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 comprising an image sensor and a lens assembly having a varying transmissivity across a field of view of the image sensor, wherein the image acquisition device comprises a rolling shutter image sensor, said device being configured to selectively operate in either:
• a full resolution image mode where an image frame corresponding to the full image sensor is provided;
• or a region of interest (ROI) mode, where an image frame corresponding to a limited portion of a limited number of rows of the image sensor is provided, wherein the full resolution image mode is selected by a face detector when a new location for an ROI bounding the vehicle occupant's face is required when facial features of the vehicle occupant's face within the image frame are not detected due to the vehicle occupant's face moving within a field of view of the image acquisition device;
• at least one infra-red, IR, light source disposed within a cabin of said vehicle and being configured to illuminate at least one occupant of the vehicle with varying illumination across the field of view of the image sensor;
• and
• an image processing pipeline configured to obtain and pre-process an image acquired from said image sensor in accordance with a lens shading map and a cabin illumination map in order to compensate for both said varying transmissivity and said varying illumination in order to provide a more uniformly illuminated image to a controller for further analysis.