Method and apparatus for correction of an image from a fisheye lens in a camera

Abstract

A method of operating a video system includes receiving an image captured by use of a fisheye lens. The image is divided into a plurality of horizontal image lines. A respective fraction of each of the horizontal image lines is sampled with a different respective sampling frequency. Each sampling frequency is inversely related to a size of the sampled fraction. The size of the sampled fraction increases with each horizontal image line in a progression from a top of the image to a bottom of the image.

What is claimed is: 
     
         1 . A method of operating a video system, comprising the steps of:
 receiving an image captured by use of a fisheye lens;   dividing the image into a plurality of horizontal image lines; and   sampling a respective fraction of each of the horizontal image lines with a different respective sampling frequency, each sampling frequency being inversely related to a size of the sampled fraction, the size of the sampled fraction increasing with each horizontal image line in a progression from a top of the image to a bottom of the image.   
     
     
         2 . The method of  claim 1  wherein each said fraction comprises a respective middle portion of each said image line. 
     
     
         3 . The method of  claim 1  wherein the size of the sampled fraction comprises approximately one-third of the image line at the top of the image and comprises the entire image line at the bottom of the image. 
     
     
         4 . The method of  claim 1  wherein the image comprises an analog image, the method comprising the further steps of:
 converting the analog image into digital image data; and 
 converting the sampled digital image lines into a second analog image. 
 
     
     
         5 . The method of  claim 1  wherein objects at the top of the image are farther away from the lens than objects at the bottom of the image. 
     
     
         6 . The method of  claim 1  comprising the further step of discarding portions of each horizontal line that are outside of the sampled fraction. 
     
     
         7 . The method of  claim 1  comprising the further steps of:
 counting the horizontal image lines; 
 counting the number of pixels in each said image line; and 
 determining times at which to begin and end the sampling of each line, the determining being based upon each of the counting steps. 
 
     
     
         8 . A method of operating a video system, comprising the steps of:
 receiving a first analog image captured by use of a fisheye lens;   converting the analog image into digital image data;   dividing the image data into a plurality of image lines;   sampling a respective middle portion of each of the image lines with a different respective sampling frequency, each sampling frequency being inversely related to a fraction of the respective image line occupied by the middle portion, the fraction of the image line occupied by the middle portion increasing with each image line in a progression from a first edge of the image to a second edge of the image; and   converting the sampled digital image lines into a second analog image.   
     
     
         9 . The method of  claim 8  wherein each said sampling frequency is approximately between one and three times greater than a master clock frequency, and is dependent upon a distortion characteristic of the lens. 
     
     
         10 . The method of  claim 8  wherein the size of the sampled middle portion comprises approximately one-third of the image line at the first edge of the image and comprises the entire image line at the second edge of the image. 
     
     
         11 . The method of  claim 8  comprising the further step of storing the sampled digital image lines in a FIFO memory device. 
     
     
         12 . The method of  claim 8  wherein objects at the first edge of the image are farther away from the lens than objects at the second edge of the image. 
     
     
         13 . The method of  claim 8  comprising the further step of discarding portions of each horizontal line that are outside of the middle portion. 
     
     
         14 . The method of  claim 8  comprising the further steps of:
 counting the image lines; 
 counting the number of pixels in each said image line; and 
 determining times at which to begin and end the sampling of each line, the determining being based upon each of the counting steps. 
 
     
     
         15 . A method of operating a video system, comprising the steps of:
 receiving a first image captured by use of a fisheye lens;   dividing the image into a plurality of horizontal image lines, each image line having a middle portion and two lateral portions, a size of the middle portion relative to the lateral portions increasing with each horizontal image line from a top of the image to a bottom of the image;   discarding the lateral portions of the image lines;   representing each of the middle portions by a substantially equal number of samples; and   forming a second image including the samples.   
     
     
         16 . The method of  claim 15  wherein the second image includes only the samples. 
     
     
         17 . The method of  claim 15  wherein the representing step includes sampling a respective said middle portion of each of the image lines with a different respective sampling frequency, each sampling frequency being inversely related to a fraction of the respective image line occupied by the middle portion. 
     
     
         18 . The method of  claim 17  comprising the further steps of:
 counting the horizontal image lines; 
 counting the number of pixels in each said image line; and 
 determining times at which to begin and end the sampling of each line, the determining being based upon each of the counting steps. 
 
     
     
         19 . The method of  claim 17  wherein the size of the sampled middle portion comprises approximately one-third of the image line at the top of the image and comprises the entire image line at the bottom of the image. 
     
     
         20 . The method of  claim 15  comprising the further step of orienting the fisheye lens such that objects at the top of the image are farther away from the lens than objects at the bottom of the image.