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08 Apr 2018
INDI development team is happy to announce the release of INDI Library v1.7.0. This new exciting release builds on the maturity of INDI Library and comes with many new supported devices and fixes for existing drivers.
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TOPIC: ASI Camera - Gain/Offset/x-Bit

ASI Camera - Gain/Offset/x-Bit 1 month 2 weeks ago #25911

Thanks a lot for sharing! Maybe the observation spot I am using for testing is too light-polluted?

When you say, fitsviewer auto‘s everything, do you mean the autostretch function is enabled? In my case it is disabled.

Could you kindly share also a screenshot with the „control“ settings of the asi drivers? Just that I can cross-check if I messed up accidentally any other parameter.

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ASI Camera - Gain/Offset/x-Bit 1 month 2 weeks ago #25915

It could be very useful to have a comprehensive ASI camera guide as Jasem suggested. Think I'm not good enough to write it but I can contribute with my personal experience on a specific camera (ASI071 pro).
- My setup is a 115/800 f/a 6.95 apo refractor on a HEQ5 mount.
- Added a field flattener and LP filter. No focal reducer.
- Cooling always at -10. It's a low noise camera, there's no real gain to cool it further (as to specs on ASI website, astronomy-imaging-camera.com/products/as...ameras/asi071mc-pro/ ).
- Tried unity gain at first, then settled on 240 gain with 300s exposures . It doesn't seem to saturate too much (see attachments for M101, M81. deepsky objects that you can easily compare with yours). Probably would change for M31 or M42.
- Ignored offset as another owner on Cloudynights says it's now fixed at 50. Not really sure about that.
- Beside gain I left all other controls to their default values.

Overall I'm satisfied with these settings but please give me your opinion, there's always a benefit in trying different approaches.
Ferrante

attachments:
- ASI071 'Control' tab from Ekos/INDI
- M81 single raw 300s exp @gain 240 + histogram
- M101 single raw 300s exp @gain 240 + histogram
- M101 single debayered 300s exp @gain 240
Attachments:

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ASI Camera - Gain/Offset/x-Bit 1 month 2 weeks ago #25921

I’m writing a guide on exposure and there are a couple of goals you can strive for in your settings. I won’t explain why for now as it will be in the guide.

One is to place the sky background peak at 2.2% of the full scale on a linear histogram like in fits viewer.

The second is to set your camera ISO/gain such that you have 11 stops/64 dB of SNR.

With regards to offset, I don’t see this as an important factor as any image will only have usable content above the background level, which is to be set at 2.2% as mentioned. So 0 offset is probably fine.

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ASI Camera - Gain/Offset/x-Bit 1 month 2 weeks ago #25922

Are the sensors really that uniform, one could take the values from others? I took biases with the qhy168 I got from a mate for gain 0, 5, 9, 11, 12, 13 ,14. For each gain set, I watched the histogram of the bias and adjusted the offset value, so that nothing of the left "foot" of the histogram was clipped to black.
The higher gain came, the higher the offset was to be set not to clip anything on the left side. The resulting offset/gain table was not linear in this case. I think in principal this should work the same way with any cmos cam.
These offset values then should be applied to all light and calibration frames of course.
What I don't understand is: why do manufacturers not normalize their setting to 0-100%, so every cam has different max gain settings now?

Andreas

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ASI Camera - Gain/Offset/x-Bit 1 month 2 weeks ago #25924

@ gbeaton:
I think this is a misconception. Calibration frames like bias or darks might be clipped on the left side of the histogram with offset 0. This could introduce artifacts during calibration.
jonrista.com/the-astrophotographers-guid...oise-and-histograms/
scroll down to "Anatomy of Signals in Histograms". The offset value prevents the "separation" of beeing negative.
Andreas

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Last Edit: by andreas.d.

ASI Camera - Gain/Offset/x-Bit 1 month 2 weeks ago #25930

andreas.d wrote: @ gbeaton:
I think this is a misconception. Calibration frames like bias or darks might be clipped on the left side of the histogram with offset 0. This could introduce artifacts during calibration.
jonrista.com/the-astrophotographers-guid...oise-and-histograms/
scroll down to "Anatomy of Signals in Histograms". The offset value prevents the "separation" of beeing negative.
Andreas


Yes, you could be right. I forgot to mentioned that as far as offset goes, I haven't studied it.

