Abstract:
A device and method for displaying variable brightness characters in a video surveillance system is provided. The system includes cameras coupled to a switch having video display monitors and a controller. The switch includes a digital logic unit for generating characters, receiving the input brightness, comparing the input brightness with a critical level, and controlling the appearance of the characters. The character generator produces pixel data that includes a body for the each character, and a dark border surrounding each character. The character data enters a shift register for processing prior to superposition with the video signal. Character brightness is variably selectable by a user. A comparator in the logic unit compares the input brightness with a preset critical level stored in the logic unit. If the input brightness is at or below the critical level, the comparator commands the shift register to remove the dark border from the characters.

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
       [0001]    This application is related to and claims priority to U.S. Provisional Application Serial No. 60/280,875, filed Apr. 2, 2001, entitled VIDEO SYSTEM AND METHOD, the entirety of which is incorporated herein by reference. 
     
    
     
       FIELD OF THE INVENTION  
         [0002]    The present invention relates to video displays, and in particular, to a device and method for displaying variable brightness characters on a surveillance system video display.  
         BACKGROUND OF THE INVENTION  
         [0003]    Video surveillance systems often use character data and text symbols superimposed over a video signal. The resulting composite display of video and text information enables the system to deliver broader, more robust and often real-time information about a scene under surveillance, such as date, time, alarm conditions, scene conditions, and other information. The characters may be generated by a separate device or by the same processors and circuitry which control the central elements of the surveillance system, such as a keyboard controller, camera controller, or multi-purpose switch.  
           [0004]    One way to produce high quality alphanumeric characters is to generate black outline characters, where bright characters are surrounded by a ring of dark video. In this way, the characters seem sharper and can be seen on bright backgrounds, such as a white cloud. In many systems, it is often advantageous to offer the ability to adjust the brightness of the symbols or characters. However, when the symbol brightness is reduced, it begins to look like the black outline, and the overall legibility and sharpness of the character text is reduced.  
           [0005]    It is desirable therefore, to provide a device and method for displaying variable brightness characters on a video display, where the overall legibility and sharpness of the character text is not reduced when the character brightness is reduced past a critical level.  
         SUMMARY OF THE INVENTION  
         [0006]    The present invention advantageously provides a method and system for adjusting the display of character borders superimposed with a video signal.  
           [0007]    According to an aspect, the present invention provides a device for generating characters on a video display. A character generator generates a first character data signal. A comparator has an input to receive a character brightness code in which the comparator compares the character brightness code with a reference code to produce a character shift command. A shift register is configured to receive the first character data signal from the character generator and to receive the character shift command from the comparator. The shift register produces a second character data signal in response to the character shift command.  
           [0008]    According to another aspect, the present invention provides a video system which includes a camera producing a video signal, a keyboard controller, a video display unit, operatively connected to each other through a switch. The switch includes a character generator. The character generator generates a first character data signal. The switch includes a comparator which receives a character brightness code and compares the character brightness code with a reference code to produce a character shift command. The switch further includes a shift register which is configured to receive the first character data signal from the character generator, and to receive the character shift command from the comparator. The shift register produces a second character data signal in response to the character shift command.  
           [0009]    In yet another aspect, the present invention provides a method of generating characters for a video display in which a reference brightness code is stored. A first character data signal corresponding to a first set of characters is generated. Each character includes a body and a border. The character brightness command is received. A character brightness code is generated corresponding to the character brightness command. The character brightness code is compared with the reference brightness code to determine a character shift command. The character shift command includes one of a no action command and a remove border command. A second character data signal is generated in response to the character shift command. The second character data signal is identical to the first character data signal if the character shift command includes the no action command. The second character data signal includes a second set of characters if the character shift command includes the remove border command.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]    A more complete understanding of the present invention, and the attendant advantages and features thereof, will be more readily understood by reference to the following detailed description when considered in conjunction with the accompanying drawings wherein like elements have like reference designators:  
         [0011]    [0011]FIG. 1 is a block diagram of an exemplary video surveillance system arranged in accordance with the principles of the present invention;  
         [0012]    [0012]FIG. 2 is block diagram of the character generation and display processors in the logic unit and circuitry of the switch displayed in FIG. 1;  
         [0013]    [0013]FIG. 3 is a flowchart of the character generation and display process controlled by the processors shown in FIG. 2; and  
         [0014]    [0014]FIG. 4 is an exemplary embodiment of several characters of varying brightness displayed in a video background. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0015]    Referring now to the drawing figures, in which like reference designators refer to like elements, there is shown in FIG. 1 a block diagram of a video surveillance system, such as a closed circuit television (CCTV) system, for use in monitoring multiple scenes from multiple locations, constructed in accordance with the principles of the present invention and designated generally as 100. System  100  includes up to “m” video cameras  105   a,    105   b,  through  105   m,  along with up to “n” video monitors or displays  110   a,    110   b,  through  110   n,  (where “m” and “n” are whole numbers) coupled to a video switch, having at least one keyboard controller  120  connected thereto.  
