Vehicle occupant monitoring system including an image acquisition device with a rolling shutter image sensor

A vehicle occupant monitoring system, OMS, comprising:

• an image acquisition device with a rolling shutter image sensor comprising an array of sub-pixels which are respectively selectively sensitive to:
• red and infra-red;
• blue and infra-red;
• and green and infra-red light, said device being configured to selectively operate in either:
• a colour mode where a multi-plane image frame corresponding to the full image sensor is provided, each plane derived from red, green or blue sensitive sub-pixels respectively;
• or a monochrome mode, where sensor information from sub-pixels is aggregated to provide a single image plane;
• and
• a controller:
• responsive to detecting light conditions decreasing when operating in a first colour mode to swap to a first monochrome mode for a first subsequent image acquisition;
• responsive to the detecting light conditions increasing when operating in the first monochrome mode to swap to a second colour mode for a second subsequent image acquisition;
• responsive to the detecting light conditions decreasing when operating in the second colour mode to increase either exposure time or gain for a third subsequent image acquisition;
• and responsive to detecting light conditions increasing when operating in the first monochrome mode to decrease either exposure time or gain for a fourth subsequent image acquisition.