This invention relates in general to radiant energy imaging systems and more particularly, to a novel method and apparatus for selectively enhancing the image of objects or voids having circular cross section, such as agricultural and like-shape objects of voids, to distinguish them from objects or voids having rectangular cross section (manufactured objects or cracks).
A common method of dissemination of plant or animal disease vectors or pests such as the Mediterranean fruit fly to areas not yet infested is by the transport of agricultural items such as infected fruit, vegetables, plants, packaged meats and birds. In particular airline travelers pose a hazard in that large distances are rapidly traversed promoting the introduction of a pest into a region devoid of its natural enemies. Such dissemination can have serious economic impact on agricultural production. Currently, the primary methods for detecting agricultural contraband in passenger baggage are by passenger questioning, and manual baggage search. Such methods are unreliable and time consuming.
In a few locations, X-ray imaging systems used for inspection of passenger baggage for security reasons and digital X-ray scanners have been introduced to inspect baggage for agricultural contraband. These methods have the disadvantage that they rely on the ability of a human operator to recognize contraband items objects solely on the basis of shadow shape and density. Thus while agricultural objects such as pineapples, pears and papayas which have distinctive shapes, can be readily distinguished from manufactured objects, other agricultural contraband such as tangerines, apples, mangos, sausages and the like which have image shapes similar to non-contraband objects cannot be readily detected. Furthermore, even in those cases where it is possible to distinguish images of agricultural objects by their shape, such an inspection requires intense operator effort resulting in operator fatigue. Furthermore, such a procedure is time-consuming. This is a disadvantage for to be successful in a commercial setting, the monitoring system must monitor a piece of luggage in about 2-4 seconds.
U.S. Pat. No. 3,808,444 discloses an automatic high energy X-ray monitoring system for detecting dense metallic objects such as guns or bullets in baggage. Objects in the density range of agricultural objects are not detected by this method.
In medical studies, X-ray imaging is commonly used to image internal organs or other objects contained in human or animal bodies. A single X-ray projection minimizes the dose and apparatus cost but does not allow depiction of the cross sectional shape of the imaged organ. Such shape information is desirable but can generally only be obtained through multiple angled exposures and reconstruction (tomography), which is expensive and exposes the patient to undesirable radiation doses. Alternatively, a very extensive analysis of the density of a single exposure is time consuming and difficult.
In industrial inspection of materials for cracks and voids X-rays are the method of choice. Single exposures are used for speed and economy, but the image does not reveal the cross sectional shape of the cracks and voids, nor does it allow automatic recognition and counting of such cross sectional shapes which are desired for quality control.