         [0016]    The cameras  105  maybe any of a variety of video or still cameras, acquiring a picture using a lens, iris, zoom and focus controls, integrated optics package, or other image acquisition device. The cameras  105  may be included inside of a housing such a semi-hemispherical dome, suitable for affixation onto a surface. The housing may also include a set of orientational controls, such as pan and tilt motors and actuators for moving and orienting the direction of the image acquisition device. An example of such a camera  105  and housing is the SPECTRA series of video surveillance units manufactured by Pelco.  
         [0017]    Each camera  105  is connected to the video switch  115 , such a multi-imput and output “matrix” switch. The switch  115  contains a variety of components, including a computer and control circuit electronics for controlling the operation of each camera  105 , through commands and codes received by the keyboard controller  120 . Both the cameras  105  and keyboard controller  120  may be disposed at remote locations from the switch  115 . The switch  115  is further connected to a number “n” of monitor displays  110 . The “matrix” therefore, contains m X n channels for m camera inputs and n monitor outputs. One example of such a matrix switch is the CM 6800 switch manufactured by Pelco, which provides m=48 and n=8. The keyboard controller  120  is further used to control the appearance of the video signals on the monitors  110 , such the overall brightness, contrast, and the nature of the display of character text onto the images acquired by the cameras  105 , as more filly described below.  
         [0018]    The switch  115  includes a character generation control unit  200 , for generating and controlling the character data to be displayed on the video signal acquired from the cameras  105 . FIG. 2 is a block diagram of various elements included in the character generation control unit  200 . The character generation control unit  200  includes a character generator  205 , a comparator  210 , a shift register  215 , and a multiplexor (MUX)  220 . The various inputs to these devices are a reference constant such as a three-bit constant, or “critical level”  225 , an input character brightness code  230  such as a three-bit code, a stream of input commands from the keyboard controller  120  of FIG. 1, and a video signal  240 . The resultant output  250  is a composite analog video signal with characters superimposed thereon.  
         [0019]    The comparator  210  is preferably a 4-bit logic unit, such as a Field Programmable Gate Array (FPGA) device, programmed with Very-High Speed Integrated Circuit Hardware Description Language (VHDL) code. Only 3 bits are used, with 1 bit tied to the ground. The comparator reads the 3-bit input brightness command  230 , representing a character brightness which is variable over discrete levels, such as 8 discrete levels, from “7” to “0” (or 111 to 000 represented in binary), with “7” being the highest level of character brightness, and a “0” being the lowest. The user of system  100  selects the character brightness using the keyboard controller  120  shown in FIG. 1. The user-selected input brightness, represented as the input brightness  230 , is read into the comparator  210 . Comparator  210  also reads a reference critical level  225 , representing a preset threshold brightness level preprogrammed into the unit  200 , and referenced to ground. While the critical level  225  may vary from “7” to “0”, a preferred setting is at level “2” brightness, or 010 in binary. The comparator  210  is arranged to compare input  230  with the critical level input  225 . If input  230  is greater than critical level input  225 , then the comparator sends a “border on” or “no action” command to the shift register  215 . If the input  230  is greater than the critical level input  225 , then the comparator sends a “border off” command to the shift register  215 .  
         [0020]    Character generator  205  generates a character data signal, namely, black and white pixel data representations for text characters and other desired symbols, according to a preprogrammed font set stored in a memory (not shown) in the switch  115 . The character data generated by the generator  205  includes both the character pixels themselves, the “body” of the character, and a ring or of border pixels around the body. The ring of border pixels, or character border, is generally a set number of pixels, such as 2, that completely circumscribe and surround the body, with space in between, and are generally black pixels. Of course the present invention is not limited to black and white pixelized characters. Color characters can also be implemented as an aspect of the present invention.  
         [0021]    The resulting character data, body and border, is routed into shift register  215 . As long as the comparator sends a “border on” or “no action” command to the shift register  215 , the character data sent by character generator  205  is unaltered and proceeds directly into the MUX  220  for superimposition with the camera video system. If however, the comparator  210  sends a “border off” or “remove border” command to the shift register  215 , then the shift register removes the character border pixels, or shift such border pixels to represent video only.  
