1. A system for performing an optical navigation operation to track relative movements of a computer input device, the system comprising: a driver circuit configured to provide a drive current to a light source to produce light on a target surface; an image sensor configured to capture frames of image data of the target surface illuminated by the light; a navigation engine operably connected to the image sensor to receive the frames of image data, the navigation engine being configured to generate displacement values based on comparisons of the frames of image data; and an automatic drive current adjuster operably connected to the image sensor to receive the frames of image data, the automatic drive current adjuster comprising a frame determination unit configured to determine whether each of the frames of image data belongs to one of at least first and second types of frames of image data with respect to brightness characteristics of the frames of image data, the automatic drive current adjuster further comprising a first counter to count the frames of image data belonging to the first type of frames of image data and a second counter to count the frames of image data belonging to the second type of frames of image data, the automatic drive current adjuster being configured to direct the driver circuit to adjust the drive current to the light source depending on counts of the frames of image data belonging to the first and second types of frames of image data, wherein the automatic drive current adjuster is configured to direct the driver circuit to reduce the drive current to the light source when the count of the frames of image data belonging to the first type of frames of image data reaches a first predefined value and wherein the automatic drive current adjuster is configured to direct the driver circuit to increase the drive current to the light source when the count of the frames of image data belonging to the second type of frames of image data reaches a second predefined value, and wherein the automatic drive current adjuster is configured to reset at least one of the count of the frames of image data belonging to the first type of frames of image data and the count of the frames of image data belonging to the second type of frames of image data when at least one of the two counts is changed, wherein the automatic drive current adjuster is configured to increase the count of the frames of image data belonging to the first type of frames of image data when a frame of image data has been determined to belong to the first type of frames of image data and when the count of the frames of image data belonging to the first type of frames of image data is less than the first predefined value and wherein the automatic drive current adjuster is configured to reset the count of the frames of image data belonging to the second type of frames of image data when the count of the frames of image data belonging to the first type of frames of image data is increased.