Image capturing device for auto exposure

An image capturing device, comprising:

• an image sensing circuit;
• and
• a processing circuit electrically connected to the image sensing circuit and configured to control the image sensing circuit to sense a first partial frame before sensing a full frame, wherein a number of pixels of the first partial frame is less than a number of pixels of the full frame, and exposure time of the first partial frame is shorter than exposure time of the full frame,
• wherein the processing circuit performs an automatic exposure procedure according to the first partial frame to calculate a first fast exposure parameter,
• wherein the processing circuit determines if a difference between an average of a plurality of signal levels of the first partial frame and a predetermined value is in a predetermined range,
• wherein if the difference between the average of the signal levels of the first partial frame and the predetermined value is in the predetermined range, the processing circuit transforms the first fast exposure parameter into an exposure parameter comprising the exposure time of the full frame,
• wherein if the difference between the average of the signal levels of the first partial frame and the predetermined value is not in the predetermined range, the processing circuit controls the image sensing circuit to sense at least one second partial frame according to the first fast exposure parameter, calculates at least one second fast exposure parameter according to the at least one second partial frame until a difference between an average of signal levels of the at least one second partial frame and the predetermined value is in the predetermined range, and transforms the at least one second fast exposure parameter into the exposure parameter,
• wherein the processing circuit controls the image sensing circuit to sense the full frame according to the exposure parameter.