Method and System for an Adaptive Auto-Focus Algorithm

Abstract

A method and system for auto-focusing is presented that receives an image at an image capture device, determines a focus measure of the image, and adjusts a focus of the image by moving a lens in the image capture device in a first direction until a maximum focus measure position is reached. The method and system then evaluates a noise level of the focus measure and continues to adjust the focus of the image by further moving the lens in the first direction until the focus measure is decreased by an adaptive threshold amount, wherein the adaptive threshold amount is based on the noise level of the focus measure. The method and system then adjusts the focus of the image by moving the lens in a second direction to the maximum focus measure position.

What is claimed is: 
     
         1 . A system for auto-focusing, comprising:
 an image capture device configured to receive an image;   a controller configured to determine a focus measure of the image and a noise level of the focus measure; and   a focus system configured to:
 determine an adaptive threshold based on the noise level; and 
 adjust a focus of the image by moving a lens in the image capture device until a maximum focus measure position is reached, using the adaptive threshold level. 
   
     
     
         2 . The system of  claim 1 , wherein the controller continuously determines the focus measure and the noise level of the focus measure. 
     
     
         3 . The system of  claim 1 , wherein the focus system determines the adaptive threshold for the focus measure as a multiple of the noise level of the focus measure. 
     
     
         4 . The system of  claim 1 , wherein the focus system verifies the maximum focus measure position by overshooting the maximum focus measure position by an adaptive threshold amount and then returning to the maximum focus measure position. 
     
     
         5 . The system of  claim 1 , wherein the controller determines the focus measure based on intensity. 
     
     
         6 . The system of  claim 1 , wherein the controller determines focus measure based on a summing of gradients of the image. 
     
     
         7 . A system for auto-focusing, comprising:
 an image capture device configured to receive an image;   a controller configured to determine a focus measure of the image and a noise level of the focus measure; and   a focus system configured to:
 determine an adaptive threshold for the focus measure based on the noise level of the focus measure; 
 adjust a focus of the image by moving a lens in the image capture device in a first direction until the focus measure value decreases by a value equal to the adaptive threshold; and 
 move the lens in the image capture device in a second direction. 
   
     
     
         8 . The system of  claim 7 , wherein the focus system moves the lens in the second direction until the focus measure reaches a maximum value and then decreases from the maximum value by the value equal to the adaptive threshold. 
     
     
         9 . The system of  claim 7 , wherein the focus system moves the lens in the second direction until a maximum focus measure position is reached. 
     
     
         10 . A method for auto-focusing, comprising:
 receiving an image at an image capture device;   determining a focus measure of the image;   adjusting a focus of the image by moving a lens in the image capture device in a first direction;   evaluating a noise level of the focus measure;   continuing to adjust the focus of the image by further moving the lens in the first direction until the focus measure is decreased by an adaptive threshold amount; and   adjusting the focus of the image by moving the lens in a second direction to a maximum focus measure position,   wherein the adaptive threshold amount is based on the noise level of the focus measure.   
     
     
         11 . The method of  claim 10 , wherein the evaluating a noise level of the focus measure is performed continuously. 
     
     
         12 . The method of  claim 10 , wherein the evaluating a noise level of the focus measure is performed on a periodic basis. 
     
     
         13 . The method of  claim 10 , wherein the adaptive threshold amount is continuously estimated. 
     
     
         14 . The method of  claim 10 , wherein the adaptive threshold amount is a multiple of the noise level of the focus measure. 
     
     
         15 . The method of  claim 10 , wherein an adaptive threshold is increased as a result of a decreasing illumination level of the image. 
     
     
         16 . The method of  claim 10 , wherein the determining of the focus measure is based on a light intensity. 
     
     
         17 . The method of  claim 10 , wherein the determining of the focus measure comprises summing gradients of the image. 
     
     
         18 . The method of  claim 10 , further comprising, prior to adjusting the focus of the image by moving the lens in the image capture device in the first direction until a maximum focus measure position is reached, moving the lens in the second direction, wherein the focus measure decreases. 
     
     
         19 . The method of  claim 18 , further comprising:
 upon determining that the focus measure is decreasing, adjusting the focus of the image by moving the lens in the first direction.   
     
     
         20 . The method of  claim 19 , wherein the determination that the focus measure is decreasing comprises moving the lens in the second direction until the focus measure is decreased by the adaptive threshold amount.