MEMS fast focus camera module
An auto focus camera module includes a camera module housing defining an aperture and an internal cavity to accommodate camera module components, an image sensor coupled to or within the housing, a lens barrel within the housing that contains an optical train including at least one movable lens disposed relative to the aperture and image sensor to focus images of scenes onto the image sensor along an optical path, and a fast focus MEMS actuator coupled to one or more lenses of the optical train including the at least one movable lens and configured to rapidly move said at least one movable lens relative to the image sensor to provide autofocus for the camera module in each frame of a preview or video sequence or both.
1. An auto focus camera module, comprising:
a camera module housing defining an aperture and an internal cavity to accommodate camera module components;
an image sensor coupled to or within the housing;
a lens barrel within the housing that contains an optical train including at least one movable lens disposed relative to the aperture and image sensor to focus images of scenes onto the image sensor along an optical path; and
a fast focus MEMS actuator comprising at least one electrostatic comb drive and coupled to one or more lenses of the optical train including the at least one movable lens and configured to rapidly move said at least one movable lens relative to the image sensor to provide autofocus for the camera module in each frame of a preview or video sequence or both, wherein the fast focus MEMS actuator is configured to alternately auto focus on two or more regions of interest, such that each region of interest is refocused every respective two or more frames of the preview or video sequence or both.
2. The camera module of claim 1 , wherein the fast focus MEMS actuator is configured to move the at least one moveable lens from a first position for a first one of the frames to a second position for a second, subsequent one of the frames to reliably refocus for the second subsequent frame within approximately 33 ms.
3. The camera module of claim 1 , comprising a face tracking module that is configured to predict a location of a face region of interest in a future frame permitting the auto focus camera module to focus on the region of interest quickly.
4. The camera module of claim 1 , comprising a face detection module that is configured to apply multiple short classifier chains in parallel to one or more windows of an image frame.
5. The camera module of claim 1 , wherein the two or more regions of interest comprise two or more sub-regions of a face.
6. The camera module of claim 1 , comprising a face recognition module that is configured to identify and prioritize one or more faces that correspond to one or more specific persons.
7. The camera module of claim 1 , wherein the fast focus MEMS actuator is further configured to move the at least one movable lens relative to the image sensor to provide local focus on multiple regions of interest within a common image frame.
8. The camera module of claim 7 , wherein the fast focus MEMS actuator is configured to cease lens motion during exposure of a first set of pixels in the common image frame, move the at least one movable lens between the exposure of the first set of pixels and exposure of a second set of pixels in the common image frame, and cease lens motion during the exposure of the second set of pixels.
9. The camera module of claim 1 , wherein the optical train comprises:
first and second fixed lenses disposed on a first side of the at least one moveable lens;
third and fourth fixed lenses disposed on an opposing second side of the at least one moveable lens; and
wherein the fast focus MEMS actuator is formed from silicon or a substantially polymeric material and has a stroke of approximately 100 microns.
10. A method, comprising:
providing a camera module housing defining an aperture and an internal cavity to accommodate camera module components;
providing an image sensor coupled to or within the housing;
providing a lens barrel within the housing that contains an optical train including at least one movable lens disposed relative to the aperture and image sensor to focus images of scenes onto the image sensor along an optical path;
providing a fast focus MEMS actuator including at least one electrostatic comb drive coupled to one or more lenses of the optical train including the at least one movable lens and configured to move said at least one movable lens relative to the image sensor to provide autofocus for the camera module in each frame of a preview or a video sequence or both; and
operating the fast focus MEMS actuator to alternately auto focus on two or more regions of interest, such that each region of interest is refocused every respective two or more frames of the preview or video sequence or both.
11. The method of claim 10 , further comprising moving, with the fast focus MEMS actuator, the at least one moveable lens from a first position for a first one of the frames to a second position for a second subsequent one of the frames to reliably refocus for the second subsequent frame within approximately 33 ms.
12. The method of claim 10 , further comprising providing a face tracking module that is configured to predict a location of a face region of interest in a future frame permitting the auto focus camera module to focus on the region of interest quickly.
13. The method of claim 10 , further comprising providing a face detection module that is configured to apply multiple short classifier chains in parallel to one or more windows of an image frame.
14. The method of claim 10 , wherein the two or more regions of interest comprise two or more sub-regions of face.
15. The method of claim 10 , further comprising providing a face recognition module that is configured to identify and prioritize one or more faces that correspond to one or more specific persons.
16. The method of claim 10 , further comprising operating the fast focus MEMS actuator to move the at least one movable lens relative to the image sensor to provide local focus on multiple regions of interest within a common image frame.
17. The method of claim 16 , wherein the operating comprises:
ceasing lens motion during exposure of a first set of pixels in the common image frame;
moving the at least one movable lens between the exposure of the first set of pixels and exposure of a second set of pixels in the common image frame; and ceasing lens motion during the exposure of the second set of pixels.
18. The method of claim 10 , wherein the optical train comprises:
first and second fixed lenses disposed on a first side of the at least one moveable lens;
third and fourth fixed lenses disposed on an opposing second side of the at least one moveable lens; and
wherein the fast focus MEMS actuator is formed from silicon or a substantially polymeric material and has a stroke of approximately 100 microns.