Patent ID: 8253090

Claim:
A method of reading voltages from an image sensor comprising an array of pixels, each pixel having at least one photodiode connectable to a storage node, the method comprising: controlling each pixel in a row of pixels to transfer charge accumulated in said photodiode above a first threshold to said storage node at the start and end of a first integration period and reading a first voltage at said storage node of each pixel in said row at the end of said first integration period; controlling each of said pixels in said row to transfer charge accumulated in said photodiode above a second threshold to said storage node at the start and end of a second integration period longer than said first integration period, and reading a second voltage value at said storage node of each pixel in said row at the end of the second integration period; controlling each pixel in a row of pixels to transfer charge accumulated in said photodiode to said storage node at the end of a third integration period longer than said first and second integration periods; comparing, for each pixel in said row, said first voltage values with a reference voltage, the reference voltage determined by reading the storage node of each pixel in said row during said first integration period; and based on said comparison, for each pixel in said row, determining a pixel output value based on said first and/or second voltage values, if said comparison indicates that transfer of charge to said storage node occurred at the end of said first integration period; and reading a third voltage value at the end of said third integration period, and determining a pixel output value based on said second and/or third voltage values, if said comparison indicates that transfer of charge to said storage node did not occur at the end of said first integration period, wherein said first integration period starts and ends during said second integration period, wherein said second integration period starts and ends during said third integration period, and wherein the second threshold used at the start and end of said second integration period is lower than the first threshold used at the start and end of said first integration period.