A LINE MONITORING SYSTEM

Abstract: A device and a method for monitoring a plane in space over an interval of time to create an image representing the time history of the plane in space. A line image sensor (2) captures a series of line images of the plane in space which are converted to digital information by an A/D converter (4) for storage in solid state memory (3). To product a time history image of the plane in space, the line images can be retrieved from the solid state memory (3) by a computer (7). The computer (7) displays the series of line images adjacent to each other to create the time history image. The present invention has a number of applications, including photo finish cameras.

Description: TITLE A LINE MONITORING SYSTEM BACKGROUND ART The present invention relates to a method and a device for monitoring a line. In particular, the present invention relates to a method and a device for monitoring a finishing line and producing a photo finish image. At sporting events such as horse racing, greyhound racing and athletics, it is necessary to obtain a photographic record of competitors crossing a finish line in order to determine the placing of the competitors. Traditionally a series of still photographs were taken, but this was not effective since it is not possible to take a sufficient number of photographs in rapid succession to obtain an image of each competitor crossing the line. The advent of video cameras and motion picture cameras has been of some assistance, but these cameras provide unsatisfactory results since video cameras and motion picture cameras still only take a series of stationary images and the frame rate of the camera is still not fast enough to determine the winners in close-call situations, especially when the competitors are travelling at high speed. One method of overcoming the above problems has been the development of photo finish cameras which take a single continuous photograph at the winning post over a period of time. Such a camera is comprised of a slit aperture such that the slit aperture produces an image of only the finish line, and not the surrounding areas. As the competitors approach the finish line, the slit aperture is opened and a continuously moving film is passed behind the slit aperture at a fixed rate. As the film travels past the slit aperture and the competitors pass the finish line, a one dimensional image is continuously taken of the finish line over a period of time. The resulting photograph appears similar to a snap shot photograph in time, but is actually a photograph of a time history of the event at the finish line as seen by the line. Consequently, not only is it possible to determine which competitor crosses the line first but it is also possible to determine the order in which all competitors cross the line from the single photo finish image. Although such a photo finish system provides significant advantages over a series of still frames, the system uses old technology comprising mainly mechanical components. Furthermore, it is very important to minimise the time between taking the photo finish image and the availability of the photo finish image for use, so that officials may be able to determine the finishing order of the competitors as soon as possible. Using the known film technique it is necessary to remove the film from the camera, develop and set the photo finish image before it is useable. If parts of the photo finish image require enlargement in order to determine close-calls, further time consuming processing is required. During processing and enlargement the film can distort, which will cause errors in the resultant image. Also, the high speed film required to record a high speed event (usually over 1000 ASA rating) suffers from poor resolution, especially when enlarged, and has only a few different gray shades. Furthermore, colour film cannot be used in photo finish cameras since colour films take too long to develop and the resolution of high speed colour film is particularly poor. SUMMARY OF THE INVENTION The present invention seeks to provide an improved line monitoring system. According to the present there is provided a line monitoring system for monitoring a plane in space, comprising: a line image capture means for capturing a plurality of line images of the plane in space over an interval of time, and an image storage means for storing the line images, wherein a image representing a time history of the plane in space is capable of being constructed from the line images stored in the storage means and displayed on a display means by placing the line images adjacent to each other. The present invention further provides a method of monitoring a plane in space comprising the steps of: positioning a line image capture means for capturing a plurality of line images over an interval of time of the plane in space, capturing the plurality of line images over the interval of time and storing the line images in a digital storage means, constructing time history image representing a time history of the plane in space over the interval of time and displaying the time history image on a display means by placing the line images adjacent to each other. There is further provided a method of obtaining a photo finish image of a finish line comprising the steps of: positioning a line image sensor to capture a plurality of line images over an interval of time of the finish line, capturing the plurality of line images over the interval of time and storing the line images in a digital storage means, constructing the photo finish image representing a time history of the finish line over the interval of time and displaying the photo finish image on a display device by placing the line images adjacent to each other. DESCRIPTION OF THE DRAWINGS Preferred embodiments of the present invention will hereinafter be described by way of