Darks and Flats Sanity check

[umasscrew39]

I've been creating darks and flats so no issue there but want to confirm a few things as, despite been doing this for a while, something occurred to me that I may be doing some of this wrong :

If I make a set of darks and flats and then apply them, will they be used to correct the individual frames if:

#1- I save each individual frame (non-live stacking) to be stacked later- I believe the answer is YES

#2- I save individual frames (option 2) as a fits during live stacking - I believe the answer is NO

Finally, if I want to go with #2 above, is the best way to correct the light frames later is to capture individual darks and flats and then use them along with my lights for pre-process calibration in PixInsight (which is what I use)?

Bruce

[admin]

Hi Bruce,

You are correct on #1 and #2. If you want to process live stacking frames later then you can either use the same darks and flats (your stacking application should be happy with that) or capture new ones. I can't see any obvious advantage in capturing new ones unless your stacking application isn't happy with the averaged frames created by SharpCap (I can imagine that this might happen on some software as the average frames will have a full 16 bits of data whereas the image frames have only 12 for most cameras).

Cheers, Robin

[umasscrew39]

".............. (your stacking application should be happy with that) or capture new ones. I can't see any obvious advantage in capturing new ones unless your stacking application isn't happy with the averaged frames created by SharpCap........"


From Robin's statement above, in case others are interested or just as a FYI, I used flats generated from SC and used those in the 'image capture' tool of PI and it worked like charm to clean up the dust motes. I had to do this on a subset of frames as I forgot to apply the flats during image capture with SC.

Bruce

[umasscrew39]

Hi Robin

I would like to revisit one aspect of this as I am now experiencing a problem with the 64-bit version of SharpCap. I tried to use the Image Calibration tool in PixInsight to apply the master flat and master dark I created in SharpCap today to the lights I captured last night. This worked great when I was using the 32-bit version but not with the 64-bit version. When I added the master dark and flat, all of my lights turned red and I was receiving an error message that there was no correction between my master dark the target images. When I adde just the mater flat, I did not get an error message but all of my lights turned blue. So, I asked the PixInsight team to make sure I was not doing something wrong and this is what I got back:

From the PixInsight Team.....

that in and of itself may be the problem... mixing calibrated frames generated with one application and another can be problematic.

presumably the calibrated flats/darks are in some kind of floating point format. there's no standard for how to represent images in FP formats. pixinsight uses the range 0.0-1.0 to represent all floating point images. sharpcap might not be doing that. i'd say the first step is to find out whether or not these precalibrated masters are represented in that format. even if they are there can still be problems with doing this.

when you use raw subs from a capture program, 99% of the time they are in 16-bit integer format, and there's no ambiguity about what the numbers mean in that format.

In PixInsight, you normally make your master flat and dark and then apply the maters in the Image Calibration tool. However, like I said above, I got it to work with the 32-bit version of SharpCap.

To avoid this, I am going to remember to apply the darks and flats to each individual frame as I capture them in SharpCap so I do not need to do this later. However, I wanted to bring this to your attention in case it is a 64-bit SharpCap issue as I do not think I was doing anything wrong.


Regards,
Bruce

[admin]

Hi Bruce,

The master dark and master flat files created by SharpCap are in 16 bit format, so the concern about floating point format is not relevant here. I wouldn't have expected the 32 and 64-bit versions to give any different results in this and would be interested in seeing your calibration files captured from each version to see if I can spot what is going on.

Cheers, Robin

[umasscrew39]

Hi Robin

Hmmm....I see. So nothing to do with 32 vs. 64 bit version.

Not sure I understand what you want to see. The final fits image or the master dark and flat? How do I attach them? All too large.

Another potential variable here is my old laptop. I collected a large number of captures last night with my new APS-C sensor camera while applying a master flat and master dark. The individual frames look excellent but when I tried to do star alignment in PixInsight my laptop kept crashing. When I tried to align just a few images at a time, they ran through the tool but some of the files became corrupted. The folks at PI and others on different forums have told me that for this camera, like with full frame cameras, I need a much more powerful computer. So, I have one on order. My current laptop is fine for capture but not for data crunching/analysis.

Regards,
Bruce

[admin]

Hi Bruce,

ideally the master dark and flat FITS files saved by SharpCap (32 and 64 bit versions). The best way to transfer large files is usually to use some sort of file sharing website (Google Drive, Microsoft OneDrive, DropBox, etc) - upload the files there and use the functionality of that site to create a sharing link which you can post on the forums.

Stacking can certainly use much more computer horsepower than simple capturing - this hobby just keeps getting more expensive

cheers, Robin

[umasscrew39]

Hi Again Robin

I have been using master dark and flat PNG files instead of FITS and they do work. However, I will make a new set of darks and flats as FITS and try them. This may also be part of the problem but they did work previously in PixInsight.

BTW- I did not tell my wife the cost of the new threadripper computer I ordered

Regards,
Bruce

[umasscrew39]

Hi Robin

I want to send you a flat FITS file I took with the ASI2600MC Pro using SC x64bit. I have it on my Google One drive to share but not sure how to link it to this forum. What address do I use?

Regards,
Bruce

[admin]

Hi Bruce,

If you create a sharing link in Google Drive and then send that to me by private message it should work – there is usually a box to tick that says something like 'anyone with the link can download'which means you don't need to know someone's email address to share with them.



Cheers, Robin