[Elphel-support] Global Shutter

[Andrey Filippov]

Abe,

Also coming back to our phone conversation - there are no perfect high
resolution global shutter sensor that I know of. The high resolution global
shutter CCDs suffer from limited shutter ratio so some light gets into the
CCD registers during readout and the image snapshot is combined with the
vertically integrated signal (each pixel charge gets a little of the
photoelectrons while travelling to the output shift registers. With CMOS
sensors it might be better, but there are still problems related to the use
of the analog memory.

The advantage of the current ERS sensors is that there is no analog memory
involved in the readout process and so there are no problems with undesired
light getting to the pixels in the wrong time.

The only real solution I can see to the rolling effect should would be to
combine memory (i.e. SDRAM) on the same chip with the sensor with wide
parallel input from the sensor part, each line digitized and stored in the
memory in parallel (should be easy when they are on the same chip). Until
high performance sensors with such technology become available, I would
rather try to use the ERS sensors perfected by the huge cellphone camera
market and try to deal with undesired effects by other means.

With the ERS sensor each line is exposed at different, but precisely known
time. I was thinking of using the additional sensor (attached to the 10359
multiplexor board with the FPGA) to run a smaller rectangular area (i.e.
16-64 pixels high by full width - it will be 500-2000fps) and using the
opposite square areas (sensor ROI has to be a single rectangle) for the
"optical mouse" correlation algorithm running in the FPGA - that could
provide additional information to find out orientation of the camera with
high temporal precision. This orientation information can be applied to the
full resolution ERS image, and used to compensate the distortions in many
cases.

Andrey
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