PixInsight Forum (historical)
PixInsight => General => Off-topic => Topic started by: Phil Leigh on 2012 April 03 09:51:26
-
Today I bought my license for PI so I'm feeling pretty good! - and I thought I would celebrate with a question to the experts :-)
Attached is a screen capture of a single bias frame and a master bias integration of 20 bias frames (using the tutorial method - no normalization, winsorized sigma clipping sigma 4 high 3 low)...
Both have been debayered to show what's going on. I can see severe banding in both images - is this normal? The single frame has horizontal banding and the integrated master has vertical AND horizontal banding!
Also the master bias looks nothing like the single frame - is this normal?
thanks for your time and expertise.
Phil
-
Hi
The master bias will have less noise so will look different from a single sub , :D they look fairly normal to me but you never debayer a bias frame
it is not used this way bias frames are applied to the flats / lights etc before the lights are debayered
Regards Harry
-
Hi
The master bias will have less noise so will look different from a single sub , :D they look fairly normal to me but you never debayer a bias frame
it is not used this way bias frames are applied to the flats / lights etc before the lights are debayered
Regards Harry
Harry - thanks - I have greatly enjoyed your tutorials!
Yes I know you don't normally debayer the calibration frames - I only debayered and auto-stretched for the screen capture (otherwise they would both just be solid green...)
If you think they look "OK" or "normal" that's good.
When I do the same with my Dark frames they look much more similar to each other - and the master dark is clearly less noisy than a single dark. That's what's foxing me, because I think the bias frames look wrong somehow - the master bias looks much noisier than a single bias frame...
regards
Phil
-
Hi
Green bias :o they sould be mono i.e shades of grey
Harry
-
Hi
Green bias :o they sould be mono i.e shades of grey
Harry
Harry,
I should have said that I'm using a (IR filter removed) Canon 450D DSLR and that the files are RAW (CR2). When I open/use the files in PI, my Format Explorer settings for DSLR_RAW are: "Create Raw Bayer Image (RGB) and "No Black Point Correction" and both white balance options are deselected.
regards
Phil
I presumed the "green" is caused by the two lots of "G" in the "RGGB" of the Bayer matrix...
-
Phil. Your bias frames look OK. The green cast is normal and you can expect that your calibration frames will be coloured, because it's DSLR.
I see what you mean about the differences in your bias frames. I have seen the same but can't say that it has been problematic.
You could try sampling the bias frames to check the consistency. Also did you do ABE on your bias sub following debayering (again, merely for the purpose of revealing the data) -might make a difference to the appearance - perhaps worth a try.
-
Phil. Your bias frames look OK. The green cast is normal and you can expect that your calibration frames will be coloured, because it's DSLR.
I see what you mean about the differences in your bias frames. I have seen the same but can't say that it has been problematic.
You could try sampling the bias frames to check the consistency. Also did you do ABE on your bias sub following debayering (again, merely for the purpose of revealing the data) -might make a difference to the appearance - perhaps worth a try.
Thanks Astropixel. I didn't do ABE - but I will try that to see what - if anything - it reveals.
many thanks for your kind help
Phil