Can anyone explain "global shutter eliminates pixelization"?

[furrysocks2]

I'm currently looking at the QHY5 III series of cameras - having played with a few webcams etc on my dob, I'm starting to try to identify something suitable for an "imaging only newt" I've got halfway built.

Of the series, the QHY5III174 appears to be the only one with a global shutter rather than a rolling shutter and quotes:

Quote

The global shutter eliminates pixelization when imaging the Planets and Moon caused by atmospheric agitation and high frame rates. 

Source: http://www.qhyccd.com/QHY5III174.html

 

Can anyone explain "pixelization" in this context?

[CraigT82]

I'm not 100% sure on it myself, but if the frame rates on a rolling shutter are slow (<30fps say) and atmospheric agitation is high, then the real image will physically distort (dues to the agitation) whilst each frame is being captured leading to artifacts in the image.

What those artifacts actually look like in a planetary image and how 'agitated' the atmosphere needs to be to produce them I don't know.

Global shutters don't suffer from this as the whole sensor is read in one 'snapshot' rather than the rolling shutter which 'scans' the image from one side to the other (or top to bottom).

EDIT: sorry just re-read and realised I haven't helped you at all!

[furrysocks2]

4 minutes ago, CraigT82 said:

... the real image will physically distort (dues to the agitation) whilst each frame is being captured leading to artifacts in the image.

What those artifacts actually look like in a planetary image and how 'agitated' the atmosphere needs to be to produce them I don't know.

Cheers, Craig.

Aye - you've got what I'm getting at in the bit I quoted above. I get the "helicopter rotor blade" analogy for moving objects, and I've seen the same "skew" if I nudge the scope while capturing.

My guess is that you could see the same data in adjacent pixels if agitation were to affect a light path such that it smeared across the sensor in sync with the progression of a rolling shutter, which I guess could be described as "pixelization"? Effectively a loss of resolution due to the temporal characteristics of capture? Not sure I quite get it yet, though.

[CraigT82]

Yes I think you're right... Data could be smeared into adjacent pixels, almost like binning dozens of pixels but without the sensitivity gain, just reduced resolution.  I guess that would look like pixelation?