Newbie questions, DSLR BatchPreprocessing

astrorunner

Member
Aug 11, 2017
11
0
Hi everyone, this is my first post here.

I'm relatively new to AP, started in January. I have been trying to learn PI for about 2 months now and I've reviewed a couple of online videos from Harry's Astroshed and I've been slowly working my way through Warren Keller's book "Inside Pixinsight". My goals were to use PI as a "one stop shop" for basically all of my processing needs, as I don't know Photoshop and I'm a bit reluctant to purchase it (just yet anyway).

I'm using a Canon T3i DSLR with a Celestron 9.25" XLT OTA and currently non-guided. I will soon upgrade to a guided system but I was hoping to master at least a basic "workflow" to get reasonable pictures to look at before upping the complexity.

My main question now involves using the BatchPreprocessing script to calibrate and stack ("integrate"). I've shot with darks and flats and various ISOs, and with 30 second exposures for my light subs (I can't really go much longer unguided). I also made master bias files for various ISOs out of sets of 600 exposures taken at the max shutter speed (and in the refrigerator, to simulate the normally cool or cold outdoor conditions I shoot in). From what I can tell, the calibration appears to go well. I get master darks that are uniform gray in color when I bring them up an apply the auto STF to them (using the radioactive-symbol button), and I can see a few hot pixels sprinkled around. My flats are also gray but you can see the dust motes and vignetting at the corners. The master bias also appears to be mainly uniformly gray with perhaps a few vertical line patterns barely visible.

The issue comes with the final product of all this. The output "master light" (I think that's what you'd call it) from the script is very very green and often grainy and noisy. I guess a lot of the noise could just be light pollution from the city I'm shooting from. The green though is bright and everywhere. I can use the "SCNR" program to remove it. But should that green be showing up at all? Is something missing or wrong with a setting that will cause this green to appear like it does?

For comparison, I also have run Deep Sky Stacker with the same dataset, and I also get green objects, but not quite as pervasive as with PI.

Also, and this is a problem I've encountered with DSS as well as PI, my stars seem to have virtually all color stripped from them, everything just looks black and white (at least after I run SCNR, and green is gone!). Is this just a matter of my needing to run additional stretching of some sort to enhance colors, or again is there a setting somewhere that is doing this? I have not yet learned or mastered any of the processing techniques beyond just calibrating and stacking (I've played with the histogram tool a bit but that's about it; in Gimp I've used "curves" and "levels").

Finally, the "Inside PixInsight" text walks me through the individual processes that make up the BatchPreprocessing procedure. However, when I try to calibrate using this approach, my master darks and master bias come out looking blue or green (after applying an STF to it). This doesn't seem right. I don't get this result when running the BatchPreprocessing. A friend of mine who has been doing AP for many years almost never uses anything beyond the BatchPreprocessing script, although PI strongly recommends you to run ImageIntegration for light frames as a separate step, for better quality.

Sorry if this is a lot on the table but I'm really looking for some basic guidance here. I'm not necessarily needing to master the most advanced features of PI right now, I just want a basic workflow that will work with my DSLR for now.

Thanks!
 

aworonow

Well-known member
Feb 19, 2013
342
12
faintlightphotography.com
Good questions. I'll take on the green-tint issue and maybe some of the other folks will pick up other issues.
It is common to get a greenish stacked image. A DSLR (I have the T2i also) has two green sensors for every 1 red and 1 blue. SCNR is very commonly used to give a better color balance. BTW, you should be working with the Raw images, not those that have been processed and compressed in the camera. This means you will need to debayer the raw images. If you first extract the individual RGB channels from the raw images, you can used linearFit to get a better color balance before combining the images. But, frankly, if you are just getting your feet wet in PI, that can wait.

Best of luck...Alex W.
 
astrorunner said:
My goals were to use PI as a "one stop shop" for basically all of my processing needs, as I don't know Photoshop and I'm a bit reluctant to purchase it (just yet anyway).
Welcome aboard!

Well, your goals fit perfectly with the aims of PixInsight - to be able to provide a one-stop shop that will meet all of your needs! Unfortunately, the idea of a one-stop shop does not mean that you are going to get a 'one-click' solution !! As time goes on you will perhaps remember this stage in your image processing career - until then, be comforted by the fact that all of us were, at some time, at this very same step as you !!!

My main question now involves using the BatchPreprocessing script to calibrate and stack ("integrate")
In fact, I would recommend that you 'step back' from the BatchPreProcessing Script. This will give you a better feel for all of the individual stages required for good pre-processing. By tackling each stage 'manually' you will get the chance to 'make changes' as you see fit - or even to ask for help when you can't seem to move forward. You will also see when the data that you have acquired might need to be improved. And, most importantly, you will learn the patience that you must endure if you are to be successful - astroimaging is not a 'point-and-click' process, and the processing steps are not 'one-click' steps either. The pleasure actually comes for the acquisition of the knowledge required to acquire and pre- and post-process the images. (At least, that is how I see it - I don't publish my images anywhere; I am not creating them for that purpose, I am creating them to allow me to master a skill)

I've shot with . . .  patterns barely visible
You talk about predominantly 'gray' images - well, if you are working with non-deBayered 'RAW' images (direct from your DSLR), then that is what you should be expecting. You do not want to be deBayering the images until the correct stage - much later in your pre-processing workflow (and, with the new tools in PixInsight v1.8.5, this can be held of right until the very last stages of the process.

. . .The output "master light" . . . is very very green and often grainy and noisy
Don't get too bogged down by 'colour' when you have completed your pre-processing steps and are starting out on your post-processing stage. You will work on extracting colour much later on in post-processing. Just trust me - it is there (or, it should be, providing you actually captured it in the first place). When you perform your first AutoSTF (with the 'radio-active' symbol !!) you can end up with some quite horrible colour-balance issues. Learn how to un-link the channel sliders before applying the AutoSTF (which will give you a better colour balanace), and then how to re-link the sliders again to modify the automagic slider positions (as a 3-channel groups) to deal with the black-point (shadows) and mid-point of the image (you will almost never need to move the white-point 'highlights' sliders). Learn how the STF does not, and cannot, affect your image data - it only affects "what you see on screen".

I can use the "SCNR" program to remove it. But should that green be showing up at all? Is something missing or wrong with a setting that will cause this green to appear like it does?
Don't bother with SCNR - not yet. You might want to start playing with DBE first, then the BN and CC processes (yes, go and look up what these shortcut names mean  ;) ). You also now have a super-powerful new tool at your disposal - PCC - but, again, get a feel for what PCC is doing by understanding the BN and CC tools first.

OK - I'll leave your other comments for just now. You have something to work with, and remember to come back to the forum if you are still struggling.

Most of all - have fun  :police:
 

John_Gill

Well-known member
Hi,

I have a small text file showing a work flow and suggested setting from tutorials www.lightvortexastronomy.com
This might help you calibrate your images and then help you process.  Once you get better at this, you will start experimenting with settings, and that's where the "fun & games" start.  Send me your email address or facebook details and I will send you the document.

Look up
John
 

astrorunner

Member
Aug 11, 2017
11
0
John_Gill said:
Hi,

I have a small text file showing a work flow and suggested setting from tutorials www.lightvortexastronomy.com
This might help you calibrate your images and then help you process.  Once you get better at this, you will start experimenting with settings, and that's where the "fun & games" start.  Send me your email address or facebook details and I will send you the document.

Look up
John
Thank you John, I sent you a PM with my info.