sCMOS camera -global vs rolling exposure? - Commercial response

[DENNIS Andrew]

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Here is an explanation of the noise in these various readout modes, there is very minimal noise difference.

If you are an advanced user and are happy dealing with light source /camera synchronisation, and you do it properly, then you can benefit from the very small noise improvement offered by rolling shutter, but if you are looking at moving objects and want simple experiment setup, like when using an Interline camera, then Global shutter is the answer.  Here is why I say this;

Historically CMOS sensors have had significantly higher read noise in global readout than rolling readout...BUT, the global shutter readout circuit in the sensor used in the Andor/PCO cameras is unique and only increases shot noise by very a small amount, these sensors have very low read noise in both readout modes.

Let's consider a practical example, say a very small amount of light falls on a pixel and results in 100 e- (the well depth is about 30,000 e-),  the shot noise on this is 10 e- RMS, rolling shutter adds 1 e- RMS and global adds 2.3 e- RMS. RMS noise is not simply added, it is added in quadrature (square both numbers, add them, then take the SQRT).

For a weak signal of 100 e- you get,
Rolling Shutter, RMS noise of 10.05 e-
Global Shutter, RMS noise of 10.26 e-

The read noise difference is basically hidden in the shot noise, and at higher light levels the contribution from read noise is even lower, there is a 0.1e- noise difference with a signal of 1000 e-.
Even at lower light levels the difference is small, at 20e- signal Rolling & Global will be 4.6 & 5.0 respectively, the difference is still very small...(In my opinion this light domain is better suited to EMCCD).

As shown there is a minimal noise difference between global and rolling shutter, and..
Global Shutter has a 100% duty cycle and it is artefact free
Rolling shutter synchronised with a light source operating at top speed would have a 50% duty cycle, and it is artefact free.

The 100% duty cycle in global shutter brings it out on top, that is unless you use Rolling Shutter with a more intense light source to compensate for the lower duty cycle, in biological applications this is typically undesirable, then you still only get the (tiny) read noise improvement. And the rolling shutter/strobe technique takes more setup synchronisation. Global Shutter is just like a typical Interline sensor readout, uses standard non pulsed/strobed lamps etc and it headache free.

Andrew

I'm very happy to answer any further questions via the listserv or by direct communication.
The read noise numbers are from the Ando Neo sCMOS camera.
[hidden email]

-----Original Message-----
From: Confocal Microscopy List [mailto:[hidden email]] On Behalf Of Andrew York
Sent: 13 August 2012 23:56
To: [hidden email]
Subject: Re: sCMOS camera -global vs rolling exposure?

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 We've some experience using the pco.edge in both global shutter and rolling-with-strobe mode. We generally don't use the pco in rolling shutter without strobe, because of the artifacts you mention. Compared to global shutter, we get higher framerates in rolling-with-strobe mode, and seem to get lower noise, although I've done nothing truly rigorous to show this.

 You can calculate how long you have to wait 'til global exposure with the
pco.edge: ~4.577 microseconds for each horizontal line in your region of interest. It's really twice this much per line, but the camera simultaneously deals with one line from the top and bottom of the chip, so effectively it's 4.577. If you're willing to work with the company's engineers, you can also get the pco.edge to indicate when all lines are exposing, vs if any lines are not exposing.

 We often use python to control our hardware, and I've written some code to talk to the pco.edge:
http://code.google.com/p/msim/source/browse/hardware_control/pco.py
 MY CODE IS NOT ROBUST CODE, IT CONTAINS KNOWN BUGS, so there isn't much here of value to the non-programmer. However, it's also the code we've used for several of our papers, so it's not worthless, either. For other python nerds, it might have some useful clues how to get the camera to perform at high frame rates. The code is open-source (GPL), so feel free to use, copy, and modify, as long as you keep it open-source.

 Overall we're extremely happy with the pco.edge, but to be clear, this is currently a camera that rewards the careful user, and can punish the casual user. A few things we learned are described in Note 3 of this document:
http://www.nature.com/nmeth/journal/v9/n7/extref/nmeth.2025-S1.pdf
I suspect the company has since addressed some of these issues, so check with them if any of these points sound like dealbreakers.

 Hope someone finds this useful.

On Sun, Aug 12, 2012 at 3:44 PM, Shalin Mehta <[hidden email]>wrote:

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>
> Hi Michael,
> We have demoed sCMOS cameras from Hamamatsu, Andor, and PCO.  I found
> that Flash 4 has better sensitivity as compared to Andor or PCO's
> cameras. I have been told by Hamamatsu's representative that the
> Micro-manager driver is very useable, but it does not handle the top
> frame-rate of Flash 4.
>
> We are still undecided and I need to understand a couple of issues
> before we make the decision.
>
> For our target application (quantitative imaging and analysis of fast
> moving specimens) the rolling shutter-only operation of Flash 4 is an
> issue. To investigate the performance of global vs. rolling exposure,
> we used Andor's Neo with the same settings in either mode. Here is a
> dark-field image of an intact sea urchin sperm beating at about 30
> waveforms per second:
> http://www.mshalin.com/interesting-data/GlobalvsRollingShutter.png
>
> From the images and intensity profiles we see that rolling shutter
> introduces motion artifacts such as skew in the shape of head and
> flagellum waveform in vertical direction. But, rolling exposure has
> visibly better sensitivity and SNR.
>
> I still don't understand the following completely. All inputs from
> community and manufacturers will be appreciated.
>
> a) How does global exposure work in Andor and PCO cameras? What
> sources of noise have increased contribution when doing global
> exposure?
>
>  b) For any camera in rolling shutter mode, we can achieve global
> exposure by strobing the light-source (such as LED or laser) so that
> * the specimen is illuminated right after all the pixels have been
> rolled active
> * the source is turned-off right before the pixels are read out in
> rolling fashion
>
> The cameras take about 10 ms 'to roll the full chip'. So if we set the
> exposure to desired global exposure + 20ms and strobe as above, it
> seems we again have global exposure. Will noise be any better with
> this custom arrangement?
>
> Thanks,
> Shalin
> website: http://mshalin.com
> (office) Lillie 110, (ph) 508-289-7374.
>
> HFSP Postdoctoral Fellow,
> Marine Biological Laboratory,
> 7 MBL Street, Woods Hole MA 02543, USA
>
>
> On Sun, Aug 12, 2012 at 1:37 PM, Cammer, Michael
> <[hidden email]> wrote:
> > We demoed an Andor Neo camera a few weeks ago and was very impressed
> with it.  We couldnt quite get the sensitivity needed for single
> molecule imaging but were very impressed by its other features.  We'd
> like to get a camera with these capabilities that we may use both with
> Nikon Elements on one microscope and with MicroManager on another
> (currently one microscope has a DU897 and we want ta bigger field and
> wider dynamic range of view for some applications and the other has decade old Orca ER).
> >
> > Two part question.
> >
> > 1.  Is anyone developing a driver for MicroManager that will take
> advantage of this camera's many many features?
> >
> > 2.  While we really liked the Andor Neo, does anybody have data or
> feelings that other sCMOS cameras out there are better-- keeping in
> mind that drivers for both software packages is also important.
> >
> > Thank you!!
> >
> > _________________________________________
> > Michael Cammer, Assistant Research Scientist Skirball Institute of
> > Biomolecular Medicine
> > Lab: [phone]  Cell: [phone]
> >
> >
> >
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