CMOS active pixel sensor with improved dynamic range and method of operation for object motion detection
A CMOS imaging array includes a plurality of individual pixels arranged in rows and columns. Each pixel is constructed the same and includes a photodetector (e.g., photodiode) receiving incident light and generating an output. A first, relatively lower gain, wide dynamic range amplifier circuit is provided responsive to the output of the photodetector. The first circuit is optimized for a linear response to high light level input signals. A second, relatively higher gain, lower dynamic range amplifier circuit is also provided which is responsive to the output of the photodetector. The second circuit is optimized to provide a high signal to noise ratio for low light level input signals. Subtraction of output signals from the amplifier circuits, preferably after gain compensation, can be used to detect moving objects in the scene where the integration times for the two circuits are not the same, e.g., are staggered in time or have a different period.
1. A method of detecting motion in a scene with an imaging array having a plurality of pixels, the array capable of generating two images in a single exposure of the array to scene radiation, comprising the steps of:
during the single exposure of the array, simultaneously in each pixel collecting a first image and a second image, wherein the first image and the second image are associated with image integration times within the single exposure which are not the same;
subtracting the first image from the second image to obtain a difference signal; and
detecting motion in the scene from the difference signal.
2. The method of claim 1 , wherein the integration time associated with the first and second images are staggered in time relative to each other.
3. The method of claim 1 , wherein the integration time associated with the first and second images commences at the same time but the duration is not the same.
4. The method of claim 1 , further comprising the step of determining pixel addresses for all pixels in which a moving object is detected.
5. The method of claim 4 , further comprising the step of determining the direction and velocity of the moving object using the pixel addresses and optical parameters of a camera incorporating the imaging array.
6. A method of detecting motion in a scene with an imaging array having a plurality of pixels, the array capable of generating two images in a single exposure of the array to scene radiation, comprising the steps of:
during the exposure of the array, in each pixel collecting a first image and a second image, wherein the first image and the second image are associated with image integration times which are not the same;
subtracting the first image from the second image to obtain a difference signal; and
detecting motion in the scene from the difference signal;
wherein the first image results from an output signal from a first relatively lower gain, wide dynamic range amplifier circuit responsive to the output of a photodetector, the first circuit optimized for a linear response to high light level input signals; and
wherein the second image results from an output signal from a second relatively higher gain, lower dynamic range amplifier circuit responsive to the output of the photodetector, the second circuit optimized to provide a high signal to noise ratio for low light level input signals.
7. The method of claim 6 , wherein the integration time associated with the first and second images are staggered in time relative to each other.
8. The method of claim 6 , wherein the integration time associated with the first and second images commences at the same time but the duration is not the same.
9. The method of claim 6 , further comprising the step of determining pixel addresses for all pixels in which a moving object is detected.
10. The method of claim 9 , further comprising the step of determining the direction and velocity of the moving object using the pixel addresses and optical parameters of a camera incorporating the imaging array.
11. A method of detecting motion in a scene with an imaging array having a plurality of pixels, the array capable of generating two images in a single exposure of the array to scene radiation, comprising the steps of:
during the exposure of the array, in each pixel collecting a first image and a second image, wherein the first image and the second image are associated with image integration times which are not the same;
subtracting the first image from the second image to obtain a difference signal; and
detecting motion in the scene from the difference signal;
wherein the imaging array comprises a CMOS imager with at least one detector per pixel and two output circuits, one for generating the first image and the other for generating the second image.
12. The method of claim 11 , wherein the integration time associated with the first and second images are staggered in time relative to each other.
13. The method of claim 11 , wherein the integration time associated with the first and second images commences at the same time but the duration is not the same.
14. The method of claim 11 , further comprising the step of determining pixel addresses for all pixels in which a moving object is detected.
15. The method of claim 14 , further comprising the step of determining the direction and velocity of the moving object using the pixel addresses and optical parameters of a camera incorporating the imaging array.