Author Topic: Calibration of Dark with Super bias  (Read 3484 times)

Offline zbadger

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Calibration of Dark with Super bias
« on: 2017 May 04 18:18:22 »
I have just been running my processing using darks but thought I would try yet again at incorporating bias frames.  SO I integrated 100 bias frames shot at 1 second each and created a Master Bias frame and then a Super Bias frame.  Then went to Image Calibration of 40 darks at 180 seconds each and check marked Master Bias and selected the SUper Bias frame.  Master Dark and Master Flat were left unchecked.  When I went to apply, instantly I receive the error "Incompatible Image Geometry" failed.  Based upon what I have read,my bias frames do not have to be similarly 180 seconds in length.   Suggestions??

Offline pfile

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Re: Calibration of Dark with Super bias
« Reply #1 on: 2017 May 04 18:50:54 »
image geometry refers to the # of planes and X/Y dimensions of the image, not the duration.

sounds like you are using a DSLR - first off a true bias frame is not possible with a DSLR so you should use the shortest exposure possible, not 1s. i think many canon cameras support 1/8192s exposures as the shortest.

second is that if it is a DSLR you have probably accidentally debayered the bias subexposures? you should be working with "raw cfa" for everything - lights, flats, darks, bias, until you've calibrated your lights; then you can debayer the calibrated lights.

rob

Offline zbadger

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Re: Calibration of Dark with Super bias
« Reply #2 on: 2017 May 14 14:35:23 »
Sorry did not see your post because I did not set the Notify Me provision of it.

No - this is not a DSLR.  It is a one shot color SBIG 8300.

Offline pfile

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Re: Calibration of Dark with Super bias
« Reply #3 on: 2017 May 14 16:07:54 »
thats OK but an OSC astro camera is very similar to a DSLR.  since it is an SBIG camera you should be able to command it to make a bias frame, which has 0s exposure.

check also that you didn't accidentally change the binning between the bias and lights.

rob

Offline zbadger

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Re: Calibration of Dark with Super bias
« Reply #4 on: 2017 May 14 18:01:46 »
Thank you.  I checked the bias and light frames and do not see any information on binning but seem to recall they were at 1 and I cannot believe I changed them.  I tried to go for as short an exposure as possible but even at a tenth of a second, you think that could somehow make the bias frames not sync for processing?

Offline pfile

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Re: Calibration of Dark with Super bias
« Reply #5 on: 2017 May 14 19:58:17 »
well the binning is something that will be set in the capture program - though usually it is a mistake to bin an OSC camera though as the results don't necessarily make sense. if one or the other were binned, they will have different X/Y dimensions.

what's important is that all the frames have the same X/Y dimensions and they are not debayered. the duration of the frame is not considered part of its geometry and should make no difference.

your camera control program should have a special setting to take bias frames so there should be no need to set a duration when taking bias frames - it's a special kind of frame. zero length exposure with the shutter closed.

rob

Offline zbadger

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Re: Calibration of Dark with Super bias
« Reply #6 on: 2017 May 15 07:51:42 »
Thanks Rob.  I have opened up a bias frame as well as a light frame.  Where would I find the x/y dimensions for comparison?

Offline pfile

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Re: Calibration of Dark with Super bias
« Reply #7 on: 2017 May 15 09:16:15 »
when the image is selected (blue border at the top) the status bar at the bottom of the screen will show the image dimensions. (w:xxx h:xxx n:1 i16 gray xx.xxMB)

x and y are the dimensions, n is the number of channels, i16 is the sample format (could also be f32 or i8 or what have you - f = floating point, i = integer, # = bit depth), and the last number is the flle size

rob