NiNeff is correct, the image sensor digitizes an entire row at once and then reads it out 16-pixels at a time to the FPGA. While the first row is being read out to the FPGA, the second row of the image can then be digitized. The time that it takes to digitize a row can be adjusted by playing with the timing parameters of the image sensor but reducing the time allowed for this operation causes a loss of image quality.
The fastest framerate at any resolution is achieved when the row readout time is equal to the row digitization time, so that we minimize the time that the image sensor is idle. And the best quality is achieved when the row readout time is long enough to allow for the maximum digitization timing (approximately 922us per row).
On the 0.3.1 release of the Chronos 1.4, the fastest row digitization time is approximately 255us, which is equal to the time it takes to read out 336 pixels. This is why there is no performance benefit to reducing the horizontal resolution below 336 pixels. On the 0.3.2 release we have managed to reduce this time to 244us, which is why we now list 320x96 as the minimum resolution for that release.