example only with reference to the accompanying drawings, in which: Figure 1 is a block diagram of the main components of a preferred embodiment of the present invention. Figure 2(a) is a top view of a finish line at a running track having a photo finish camera and Figure 2(b) is a front view of the finish line, Figure 3 is a more detailed block diagram of the preferred embodiment of Figure 1, Figure 4(a) is a rear view of the photo finish camera according to a preferred embodiment of the present invention and Figure 4(b) is a side view of the photo finish camera of Figure 4(a), and Figure 5 shows a perspective compensated line sensor according to a preferred embodiment of the present invention. DESCRIPTION OF THE PREFERRED EMBODIMENT A line monitor system has applications where events in one plane in space is to be recorded over a period in time. A side view of such a plane is a line in space and if the line in space is observed over a period of time, it is possible to create a time history of the plane, as seen from its edge. In the preferred embodiment of the present invention the line monitor system is a photo finish camera at a winning line. The line monitor system of Figure 1 is a photo finish system 1 having a line image capture means comprising a CCD (charge coupled device) line camera having line image sensor 2, storage means comprising solid state memory 3, and display means comprising computer 7 having a screen (not shown) . In order to maximise the rate at which data can be stored and the reliability of the memory, it is preferred that Static Random Access Memory (SRAM) is used for the solid state memory 3. The CCD line image sensor 2 is a one dimensional array of photo sensitive diodes capable of capturing line images. The solid state memory 3 is capable of storing images captured by the sensor 2. The computer 7 may be used to interact with the sensor 2 and the solid state memory 3 so as to capture images and to view the images captured by the sensor 2. The sensor 2 is controlled by sensor controller 6 and the solid state memory 3 is controlled by memory controller 5. As shown in Figures 2(a) and 2(b), in use, the photo finish system 1 is placed at the winning line 50 inside a winning post viewing box 51 so that the line images taken by the sensor 2 of the photo finish system 1 correspond to the side view of the plane perpendicular to the ground through with the winning line 50 passes. Competitors passing over the winning line 50 are recorded by the photo finish system 1 as a line image of the winning line plane. When the competitors are in close proximity to the finish line, computer 7 readies the sensor controller 6 and the memory controller 5. The memory controller 5 resets the solid state memory 3 to prepare it for receiving line images of the finish line from the sensor 2. Sensor controller 6 initialises the sensor 2 and synchronises the communication of the line images from the sensor 2 to the solid state memory 3. When capturing a photo finish image, the sensor 2 detects a line image of the plane in which the winning line is located by a row of photo sensitive diode sensors within the line sensor 2. A series of voltage levels corresponding to the intensity of the light received by each of the photo sensitive diodes is produced. These analog voltage signals from the sensor 2 are sent to an analog-to-digital (A/D) converter 4 which quantises the voltage output of each diode to a digital value representing one pixel of information in the line image. The sensor controller 6 indicates to the memory controller 5 that an image is ready to be stored in solid state memory 3, and under control of memory controller 5, the pixels of the line image are stored in the solid state memory 3. In the preferred embodiment the sensor 2 and the solid state memory 3 operate synchronously so that line images are continually received by the sensor 2 and stored to the solid state memory 3. This increases the rate at which line images can be captured so that the line images can be captured and stored in real-time. Furthermore, by simply changing the clock rate, it is possible to change the rate of capturing images. The line image capturing process is stopped by the computer 7 when enough line images have been received to construct a photo finish image, or if the memory controller 5 stops the process when the solid state memory 3 becomes full. After completion of the photo finish image capturing process the computer 7 extracts the line images from the solid state memory 3 by instructing the memory controller 5 that it is ready to receive the line images. The memory controller 5 prepares solid state memory 3 for sending the data, and the solid state memory 3 sends the line images pixel by pixel to the computer 7. In another preferred embodiment of the present invention the computer 7 is able to address the solid state memory 3 directly as a memory mapped address. Once the computer 7 has received all the line images it constructs a photo finish image which is a time history of the finish line. This is done by placing the individual line images side by side on a display, such as on a computer screen, or by printing to a hard copy medium. Once the photo finish image is constructed it is possible to zoom in on specific areas of the photo finish image using the computer 7 to enlarge areas of interest in the photo finish image. It is also possible to improve the image quality using electronic filtering and image processing to improve, for example, the shading and contrast of the image. Figure 3 is a block diagram showing the components of the photo finish camera system of Figure 1 in greater detail. The sensor 2 of the photo finish camera system has a lens 21 which focuses an image of the finish line onto a linear array of photo sensitive diodes 22 which are sensitive to varying light intensities. The photo