Method and system for generating focus signal

#1. Field of the Invention

#The subject matter disclosed generally relates to auto-focusing electronically captured images.

#2. Background Information

#FIG. 1 is an illustration of an auto focus image system;

#FIG. 2 is a flowchart showing an auto-focus process;

#FIG. 3 is a schematic showing a controller of the system;

#Disclosed is an auto focus image system that includes an image sensor coupled to a controller. The image sensor captures an image that has at least one edge with a width. The controller generates a focus signal that is a function of the edge width. A lens receives the focus signal and adjust a focus. The edge width can be determined by various techniques including the use of gradients. A histogram of edge widths can be used to determine whether a particular image is focused or unfocused. A histogram with a large population of thin edge widths is indicative of a focused image.

#Referring to the drawings more particularly by reference numbers, FIG. 1 shows an embodiment of an auto-focus image system 102. The system 102 may be part of a digital still camera, but it is to be understood that the system can be embodied in any device that requires controlled focusing of an image. The system 102 may include a lens 104, an aperture 106, an image sensor 108, an A/D converter 110, a processor 112, a display 114, a memory card 116 and a lens actuator 118. Light from a scene enters through the lens 104. The aperture 106 controls the amount of light entering into the image sensor 108. The image sensor 108 generates an analog signal that is converted to a digital signal by the A/D Converter 110. The digital signal is then sent to the processor 112 that performs various processes, such as interpolation. The processor 112 generates a focus control signal that is sent to the lens actuator 118 to control both the aperture 106 and the lens 104. A focused image is ultimately provided to the display 114 and/or stored in the memory card 116. The algorithm(s) used to focus is performed by the processor 112. The image sensor 108, A/D Converter 110, and processor 112 may all reside on the same integrated circuit chip.

#FIG. 2 shows a flowchart of a process to auto-focus an image. An image is captured at the current focus position in block 202. In block 204 the image is processed to determine a focus signal, FEV. In decision block 206 the processor determines whether the image is focused based on the focus signal, FEV. If the image is deemed to be blurred, the process proceeds to block 208, where a different focus position is selected and process blocks 202, 204 and 206 are repeated. If the image is focused the process ends.