madratter]
      #6070312 - 09/08/13 09:44 PM Attachment (9 downloads)

The defaults are reasonable, but I like changing the Noise Threshold parameter. On this image setting it to .05 will pick up a few more stars.

Change that parameter if you wish and then drag the triangle at the bottom of the StarMask window over the image of M33. A new window will come up containing the star mask that was created. Don't worry that it does not show every star in the image. We are only using it to protect the brightest stars and it has found those.

(You can do a screen transfer function on it or use [ctrl]a. You will see that it really did pick up only the bright stars).

I save this image as a 32 bit fit (it will want to default to 16 bits). I called mine star_mask.

Edited by Madratter (09/08/13 09:44 PM)


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Madratter
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Re: Processing Messier 33 in PixInsight - A Tutorial new [Re: Madratter]
      #6070325 - 09/08/13 09:52 PM Attachment (7 downloads)

The last step of preparation for deconvolution is creating a protective mask. For this I'm going to star by using the Screen Tranfer Function. Click the radiation symbol to get the default stretch. Make sure you have selected the M33 image or else you will be stretching something like your star mask or your PSF image.

Now bring up the HistogramTransformation process. HistogramTransformation is used to stretch the data in a permanent way. Once you do this your data is no longer linear (and no good for doing deconvolution).

Since we want to create a mask, we need a copy of the M33 image. We can get a copy by clicking the clone button up on the PixInsight Toolbar. (It is about 4 icons over from the left and looks like two windows with a green plus sign over them). Alternatively, we can right click in the M33 image window and select the duplicate entry.


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Madratter
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Re: Processing Messier 33 in PixInsight - A Tutorial new [Re: Madratter]
      #6070331 - 09/08/13 09:59 PM Attachment (16 downloads)

Ok, now is we play Felix and reach into our bag of tricks. If you followed the instructions and used the screen transfer function to stretch the image, we can apply the settings of the screen tranfer function to the histogram transformation process. You do this by dragging the triangle on bottom left of the STF window up to the bottom of the histogram transformation window.

Unfortunately, this is one of those things that is better demonstrated in video.

Once you have it positioned as shown, then release the left mouse button, and the settings from STF will be applied to HistogramTransformation.


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