The present invention relates to image sensors for use in digital cameras.
In general, aberrations that are present in images taken by digital cameras are normally not compensated for in low end digital cameras. Alternatively, such aberrations may be post-processed after recording to remove them, which is done in some more-expensive digital cameras.
Canon and Nikon digital cameras move lens elements to adjust for camera shaking. For example, this is done in Canon's Image Stabilization series of cameras and Nikon's VR series of cameras. However, manufacturing tolerances, for example, still produce some aberrations.
A Minolta DiMage A1 camera has an image stabilization mechanism that moves a charge coupled device (CCD) sensor. This mechanism moves the entire sensor along x and y axes and does not use any intra-pixel movement. In addition, U.S. patent application No. 2002/0028071 (Claus Molgaard) describes how accelerometers can be used to discover camera motion. That application discusses how this can be either recorded or trigger an alarm, and in paragraph 0021, reference is made to compensation that may be performed by image processing or physically moving the sensor.
Applicants are not aware of any embodiment of a digital camera having a sensor that is flexed to adjust for aberrations.
The present invention comprises systems embodied in a digital camera, or image capture device, that provide for a thin, flexible image sensor that is flexed to correct for sensor aberrations and lens deformities. In implementing the present invention, a thin deformable or flexible image sensor is used, and small deformations (strain deformation) of the sensor are made by an array of (piezoelectric) attachments on the back side of the sensor. These attachments are pushed and pulled using digital control such that small variations in the flatness of the sensor can be effected. This allows for correction of field flatness and some other lens aberrations. A variation of the present invention allows adjustment in gross levels, where the resulting sensor need not be approximately flat, and may be tilted, or deformed into concave or convex shapes, for example, to correct for such an irregularity.
The present invention implements a technique that is similar to one used in large telescopes to implement small mirror deformations. The deformation ability there is used not only to correct for fixed aberrations but also dynamically for atmospheric, temperature, and other changes. The difference with regard to the present invention is that image and video capture devices, such as cameras, do not use mirrors such as are used in catadioptric telescopes, but instead lenses and digital sensors.
The various features and advantages of embodiments of the present invention may be more readily understood with reference to the following detailed description taken in conjunction with the accompanying drawings, wherein like reference numerals designate like structural elements, and in which:
a and 1b are rear and front views, respectively, of an exemplary digital camera employing a flexible image sensor in accordance with the principles of the present invention; and
Referring to the drawing figures,
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An image sensor 11 in accordance with the present invention is coupled to processing circuitry 12 (illustrated using dashed lines) that are housed within the body section 30, for example. An exemplary embodiment of the processing circuitry 12 comprises a microcontroller (μC) 12 or central processing unit (CPU) 12. The (μC 12 or CPU 12 is typically coupled to a nonvolatile (NV) storage device 14, such as flash memory 14, for example, and a high speed (volatile) storage device 15, such as synchronous dynamic random access memory (SDRAM) 15, for example.
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The processing circuitry 12, 12a (microcontroller (μC) 12, 12a or CPU 12, 12a) in the digital camera 10, embodies firmware 13 comprising one or more algorithms 13 in accordance with the principles of the present invention. The firmware 13 or algorithm 13 is operative to control movement or deformation of the attachments 17 or piezoelectric devices 17, to vary the flatness of the image sensor 11.
This allows for correction of field flatness and certain lens aberrations. Alternatively, the image sensor 11 may be adjusted in gross terms, so that the image sensor 11 need not be approximately flat, and may be tilted or deformed into concave or convex shapes to correct for optical abnormalities. Thus, the sensor 11 need not be approximately flat, and may be tilted, or deformed into concave or convex shapes, for example.
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A relatively thin image sensor 11, such as a charge coupled device (CCD), for example, is used in an image capture device, such as a digital camera. The image sensor 11 is thin enough so that a small array of attachments 17 on its back side can easily flex the sensor 11 to provide for small variations in flatness. These controlled variations correct for aberrations such as propagation delay, and angle of refraction that result from the way the light is captured through the lens 41.
This technique not only allows for correction of aberrations caused by the lens 41 but also can correct for inconsistencies in the manufacturing process of the image sensor 11, camera body (body section 30), or lens mount 41a.
The lens mount is where the lens attaches to the body of the camera 10 and is typically a close tolerance area—meaning that production dimensions should be precise and distances from this mount to the film/sensor should be maintained very accurately. Allowing some movement of the sensor allows these tolerances to be loosened (or any existing irregularity to be fine-tuned) as long as there is a method to find the correct distance.
For example, if the image capture device had the image sensor 11 attached slightly unevenly, this would normally result in the product being rejected. With a sensor 11 that can be flexed, firmware 13 in the processing circuitry 12, 12a may be used to set a default sensor position to correct for this manufacturing defect, and the net result would only be the device's inability to compensate as much for lens aberrations. Lens distance tolerances may be relieved, or the resulting performance improved, by allowing the entire sensor to move slightly forward or back by appropriately controlling the attachments 17.
Also, changing the resulting image using lens settings produces barrel and pincushion spatial distortions. A typical zoom lens 41 will produce barrel distortion at wide angle position and pincushion distortion in telephoto position. By producing compensating distortion in the image sensor 11 by appropriately controlling the attachments 17, the end result is that some of this distortion is removed.
Lastly, the present invention can be used in high end instruments such as astrophotography sensors, for example. Typically, in high end instruments that include a mirror in the optical path, the mirror must be modified to compensate for distortion. By using the present invention, the mirror can be unchanged or the mirror and sensor can work in tandem to allow faster compensations (due to the sensor size compared to the mirror size), or more compensation may be achieved compared with what is achievable with just one adaptive device.
The present invention allows for imaging devices, such as digital cameras 10, to correct physically for aberrations instead of relying on post processing to correct. The present invention also allows a manufacturer to have a wider tolerance for defects in production of both the imaging device and the lenses.
Thus, improved digital cameras having a deformable image sensor has been disclosed. It is to be understood that the above-described embodiments are merely illustrative of some of the many specific embodiments that represent applications of the principles of the present invention. Clearly, numerous and other arrangements can be readily devised by those skilled in the art without departing from the scope of the invention.