Video Display Touch Detection Digitizer

This invention relates to apparatus for determining the coordinate location of a surface contact of a cathode ray tube (CRT) and, more particularly, to a touch detection apparatus which utilizes the synchronized light source of the CRT.

Modern video displays, such as interactive graphics stations, enable the operator or user to perform certain operations by selecting functions from a displayed menu of possible choices. At an interactive graphics station, user controlled functions typically involve selecting a system operating capability from a menu and then selecting the location on the display image where the operation is to be carried out. While the selection of the operation from the menu typically requires only a low resolution touch detection apparatus, the selection of the location on the image at which to perform the operation often requires a high resolution touch detector or digitizer. Existing digitizers which allow the user to select the X and Y coordinates either use high resolution off-the-screen digitizers or low resolution on-the-screen devices. The off-the-screen digitizer is undesirable since the user cannot work directly with the displayed image. The on-the-screen devices typically are touch sensitive devices where the resolution is limited by the resolution of the touch detection screen matrix or the pointer or finger used to touch the screen. What is desired is an on-the-screen device having the high resolution of off-the-screen digitizers.

The present video display touch detection digitizer solves the existing problems by providing an on-the-screen digitizer where a user can work directly on the image using either his or her finger or a pointer and, secondly, providing a resolution which is limited by the resolution of the display device.

According to the present invention, during the vertical blanking period, selected line scanning signals of the video display (CRT) are unblanked and a row of picture element (pel) sized dots of light are generated. Additionally, during the normal horizontal blanking period a column of pel-sized video dots are formed by unblanking the video signal and generating a column of pel sized dots, one for each scan line of the display. The row and column of lighted pel-sized light sources or video dots are reflected by mirrors across the face of the display forming, respectively, an X and Y coordinate matrix of light beams which are then reflected, respectively, to an X position and Y position detector. Control circuitry detects and calculates the X and Y coordinate location of the centroid of a pointer or a finger which interrupts the light beams and outputs an appropriate address signal in response thereto. A cursor generator receives this address signal and provides a cursor on the CRT display at the X and Y coordinates of the touch location.

The detailed description of the invention will be more fully appreciated from the illustrative embodiment shown in the drawing in which:

FIG. 1 shows a CRT illustrating the present invention;

FIG. 2 shows various possible dot generating arrangements for use with the present invention;

FIG. 3 shows a top view of apparatus for providing optical reflection and collection of the light beams or signals generated by the CRT of FIG. 1;

FIG. 4 shows a perspective view of the optical apparatus of the present invention in association with the CRT of FIG. 1;

FIG. 5 shows the video control and signal processing circuit of the present invention;

FIG. 6 shows the waveforms useful in describing the generation of a row of video dots used for horizontal address detection;

FIG. 7 shows the waveforms useful in describing the generation of a column of video dots used for vertical address detection; and

FIG. 8 shows the waveforms useful in describing the detection of interruption of light beams by the video control and signal processing circuit of FIG. 5.

Shown in FIG. 1 is CRT 100 arranged in a standard manner such that an electron beam from an electron gun (not shown) impinge upon a phosphorescent coating on the inner surface of the display screen or face 101 of the CRT in a raster scan pattern, sequentially line by line from top to bottom. As the electrons hit the phosphorescent inner surface, the screen 101 of CRT 100 glows. Illustratively, screen 101 and display area 102 of CRT 100 are shown as having a rectangular shape herein.

The screen 101 of CRT 100 is divided into two display areas 102 and 103. Typically, a bezel covers all but the display area 102 of the screen 101 of CRT 100. Display area 102 is the image display area which typically uses a medium-short persistence phosphor. According to the present invention, a coordinate display area 103 is used to generate the light beams or signals used in detecting the X, Y coordinates when the image area 102 is touched. Coordinate display area 103 may use a short persistence phosphor whose decay time is less than the image pel time.

