The IMX236 and IMX290 sensor turn into Global Reset Shutter mode, if trigger mode is enabled. Therefore, the image may is over exposed or it becomes brighter from top to bottom.  That means, the lines of the sensor are light sensitive from trigger pulse until they are readout and transferred to the computer. The readout time is determined by the frame rate. If the frame rate is e.g. 30 fps, then the whole sensor is readout within 33 ms  from top to bottom. That means, the last lines are exposed over 33ms in this case.