Abstract:
An image recognition method is conducted by extracting characteristic points of the pattern of an image formed by video signals from an image pickup device, within the whole or a limited area of a frame of a display, and measuring the distribution of the characteristic points of the image pattern. With this method, images can be recognized with minimal image processing time and with reduced influence of noises.

Description:
This application is a continuation of application Ser. No. 07/850,157 filed Mar. 13, 1992, which in turn is a continuation of application Ser. No. 07/474,302 filed Feb. 5, 1990, which in turn is a continuation of application Ser. No. 07/180,617, filed Apr. 4, 1988, which in turn is a continuation of application Ser. No. 06/880,152, filed Jun. 30, 1986, all now abandoned. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a method of recognizing images. 
     2. Description of the Prior Art 
     An image recognition method for use in, for example, image chasing device has been known in which an image is recognized through detection of the maximum amplitude points of a video signal from an image pickup device or a point where the curve representing the amplitude of the video signal crosses a predetermined threshold value. This known method, however, is disadvantageous in that the image recognition tends to be disturbed by image noises, often resulting in an erroneous operation of the device which makes use of this recognition method. 
     In another known method, a pattern is recognized through determination of the barycentre of the brightness in a predetermined area, while still another known method employs a reference image which is stored in a memory so that the image is recognized through detection of a point where the correlation coefficient between the image outputted from the image pickup device and the reference image is maximized. These methods, however, necessitate too many pieces of information and long processing time, as well as a highly complicated construction of the system. 
     SUMMARY OF THE INVENTION 
     Accordingly, an object of the invention is to provide an image recognition method which enables a correct image recognition without suffering from the problems of the prior art. 
     Another object of the invention is to provide an image recognition method which enables a correct image recognition with fewer number of pieces of information than in the known methods. 
     Still another object of the invention is to provide an image recognition method which enables a quick recognition of an image. 
     A further object of the invention is to provide an image recognition method which facilitates the construction of an image recognition apparatus. 
     A still further object of the invention is to improve a known image recognition method for recognizing an image within a limited region of the picture frame in an image pickup device such as a camera and an image scanner. 
     A still further object of the invention is to provide an improved image recognition method which enables compensation for any unintentional movement of the picked-up image. 
     To these ends, according to one aspect of the invention, there is provided an image recognition method comprising the steps of detecting the characteristic points of an image and producing signals corresponding to the concentration of the detected characteristic points in predetermined reference locations. 
     According to another aspect of the invention there is provided apparatus for image recognition comprising means for detecting the characteristic points of an image and means for producing signals corresponding to the concentration of the detected characteristic points in predetermined reference locations. 
     As used herein, the term `characteristic point` means a location on a detectable image which is different, in respect of a given measurable feature, from an adjoining location. The difference may be, for example, color or brightness. 
     The above and other objects, features and advantages of the invention will become clear from the following description of the preferred embodiments taken in conjunction with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE INVENTION 
     FIG. 1 is a simplified block diagram of a system for carrying out the method of the invention; 
     FIG. 2 is a timing chart illustrating the timing of horizontal and vertical synchronizing signals used in the system of FIG. 1; 
     FIG. 3 is a block diagram of a region setting section in the system of FIG. 1; 
     FIG. 4a is a schematic illustration of a screen for explaining the method of the invention; 
     FIGS. 4b and 4c are illustrations of distributions of numbers of image characteristic points formed on the screen of FIG. 4a; 
     FIG. 5 is a circuit diagram of a characteristic point extracting section and a characteristic point measuring section in the system of FIG. 1; 
     FIG. 6 is an illustration of a modification of the embodiment shown in FIGS. 4a, 4b and 4c; and 
     FIG. 7 is a table showing the content of a memory which stores distribution of numbers of the characteristic points. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 shows a system which is suitable for use in carrying out the image recognition method of the invention. The system of FIG. 1 includes an image pickup device 1, a region setting section 2 for setting a region of a predetermined size in the picture frame which is formed by video signals derived from the image pickup device 1, characteristic point extracting sections 3 and 5 which extract characteristic points from an image, upon receipt of a video signal corresponding to the region of the size set in the region setting section 2, and measuring sections 4 and 6 for measuring the distributions of numbers of characteristic points outputted from the characteristic point extracting sections 3 and 5. 