Illustratively, coordinate display area 103 is further divided into areas or sections 104 and 105. Section 104 generates the row of discrete light sources or video dots 105 used in detecting the X coordinate of display area 102. During the normal vertical blanking period, the video signal is unblanked and a row of dots 106 are generated in section 104, where the number of dots may be equal to the number of picture elements (pels)/line in the image display area 102. Section 105 generates the discrete light signals used in detecting the Y coordinate of display area 102. During the normal horizontal blanking period, the video signal is unblanked for about one pel period and a column of video dots 107 are generated in section 105, where one dot may be generated for each horizontal line in the image display area 102.

As shown in FIG. 1, when a resolution of less than 1 pel is desired, the number of dots in row 106 and column 107 are less than the number of pels/line or number of video scan lines, respectively. However, when a resolution of one pel is desired, each pel in the image display area 102 is defined by a dot of light (one per pel) determining its X coordinate and a dot of light (one per scan line) determining its Y coordinate.

Even though display area 104 may use a short persistence phosphor, once a dot in row 106 is illuminated by the scanning electron beam, it is likely that the time constant of the phosphor persistence will cause that dot to glow for a while after the scanning electron beam has moved to the next dot in row 106. Since the ability to detect when a particular area of the display has been touched is enhanced when only one dot at a time is illuminated, the arrangements of dots shown in FIG. 2 would improve detection.

Shown in FIG. 2 are two dot arrangements, 201 and 202, for section 104 using 2:1 interlaced raster scanning. Dot arrangement 201 uses dots which alternate between field 1 (f1) line n and field 2 (f2) line n. In 201, the odd pels (P1, P3, P5, etc.) light dots are generated first during field f1 line n, while the even pels (P2, P4, P6, etc.) light dots are generated during field f2 line n. Thus, the elapsed time between the illumination dots on the same line, e.g., pel P3 and pel P1 is two pel times rather than one pel time, when all the dots are on the same frame and line number. Hence, the effects of the persistence of the phosphor on touch detection accuracy is reduced. The result is that touch detection accuracy is enhanced or that the same touch detection accuracy can be had with phosphor having a time constant twice as long. Shown in 202 is another possible dot arrangement where the dot for every pel in the display, P1-PM, is generated alternately on frame F1 field f1 line n, frame F1 field f2 line n, frame F2 field f1 line n+1 and frame F2 field f2 line n+1. Since there are four pel times between dots on the same frame and line, there is an effective reduction of the persistence time constant of the phosphor by about a factor of four. Obviously, the techniques described above can be utilized to generate lines of dots on successive frames rather than on successive fields of the display. Note, since there is a scan line time period between the generation of each dot in the column of dots 107, the utilization of dot arrangements similar to those discussed above are typically not required for section 105.

FIG. 3 shows a top view of the optical apparatus and photodetector layout for detecting the Y coordinate of the image display area 102. The layout for detecting the X coordinate is identical except that it is rotated 90 degrees with respect to the layout for the Y coordinate.

In one embodiment, a front surface mounted light deflector or mirror 301 is placed in front of the column of Y coordinate dots 107 and angled to deflect the light beams 302 generated by dots 107 across display area 102 of CRT 100 as illustrated by the dashed lines 303. The resulting row beams of light, 303, crossing the screen of CRT 100 are collected and focused, 305, by a parabolic reflector 304 or equivalent optical apparatus onto the Y coordinate photodetector 306. This optical apparatus layout provides a means for generating rows of scanning light beams across the image display area 102 of CRT 100, one for each horizontal scan line in the displayed picture. Obviously, if desired the disclosed apparatus can be arranged to deflect the light beams across any predetermined part of the image display area 102.

Shown in FIG. 4 is a perspective view of CRT 100 with mirror 301, deflector 304 and photodetector 306. Also shown in FIG. 4 is an equivalent optical apparatus layout, including front surface mirror 401 for deflecting light beams generated by the row of X coordinate dots, parabolic reflector 402, and photodetector 403 for detecting the columns of scanning light beams which cross display area 102. It is contemplated that other light collecting means, e.g., multiple photodetector means, could be appropriately positioned to obviate the need for parabolic reflectors 304 and 402.

