System and method for focusing a digital camera

A digital camera module for capturing a single image depicting a predetermined test target at a known location and a background, the digital camera module comprising:

• an image sensor configured to operate in a focus mode in which the image sensor is configured to determine a focus quality of the single captured image based on a determined plurality of analysis regions of the single captured image, and to generate a signal relating to the focus quality, each of the analysis regions including a respectively different portion of a boundary between the predetermined test target and the background;
• and
• a lens spaced from the image sensor, wherein a distance the lens is spaced from the image sensor is adjustable based upon the focus quality of the captured image,
• wherein the image sensor analyzes the plurality of analysis regions exclusive of remaining regions in the single captured image to determine the focus quality of the single captured image such that the image sensor collectively analyzes less than 50% of the single captured image, and the plurality of analysis regions that are analyzed for focus quality and the remaining regions remaining regions that are not analyzed for focus quality are determined prior to image-capture and are based on the known location of the predetermined test target, and
• wherein the image sensor is configured to determine the focus quality by determining a variance of a spatial first derivative of the single captured image.

A focusing station for fixing the focus of a digital camera module, the focusing station comprising:

• a background;
• a predetermined test target at a known location and the background set in a predetermined spatial arrangement with the digital camera module such that the predetermined test target and background provide color contrast at each boundary between the predetermined test target and the background;
• an actuating assembly configured to interface with a barrel of a digital camera module;
• a microcontroller configured to receive focus quality signals output from the digital camera module exclusive of other signals, the focus quality signals being proporationate to a contrast for predetermined portions of respective boundaries between the predetermined test target and the background of respective images captured by the digital camera module and to determine which direction to rotate the barrel to improve the focus quality of subsequent images based on the focus quality signals received from the digital camera module,
• wherein the digital camera module determines the focus quality signals associated with the predetermined portions of the respective boundaries of a single captured image by analyzing a corresponding plurality of analysis regions encompassing the predetermined portions of the respective boundaries, collectively defining less than 50% of the single captured image, exclusive of remaining regions in the single captured image and determining a variance of a spatial first derivative of the single captured image.

A method of determining focus quality of a camera module using a predetermined test target at a known location that includes a background and at least one object on the background, the background and the at least one object having contrasting colors, the method comprising:

• capturing images of the predetermined test target with the camera module;
• defining, prior to the image-capture of the first image in a sequence of the images, a plurality of common analysis regions within the images that are to have focus quality analyzed and remaining regions within the images that are not to have the focus quality analyzed based on the known location of the test target;
• and
• analyzing analysis regions within the images to determine the focus quality of the camera module, wherein the analysis regions, exclusive of the remaining regions of the captured images, are analyzed for a highest variance of a spatial first derivative among the captured images in the analysis regions that depicts portions of the background and portions of the at least one object and the analysis regions are collectively less than the entire captured image.

A method of focusing a digital camera module with an image sensor, the method comprising:

• capturing a first image of a predetermined test target at a known location and a background with the digital camera module;
• determining a focus quality of the captured first image based on a plurality of regions of interest of the captured first image, each of the regions of interest including a respectively different portion of a boundary between the predetermined test target and the background, the determining of the focus quality of the captured first image including analyzing the plurality of regions of interest, collectively defining less than 50% of the captured image, exclusive of other regions in the captured first image;
• changing a position of a lens with respect to the image sensor within the digital camera module to adjust a focus quality of a second image to be captured;
• and
• repeating the capturing, and the determining steps for the second image, while maintaining a common size and a common position for the plurality of regions of interest which are normalized to the regions of interest of the first image based on the changed position of the lens for the captured second image, wherein
• the determining of the focus quality of the captured first image includes determining a variance of a spatial first derivative of the captured first image, and the determining of the focus quality of the captured second image includes determining a variance of a spatial first derivative of the captured second image.