Image sensor based vignetting correction

Abstract

A method and apparatus for constructing an inexpensive camera with vignetting correction in the camera electronic hardware. The hardware is programmable through the use of a register storing a constant value corresponding to the amount of vignetting of a particular lens used in the camera. The register value is provided to a correction circuit which implements an algorithm that corrects for the amount of vignetting of pixels depending upon the pixel position.

1 . A method for manufacturing a camera which connects to a computer, comprising: 
 determining a vignetting effect of a first lens;    installing said first lens in a first camera housing;    determining a vignetting effect of a second lens;    installing said second lens in a second camera housing;    installing in each housing a photosensor array mounted behind said lens;    coupling an analog processing circuit to each said photosensor array;    coupling an analog to digital converter to each said analog processing circuit;    coupling a digital processing circuit to an output of each said analog to digital converter, said digital processing circuit including    a register for storing a constant corresponding to a vignetting rating of said lens,    a correction circuit, coupled to said register, for adjusting a value of selected pixels according to a formula using said constant, to correct for vignetting of said lens;    coupling a bus interface circuit to an output of each said digital processing circuit for connecting to a bus for transfer of data to said computer;    storing a first constant in said register in said first camera housing, said first constant corresponding to said vignetting effect of said first lens;    storing a second constant in said register in said second camera housing, said second constant corresponding to said vignetting effect of said second lens.    
   
   
       2 . The method of  claim 1  wherein said correction circuit does not adjust the value of pixels within a selected distance of a center of said lens.  
   
   
       3 . The method of  claim 1  wherein said correction circuit also corrects for a pixel aspect ratio.  
   
   
       4 . The method of  claim 1  wherein said constant has a number of bits equal to a number of bits used to represent a brightness of said selected pixels.  
   
   
       5 . The method of  claim 1  wherein said correction circuit further comprises a scaling input for scaling said constant.  
   
   
       6 . A camera for connecting to a computer, comprising: 
 a lens;    a photosensor array mounted behind said lens;    an analog processing circuit coupled to said photosensor array;    an analog to digital converter coupled to said analog processing circuit;    a digital processing circuit coupled to an output of said analog to digital converter, said digital processing circuit including    a register for storing a constant corresponding to a vignetting rating of said lens,    a correction circuit, coupled to said register, for adjusting a value of selected pixels according to a formula using said constant, to correct for vignetting of said lens; and    a bus interface circuit coupled to an output of said digital processing circuit for connecting to a bus for transfer of data to said computer.    
   
   
       7 . The camera of  claim 6  wherein said correction circuit does not adjust the value of pixels within a selected distance of a center of said lens.  
   
   
       8 . The camera of  claim 6  wherein said correction circuit also corrects for a pixel aspect ratio.  
   
   
       9 . The camera of  claim 6  wherein said constant has a number of bits equal to a number of bits used to represent a brightness of said selected pixels.  
   
   
       10 . The camera of  claim 6  further comprising a scaling input to said correction circuit, for scaling said constant.