sensitive diodes are particularly advantageous due to their compactness, ruggedness, low power drain, high resolution, and high sensitivity. Other optical sensors may be used to achieve similar results. In the preferred embodiment of the present invention the computer 7 may be a computer dedicated to controlling the camera and capturing the line images, or it may be a conventional personal computer which runs appropriate software and which has an interface card fitted to the computer to communicate with the solid state memory and sensor. When a photo finish image is to be taken, the operator of the photo finish camera system 1 may instruct the computer 7 to control the sensor 2 and solid state memory (in this embodiment being SRAM 27) to capture images of the finishing line. Alternatively, an approach sensor 35 may be used. This sensor 35 is typically connected across the track some short distance before the finishing line and to the computer, so that when the competitors pass the approach sensor 35, the computer 7 commences the image capturing sequence. Upon instruction to proceed with capturing line images, the computer 7 writes a command to control port 32 that the photo finish capturing sequence is to commence. The control port 32 communicates with memory address controller 28 which resets the static random access memory (SRAM) 27, resets the memory address generation part of the memory address controller 28 and informs frame controller 25 to initialise and instruct the sensor 2 to commence capturing line images. The frame controller 25 initialises the camera by instructing the sensor timing and synchronisation controller 24 to operate the sensor. The sensor timing and synchronisation controller 24 communicates with the photo diodes 22 by sending appropriate timing sequences to synchronise the capturing and storage of line images. The sensor 2 is an analog device which outputs voltage levels corresponding to the light intensity reading of each of the diodes within the photo diode array 22. The analog voltage signals are sent to a black reference controller 23 where the voltage signals are compared with dark references to calibrate the image in a grey scale, and also to compensate captured data for temperature variations, thereby ensuring fidelity. After compensation the voltage levels are communicated to A/D converter 4. The sensor timing and synchronisation controller 24 indicates to the frame controller 25 when the end of one line image has been reached and the frame controller 25 communicates this to the A/D converter 4. The A/D converter 4 digitises the analog information so that the light intensity output of each diode is converted to a digital value corresponding to one pixel in the line image. Each of the pixel values is then made available to the SRAM 27 through buffer 26. As soon as a pixel has been captured the frame controller 25 informs the memory address controller 28 that the pixel is ready for sending to memory. The memory address controller 28 generates an address for the SRAM 27 corresponding to where the pixel information from the A/D converter 4 can be stored. The memory address controller 28 controls the SRAM 27 to behave like an auto-incrementing FIFO stack so that captured pixels of the line images are stored sequentially within SRAM 27. Each pixel of each line image is thus stored into solid state memory for retrieval at a later point in time. The SRAM 27 may be constructed of a number of individual SRAM chips, with the number of chips depending on the amount of memory required to store the captured images. The more memories available, the more line images that can be stored. The SRAM chips within the memory are activated by the chip select 29 under control of the memory controller 28. As soon as a byte of information is available in buffer 26 from A/D converter 4, the frame controller 25 informs write controller 30, which enables the information of buffer 26 to be written to the memory location in SRAM 27 corresponding to the chip and memory location selected by memory address controller 28 and chip select 29. Whilst storing the captured line image to memory on a pixel by pixel basis, the sensor 2 would have commenced detecting the next line image of information under control of frame controller 25. The captured images would have been referenced and converted to digital pixel values and made available on buffer 26 ready for storing in memory. This process continues until computer 7 instructs control port 32 to cease capturing images, or when memory 27 is filled. When the operator instructs the computer to stop capturing images, the computer 7 communicates with control port 32 which is in communication with frame controller 25 and memory address controller 28. Frame controller 25 stops the sensor 2 and memory address controller 28 stops the solid state memory 27 from receiving information from buffer 26. Once all the necessary line images have been captured by the sensor and stored into SRAM 27, the line images are read back to computer 7 for further processing. In order to read the captured line images from solid state memory, the computer 7 indicates to the control port 32 to proceed with a read image procedure. Control port 32 resets the memory address controller 28, disabling further writing to solid state memory 27, and commences a procedure to sequentially communicate each pixel of the line images captured by sensor 2 and stored in SRAM 27 to the computer 7 for processing. The pixel data is communicated to data port 33 which is read by the computer 7. Port 33 may also be designed as a memory mapped address in order to improve the speed of the system. Each of the pixel values of the line images is then. read in the correct sequence into the computer's memory from the SRAM 27. From the read pixel values the computer 7 is able to reconstruct a time history of