     The image pickup device 1 may be a video camera or any other well known device, for example a CCD (charge coupled device) for converting an optical image into a group of electrical signals which are organized by means of horizontal and vertical synchronizing signals. The details of the region setting section 2, the characteristic point extracting sections 3 and 5 and the measuring sections 4 and 6 are described hereinbelow. 
     FIGS. 4a to 4c illustrate the principle of image recognition in accordance with the invention. A picture frame 10 is formed by a video signal Vi derived from the image pickup device 1. The region setting section 2 sets a region 11 of a predetermined size within the area of the picture frame 10. The pattern of an image 12 to be recognized is contained in the region 11. Horizontal lines X 1  . . . X n  represented by a line X k , on the picture frame 10 are reference lines which are used as references for measurement of the distribution of the characteristic points by the distribution measuring section 4. Similarly, vertical lines Y 1  . . . Y n  represented by Y k  on the picture frame 10 are reference lines which are used as references for measurement of the distribution of numbers of the characteristic points by the distribution measuring section 56. FIG. 4b is a graph which shows the distribution in the vertical direction (indicated by arrow X) of the numbers n of characteristic points found on respective horizontal reference lines X 1  . . . X n . Similarly, FIG. 4c shows the distribution in the horizontal direction (indicated by Y direction) of the numbers n of characteristic points found on respective vertical reference lines Y 1  . . . Y n . For instance, in FIG. 4b, a dot P k  shows the number of characteristic points of the image 12 found along the horizontal reference line X k , whereas a dot Q k  shows the number of the characteristic points of the image 12 found on the vertical reference line Y k . 
     As stated before, the region setting section 2 sets the image recognition region 11 of a predetermined size within the picture frame 10. For instance, counting of the number of the horizontal synchronizing signals HSYNC (not shown) contained by the video signal V i  derived from the image pickup device 1 is commenced in synchronism with the vertical synchronizing signal VSYNC which determines the upper side X 1  and the lower side X n  of the image starting or original point of the picture frame, whereby recognition region 11 are determined. On the other hand, the horizontal scanning direction is divided into predetermined time intervals, in accordance with reference clock signals CLK which are synchronous with the horizontal synchronizing signal HSYNC. The number of the clock signals CLK is counted so as to determine the right side Y 1  and the left side Y n  of the image recognition region 11. 
     In this embodiment, the region setting section 2 passes only the video signals which correspond to the image recognition region 11. 
     FIG. 3 shows the detail of the region setting section 2, while FIG. 2 is a time chart showing the timing of the signals CLK, VSYNC and HSYNC. 
     Referring to FIG. 3, a line memory 40 stores a series of the video signals V i  of 8-bit gradation corresponding to one line. For instance, the line memory 40 stores data corresponding to one line in Y-direction obtained by a read line sensor such as a CCD in the image pickup device 1 (FIG. 1). An AND gate 41 (FIG. 3) operates to transmit only the data corresponding to the image recognition region 11 (FIG. 4a) and outputs the same as video signals VIDEO to the characteristic point extracting sections 3 and 5 (FIG. 1). An AND gate 42 (FIG. 3) which controls the state of the AND gate 41 in response to control signals which are formed by a start bit counter 43, an end bit counter 44, a start line counter 46 and an end line counter 47. Addresses Y 1  and Y n  of the region boundaries in the Y-direction (see FIG. 4a) are set in the counters 43 and 44. Upon counting Y 1  consecutive clock signals CLK, the counters 43 and 44 set a flip-flop 45 so as to deliver to the gate 42 a control signal thereby enabling the gate 41 to output the video signal VIDEO. Thereafter, upon counting Y n  consecutive clock signals, the counters 43 and 44 reset the flip-flop 45, thereby terminating delivery of of the region boundaries X 1  . . . X n  in the X-direction have the control signal. If, on the other hand, the addresses been set in the counters 46 and 47, these counters operate to set a flip-flop 48 upon counting the horizontal synchronizing signal HSYNC up to X 1  and resets the same upon counting the horizontal synchronizing signal HSYNC up to X n . In consequence, these counters deliver the control signal only in the period corresponding to the region between X 1  and X n . It will be seen that the gate 41 transmits only the data corresponding to the region defined by the horizontal lines X 1  . . . X n  and the vertical lines Y 1  . . . Y n . The coordinate values X 1  . . . X n  and Y 1  . . . Y n  are designated by a digitizer or a ten-key input device and are stored in a memory 49. The counters 43 and 44 are reset by the horizontal synchronizing signals HYSNC, while the counters 46 and 47 are reset by the vertical synchronizing signals VSYNC. 
