Real-time exposure control for automatic light control

A method of controlling an imager comprising an array of pixels, said method comprising the acts of:

• starting an exposure period;
• obtaining pixel signals from a set of pixels in the array;
• comparing a value of each pixel signal to a reference level;
• comparing a current exposure time to a maximum exposure time;
• determining if a predetermined number of pixels have a pixel signal value greater than the reference level;
• determining a time interval for the current exposure time;
• and
• setting a readout gain to a gain between a maximum gain and a minimum gain and setting the reference level to a full scale level divided by the gain between a maximum gain and a minimum gain if it is determined that a predetermined number of pixels have a pixel signal value greater than the reference level and the current exposure time is within a predetermined time interval that spans a first time based on a preferred exposure time and a maximum gain value and a second time based on the preferred exposure time and the gain between the maximum and minimum gains.

A method of controlling an imager comprising an array of pixels, said method comprising the acts of:

• starting an exposure period;
• obtaining pixel signals from a set of pixels in the array;
• comparing a value of each pixel signal to a reference level;
• comparing a current exposure time to a maximum exposure time;
• determining if a predetermined number of pixels have a pixel signal value greater than the reference level;
• if the current exposure time is less than the maximum exposure time and the predetermined number of pixels do not have a pixel signal value greater than the reference level, the steps of obtaining pixel signals, comparing a value of each pixel signal to a reference level, comparing a current exposure time to a maximum exposure time and determining if a predetermined number of pixels have a pixel signal value greater than the reference level are repeated until the exposure time is greater than the maximum exposure time or the predetermined number of pixels do have a pixel signal value greater than the reference level;
• determining a time interval for the current exposure time;
• comparing the time interval for the current exposure time to a set of two predetermined time intervals;
• if the time interval for the current exposure time is less than both of the predetermined time intervals, setting a readout gain to a minimum gain, setting the reference level to a full scale level, and repeating the steps of obtaining pixel signals from the set of pixels in the array, comparing a value of each pixel signal to the reference level, comparing the current exposure time to the maximum exposure time until it is determined that the exposure time is greater than the maximum exposure time or the predetermined number of pixels have a pixel signal value greater than the reference level, at which point the exposure period is ended;
• if the time interval for the current exposure time is greater than both of the predetermined time intervals, setting a readout gain to a maximum gain and ending the exposure period;
• and
• if the time interval for the current exposure time is between the predetermined time intervals, setting a readout gain to a middle gain that is between the maximum gain and the minimum gain, setting the reference level to the full scale level divided by the middle gain, and repeating the steps of obtaining pixel signals from the set of pixels in the array, comparing a value of each pixel signal to the reference level, comparing the current exposure time to the maximum exposure time until it is determined that the exposure time is greater than the maximum exposure time or the predetermined number of pixels have a pixel signal value greater than the reference level, at which point the exposure period is ended.