Setting pixel exposure levels based on initial row reset, calibration read, and threshold comparison operations

摘要

A method of imaging a scene with a digital image sensor comprising a pixel array comprises: performing a reset operation 500 across one row of the pixel array; integrating pixels in the row for a first calibration time; at the end of this (initial) calibration time, reading 502 pixel values of the row of pixels; comparing the pixel values with one or more predetermined thresholds (e.g., using a DAC ramp, stepped according to the threshold levels); and setting subsequent exposure levels for pixels in the pixel array based upon the pixel values. Thus, a signal is read out for a selection of pixels which acts as a calibration to govern the choice of exposure levels to be applied to the rest of the array, meaning the sensor can adapt to variations in scene intensity, improving dynamic range. Array pixels can also be vertically and horizontally addressed, enabling small areas of intensity variation across an imaged scene to be accounted for. The exposure levels can be stored as decision data, subject to low pass filtering (LPF) and controlling analogue readout circuit gain; only decision data changes applying from one pixel to another may be stored.