     The characteristic point extracting portions 3 and 5 extract characteristic points of the pattern of the image 12 within the image recognition region 11 (FIG. 4a). By way of example, a description will be made hereinafter as to a method in which the edge of the image, as detected by its contrast, is extracted as the characteristic point. 
     As shown in FIG. 5, each of the characteristic point extracting sections 3 and 5 has a comparator C 1  and C 2 , which effects amplifude discrimination of the video signal VIDEO according to a predetermined binarizing level L 1  and L 2 , whereby the contrast between the pattern of the image 12 and the background is detected; and as a result, a binarized image is formed. Each of the characteristic point extracting sections 3 and 5 produces pulses corresponding to the rise and fall of the binarized image, i.e., the characteristic points of the pattern of the image 12 (FIG. 4a), and delivers the pulses to the corresponding distribution measuring section 4 or 6 which measures the distribution of the numbers of the characteristic points. The characteristic point extracting section 5 operates to temporarily store the binarized image data in a frame memory and, thereafter, reads the image data along each of the successive vertical lines Y 1  . . . Y n  in the direction towards the line X n , and delivers the thus obtained data in the form of pulses to the measuring section 6. 
     Pieces of data binarized by the comparator C 2  are successively written in the frame memory in response to the horizontal scanning. As a result, the binarized data of the area 11 shown in FIG. 4a, i.e., the edge pattern, is stored. After the completion of the storage, a reading operation is conducted by scanning the frame memory in a sequence of the addresses corresponding to the vertical lines Y 1  to Y n  shown in FIG. 4a. The data obtained through the reading scanning is sent to the counter 6 which is adapted to count the number of the data &#34;1&#34; which corresponds to the edge. 
     The distribution measuring section 4 for measuring the distribution of the numbers of the characteristic points has a counter/decoder C/D1 which counts the number of the characteristic points of the pattern of the image 12 counted on each of the successive reference lines X 1  . . . X n  in the image recognition region 11 (FIG. 4a) which is scanned with a predetermined resolution, and measures the distribution of the numbers of the characteristic points along the horizontal line represented by Y k . Namely, the measuring section 4 produces signals P 1 , P 2 , and so forth which bear data concerning the numbers of the characteristic points found on respective horizontal reference lines X 1  . . . X n . 
     When the image is a line image which has a high contrast against the background, the binarized image produced by the characteristic point extracting section 3 is equivalent to the pattern of the image 12. Therefore, the number of the pulses outputted from the characteristic point extracting section 3, corresponding to the characteristic points of the pattern of the image 12, is represented by the number of points where the pattern of the image 12 crosses the reference line X 1 . Thus, the distribution measuring section 4 first measures the number of the points where the pattern of the image 12 is crossed by the first reference line X 1 . Since the number of the crossing points is zero in this case, the measuring section 4 produces a signal representing a point P 1  as illustrated in FIG. 4b, and then conducts similar measurement for each of the successive lines X 1  . . . X n . For instance, the number of crossing points between the reference line X k  and the pattern of the image 12, which is in this case 2 (two), is plotted as P k , as shown in FIG. 4b. The measurement is then conducted for successive lines, whereby, as will be explained, a series of data P 1  . . . P n  are stored in a memory 20 in relation to the positions of the lines X 1  . . . X n , in an arrangement as shown in FIG. 7. The thus stored data can be used for a subsequent image processing or for the purpose of display. The display shown in FIG. 1 can comprise a binarized image, as well as the binarized data P 1  . . . P n . The printer is capable of printing the binarized image. 
