Optics: measuring and testing – Range or remote distance finding – Triangulation ranging with photodetection – but with no...
Reexamination Certificate
2000-06-19
2002-02-05
Tarcza, Thomas H. (Department: 3662)
Optics: measuring and testing
Range or remote distance finding
Triangulation ranging with photodetection, but with no...
C356S004040, C359S558000, C235S462220, C235S462230, C235S462240, C235S462350
Reexamination Certificate
active
06344893
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an imaging system. More particularly this invention relates to a super-resolving imaging apparatus having increased depth of field which can be employed in collision avoidance systems for vehicles, and for distance estimation applications in general.
2. Description of the Related Art
Nowadays distance estimation is mainly performed using two basic techniques: active sensing and image processing. In the active sensing category are included radar-type devices which illuminate the region of interest by scanning and then estimating the distance by measuring the time between the transmitted and received signals. Although such devices are relatively simple, they are presently too expensive to be practical in private vehicles. These devices have limited resolution, and are generally too slow for real-time collision avoidance applications for terrestrial vehicles.
The other major category distance estimation devices are passive systems based on detector arrays, such as CCD, CMOS, and ICCD gated CCD, which employ advanced image processing algorithms. Such systems, in order to obtain algorithmic convergence, require high resolution and thus have a restricted field of view. These systems also suffer from a limited depth of focus. In addition, the postprocessing algorithms that perform the time-to-impact evaluation require heavy computation. Despite their present limitations, the passive systems are constantly being upgraded in technological performance, and are being dramatically reduced in price.
Technical problems in the field of optical scanning are similar to those of the immediate field of the invention. Imaging based scanners are required to convert spatial degrees of freedom in order to obtain high horizontal and vertical resolution, and adequate depth of focus. Here are several related patents that deal with high resolution and extended depth of field scanning of objects as bar codes. Several disclosures are known to deal with similar problems. U.S. Pat. No. 5,657,147 discloses an optical scanner which includes a light source and optical deflector for scanning a light flux from the light source. Beams with extended confinement for scanning purposes, as proposed in U.S. Pat. No. 5,315,095, may be the basis for scanners usable, for example in a bar code reader, by generating a multitude of Gaussian beams derived from a common light source. A scanner using this technique has an extended working range. An optical scanner for reading barcodes detected within a large depth of field is disclosed in U.S. Pat. No. 4,748,316, which proposes the use of a plurality of scan lines having different focal lengths. If at least one of the scan lines is small relative to irregularities of the surface on which the label appears, an extended depth of scanning can be achieved. U.S. Pat. No. 4,820,911, describes an apparatus which is adapted to be hand-held and utilizes anamorphic optics for scanning and reading a bar code. The optics provides a beam having an oblong cross-section in the nominal plane of the bar code. U.S. Pat. No. 5,680,253 discloses a light beam scanning apparatus comprising a first and second diffraction grating plate which provides a high resolution scanning apparatus utilizing mass producible holograms instead of utilizing auxiliary optical systems. An optical system for a large depth of field barcode scanner was suggested in U.S. Pat. No. 4,978,860 to Bayley et al. The working range of this device is determined not by the lens aperture, but by the dimension and orientation of the detector array using a modified Scheimpflug arrangement.
Nevertheless, the existing prior art devices do not fully solve the technical problems required for imaging systems to be used for distance estimation and collision warning for vehicles.
SUMMARY OF THE INVENTION
The invention provides super-resolving devices and their applications. More particularly, it provides geometrical super-resolution, i.e. resolution that is better than the resolution defined by the geometry of the detector array. In addition, the disclosed technology also provides apparatus to extend the depth of field of the system.
It is a primary object of some aspects of the present invention to improve imaging systems in the fields of distance estimation and collision warning for vehicles.
It is another object of some aspects of the present invention to provide apparatus for estimating distance that affords wide depth of focus and a large horizontal field of view.
It is yet another object of some aspects of the present invention to improve the speed of distance estimation in collision warning systems.
These and other objects of the present invention are attained by imaging apparatus in which special optical elements placed on the imaging lens and the detector array allow the conversion of degrees of freedom in one axis of a field of view to a larger degree of freedom in another axis in order to obtain a high resolution image with a wide depth of focus and large field of view suitable for performing distance estimation on an object within the field of view.
The invention employs a numerical algorithm which is simple and can be rapidly performed to yield the desired result.
According to some aspects of the invention a detector array with a specially designed optical element is directed toward a large volume of space in which a target may be found. In certain applications, such as vehicular warning systems, the vertical field of view required is significantly smaller than the actual vertical field of view of the apparatus. The special optical element converts the unneeded vertical pixels (degrees of freedom) into an increased depth of focus resolution. The apparatus provides a view comprising several horizontal “stripes” wherein each stripe represents a planar object and corresponds to an optical element which has both a unique focal length and thus a unique depth of focus region. In a preferred embodiment of the invention a distance evaluation is performed by evaluating the amount of misfocus of each of the various stripes.
In an alternate preferred embodiment of the invention the distance estimation is performed by employing two cameras, each having similar structure to that of the first embodiment. A triangulation calculation is performed in order to extract the distance of the object seen by both cameras.
In another aspect of the invention, a diffractive optical element that is attached to the aperture of the system further improves the geometrical resolution of the imaged scene by converting vertical degrees of freedom into horizontal resolution. A system including a camera employing the apparatus according to the invention provides high resolution performance both in the vertical and in the depth axes together enabling determination of the desired distance estimation.
In yet another aspect of the invention an optimal filtering approach is applied in order to perform the recognition of the high-resolution image.
The invention provides a method of imaging, which is performed by tilting an image plane with respect to an object plane, defining pixel units on the image plane, and defining a field of view on the object plane, wherein a vertical dimension of the field of view differs from a horizontal dimension thereof. A plurality of images of the field of view are formed on the image plane, the images being spatially interrelated by subpixel shifts. The formed images are then super-resolved into an enhanced image.
According to an aspect of the invention the step of super-resolving is geometrically performed by transforming the images according to a Gabor transform.
According to another aspect of the invention the step of super-resolving also has applying a spatial mask to the image plane.
According to still another aspect of the invention the images are oriented according to the larger of the horizontal dimension and the vertical dimension.
In a further aspect of the invention there is a further step of deconvolving out-of-focus point spread functions of the
Karako Sharon
Konforti Naim
Levy Uriel
Marom Emanuel
Mendlovic David
Mull Fred H
Ramot University Authority for Applied Research and Industrial D
Rosenman & Colin LLP
Tarcza Thomas H.
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