the finish line by placing each of the lines of pixels next to each other from right to left. Between each line of the image there is a discrete time difference due to sampling effects, and it is therefore possible to accurately determine the time difference between events which occur at the finish line. The image is displayed on display 36, and the operator can zoom into specific areas of the time history image by simply enlarging the captured pixels in the area of interest. At all times the computer 7 is made aware of the status of the solid state memory 27 and the sensor 2 through status port 34 which is connected to both the frame controller 25 and the memory address controller 28. In order to ensure the accuracy and integrity of the photo finish image, it is necessary to ensure that the sensor 2 is accurately aligned with whichever line has been defined as the winning line. Figures 4(a), (b) and (c) illustrate the mounting of the sensor 2 and the method of aligning the sensor 2. The photo diode array 22 of the CCD line scan sensor 2 is mounted on a carriage 41 on a body 40 of the photo finish system 1 which allows the photo diode array 22 to be moved with respect to the lens by sliding the carriage 41 left and right with respect to the body 40. Also mounted on the carrier spaced from the photo diode array 22 is an opaque ground glass 42. The ground glass acts as a screen onto which an image of the winning line is projected. This allows a direct visual verification of the alignment of the sensor 2 with the winning line. When aligning the sensor 2 with the finishing line, the carriage 41 is slid to the right so that the ground glass 42 is at the focal point of the lens 21. The photo finish system 1 is then aligned so that an image of the finish line is projected onto the ground glass. The carriage 41 is then slid to the left so that the sensor 2 is in the position where the ground glass 42 was. By fixing the distance between the ground glass and the sensor 2 and moving the carriage 42 by that amount only, it is possible to ensure that the sensor 2 is perfectly aligned with the winning line. The image seen on the ground glass is the image which the sensor 2 sees, rather than a derived image, such as one created with prisms. One problem all photo finish cameras suffer from is the perspective distortion which occurs due to the fact that objects further away from the observer appear smaller and distances between two object appear smaller at a distance. This can cause a distorted picture in photo finish cameras since the competitor most distant from the photo finish camera travels, as observed by the camera, less distance than a closer competitor. This effect can be observed when travelling in a car. Closer objects appear very blurred since they travel a greater apparent distance past the car than a more distant object. Similarly, photo finish cameras would record a more blurred image for closer competitors than for more distance competitors and significant distortion of the photo finish image can occur. This can give certain competitors a greater advantage in a photo finish situation, depending on their position in the field. According to one preferred embodiment of the present invention it is possible to compensate for the perspective distortion by altering the surface area of the light sensitive diodes in the sensor. This is done by distributing exposure over the sensor elements according to a radial exposure technique. One method of doing this is to place an exposure edge partially over the elements of the sensor, such that all of one element of the sensor at one end is uncovered, but subsequent elements are all covered to a greater extent so that each element appears progressively smaller and smaller. This creates a sensor with a "wedge" appearance. Alternatively, the sensor can be manufactured such that each element's surface area is smaller than its preceding neighbouring element. Such a sensor is illustrated in Figure 5, in which a sensor 2 has and end 61 where the elements 62 are smaller than the elements 62 towards the other end 63. The preferred embodiment of the present invention is particularly advantageous in that it is possible to capture a time history of the winning line in real time and store into memory. This provides a picture resolution far greater than that of other known technologies, such as still frame photography and video images. This speed is particularly achievable due to the development of static solid state memory which is much faster than conventional dynamic memory, and does not require complicated circuits to refresh the memory. " Another advantage is that the above embodiment overcomes many of the problems of the conventional time history photograph described above which required development and fixing. Using the preferred embodiment of the present invention it is possible to obtain a picture virtually instantaneously and allows a person with very little knowledge of the system to obtain a photo finish photograph and to enlarge areas of interest. It is also possible to produce colour images with a colour sensor, which is not possible with known systems. Furthermore, a greater number of grey shades are available using the preferred embodiment of the present invention. Conventional photo finish cameras have less than 10 grey shades, whilst the present preferred embodiment can distinguish between more than 64 grey shades. It will be appreciated that features of the above invention may be varied for different applications, such as run-out monitors in cricket and line monitors at tennis games. The foregoing description of embodiments of the invention have been presented for purposes of illustration only. It is not intended to be exhaustive or to limit the invention to the embodiments, and many variations and can be made as would be obvious to one skilled in the art.