With joint reference to FIG. 3 and 4, if a finger or pointer object, e.g., 307 is used to select or point to a location X1, Y1 on display, 102, the resulting interruption of the beams of light, e.g., 303 and 403, at the selected location X1, Y1 is detected at photodetectors 306 and 403. This interruption of light is processed by circuitry, discussed in subsequent paragraphs, to determine the X and Y coordinates of the pel selected on the display (or the centroid if the pointer covered multiple pels on the display) by pointer 307. Note, since all the row scanning beams of light are focussed 404 onto one photodetector 306 and all the column scanning beams of light are focused 405 onto one photodetector 403, the processing circuitry requires the scan timing signals of CRT 100 to determine the exact row(s) and column(s) of light beams interrupted by pointer 307.

Shown in FIG. 5 is the control and signal processing circuits of the present invention. These circuits includes sync, address, blanking and video circuits 50; dot generator 51; and coordinate detector 52. Illustratively, in the following description the CRT is assumed to operate at the standard television interlaced field format.

In video circuit 50, the standard system clock 500 generates a clock signal at the pel rate, which is applied over lead 501 to horizontal sync generator 502, AND gate 503, and divide by two counter circuit 504.

Horizontal sync generator 502 and vertical sync generator 505 utilize well known counting circuits to generate X and Y coordinate address information as well as the standard synchronization signals used for cameras and video display devices. Lead 506 supplies vertical sync generator 505 with a 2X horizontal pulse from the horizontal sync generator 502 to provide the arrangement or digitizer system with standard 2:1 interlace. Lead 507 from horizontal sync generator 502 and lead 508 from vertical sync generator 505 supply well known deflection amplifiers 509 with standard drive pulses to generate scan or sweep signals for CRT 100. The horizontal sweep signals on lead 510 and the vertical sweep signal 511 are applied to the corresponding deflection yokes of CRT 100.

Video combiner 512 receives standard baseband video signals on lead 513, standard vertical blanking signals on lead 514, standard horizontal blanking signals on lead 515, the inventive row of dot signals on lead 516, the inventive column of dot signals on lead 517 and a cursor signal on lead 518. These signals are combined, using standard techniques, to generate a composite video signal on lead 519 which is applied to CRT 100. These combined signals cause CRT 100 to display the usual video signal in image display area 102, and to display a row of dots in area 104 and a column of dots in area 105 of the conventionally blanked areas of the screen.

The displayed row of dots (i.e., 201 of FIG. 2) is generated from signals from dot generator 51. With joint reference to FIG. 5 and 6, vertical sync generator 505 selects one horizontal scan line period per field, 601 of waveform 60, near the end of its normal blanking period, 600, and outputs on lead 520 to one input of AND gate 521 a positive pulse, waveform 61, for the 63 .mu.sec duration of that horizontal scan line period.

Horizontal sync generator 502 supplies its blanking signal (waveform 62), which is high during the active display time 602, on lead 515 to the other input of AND gate 521. The output, lead 522, of AND gate 521 which is high during the active display time, 603, of one horizontal scan period of a field, waveform 63, is applied to AND gate 523. This signal gates the row of dot signals used in determining the X coordinate or horizontal address. This input 522 in combination with the divided by two clock signal, waveform 64 on lead 524, causes AND gate 523 to output one line of signals at one-half the pel rate on lead 516. As shown in waveform 64, the signals for one-half of the row of dots are generated in each field, F1 and F2, for a total of 512 dots/frame for a standard broadcast video picture. Obviously, if a half horizontal detection resolution is desired, such as shown in 106 of FIG. 1, only the field 1 or field 2 signal of waveform 64 need be used.

The signals for 2 fields on lead 516, as shown in waveform 65, is applied to video combiner 512 and AND gate 525. Video combiner 513 generates the signals which result in a display of a row of dots on the screen of the CRT. As noted, when a lower touch detection resolution is desired, dot generator 51 can be arranged to provide dots at less than the pel rate.