     The section 3 is the section which binarizes the image. A monotone printer (line printer) is adapted to be driven by the thus binarized data (1,0) so as to reproduce the line pattern, i.e., the edge pattern. 
     It will be seen that the image recognition can be conducted in real time, simultaneously with the pickup of the image, while displaying and printing the image. 
     Similarly, the measuring section 6 has a counter/decoder C/D2 which counts the number of the characteristic points of the pattern of the image 12 on each of the vertical reference lines Y 1  . . . Y n  in the image recognition region 11 which is scanned with a predetermined resolution, and measures the distribution of the numbers Q 1  . . . Q n  of the characteristic points along the vertical direction represented by the reference line Y k , thus forming a distribution pattern as shown in FIG. 4c. The thus obtained data comprising the numbers Q 1  . . . Q n  of the characteristic points are stored in the memory 20 (FIG. 7), in relation to the positions of the vertical reference lines Y 1  . . . Y n . 
     The gates of the memory 20 are connected to a data processor (not shown) through respective BUS lines. The data processor operates in such a manner that the outputs from the gates obtained at the moment t 1  are stored as the data P 1  . . Q n  in the address areas X 1  . . . Y n  of the memory corresponding to the gates. Similarly, the outputs obtained at the moment t 2  are stored as the data P&#39; 1  . . . Q&#39; n . After the storage of the groups of data obtained at the moments t 1  and t 2 , the data processor reads from the address X 1  of the memory 20 the data P 1  and P&#39; 1  which were obtained at the moments t 1  and t 2 , and compares them with each other. The difference between this data is stored in the memory 20. It will be seen that the difference is zero, in case of the data read from the address X 1 . Then, the data processor reads the data from the address X 2  of the memory at moments t 1  and t 2  and stores the result of the comparison between this data in the memory. This operation is continued down to the data from the address Y n , and the state of movement of the image is judged from the data in the memory obtained as the result of comparison between corresponding data obtained at the moments t 1  and t 2 . 
     Referring to FIG. 5, the distribution measuring sections 4 and 6 have gates G 1  . . . G n  and G y1  . . . G y2  which are adapted for outputting the count data for each of the data P 1  . . . Pn and Q 1  . . . Q n , thereby to distribute the data for respective lines X 1  . . . X n  and Y 1  . . . Y n . 
     The input signals X 1  . . . X n  inputted to the gates can be obtained by using a counter (not shown) the content of which is incremented for each of the successive horizontal lines during the horizontal scanning. Similarly, the input signals Y 1  . . . Y n  are obtained by a counter (not shown) which is incremented for each of the successive vertical lines Y 1  . . . Y n  during the vertical scanning. In the arrangement shown in FIG. 5, the accuracy of the image recognition is enhanced because the video signal VIDEO is first binarized by the comparator C 2  and then stored in the frame memory. The pitch of scanning along the lines Y 1  . . . Y n  may be greater than that of the scanning along the lines X 1  . . . X n . 
     The signals X 1  . . . X n  and the signals Y 1  . . . Y n  are derived from different terminals of a decoder which produce an output each time of counting by a first counter and a second counter which are not shown. More specifically, when the horizontal scanning at the address X 1  is finished, the content of the first counter is incremented by &#34;1&#34; and the signal X 1  is outputted from an X 1  terminal of the decoder. Then, when the horizontal scanning at the address X 2  is finished, the content of the first counter is further incremented by &#34;1&#34; and the signal X 2  is outputted from the decoder. Similarly, when the vertical scanning at the address Y 1  is finished, the content of the second counter is incremented by &#34;1&#34;, and the signal Y 1  is outputted from the Y 1  terminal of the decoder. Then, when the vertical scanning at the address Y 2  is finished, the content of the second counter is further incremented by &#34;1&#34; and the signal Y 2  is outputted from-the decoder. 
