Abstract:
A method of processing an X-ray image of articles contained in a transilluminated object and made visible for an observer on a monitor screen, includes the following steps: Placing individual markings about the image of certain, previously determined articles and automatically and stepwise combining the individual markings into a final added marking if at least two individual markings mutually fit. The combining step includes the steps of comparing for fit mutually facing sides of two adjoining individual markings and determining a ratio of an overlapping area of the two adjoining individual markings to the total area of at least one of the two adjoining individual markings.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
   This application claims the priority of German Application No. 199 16 664.1 filed Apr. 14, 1999, which is incorporated herein by reference. 
   BACKGROUND OF THE INVENTION 
   This invention relates to a method of processing X-ray images. Articles contained in a transilluminated object are made visible to an operator/observer on a monitor and markings are placed around earlier-defined articles. 
   To facilitate the evaluation of an X-ray image of transilluminated objects for an observer, the X-ray image is automatically examined in the X-ray system based on various properties. In such an arrangements a software is used to search in the transilluminated object for certain previously defined articles such as firearms, piercing weapons or explosives. 
   A method of the above-outlined type is described in German Patent document 198 55 250.5. If such an article is detected, the observer receives information that the article in the transilluminated object has to be more thoroughly investigated. Such an information is the marking of the discovered article on the monitor, for example, by drawing a circle or frame therearound. Since the detected articles are not recognized as a whole, a marking is placed about each detected article. An evaluation by the observer is made difficult if a plurality of such markings appear on the monitor. Such an event is of significant disadvantage for the observer if the run-through period is, for example, approximately 6 seconds. 
   SUMMARY OF THE INVENTION 
   It is an object of the invention to provide an improved method of processing an X-ray image in which the placed markings are optimized to facilitate the evaluation of an X-ray image for the observer. 
   This object and others to become apparent as the specification progresses, are accomplished by the invention, according to which, briefly stated, the method of processing an X-ray image of articles contained in a transilluminated object and made visible for an observer on a monitor screen, includes the following steps: Placing individual markings about the image of certain, previously determined articles and automatically and stepwise combining the individual markings into a final added marking if at least two individual markings mutually fit. The combining step includes the steps of comparing for fit mutually facing sides of two adjoining individual markings and determining a ratio of an overlapping area of the two adjoining individual markings to the total area of at least one of the two adjoining individual markings. 
   The invention is based on the principle to automatically couple to one another the numerous visible markings, so that on the monitor only a single marking as the sum of the individual markings appears to thus provide for the observer a central marking to make possible a rapid and reliable evaluation concerning the article in the transilluminated object. The coupling of the markings is effected by a function which is inputted in the X-ray system and which combines the mutually fitting markings and places a combined marking into the X-ray image. Only markings which belong to one another are combined. Whether two markings belong to one another is determined by their spatial proximity and their overlap. 
   According to an advantageous feature of the invention, joined markings may again be removed, for example, when the operator wishes to see the markings individually. Also, the extent of the combination of the markings may be adjusted. As a result, the markings may be shown unchanged or combined. Further, intermediate steps are possible in which case then maximum 2, 3, 3, 5, etc. markings may be coupled to one another, so that on the monitor two to three markings, etc. may be made visible as individual added markings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a simplified schematic illustration of an X-ray system adapted to perform the method according to the invention. 
       FIG. 2  is a block diagram of a computer system in an X-ray system for performing the method according to the invention. 
       FIGS. 3   a ,  3   b  and  3   c  are visual representations for providing a common marking on the monitor. 
       FIGS. 4   a ,  4   b  and  4   c  are visual representations of the method for removing the common marking from the monitor. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 1  illustrates an X-ray system having a conventional X-ray generator  1  and a detector  2 , between which an object  3  to be transilluminated is positioned. The object  3  may be a piece of luggage in which various articles  4 ,  5 ,  6  are contained. Non-illustrated known components couple a computer system  7  with the detector  2 . The measuring results are made visible on a monitor  8  and/or a printer  9  coupled to the computer system  7 . 
     FIG. 2  illustrates the essential component groups of the computer system  7  for performing the method according to the invention. The output of the detector  2  is connected with an image processing device  10  which is, in turn, connected with a marking memory  11  and a memory  12  for the marking lists. The marking memory  11  is bi-directionally connected with the memory  12  and thus gains access to the marking list accumulated during the process. The marking memory  11  is provided with a sub-marking memory  11 . 1  which will be described in more detail as the specification progresses. 
   The method according to the invention is performed as follows: 
   The X-ray generator  1  directs an X-ray beam FX 1  to the object  3  to be transilluminated. The X-ray beam FX 1  is weakened by the respective absorption behavior of the articles  4 ,  5 ,  6  in the object  3  as well as by the housing material of the object  3  and is received by the detector  2 . The detector  2 , for example, a line camera formed of a plurality of X-ray detectors, produces signals from the non-absorbed part of the X-ray beam and applies the signals, as image data information about the transilluminated object  3 , to the computer system  7  for image processing. Such an inputting is performed preferably line-by-line and in a continuous manner. The image data are evaluated in a known manner in the image processing device  10  and are readied for a visual representation on a monitor. An X-ray image represented in this manner is composed of image dots having various properties, for example, a gray scale and material value from which the article  4 ,  5 ,  6  may be recognized. 
