ZWO ASI174MM-COOL binning, bit-depth

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ProtoBrian
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Joined: Fri Jul 07, 2017 1:35 pm

ZWO ASI174MM-COOL binning, bit-depth

Post by ProtoBrian » Fri Jul 07, 2017 1:41 pm

Hi,
I am trying to use 2x binning on my ZWO ASI174MM-COOL camera in 16-bit mode, but my results always look identical to 1x binning mode.

I've tried 8-bit mode and seen a massive brightness increase in 2x bin over 1x bin, as expected, but see no difference in 16-bit mode. I've processed my PNGs in several programs (ImageJ and Photoshop CS) and cannot tell the difference.

Would this be a SharpCap bug or unsupported feature of the camera? (I realize the camera is actually only 12-bit).

I've tried in SharpCap 3.0 as well as 2.9.

Kind regards,

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Re: ZWO ASI174MM-COOL binning, bit-depth

Post by admin » Fri Jul 07, 2017 5:00 pm

Hi,

this is actually as-designed. There are two ways to do binning (2x2 for example)

1) add up the value of the four pixels to give the value of the new pixel.

2) average the value of the four pixels to give the value of the new pixel.

Both give the same improvement in the image (increase in signal-to-noise ratio), but in different ways...

Option 1) increases the signal by a factor of 4 and increases the noise by a factor of 2, net gain in S/N ratio = 2.
Option 2) leaves the signal the same but reduces the noise by a factor of 2 - net gain in S/N again a factor of 2.

From memory the ZWO cameras do average binning in 16 bit mode. If you want a brighter image then just turn up the gain. Turning up the gain adds more noise but you have already reduced the noise by a factor of 2 by binning, so you can afford to do that.

cheers,

Robin

ProtoBrian
Posts: 2
Joined: Fri Jul 07, 2017 1:35 pm

Re: ZWO ASI174MM-COOL binning, bit-depth

Post by ProtoBrian » Fri Jul 07, 2017 5:26 pm

Thanks Robin,

I didn't realize they could use 2 different modes. I suppose that would be good for "normal" users. (I'm actually using it for a non-astrophotography use)

Unfortunately for me, my signal is very weak, so I already have a high gain. My camera noise is far less than my source noise (image intensifier), so I couldn't see the difference between 16 bit 1x bin and 16 bit 2x bin, though I will look more closely at it.

Thanks again

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