Author Topic: A SuperBias, or not a SuperBias...that is the question.  (Read 3520 times)

Offline RichInLesta

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A SuperBias, or not a SuperBias...that is the question.
« on: 2017 October 10 11:12:35 »
I'm in the process of re-creating my bias frames, since they were last made over a year ago and I want to see if things have changed.  I'm creating SuperBias frames at the same time, but don't know if I'm doing it right.  The process is fairly simple, so I'm not confused about that, but the resultant image is so far removed from my master bias that I'm scratching my head trying to decide if the SuperBias is "right."  Any thoughts?

Also, my Canon 70D, which I use for virtually all my imaging, is a CMOS sensor camera.  I read somewhere that a SuperBias is not as effective on CMOS as it is for CCD.  Any opinions on that?

thanks, in advance, for ALL your input.

Offline John_Gill

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Re: A SuperBias, or not a SuperBias...that is the question.
« Reply #1 on: 2017 October 10 23:33:00 »
Hi,

I have been wanting to ask this same question as I am seeing the same result from my DSLR (Canon 600d).
Perhaps a PixInsight Guru can answer ....

Look up
John 
APM 107/700 apo on CGX mount
ZWO Optics - Autoguiding
ZWO1600mm and filters
... when there are no clouds ...

Offline msmythers

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Re: A SuperBias, or not a SuperBias...that is the question.
« Reply #2 on: 2017 October 11 00:04:26 »
This posting might be of some help if you haven't seen it.
https://pixinsight.com/forum/index.php?topic=7286.msg49014#msg49014

Also when viewing the superbias image with STF make sure the 24bit look up table icon is on. Your superbias will not look correct otherwise.


Mike

Offline John_Gill

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Re: A SuperBias, or not a SuperBias...that is the question.
« Reply #3 on: 2017 October 11 00:50:11 »
Hey Mike,

Thanks for your advise and pointing me in the right direction.  At least I understand Bias/SuperBias it a little better now!

Look up
John
APM 107/700 apo on CGX mount
ZWO Optics - Autoguiding
ZWO1600mm and filters
... when there are no clouds ...

Offline RichInLesta

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Re: A SuperBias, or not a SuperBias...that is the question.
« Reply #4 on: 2017 October 11 07:44:00 »
"Thanks a million msmythers," he said sheepishly.  I suppose if I hadn't experienced a moment of laziness I could have found that on my own, so thanks for your understanding.

As for the the link you provided, that helps TREMENDOUSLY!  Although it doesn't seem to have been written for we mere mortals, I was able to take away enough from Juan's explanation of Superbias to get me well on my way to understanding.  But equally as important was your suggestion to be sure I was using the 24 bit STF table, which made a huge difference in how I was looking at my Superbias (literally).

Attached is a shot of my bias/superbias with my new-found knowledge.  Across the top is my original master, the superbias, and the difference between the two.  When I finally saw my superbias in it's true form, I noticed the banding which is a function of the canon camera I created these with.  So, as a part of a thought experiment, I debanded the superbias and again show the difference between the original master and the debanded superbias (bottom row).  As expected, the difference image puts the banding BACK because it's in the master but not the debanded superbias.

I'm digging into the forums to find if there's any related experimentation with applying debanding at such an early stage (virtually all the workflows I've seen apply it after integration, which is what I've been doing) and will tinker myself, but I digress....

Again, thanks for your direction.  Today I'm just a little bit smarter.

Offline msmythers

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Re: A SuperBias, or not a SuperBias...that is the question.
« Reply #5 on: 2017 October 11 22:10:53 »
No problem guys.



Mike