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INDI Library v1.9.9 Released (30 Nov 2022)

Bi-monthly INDI Library released with new drivers and bug fixes.

Dual Gain mode settings

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Hello!

Apparently as per the Indi tab my camera supports dual gain mode (Omegon 533c).

  

I would like to know how do you calculate and set your settings? The only reference I could find are these:

Dual Gain

Modern CMOS sensor often support Dual Conversion Gain with a Low and High Conversion Gain setting (LCG/HCG). When the camera supports Dual Gain, three additional parameters are displayed at the Control Tab. High Conversion Gain (HCG) multiplies the gain with an additional factor. This has a positive impact on the read noise. The regular Gain parameter has a continuous range taking the conversion gain setting into account.

The HCG Threshold is the gain setting at which the camera switches over to HCG. For example with IMX294 sensors this is usually set to 900. The HCG/LCG gain ratio is a fixed property of the camera and needs to be set to the design value. For the IMX294 the value is 4.5. For other camera's it is usually 2.0. The Dual Gain Mode parameter enables the special HDR mode of the camera, as well as overriding the HCG/LCG setting.

Dual Gain can be disabled by setting HCG/LCG gain ratio to 1.0. Dual Gain is disabled when HDR is selected
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The following user(s) said Thank You: Francisco Bitto
11 months 6 days ago #80837
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Replied by Udo on topic Dual Gain mode settings

Hello,
i have had the same problems/questions, but i think i have figured it out:

Sensors with Dual Gain have a fixed gain ration between LCG and HCG. Ideally the manufacturer publishes this ratio.
Some values for some sensor are e.g. published here:

www.altairastro.help/info-instructions/c...-for-altair-cameras/

If not you can determine the correct ratio for your sensor by yourself. Just do a sensor analysis in Sharpcap first in LCG mode than in HCG mode. You should find instructions for this in the web. We need the Unity Gain for LCG and HCG modes.

The HCG/LCG ratio is now the LCG Unity Gain divided by the HCG Unity Gain. For my Omegon 533C this is 313/103 => 3.04.

This value has to be entered in the HCG/LCG ratio field.
In the field HCG Threshold you should enter the LCG Unity Gain (or this).

Now LCG/HCG setting works this way:

Abbriviations:
HCG Threshold = HCGT
HCG/LCG Ratio = Ratio

Taking an image with a gain setting between 100 and a value just below the HCGT uses LCG mode.

Taking an image with a gain setting at least as high as the HCGT switches to HCG mode and sets the actual gain to Gain/Ratio.

For my camera i have set:

HCG Threshold = 314
HCG/LCG Ratio = 3.04

Images with gain settings up to 313 now are taken using LCG mode.
Images taken with gain setting 314 and above use HCG. E.g. Gain 314 uses a "real gain" of 103,3 in HCG mode which practically is the HCG Unity Gain.

Or as a table:
Gain 100 => LCG Gain 100
Gain 200 => LCG Gain 200
Gain 300 => LCG Gain 300
Gain 313 => LCG Gain 313 (LCG Unity Gain)
Gain 314 => HCG Gain 103,3 (HCG Unity Gain)
Gain 400 => HCG Gain 131,6
Gain 600 => HCG Gain 197
Gain 1000 => HCG Gain 329
...

I hope this helps. Should be applicable for other sensors too.

Ciao, Udo

P.S.: I do not know why this is implemented this way instead of a simple LCG/HCG (and possible HDR) switch. Maybe to be able to use different gain conversion modes without using the options in the driver settings.
7 months 2 weeks ago #83580

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