     The signals Y 1  . . . Y n , which correspond to addresses Y 1  . . . Y n  shown in FIG. 4a, are produced each time a reading scanning corresponding to the vertical scanning of the image is finished during reading of the content of the frame memory. 
     The distribution data P 1  . . . P n  and Q 1  . . . Q n  concerning the distribution of the numbers of the characteristic patterns can be obtained in the manner described hereinbefore. 
     The thus obtained data can be used for various purposes. For instance, it is possible to detect the direction and distance of movement of the image 12 within the picture frame 10. To this end, the characteristic points are extracted at a first moment t 1  in the above-described manner; and, at a second moment t 2 , a new image recognition region 11 of the same size and shape as those of the first region is set within the area of the picture frame 10, and the distributions P&#39; 1  . . . P&#39; n  and Q&#39; 1  . . . Q&#39; n  of the characteristic points at the record moment t 2  are determined in the same manner as described above. Then, the direction and amount of movement of the image 12 within the picture frame 10 can be known by determining the correlation between two groups Of distribution data P 1  . . . P n , Q 1  . . . Q n  and P&#39; 1  . . . P n  &#39;, Q&#39; 1  . . . Q n . This method can be applied to the judgement of occurrence of any unintentional 10 movement of a camera during shooting. For instance, it is possible to produce a warning signal which indicates the unintentional movement of the camera and, hence, movement of the image pattern. 
     In a practical application, the video signal VIDEO is inputted to a correction filter circuit in response to the detection of the movement of the image, so as to remove the data of the pattern measured at the moment t 2 , thereby recovering the image pattern as obtained at the moment t 1 . Therefore, if the image is to be reproduced by the printer in the system shown in FIG. 1, the arrangement may be such that the printer is driven by an enable signal E when no movement of the image is confirmed or only after the image correction has been accomplished through elimination of the component attributable to the image movement. 
     For instance, referring to FIG. 7, if the value of the data P&#39; 1  as measured at the moment t 2  is the same as the value of the corresponding data P1 measured at the moment t 1 , while the values of the data P&#39; 2  and P&#39; n  as measured at the moment t 2  are 0 (zero) and 2 (two), respectively, it is understood that the image has been moved translationally downward towards the line X n  (see FIG. 4a) by a distance equal to one pitch of the horizontal reference lines X 1  . . . X n . 
     If the printer for reproducing the image is not a binary printer but a printer or a display which is capable of reproducing or displaying halftone, such a printer or display can directly receive the video signal VIDEO. 
     The characteristic point extracting sections 3 and 5 may be constituted by different systems which employ different extraction methods which will be mentioned later. If it is allowed to use the same extraction method for the extraction in both directions, it is possible to use a single extracting section instead of two independent extracting sections. 
     The image recognition region 11 may be as wide as the entire area of the frame 10. Also, the image extraction region 11 can have any desired shape such as a circular shape, although in the described embodiment the region 11 has a substantially rectangular form. The measurement of the distribution of numbers of the characteristic points may be made in at least one direction which may be inclined with respect to the frame, for example, as shown in FIG. 6; and it may be conducted along curved reference lines although the described embodiment makes use of linear reference lines. 
     More specifically, the arrangement shown in FIG. 6 employs a pair of frame memories: namely, a first frame memory and a second frame memory. The first frame memory stores the image data V&#39;c. The pattern stored in this first frame memory is read after a rotation through an angle α, i.e., in terms of addresses which are obtained by rotation of the coordinate of the memory through the angle α, and the thus read data is stored in the second frame memory. Then, the data in the second frame memory is read in terms of the normal address, and the characteristic points are extracted in the same manner as that explained before in connection with FIG. 4 and other Figures. 
     The characteristic points which are to be extracted by the extracting sections 3 and 5 may be the contrast points such as the points where the video signals derived from the image pickup device cross a predetermined threshold level as in the described embodiment, or they may be a minimum or maximum value of the video signal. It is also possible to use a color difference as the basis for the characteristic points. The characteristic points may also be points which are obtained through a suitable processing of the video signal, such as the maximum or minimum values of a signal obtained through differentiation of the video signal, and a point at which the differentiated video signal reaches a predetermined threshold value.