Stupid newbie question on Bias frames...

[Phil Leigh]

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

[Harry page]

Hi

The master bias will have less noise so will look different from a single sub ,    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

[Phil Leigh]

Hi

The master bias will have less noise so will look different from a single sub ,    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

[Harry page]

Hi

Green bias    they sould be mono i.e shades of grey

Harry

[Phil Leigh]

Hi

Green bias    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...

[astropixel]

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 Leigh]

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