Splotchy background after Batch Preprocessing and DBE or ABE

[pfile]

format explorer > double click fits > untick "thumbnail image" in 'override embedding settings' section, click OK.

rob

[alanrock]

Well, I think I have somehow rendered my flats completely useless now. After mirroring them vertically and running BPP, the resulting finished product looks very blue. The c_d_r files look good if I run it without the flats though.

[pfile]

well the flats were weak in one channel and that can definitely produce a color cast, but it doesnt matter - you need to do color calibration (or at least view with STF channels unlocked) to see if the data is OK.

rob

[alanrock]

Well, what makes the data “ok”? We don’t know if it’s flipped or whatever, at this point, do we? There’s no screen door effect in the flats of course, but maybe I don’t know what makes them good or bad. I thought it was just the orientation that was the problem.

[alanrock]

OK, so this is interesting. I created some new darks, although they are only 300 seconds, not 600 like the lights. Here's the result of a BPP with the new darks and the mirrored flats. I'm a bit surprised at the amount of amp glow, but when I just do a straight STF (click the button in the toolbar), the result is actually not terrible, although there seems to be a serious gradient. Not sure how I'd go about fixing it. https://drive.google.com/open?id=1VHBdPMUqyLMmcfA6mqKcpRoQroub7har

[pfile]

well by OK, i mean that the colors seem somewhere in the ballpark (galaxies are white/tan, stars don't look insane), there's no vignetting or dust bunnies (if the flats are upside-down and you have dust, you'll definitely see that.).

anyway the right thing to do is just redo all the calibration frames in SGP; i consider trying to fix the calibration frames kind of a hack (but fun to try)

i processed the image you posted and the colors seem correct. the gradient is removable with DBE. i'm also seeing some  'typical' OSC + refracting optics problems - the blue channel is not well-focused while the red and green seem OK. or, the blue channel might just be suffering from "blue bloat" which i guess is normally taken care of with a UV filter.

rob

[alanrock]

Perhaps this is a bit off topic, but can you give me some hints on removing the gradient with DBE? I've watched all the tutorials and read the book, but the settings in DBE are still a bit mysterious to me. Thanks!
A

[pfile]

the main gradient here is pretty well behaved so i just put a few samples in the corners and in the middle of each side, and a few along diagonals near the center of the image. i had to increase the tolerance to 2 to make sure all 3 channels were being picked up.

after extraction there is something of a large-scale blotchiness in the image but that's not super unusual if you're shooting in LP (and perhaps also the flats don't perfectly match).

the amp glow is still there on the right, indicating that the darks are not right though.

rob

[alanrock]

I ran ABE on the image, saw the large scale blotchiness, and didn't go any further since my darks didn't match and I need to reshoot my flats. If I still have the blotchiness after the calibration files are corrected, is there any way to deal with _that_?

[pfile]

well, DBE gives finer control so there is a chance you can get a better background model by carefully placing samples.

there is a trick to eliminate background color gradients which is essentially to mask off the foreground and then use AtrousWavelets in chrominance mode and remove the largest scales, or some subset of larger scales. see this post:

https://pixinsight.com/forum/index.php?topic=5498.msg37760#msg37760

over the years alejandro has posted a lot of tutorials and flows here:

https://pixinsight.com/forum/index.php?action=profile;u=3800;area=showposts;sa=topics;start=0

also he has a website here: http://pixinsight.com.ar/ with lots of good stuff.

rob

[alanrock]

I finally got my 600 sec darks done today. I'm happy to report that when I used BPP without flats, all the amp glow is gone. Here's the result after an ABE, a DBE using Division(in an attempt to flatten out the background), and a couple of passes with Histogram Transformation. I didn't do any color correction or anything else, but I feel like I'm finally on the right track. Thanks for all your help!

[pfile]

you're welcome, glad that is sorted out. hopefully you can get the new flats soon.

rob