Auto Exposure Techniques for Variable Lighting Conditions

An auto exposure system comprising:

• an image sensor for capturing an image representative of a scene;
• a memory coupled to the image sensor;
• and
• a programmable control device communicatively coupled to the image sensor and the memory, wherein the memory includes instructions for causing the programmable control device to perform an auto exposure method on image information received from the image sensor, the method comprising:
• defining an exposure metering region over a desired area of the image;
• calculating a weighted average value for the exposure metering region;
• calculating a magnitude of the difference between the calculated weighted average value and a predetermined target value;
• multiplying the calculated magnitude of the difference between the weighted average value and the predetermined target value by a predetermined step size factor, wherein the result of the multiplication comprises a first step size value;
• and
• adjusting an exposure parameter for the image sensor based at least in part on the magnitude of the first step size value.

A mobile videoconferencing method comprising:

• receiving image information representative of the physical scene and comprising a plurality of pixels from an image sensor at a near-end videoconferencing unit;
• defining an exposure metering region that is centered over the image information;
• adjusting an exposure parameter for the image sensor based at least in part on a comparison of luminance values of pixels in the exposure metering region to a predetermined target luminance value;
• encoding the received image information into a video stream;
• and
• sending the encoded video stream to a far-end videoconferencing unit.

A method of auto exposing a physical scene comprising:

• receiving a first image frame from an image sensor, wherein the first image frame comprises information representative of the physical scene and comprising a plurality of pixels;
• defining an exposure metering region that is centered over the first image frame;
• adjusting an exposure parameter for the image sensor based at least in part on a calculated step size value, wherein the calculated step size value is based at least in part on a comparison of a weighted average of pixel luminance values in the exposure metering region centered over the first image frame to a predetermined target luminance value;
• receiving a second image frame from an image sensor, wherein the second image frame comprises information representative of the physical scene and comprising a plurality of pixels;
• and
• defining an exposure metering region that is centered over the second image frame,
• wherein the second image frame is representative of the physical scene at a later point in time than the first image frame, and
• wherein the magnitude of the adjustment to the exposure parameter is configured such that a weighted average of pixel luminance values in the exposure metering region of the second image frame differs from the weighted average of pixel luminance values in the exposure metering region of the first image frame by the step size value.