Method, apparatus, and system providing an imager with pixels having extended dynamic range

1. A method of operating an imager array containing a plurality of pixels, each having an associated photosensor, the method comprising:

determining for each of the pixels of the array an associated light intensity that the pixel photosensor will be exposed to during an image capture period;

assigning to each pixel one of a plurality of brightness values, each brightness value being associated with a different pixel photosensor reset timing; and

accumulating in the photosensor of each pixel a light intensity value during the image capture period and using a photosensor reset timing associated with an assigned pixel brightness value of each pixel to reset the accumulated light intensity value of the photosensor of each pixel during the image capture period,

wherein each pixel comprises a floating diffusion region for receiving charge from a photosensor through a transfer transistor, a reset transistor for resetting charge on the floating diffusion region and a photosensor reset transistor for controlling operation of the transfer transistor, the method further comprising operating the reset transistor with reset control signals to reset the floating diffusion region a plurality of times during the image capture period and operating the photosensor reset transistor to control operation of the transfer transistor such that the photosensor is reset during the image capture period by connection to the floating diffusion region at a time corresponding to a reset of the floating diffusion region by the reset transistor.

2. A method as in claim 1 , further comprising storing the brightness value assigned to each pixel of the array in memory.

3. A method as in claim 1 , further comprising grouping pixels having the same brightness value into brightness zones and storing coordinates of the brightness zones in memory.

4. A method as in claim 3 , wherein a zone having a complex shape is approximated by a shape having one of a plurality of predefined areas.

5. A method as in claim 4 , wherein the predefined areas include circles, rectangles, ovals, triangles, and annular shapes.

6. A method as in claim 2 , wherein different pixel reset timings are such that pixels having a higher brightness value have their photosensors reset later in time in the image capture period than pixels having a lower brightness value.

7. A method as in claim 1 , wherein each different photosensor reset timing has an associated time of application of a pixel photosensor reset signal during the image capture period.

8. A method as in claim 1 , wherein each pixel photosensor of the array is reset at least once at the end of an image capture period and pixels of the array which have brightness values above a lowermost brightness value also have their photosensors reset during the image capture period at a reset timing associated with the assigned pixel brightness value.

9. A method as in claim 1 , wherein the different photosensor reset timings are arranged to establish a plurality of integration periods during an image capture period corresponding to the plurality of brightness values which can be assigned to a pixel.

10. A method as in claim 1 , wherein the photosensor reset transistor operates the transfer transistor at the end of the image capture period and during a time when the floating diffusion region is not being reset by the reset transistor to produce a pixel output signal at the floating diffusion region.

11. A method as in claim 1 , wherein a plurality of pixels share a common floating diffusion region and reset transistors.

12. A method as in claim 1 , wherein the photosensor reset transistor is operative in response to a first control signal and a second control signal and wherein the first and second control signals are applied during operation of the reset transistor and during the image capture period to reset the photosensor at a timing corresponding to the assigned pixel brightness value.

13. A method as in claim 1 , wherein the number of brightness values is four.

14. A method of operating an imager array containing a plurality of pixels, each having an associated photosensor, the method comprising:

determining for each of the pixels of the array an associated light intensity that the pixel photosensor will be exposed to during an image capture period;

assigning to each pixel one of a plurality of brightness values, each brightness value being associated with a different pixel photosensor reset timing; and

accumulating in the photosensor of each pixel a light intensity value during the image capture period and using a photosensor reset timing associated with an assigned pixel brightness value of each pixel to reset the accumulated light intensity value of the photosensor of each pixel during the image capture period,

wherein each pixel comprises a floating diffusion region for receiving charge from a photosensor through a transfer transistor, a reset transistor for resetting charge on the floating diffusion region, a transistor for draining charge from the photosensor, and a photosensor reset control transistor for controlling operation of the charge draining transistor, the method further comprising operating the photosensor reset transistor during the image capture period to turn on the charge draining transistor at a timing corresponding to a brightness value associated with the pixel to thereby reset the photosensor during the image capture period.

15. A method as in claim 14 , wherein the photosensor reset transistor is operative in response to a first control signal and a second control signal and the first and second control signals are applied during the image capture period to reset the photosensor at a timing corresponding to the assigned pixel brightness value.