Problem calibrating Red channel frames only

[peterbrack]

I am using the BPP script. On the last two objects I have imaged using LRGB, I am having an issue with Image Calibration for the Red channel. It will work fine only if I take out the flat frames, so there seems to be an issue with them only.

But when I compare the images, and the FITS headers for the Red flats, and to the LGB flats, there appears to be no difference.

I had obtained the flats using ACP Sky Flats and hadn't previously had an issue, but am now.

I get the same error message :

Applying bias correction: master dark frame...

Dark frame optimization thresholds:
Td0= 0.00030316 (162416 px= 0.968%)
Computing master flat scaling factors...
Error: Zero or insignificant scaling factor for flat frame channel#
0. (empty master flat frame image?)
<*failed*>

It will produce this whether I have a master flat, or the individual flat frames.

In the FITS header for red, which is the same for the LGB there is :

BITPIX 16
BSCALE 1.0000000000000 ( or so)
BZERO 32768.000000000

I am using a master bias and master dark which work fine on the other channels.

Unsure what is going on. Have tried it through Image Calibration instead but produces the same result.

Any suggestions?

Thank you.

Peter

[peterbrack]

I managed to do with MaxIm and didn't bring up any errors. Am a bit stumped as to what is causing the problem

[pfile]

i think you would need to post the images here so someone can take a look. could be that the images are not in 16-bit unsigned integer format?

rob

[peterbrack]

Rob

Here is a dropbox link to the flats, one light image and the dark and bias I was using. i have tried without the dark and bias and still get the same result

https://www.dropbox.com/sh/9lzdkusm54079y9/AABdVkurW7PQvQw25Ps7scnra?dl=0

[pfile]

first thing is, it looks like the master bias and master dark came out of pixinsight, but the master flat was created with maxim? usually that's not a good idea to mix calibration frames like that.

second is, master darks created by the BPP script are uncalibrated, so if you load both the master bias and the master dark when calibrating a light, you need to tick "calibrate" in the master dark section.

if i load all 3 masters and calibrate the light (with dark calibration as mentioned above) it seems to work mostly OK, but the light is very slightly overcorrected on close inspection. it would probably help to remake the master flat in Pixinsight.

rob

[peterbrack]

That's great Rob. Thanks for working that out.

The master flat there was a mistake to be put there, I did create the master in Pixinsight, but had been testing whether it would work in Maxim which is seemed to okay.
I am glad it is working. I wonder why that it has only been the Red channel that hasn't worked, where the LGB does work with the same settings. Would there be any reason for that?

Peter

[peterbrack]

Rob, in BPP I can't see anywhere to tick Calibrate.

Would I have to do it through Image Calibration and the long way , which i did try and did tick the Calibrate box but didnt seem to work

peter

[pfile]

OK i didn't try making the flats out of the flat subs with PI... maybe there is still some problem.

BPP should set up ImageCalibration the right way, meaning it knows that it always creates Master Darks which are not bias subtracted, so when it calls ImageCalibration it sets it up right (meaning, master dark need to be bias subtracted, which is what Calibrate in the master dark section does.)

so i don't know what's wrong i guess. you might try running ImageCalibration manually (which is what i did) and see if you get the same result with the maxim master flat. maybe there is some problem with the BPP-generated master flat that is not present in the Maxim-generated master flat?

rob

[peterbrack]

Right . So I tried what you did and yes I had the same result using Image Calibration. So the problem seems to be with the Red Master Flat, which was created using BPP.
And it has happened the last two objects, but was okay previously.

I might have to use MaxIm for calibration maybe?

Peter

[pfile]

no, in theory there shouldn't be the need to use maxim to calibrate.

perhaps the flat sub calibration was funny - i usually just calibrate my flats with bias frames since the flats are relatively short. but i think BPP always tries to load and scale any darks that are present. i've been using PI so long that i never use BPP so for me its easy to do the flat calibration the way i want. i guess since BPP works right on the other flats then there must be something different about the red flats but that seems unlikely (unless the maxim config changed somehow between the GB and the R flats)

anyway, at this point i'm not sure what the problem really is.

rob