         [0022]    The resulting character data signal, with or without borders, is then routed to the MUX  220  as shown. The entire process carried out by the comparator  210 , character generator  205 , and shift register  215  may be executed on one or more FPGA units, with each subcomponent programmed with a suitable code such as VHDL. In other words, the foregoing comparison of inputs  225  and  230  by comparator  210 , character generation  205 , and shifting by shift register  215  may all represent a FPGA implementation of a VHDL code.  
         [0023]    Once the digital character information enters the MUX  220 , it is combined with the video signal  240  acquired from any one of the cameras  105 . The MUX  220  thereafter superimposes the characters over the video, and a composite signal  250  is output to one or more of the monitors  110 . The brightness of the characters displayed is adjusted by the video display circuitry connected to any one of the monitors  110 , as adjusted by the user and corresponds to the selected input brightness code discussed in reference to FIGS. 2 and 3.  
         [0024]    [0024]FIG. 3 shows a flowchart illustrating the process by which the characters are added to the video signal as discussed with regard to FIG. 2. The process starts at step S 300 , whereby the video surveillance system  100  of FIG. 1 is activated and acquires a video signal from one of the cameras  105  of FIG. 1. The signal is received by the matrix switch  115  for routing and processing therein. The user defines and selects a character brightness, and the comparator  210  reads the command code from the keyboard controller  120  representing such character brightness (“IB”) (step S 305 ). At step S 310 , the comparator  210  retrieves the critical level (CL) brightness stored therein. The comparator determines the outcome of such comparison (step S 315 ). If IB&gt;CL, then the process proceeds to step S 320 , where the comparator  210  does not alter the characters routed through the shift register  215 . If IB is less than or equal to CL, then the process proceeds to step S 322 , where the shift register removes the black border pixels from the character data produced by character generator  205 , leaving a “no action”, or “video only” command instead. In either case, the process proceeds to step S 325 , where the character data is output from the digital logic circuitry of the character generation unit  200  to the MUX  220 , and the character data is combined with the analog video signal.  
         [0025]    [0025]FIG. 4 shows an exemplary representation of eight characters,  400   a  through  400   h  (referred to collectively herein as characters  400 ), superimposed on a video background  410  on a monitor viewing area  420 . Each character  400   a - 400   h  includes a respective body  430   a - 430   h,  and may or may not include a border  435 . The characters are of varying brightness. And in this embodiment of the present invention, the brightness levels vary in eight discrete levels from “7” to “0”. The following table sets forth the brightness levels for each displayed character  400 :  
                                                     Character   Brightness (Decimal)   Brightness (Binary)                                400a   7   111       400b   6   110       400c   5   101       400d   4   100       400e   3   011       400f   2   010       400g   1   001       400h   0   000                  
 
         [0026]    As shown in FIG. 4, if the critical brightness level is set at “2” or 010, when the comparator  210  in FIG. 2 reads this critical level and compares the character brightness thereto, a character brightness of “2” or less results in a character without the dark border, as characters  400   f,    400   g,  and  400   h  shown. It is understood, that although a 3 bit character brightness is discussed herein, a much wider, or narrower, range of character brightness may be implemented. Furthermore, critical brightness itself need not be stored in the device for automatic operation, but may be manual adjusted by the user through keyboard  120 , or some other suitable input device. The present invention advantageously incorporates the character generation unit  200  in the matrix switch  115  to generate characters with dark borders which may be selectably turned on or off based on a comparison to a threshold brightness. This allows for easier viewing of characters imposed on a background signal that may vary greatly in brightness. To retain a measure of sharpness and legibility, the user may adjust the character brightness, which thereafter may trigger the character border to switch off if the adjusted brightness is lower than a threshold level, as elaborated above.  
         [0027]    It should also be readily understood that the foregoing description of the invention is not strictly limited to video surveillance systems. Rather, the foregoing implementation of a character border around a character body of varying brightness, wherein such border is automatically turned off if the brightness is lowered beyond a set threshold, may be applied in any system which includes a video signal, a display device such as a monitor, and is connected by a network. The network may be wireless or wired, and may include other components to process and condition the video signal.  
         [0028]    It will be appreciated by persons skilled in the art that the present invention is not limited to what has been particularly shown and described herein above. In addition, unless mention was made above to the contrary, it should be noted that all of the accompanying drawings are not to scale. A variety of modifications and variations are possible in light of the above teachings without departing from the scope and spirit of the invention, which is limited only by the following claims.