Patent ID: 7259787

Claim:
A black clamp circuit for an electronic imager having black reference pixels, said circuit comprising: an input receiving the black reference pixels; an analog to digital converter outputting image pixels; an average value circuit coupled to said analog to digital converter and determining an average of a number of the black reference pixels, wherein said average value circuit comprises: an average value register outputting the average value as a group of the most significant bits of contents of the register; and a two port adder having a first port and having a second port coupled to said average value register, and adding input black reference pixels from said input to contents of said register, forming an adder accumulator with a group of the most significant bits of contents of the register; a level correction circuit coupled to said average value circuit and determining a black level from the average; a digital to analog circuit coupled to said level correction circuit; and a summing circuit coupled to said input and said digital to analog circuit, and summing the black level and image pixels.