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Ouroboros

Pixinsight: comparing batch with manual preprocessing

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Posted (edited)

I'd welcome the comments from experienced pixinsight users on this.

In the screen shot below, the image on the left is batch preprocessed data. The image on the right is manually preprocessed stepping through the chapters in Inside Pixinsight 2nd Ed by Warren Keller. I followed Warren's recommended settings. 

The only difference is that in the case of the manual processing I applied Canon Banding Reduction to all light frames after calibration and debayering but before integration. Also in image integration I applied large-scale pixel rejection. 

You can see there is a huge difference in the two outputs. I have only applied STF and no other post processing.

The batch preprocessed data has a horrible red cast and there's a lot of banding. The manually processed data has lost the red cast and much though not all of the banding structure. I was hoping I would improve the banding by applying CBR to each light subframe separately, but I was surprised to have lost the red cast and some of the colour noise too. Incidentally the  red has gone into the high rejected data image. 

The manual looks like a better starting out point for post processing than the batch preprocessed.  Is this difference to be expected?

[The data was collected 20 September to test for the first time  KStars controlling my mount, guiding, dither and DSLR. There are 33 X 5 minute light subs. Bias and flats taken, but no darks. ]

image.png

PS I should have added that applying canon banding reduction to the batch preprocessed data was very ineffective. 

Edited by Ouroboros

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Interesting, I've just bought Pixinsight and Warren Kellers Book, I'm just in the process of having a scan through the book first before getting down to read it and use PI in earnest.

Looking at your outputs it shows that it's good to understand how to do things manually by stepping through each process and understanding what it does, then if running a script gives the same result all well and good, it can be used. By not understanding the principles behind the Script it and always using it, you could think that PI was doing a poor job.

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@Mark HaythorneIndeed. Though in my case I don't understand why the two results were so different - particularly in the removal of the red cast to the background. What I should do I suppose is take a few of the subs and step through the batch and manual processes noting all the settings as I go. I haven't done that, and just accepted that the manually produced result was better, so went on to process that.  

Something I'm not clear on, and didn't really understand what  Warren Keller says on  this, is what to do in manual pre-processing when you don't have any darks. As I understand it (might be wrong) batch pre-processing handles this situation automatically somehow by using master bias as darks (?). I thought I'd replicated that in the manual process, but maybe I got this wrong I don't know. 

Edited by Ouroboros

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I highly recommend the Adam Block Pixinsight series.  Not cheap at $180 but well worth it.  When you think of the thousands we spend on gear and the time we put into getting the data, well worth investing in the soft skills to process it all.

Edited by kirkster501

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I'm interested in this comparison but not prepared to spend yet more and can't afford it ATM.  What does the Adam Block PixInsight series of tutorials do that other free ones and the Warren Keller book don't?

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I have the Adam Block Photoshop tutorials and they are very good if somewhat disjointed, each one has an overlong duplicated intro that has to be skipped through, but that's a minor quibble.

He also charged an extra $20.00 to download the videos to your computer otherwise you needed to be online to view them.

Dave

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Interesting, you'd expect them to be the same but there's probably some obscure setting in BPP that's different to how you'd set in manually..  I gave up with BPP and do it all manually so I know what's happening...  Kayron Mercieca's tutorials on his "LightVortexAstronomy" website are also pretty good..

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+1 for doing things manually. Have you tried to run things through DSS? It gives you a pretty good idea of what's in your data before you go through the intensive PI pre process.

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