Methods for enhancing quality of pixel sensor image frames for global shutter imaging
AssigneeInernational Business Machines Corporation
InventorsJohn J. Ellis-Monaghan, Mark D. Jaffe
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Abstract
The image quality of an image frame from a CMOS image sensor array operated in global shutter mode may be enhanced by dispersing or randomizing the noise introduced by leakage currents from floating drains among the rows of the image frame. Further, the image quality may be improved by accounting for time dependent changes in the output of dark pixels in dark pixel rows or dark pixel columns. In addition, voltage and time dependent changes in the output of dark pixels may also be measured to provide an accurate estimate of the noise introduced to the charge held in the floating drains. Such methods may be employed individually or in combination to improve the quality of the image.
Claims8
A method of operating an array of pixel sensor cells comprising:
- exposing an entirety of an array of pixel sensor cells, wherein each of said pixel sensor cells contains a light conversion unit and a floating drain;
- simultaneously transferring electrical charges from said light conversion unit to said floating drain in each of said array of pixel sensor cells;
- sensing said electrical charges in said floating drains one row at a time and for each row in said array to generate raw pixel values for each pixel sensor cell;
- measuring pixel values for dark pixels and generating wait-time-dependent background signal values for said array of pixel sensor cells, wherein said wait-time-dependent background signal values are dependent on a row read wait time for each row;
- and
- generating a set of noise-compensated pixel values by subtracting a corresponding wait-time-dependent background signal value from each of said raw pixel values.
A method of operating an array of pixel sensor cells comprising:
- exposing an entirety of an array of pixel sensor cells, wherein each of said pixel sensor cells contains a light conversion unit and a floating drain;
- simultaneously transferring electrical charges from said light conversion unit to said floating drain in each of said array of pixel sensor cells;
- sensing said electrical charges in said floating drains one row at a time and for each row in said array to generate raw pixel values for each pixel sensor cell;
- measuring pixel values for dark pixels and generating wait-time-dependent background signal values for said array of pixel sensor cells;
- and
- generating a set of noise-compensated pixel values by subtracting a corresponding wait-time-dependent background signal value from each of said raw pixel values, wherein said dark pixels are located in an array of dark pixel rows and dark pixel columns interspersed among said array of pixel sensor cells, wherein said wait-time-dependent background signal values comprises an interpolated time-dependent map spanning said array of pixel sensor cells, and wherein said corresponding wait-time-dependent background signal value is interpolated from said interpolated time-dependent map.
Dependencies are inferred from the claim text.