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ASI Camera - Gain/Offset/x-Bit 1 month 2 weeks ago #25957

HelgeMK wrote: Thanks a lot for sharing! Maybe the observation spot I am using for testing is too light-polluted?

When you say, fitsviewer auto‘s everything, do you mean the autostretch function is enabled? In my case it is disabled.

Could you kindly share also a screenshot with the „control“ settings of the asi drivers? Just that I can cross-check if I messed up accidentally any other parameter.


Helge,

Yes, I set kstars fitsviewer settings to include autostretch and occasionally debayer as was in that image. I included my settings page for both cameras. I hope you have better luck with the camera.

WHERE is everyone getting this gain of 50 for HDR on the asi cooled cmos cameras? I keep seeing post with that value included but it's not what Sam at ZWO states as Highest Dynamic Range (widest range of signal that the sensor can record) Cooled ASI Camera Settings
Attachments:
The following user(s) said Thank You: HelgeMK

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ASI Camera - Gain/Offset/x-Bit 1 month 2 weeks ago #25958

ElevatedG wrote:

HelgeMK wrote: Thanks a lot for sharing! Maybe the observation spot I am using for testing is too light-polluted?

When you say, fitsviewer auto‘s everything, do you mean the autostretch function is enabled? In my case it is disabled.

Could you kindly share also a screenshot with the „control“ settings of the asi drivers? Just that I can cross-check if I messed up accidentally any other parameter.


Helge,

Yes, I set kstars fitsviewer settings to include autostretch and occasionally debayer as was in that image. I included my settings page for both cameras. I hope you have better luck with the camera.

WHERE is everyone getting this gain of 50 for HDR on the asi cooled cmos cameras? I keep seeing post with that value included but it's not what Sam at ZWO states as Highest Dynamic Range (widest range of signal that the sensor can record) Cooled ASI Camera Settings


It’s not camera dynamic range you are trying to achieve. It’s star SNR. If you have high gain the bright stars with high SNR will be saturated. These are all trade offs of course so it’s also related to exposure time. Because you probably have to have longer exposures for guiding to smooth things out. You’ll have to turn down the gain. You can corroborate what I’m saying with PHD2 “best practices”

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ASI Camera - Gain/Offset/x-Bit 1 month 2 weeks ago #25960

gbeaton wrote:

ElevatedG wrote:

HelgeMK wrote: Thanks a lot for sharing! Maybe the observation spot I am using for testing is too light-polluted?

When you say, fitsviewer auto‘s everything, do you mean the autostretch function is enabled? In my case it is disabled.

Could you kindly share also a screenshot with the „control“ settings of the asi drivers? Just that I can cross-check if I messed up accidentally any other parameter.


Helge,

Yes, I set kstars fitsviewer settings to include autostretch and occasionally debayer as was in that image. I included my settings page for both cameras. I hope you have better luck with the camera.

WHERE is everyone getting this gain of 50 for HDR on the asi cooled cmos cameras? I keep seeing post with that value included but it's not what Sam at ZWO states as Highest Dynamic Range (widest range of signal that the sensor can record) Cooled ASI Camera Settings


It’s not camera dynamic range you are trying to achieve. It’s star SNR. If you have high gain the bright stars with high SNR will be saturated. These are all trade offs of course so it’s also related to exposure time. Because you probably have to have longer exposures for guiding to smooth things out. You’ll have to turn down the gain. You can corroborate what I’m saying with PHD2 “best practices”


Gain does not make your camera more sensitive. It boosts the noise as well as the signal and does not help the signal to noise ratio (SNR) in and of itself. Gain trades off dynamic range and quantization error.

It is camera dynamic range I am trying to achieve when I want the faintest signal and also stars with strong signal to be recorded. I am referring to taking images of DSO's with my cooled ASI071mc-pro.

With your comments above, it looks like you are referring to guiding that has exposures less than 5s where noise is not as important to manage as it is in a main imaging camera. I want the sensor well on my main camera to fill up slowly with the stronger signals to give the fainter signals time to register on the histogram without oversampling. GAIN AND OFFSET EXPLAINED ....the statement about gain above is in bold on this article.

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ASI Camera - Gain/Offset/x-Bit 1 month 2 weeks ago #25962

Maybe I lost track of the thread but the 50% was a reference to a question Helge had about an ASI guide cam setting.

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