The displayed column of dots (i.e., 107 of FIG. 1) is also generated from signals from dot generator 51. With joint reference to FIG. 5 and the waveforms of FIG. 7, horizontal sync generator 502 generates, in a standard manner, a signal 526, which is less than the width of two clock periods, waveform 71, at the trailing edge of the normally blanked segment of the horizontal scan signals, 701 of waveform 70. This signal is applied on lead 526 to AND gate 503. This signal in combination with the clock pulses 501, waveform 72, on lead 501 causes AND gate 503 to generate a positive pulse signal on lead 517 which is one pel time wide each horizontal scan line period of each frame as shown by waveform 73. The signal on lead 517 is applied to video combiner 512 which generates a signal to produce a column of dots, one per scan line on the CRT. This column of dots provides Y coordinate or vertical address information. The signal on lead 517 is also applied to AND gate 534 in the detector circuit 52. Obviously, if a lower touch detection resolution is desired, dot generator 51 can be arranged to provide less than one dot per horizontal scan line (e.g., one dot for every two scan lines, etc.).

Coordinate detector 52 determines both the X and Y coordinates of the display area touched by a finger or pointer. With joint reference to FIG. 4, FIG. 5 and the waveforms of FIG. 8, the determination of the X-axis touch coordinate is desired. The X axis photodetector 403 generates on lead 528 a string of logic 1s, one for each pel of a horizontal scan line of a frame, waveform 80, if the light beam path across the face or screen of CRT 100 is not interrupted. When the light path is interrupted, the absence of light on X-axis photodetector 403 causes one or more logic 0s to appear on output lead 528 (depending on the size of the point or finger, 307 of FIG. 3). The logic 0s on lead 528 are converted to logic 1s by inverter 529 and appear as waveform 81 on output lead 530. Lead 530 is ANDED with row dot signals on lead 516, waveform 82, to produce logic 1s, waveform 83, on lead 543 of AND gate 525. The logic 1 signals on lead 543 are gated by AND gate 544 to lead 529 using the horizontal blanking period signal on lead 527. Lead 529 applies the logic 1s, each representing an X coordinate, X1, or pointer 307, to the input of the X averaging circuit 530, which determines or calculates the average X coordinate or address. The average or centroid of the X address (X1 of waveform 83) is calculated because the size of point 307 will probably block the light coming from several dots. The X averaging circuit 530 is reset once each frame time by a pulse arriving on lead 531 from vertical sync generator 505.

The Y-axis touch coordinate determination and calculation are processed in the same manner as the X-axis address. Thus, Y-axis photodetector 306 generates on lead 531 a string of logic 1s, one for each horizontal scan line, as long as light is received and, accordingly, generates one or more logic 0s when the light is interrupted. Output 531 from Y-axis photodetector 403 is inverted in inverter 532 and gated with the column dot signals on lead 517 in AND gate 534. The output 535 of AND gate 534 is gated in AND gate 537 with a vertical blanking interval signal on lead 536. The output 538 of AND gate 537 is applied to Y averaging circuit 539 which determines or calculates the average Y coordinate address. The Y averaging circuit 539 is reset once each frame from a signal on lead 531 from vertical sync generator 505.

The output of X averaging circuit 530 on lead 540 and the output of Y averaging circuit 539 on lead 541 are applied to a well known cursor generator 542, which generates a signal on lead 518 which is combined with other signals by the video combiner 512 to place a video dot or mark in the active display area 102 on CRT 100 to indicate the X1, Y1 coordinate location to which pointer 307 pointed. The X and Y coordinate or address signals on leads 540 and 541, respectively, may also be used by other circuitry in another part of the video system (not shown) to select a pel or parts of the picture for special processing.

What has been disclosed is merely illustrative of the present invention. Equivalent components and circuitry are well known which can replace the apparatus or devices shown and described herein. Thus, while the present invention was particularly described for use with a CRT, it is contemplated that the invention can be utilized with any raster scanned video display by implementing a coordinate display area equivalent to the one disclosed herein by utilizing the technology or the devices utilized to implement the associated image display area. Additionally, it is contemplated that the disclosed circuitry can be incorporated into and implemented as part of any system incorporating a scanned video display terminal. Hence, other arrangements can be implemented by those skilled in the art without departing from the spirit and scope of the present invention.