ZWO camera: Mean Threshold and Mean Target settings

[peng155]

Hi Folks,

I'm trying to trouble shoot some "removeBadImages.sh: File is bad: removed 'image-20240410051352.jpg' (below threshold: MEAN=0.98, threshold = 1)"

Per what I've read in the Wiki and in Discussion threads, I have my ZWO ASI224MC set-up with Auto-Exposure / Manual Gain..

I also found the following in a thread:

With the RPi cameras you want to use auto gain and auto exposure. The algorithm increases the exposure to
its max, then increases the gain.

The "Target Mean" values determine the brightness of your images, so if they are too bright than lower that
number.

The "Threshold" number states how close it should stay to the mean. For example, I use a nighttime target
mean of 0.2 and a nighttime threshold of 0.1.

That means the brightness will range from 0.1 to 0.3 which is 0.2 plus or minus 0.1.

Based on above with my settings of Auto-Exposure / Manual Gain, this statement "The algorithm increases the exposure to
its max," will hold true and my Gain will be set at what ever it is set for, in my case 200

Do the other statements for "Target Mean" and "Threshold" remain true for ZWO camera's, or per what I've read about the Allsky algorithm and ZWO camera's not really working well together come into play??

Thanks

[EricClaeys]

@peng155, the Allsky ZWO exposure algorithm isn't nice as the RPi one, which can handle both exposure and gain.
With ZWO, auto-exposure is done with the Allsky algorithm but auto-gain is handled by the camera, and those often fight each other so we suggest with ZWO to use auto-exposure but manual gain. That's what you have which is good.
Unlike the camera in your phone which sets the final brightness based on what Apple or Samsung think it should be, YOU must determine how bright your Allsky images are via the Target Mean. That's true for ZWO and RPi cameras.

A mean brightness of 0.98 out of 100 is almost pure black. By default, anything under 1.0 is considered "too dark" so is deleted. I suggest setting the LOW threshold to 0.5 and looking at the really dark pictures. If you like them you are done. But iIf they are too dark then increase the number until you find a LOW number you like. I think I use 0.5 for one of my cameras and 1.0 for the others.

[peng155]

Thanks @EricClaeys