SC subs - internal OR external calibration?

[VPR]

I would like to know how many SharpCap users are using the program's internal Darks/Flats/Bias routine to automatically generate calibrated subs? OR are you generating the Darks/Flats/Bias/Lights separately and then using an external program like PI to generate calibrated subs? I see a few different hits on this topic already.

I am using SharpCap (64bit) to generate calibrated subs. I have tried it with SharpCap (internal) and with PI (external) and find no difference (all frames in FITs format). As a result I am sticking with SharpCap generated calibrated subs for now. Interested in seeing if anyone has done extensive testing on this and reached a different conclusion.

Regards to all,
V.P

[BlackWikkett]

Hi VPR

I've been using the internal calibration tools exclusively for well of a year. I also have been exclusively Live Stacking in SharpCap and applying the calibration frames there. I've had mixed results trying to use "master" flats and darks created in SC in applications like DSS. I find the best practice was to shoot separate calibration and light frames then stack in DSS and Process in Photoshop. I've not used PI but have spoken we folks capturing in SharpCap then using the individual frames to create the final image in PI as best practice for them. It's been a while since I tried all this since I've been Live Stacking

Here's a thread where I did some extensive testing a while back tracking calibration frames issue. May be worth a read. Keep in mind most of these issues were solved in newer versions of SC but I did some testing on using calibration frames and stack in other apps.

viewtopic.php?f=5&t=1282

-Chris

[umasscrew39]

Hi VPR

I create my master dark and flat in SC and use them in PI. It works extremely well and very easy to do considering the complexity of PI. It is part of my PI workflow. There is more than one way to do it but I simply use the Calibration Image Tool to add both the master dark and flat to the light frames then you move on to debayering.

[turfpit]

VP

If using Live Stack I use SharpCap to create master dark and flat as this is convenient to apply directly to the frames being stacked.

If doing traditional deep sky imaging I capture darks, flats and bias frames with SharpCap in the same way as lights. These calibration frames I have processed using Deep Sky Stacker, Siril, Astro Pixel Processor and Nebulosity without issue.

I never create calibration masters in one application and then use them in another application - that is just not logical.

Dave

[VPR]

Hi Chris, Bruce and Dave,

Chris ….. Thanks for pointing me to your prior tests. That was an extensive set of tests for which we in the SC community are grateful (will have to study it in more detail if I run into issues). I am not using Live Stacking but just using SC as an acquisition tool just because of its ability to generate calibrated subs. Point noted with regards to DSS.

Bruce …… Beautiful images in Astrobin. Hope you were not adversely affected by any loss of data. I am using PI exclusively for Deep Sky. Have tried the scripts where you use separate cal frames and let PI do the work. It just seems a lot easier letting SC generate calibrated Light subs. Main issue I see with this approach is that there is no way to go back and evaluate or troubleshoot because the Lights are already calibrated. So far, the process is working as specified without issue. So, have not felt the need for uncalibrated Light subs.

Dave …… Your perspective is interesting where you are using internal calibration for Live Stack and external calibration for Deep Sky. I am looking for a good reason that would indicate the need for external calibration for Deep Sky and hence justify the extra work. So far, not coming up with anything. Oh well ..…..

V.P

[oopfan]

V.P.,

From a software developer's perspective there are indeed standards like FITS but I am not aware of a standard that describes Master Darks. So depending on the software architect he or she might determine that a particular representation of data is faster or more efficient than some other architect. Sure, there are properties in the FITS header that the architect can use to help describe his implementation but do all software products like DSS, APP, Siril, PI know how to use it? Some of these freeware programs are not updated very frequently. So FITS just means that you can browse its contents but it doesn't mean you know what to do with its contents.

Brian

[VPR]

Brian …….. your point would be in favor of doing internal calibration of Light subs – correct? Using the internal calibration routine (via 'Dark Capture' and 'Flat/Bias Capture' and the preprocess tab), SharpCap will then output the most efficiently calibrated Light sub.

V.P

[oopfan]

V.P.... Yes, in other words if you want SC to calibrate lights then use SC to capture and create the calibration masters. If you let SC handle creation and application of masters then you are assured of accurate results. I don't have privileges to browse SC code but I would imagine it has some advanced code to handle the high throughput demands of Live Stack. In other words SC may represent data in the master file in a form that optimizes calculation efficiency. Other software vendors may have different priorities than SC. FITS enables you to browse a file and read its contents but the calibration master data is not transferable between vendors. You may find that some vendors files will inter-operate but you ought to take the conservative approach and not make that assumption.

Brian

[turfpit]

V.P.

looking for a good reason that would indicate the need for external calibration for Deep Sky and hence justify the extra work. So far, not coming up with anything

Easy answer is caution. If I am going to spend several hours collecting data, then if something goes wrong with the calibration frames/process my RAW data gets trashed as it comes out of the capture program. My way if something is wrong with any of the calibration frames then my RAW data is still intact and I have the opportunity to recreate those frames away from the capture session. I believe that capture and processing are two separate operations.

Look on Astrobin https://www.astrobin.com/ and find the Top Picks/Image of The Day for any object you like. These high quality images, produced by people who obviously know what they are doing, seem to be produced in the traditional way of capturing light frames and calibration frames, then processing away from the scope. I am quite happy to follow the methodology of people who clearly know what they are doing. Perhaps you could have a look around the site and see if there are any images in the Top Pick/Image of The Day categories produced via the processing during capture method.

For me, a practical use of the Live Stack process is when working with astronomy clubs or educational/public gatherings where a quick result is desirable over higher quality.

Dave

[VPR]

Brian ….. thank you. We were on the same page.

Dave …... all your points are very valid. For example, I just came in after 4hr of imaging – and will not know if the calibrated subs are any good till I process them further. There is no going back in this case. Also, can’t argue with results …. as to what is published on astrobin. No sense in reinventing the wheel !!

Comes down to Risk Management I guess.

Again, thanks to all and best regards,
V.P