Can anyone advise how I can change screen resolution when using DeviceRead["RaspiCam"]

I started playing with Mathematica and a Webcam on the Raspberry Pi with a view to building a line following robot, I'm very nearly there.

The webcam worked well using << "!fswebcam -r 160x120 --no-banner /home/pi/test.jpg" the small image helped with processing speed on my old RPi but using external files also added to the processing time. If lighting was right and the line well defined the time was fairly good.

Now I've upgraded the Pi and added a PiCam. Using DeviceRead["RaspiCam"] I can see performance improvements but whilst the default resolution appears low (320x240) I wondered if we can tweak it down to what I was using before.

Thanks in advance, Colin