Claims: THE CLAIMS DEFINING THE INVENTION ARE AS FOLLOWS: 1. A line monitoring system for monitoring a plane in space, comprising: a line image capture means for capturing a plurality of line images of the plane in space over an interval of time, and an image storage means for storing the line images, wherein a image representing a time history of the plane in space is capable of being constructed from the line images stored in the storage means and displayed on a display means by placing the line images adjacent to each other. 2. A line monitoring system according to claim 1, further comprising a converter means for digitising the line images. 3. A line monitoring system according to claim 1 or 2, wherein the line image capture means comprises a line image sensor for producing an analog signal representing the line images. 4. A line monitoring system according to claim 3, wherein the line image sensor comprises a change coupled device (CCD) having a plurality of light sensitive elements arranged in a straight line. 5. A line monitoring system according to claims 2 and 3, wherein the converter means comprises an analog to digital converter for converting the analog signal into digital data. 6. A line monitoring system according to claim 5, wherein the storage means comprises solid state memory for storing the digital data produced by the analog to digital converter. 7. A line monitoring system according to any one of the preceding claims, wherein the line image capture means includes perspective correcting means for perspective correction of the line images. 8. A line monitoring system according to claim 7, wherein the perspective correcting means includes is comprised of a slit having two non-parallel edges in the same place. 9. A line monitoring system according to claims 4 and 7, wherein the perspective correcting means comprises an exposure edge which partially obscures the light sensitive elements, each element being obscured more than an adjacent element. 10. A line monitoring system according to claims 4 and 7, wherein the perspective correcting means is comprised of the light sensitive elements each having a different surface area, such that each element is smaller than an adjacent element. 11. A line monitoring system according to claim 3 further comprising a body, and the line image capture means further comprising a lens mounted on the body for focusing a line in space, being a side view of the plane in space, on the line image sensor, and an exposure edge on the body for aligning the line monitoring system to the plane in space. 12. A line monitoring system according to claim 11, further comprising a carriage onto which the line image sensor is mounted, wherein the carriage is movable with respect to the body so as to align the line image sensor with the plane in space. 13. A line monitoring system according to claim 12, wherein a ground glass is mounted on the carriage at a predetermined distance relative from the line image sensor, such that an image of the line in space can be formed on the ground glass when the carriage is in a first position, so as to provide a direct visual verification of the line images, and the line image sensor is aligned with the line in space when the carriage is in a second position, the second position being the predetermined position away from the first position. 14. A line monitoring system according to claim 3, wherein the line image capture means comprises a sensor control means for controlling the image sensor, including initialising the image sensor and providing timing signals for the image sensor and for synchronising the image sensor with the storage means. 15. A line monitoring system according to claim 3 or 13, wherein the line image capture means comprises a reference means for analysing the analog signal representing the line images to calibrate the analog signal relative to a black reference. 16. A line monitoring system according to claim 6, wherein the storage means comprises a memory address control means for generating an address at which the digital data is to be stored in the solid state memory and generating a write signal and chip select signal such that the digital data is stored in the solid state memory. 17. A line monitoring system according to claim 16, wherein the memory address control means controls the solid state memory to create a FIFO auto-incrementing stack to store the digital data sequentially so as to protect the integrity of the digital data. 18. A line monitoring system according to any one of the preceding claims, wherein the line image capture means and the storage means is capable of synchronous operation so as to maximise the operation rate of the line monitoring system and provide a single means for adjusting the operating rate of the line monitoring system. 19. A line monitoring system according to any one of the preceding claims, wherein the display means comprises a computer capable of interfacing with the storage means so as to retrieve the line images stored in the storage means and a display device onto which such retrieved line images are displayed adjacent to each other to generate the two- dimensional image. 20. A line monitoring system according to claim 19, wherein the computer is provided with means for determining events in time recorded by the line image capture means. 21. A method of monitoring a plane in space comprising the steps of: positioning a line image capture means for capturing a plurality of line images over an interval of time of the plane in space, capturing the plurality of line images over the interval of time and storing the line images in a digital storage means, constructing time history image representing a time history of the plane in space over the interval of time and displaying the time history image on a display means by placing the line images adjacent to each other. 22. A method according to claim 21, wherein the line image capture means produces an analog signal representing the line images and the analog signal is converted to digital data for storage in the digital storage means. 23. A method according to claim 22, wherein the time history image is produced by retrieving the digital data from the storage means and displaying the line images represented by the digital data on a display device by placing consecutive line images adjacent to each other on the display device. 24. A method according to claim 23, wherein events occurring at the plane in space are determined in time from the time history image. 25. A method according to any one of claims 21 to 24, wherein the line image capture means is positioned to capture the line images of the plane in space by placing a ground glass at a location to produce a focusing image of the plane in space on the ground glass and then positioning the line image capturing means at the location. 26. A method of obtaining a photo finish image of a finish line comprising the steps of: positioning a line image sensor to capture a plurality of line images over an interval of time of the finish line, capturing the plurality of line images over the interval of time and storing the line images in a digital storage means, constructing the photo finish image representing a time history of the finish line over the interval of time and displaying the photo finish image on a display device by placing the line images adjacent to each other.

Inventors: ALEXANDROVICS PETER JOHN, ALEXANDROVICS, PETER, JOHN
Applicants: ALEXANDROVICS PETER JOHN, ALEXANDROVICS, PETER, JOHN
Application year: 1993
Main classification: H04N7
IPC codes: A63K3, H04N7