   In principle, about each detected article defined as dangerous, for example articles  4 ,  5 ,  6 , automatically a respective separate individual marking M 1 , M 2 , M 3  is placed, as shown in  FIG. 3   a . Thus, about the first-recognized article  4  the marking M 1  and about the second-recognized article  5  a marking M 2  is placed. Already at this point the two markings M 1 , M 2  are compared with one another by means of a function to determine whether the two markings M 1  and M 2  fit to one another. For this purpose the mutually fitting or mutually facing sides of the markings M 1  and M 2  are compared by means of coordinate comparison. The more these sides correspond to one another in position and length, the better their fit. The distance between the individual markings M 1  and M 2  must not exceed a previously set, variable limit value. 
   In the present illustration the individual markings M 1  and M 2  are situated too far from one another so that no common marking is established. Both markings M 1  and M 2  are inputted into the list memory  12  as well as the sub-marking memory  11 . 1  of the marking memory  11 . 
   Approximately at the same time the detection of the article  6  and placing the marking M 3  thereabout occur. In a further step the marking M 3  is compared with the marking M 1 , that is, it is determined whether the individual markings M 1  and M 3  mutually fit. Since both markings M 1  and M 3  overlap on the fitting sides, additionally the ratio of the common (overlapping) surfaces of the two markings M 1  and M 3  to the surface of the smaller of the two markings M 1  and M 3  is determined for verifying the mutually fitting sides. The greater the ratio the better the mutual fit of the markings M 1  and M 3 . As shown in  FIG. 3   b , the markings M 1  and M 3  are replaced by a new marking as an individual added marking M 1 / 3  in which the respective outer sides of the markings M 1  and M 3  yield the size of the new individual added marking M 1 / 3 . To ensure that the individual markings M 1  and M 3  are not lost in the computer system, they are stored in the sub-marking memory  11 . 1  as sub-markings M 1  and M 3  of the individual added marking M 1 / 3 . 
   Approximately at the same time, the new individual added marking M 1 / 3  is compared for correspondence with the individual marking M 2  from the marking list. As a result of such a comparison, a new marking Mg as a final added marking is applied to the monitor  8 . As shown in  FIG. 3   c , the articles  4 ,  5  and  7  are found within the final added marking Mg. The individual marking M 2  and the individual added marking M 1 / 3  become sub-markings of the final added marking Mg. Thus, for the observer there is obtained a well ascertainable X-ray image on the monitor  8  on which advantageously only a single final added marking Mg is shown without, however, losing the relationships between the individual markings M 1 , M 2 , M 3  and the representation of the final added marking Mg on the monitor  8 . 
   The information concerning the individual markings M 1 , M 2 , M 3  as well as their assignment as sub-markings in relation to the individual added marking M 1 / 3  and the final added marking Mg remain in the computer system  7  in the memory  12  as well as in the sub-marking memory  11 . 1 . This makes it possible to again separately display, upon extinguishing the final added marking Mg, all sub-markings M 1  and M 3  of the individual added marking M 1 / 3  as well as the sub-marking M 2 . For this purpose the final added marking Mg is removed by the operator from the monitor  8 , for example, by pushbutton operation, whereupon the computer system  7  again renders visible the individual stored markings M 1 , M 2  (M 3  is not shown) on the monitor  8 , as shown in  FIGS. 4   a ,  4   b  and  4   c.    
   Such necessary information is taken in steps from the sub-marking memory  11 . 1  as well as from the marking list in the memory  12 . The computer system  7  proceeds with the earlier-described steps in a reverse order. First it is determined which final added marking Mg was removed and the sub-marking memory  11 . 1  is searched for the individual, associated sub-markings. In this proceeding the sub-marking M 1 / 3  belonging to the final added marking Mg as well as the sub-marking M 2  are found. The final added marking Mg is extinguished in the marking list and the sub-marking M 1 / 3  found in the sub-marking memory  11 . 1  and the sub-marking M 2  are added to the marking list of the memory  12 . Further, by means of the software of the computer system  7  it is recognized that the sub-marking M 1 / 3 , as an individual added marking, is composed of the markings M 1  and M 3 , while the sub-marking M 2  has no further sub-markings and thus represents an individual marking. In the marking list the individual added marking M 1 / 3  is extinguished and replaced by the sub-markings M 1  and M 3  which are then inputted from the sub-marking memory  11 . 1  in the memory  12 . The individual markings M 1 , M 2  and M 3  are applied to the monitor  8  from the marking list and displayed thereon. In this manner the observer may decide whether the common marking Mg or the sub-markings/individual markings M 1 / 3 , M 2  or only the individual markings M 1 , M 2 , M 3 , etc. should be shown on the monitor  8 . 
   It is to be understood that upon detection of several articles, that is, more than the mentioned three articles  4 ,  5  and  6  the set markings M 1 , M 2  and M 3 , etc. are compared with one another as long as no mutually fitting markings (individual added markings) are found. 
   Several variants are feasible within the scope of the invention. Thus, the degree and combination of the marking may be set. With such a setting it may be achieved that the markings are not always combined or are only partially combined, that is, intermediate steps with respect to the degree of combination are possible. In this manner too, individual markings may be removed from the combined markings which will thus decompose into several parts. 
   It will be understood that the above description of the present invention is susceptible to various modifications, changes and adaptations, and the same are intended to be comprehended within the meaning and range of equivalents of the appended claims.