Optical: systems and elements – Single channel simultaneously to or from plural channels – By surface composed of lenticular elements
Reexamination Certificate
1999-10-13
2001-10-23
Mack, Ricky (Department: 2873)
Optical: systems and elements
Single channel simultaneously to or from plural channels
By surface composed of lenticular elements
C359S620000
Reexamination Certificate
active
06307680
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to optical filtering and more particularly to an optical blurring filter for intentionally introducing a desired degree of optical blurring into a camera so as to comply with resolution limits such as those specified by a treaty.
BACKGROUND OF THE INVENTION
The use of aerial photography in surveillance applications is well known. Typically, an aircraft flies over the desired area and photographs the ground utilizing equipment and techniques which tend to optimize the resolution of the resulting photographs. Such optimization of the resolution of the photographs is typically desirable so as to enhance the photointerpreters ability to accurately and reliably determine the content of the photographs.
However, in some instances, it is desirable to limit the resolution of the photographs obtained from aerial photography and the like. One instance where such resolution limitation is desirable is when such aerial photography is being performed according to a treaty which specifies the maximum, i.e., best, resolution, with which such photographs may be taken. For example, the Open Skies Treaty limits the ground resolution of aerial photography performed according thereto to 30 cm.
Thus, in order to comply with such a treaty, or so as to otherwise limit the resolution of a camera or other optical instrument, it is desirable to provide means for blurring photographs which is low cost, easy to use, and verifiable according to the terms of the treaty, if any.
It is further desirable that such means for limiting the resolution of pictures not require the blurring process take place after an original image is created. The reason is that the original must be disposed of in a secure manner. Those skilled in the art will appreciate that if the original image is formed at full resolution and after that a second image is generated therefrom at the desired resolution, such procedure makes it possible for some people to have access to the original, full resolution image. Thus, it is desirable to provide means for limiting the resolution of a camera such that only a degraded, i.e. resolution limited, image is formed.
It is further desirable that any such resulting resolution limited image not be capable of digital resolution enhancement. Thus, the image must be degraded in a manner which introduces substantially random noise so as to avoid subsequent reconstruction of an imaging having greater resolution than that of the original blurred image.
SUMMARY OF THE INVENTION
The present invention specifically addresses and alleviates the above mentioned deficiencies associated with the prior art. More particularly, the present invention comprises an optical blurring filter for intentionally blurring camera images, the filter comprising a generally transparent material and a plurality of optical distortions formed in the transparent material. The optical blurring is done in a place where there is control of the amount of blurring as a function of position in the film plane. Placement of the transparent material in front of a wide angle camera lens, e.g., where filters are typically positioned, effects this control. According to the preferred embodiment, such image blurring is performed in a manner which substantially mitigates the possibility and amount of subsequent digital reconstruction of the image at its original resolution. Also, no full resolution image is created in the process which might subsequently escape destruction.
The optical blurring filter comprises a transparent material having a plurality of optical distortions formed therein. The optical distortions are formed so as to have substantially random point spread functions throughout the image. The point spread functions have a width and a shape which causes a predetermined degree of blurring, so as to provide a desired loss of resolution which is similar to the loss of resolution which results when the altitude of an aerial camera is increased above the scene being photographed.
According to a first embodiment of the present invention, the optical distortions preferably are caused by lenslets.
The transparent material preferably comprises a sheet of transparent material, which is formed into a filter configuration such that it may be mounted to a camera in a manner similar to that in which colored and effects filters are typically mounted to the camera.
According to the preferred embodiment of the present invention, the transparent material comprises glass. However, those skilled in the art will appreciate that various other transparent materials are likewise suitable. For example, various different polymers, plastics, acrylics, minerals (e.g., diamond, quartz), may likewise be utilized.
The optical distortions are formed in a gradient on the transparent material and positioned in front of the aperture stop to provide greater resolution reduction on one side than on the other side. This is of value when performing oblique photography where treaty limits ground resolution. This can compensate for the inherently greater resolution of the near side of an image according to contemporary methodology for performing oblique photography.
In a similar manner, optical distortions formed in the transparent material are formed so as to provide greater blurring in selected directions through the lens so as to compensate for areas of greater resolution of the camera. For example, camera lenses typically provide better resolution on-axis, where aberrations of the lens are typically at their lowest value. By providing greater blurring for angles near the lens axis the resolution of the photographic image will tend to be more uniform.
According to a first preferred embodiment of the present invention, the optical distortions occur in a lenticular filter. As used herein, the term lenticular filter is defined to include a generally planar sheet of material having a plurality of lenslets formed thereon.
Thus, according to the first embodiment of the present invention, the optical distortions are preferably created by a lenticular filter which comprises a plurality of small lenses or lenslets formed in a generally transparent material. The lenses are preferably formed such that a photograph taken therewith is formed only with light which was transmitted through at least one of the lenses. Thus, the blurring can be created by introducing a few lenslets which distort only a portion of the imaging light. Alternatively, all of the light can be distorted. The lenses are preferably formed to have lens powers randomly selected according to a Gaussian or any other distribution about a selected power. Preferably, the lenses are formed so as to substantially overlap one another on the surface of the transparent material.
Optionally, the lenticular filter comprises a plurality of lenslets wherein each lenslet has a generally circular or elliptical periphery. The major axis and the minor axis for each lenslet is preferably substantially random in length and angular orientation, thereby providing a plurality of substantially overlapping, randomly oriented lenslets, each having a substantially random power.
The lenticular filter preferably comprises a plurality of lenslets formed so as to define a plurality of different lenslet diameters on the sheet of transparent material.
Alternatively, the lenticular filter comprises a twodimensional array of non-overlapping constant width lenses, but each lens formed so as to be substantially random in power.
According to a second embodiment of the present invention, the optical distortions comprise a phase filter for randomizing the phase of local regions of imaging light. More particularly, the phase filter is so completely randomized the ability to restore the original image with a computer is difficult. Those skilled in the art will appreciate that image resolution is dependant on the width of the in-phase beam of light according to the Raleigh Limit, as discussed in detail below.
The optical distortions according to the second preferred embodiment of the present embod
Anderson Terry J.
Hoch, Jr. Karl J.
Mack Ricky
Northrop Grumman Corporation
LandOfFree
Optical blurring filter which is resistant to digital image... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Optical blurring filter which is resistant to digital image..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Optical blurring filter which is resistant to digital image... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2610249