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Publication numberUS3918039 A
Publication typeGrant
Publication dateNov 4, 1975
Filing dateNov 7, 1974
Priority dateNov 7, 1974
Also published asCA1056967A1
Publication numberUS 3918039 A, US 3918039A, US-A-3918039, US3918039 A, US3918039A
InventorsClark Robert John
Original AssigneeRca Corp
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
High-resolution digital generator of graphic symbols with edging
US 3918039 A
Abstract
A graphic symbol, completely digital, video signal generator, suitable for use in a television broadcast display control system, derives high resolution (50 nanosecond video dot period) symbols with edging employing off-the-shelf low resolution (200 nanosecond period) shift registers. This is accomplished by employing four different phase clocks each having a low repetition rate (5 MHz). Separate independent edge key and monochrome video signals are derived as the symbol video output of the generator.
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[ Nov. 4, 1975 3,725,723 4/1973 Colston e1 340/324 AD $786,478 l/l974 340/324 AD 3 786,48l l/I974 Hartman.i.i.u,......,....i.i 340/324 AD 1812,491 5/l974 Barrzlclough et 340/324 AD Primary ExaminerDavid L. Trafton Attorney, Agent, or Fz'rmEdward J. Norton; George J. Seligsohn [57] ABSTRACT A graphic symbol, completely digital, video signal generator, suitable for use in a television broadcast display control system, derives high resolution (50 nanosecond video dot period) symbols with edging employing otf-the-shelf low resolution (200 nanosecond period) shift registers. This is accomplished by employing four different phase clocks each having a low repeti- GENERATOR OF GRAPHIC SYMBOLS WITH EDGING Inventor: Robert John Clark, Dorion, Canada Assignee: RCA Corporation, New York, NY.

Filed: Nov. 7, 1974 Appl. No: 521,784

US. Cl. 340/324 AI); 178/75 D Int. G06F 3/14 Field of SearchWHW. 340/324 AD; 178/745 D,

l78/DIG. 22

References Cited UNITED STATES PATENTS United States Patent Clark I HIGH-RESOLUTION DIGITAL Y o y e S g e e 4 ii 252 s A. m m d mwmm m5: Sumo c .HH M "n e e m 65 $523 5 m a we m .w r a 25 F0 m P am 2 e m we 4 an mmu u A500 w H e; ra pm fi e 0 m m i d e l n u u l l| i i .m m m We 52 m a s w v C m h m m 35; 4r M m m m m 165 a 22 Km iv E D VMMW e i we 9 i ysr any e mm mm D s l C a m i 25% m mvwm m an H .n\. f oronx 2 ill r W A o a 533 4 2 E H m t O 6 26 5 2E 52; h 0 Q 4 M l 2 M 0 w 6 m 4 4 0 m 5 w 5 r m m r23 m o s m -9% w w w N c o 0 25m w w 4 e m o c was 58 m 0 n or 9 2222 r m w A m G 25 W n l P 4 ECU rlllrlll 2 I o m o m 5 Li F E E o 0 0 0 A a c 0 A m Q m flab HT MEMM 000m 0000 Q wwww m M M D no l l V W W W V W V W M w E N D D D D D L BM Q A A A A A l mm L 4 4 4 4 4 0 P .HOE 0 4 n n n n w w wmm o m o m w mwww o s m 4 4 4 4 4 A 3 3 3 1 3 TNEE l. H H m mmw 6 B m w. sstc m ws U o w m A mM m 0 L H S RNFEP 4 h m wS DEM m I W 4 WWW. H H a I, H Cr n r t a n om nn t a m a t m e t e WEE n e k TT TL ARM 8 m mm so WW mmwmw Mmr mmm m m mw mm D S S W D M0 Wm AR 1) D0 5 l 2 2 2 6 7 7 7 7 D 9 9 9 9 9 R 0 H HHHH 0 m 0 5 4 3 7 7 NNK B 4 A v N w E 0%? K 8 9 Z 7 6 5 O 8 7 9 7 3 .2 2 3 O0 00 O u 8 7 4 7 00 b 3 3 3 3 3 U.S. Patent Nov. 4, 1975 Sheet 1 GT5 3,918,039

HDRIVE: L IFE O /l00 PRIOR ART SIGNAL T SOURCE IZBEQ v DRIvE H2 I GRAPHIC COMPOSITE SYMBOL vIDEo DIGITAL SIGNAL TO VIDE SYMBOL DERIVATION TRANSMITTER SIGNAL GEN vIDEO MEANS COMPOSITE VIDEO /II4 SYMBOL ll0 /||8 DISPLAY a TIMING AND COLOR IGOLOR CONTROL MEANS CONTROL TELEVISION BROADCAST DISPLAY CONTROL SYSTEM 6 BIT 9 BIT CHARACTER SYMBOL GENERATOR ADDRESS STORES 64 CODE SYMBOLS (8x a MATRIX) I GENERATOR MEMORY 200 3 BIT Tv LINE A BIT DOT PATTERN CODE 204 CODE TV SYNC SYMBOL LOAD DOT PULSE 2 2? TV BLANK I O REGISTER SERIAL vIDEO OUT PULSE OUTPUT DOT CLOCK PULSESEA 202 vIDE0 MIXER/AMP LOW RESOLUTION PRIOR A RT CHARACTER GENERATOR U.S. Patent Nov. 4, 1975 Sheet 2 of5 3,918,039

6 EBT SYM L STORES e4 CODE 300 SYMBOLS ADDRESS CHARACTER (32 32 MATRIX) /6'. 34

GENERATOR MEMORY 5 BIT TV LINE /52 BIT DOT PATTERN CODE 306 CODE 32 BM Tv SYNC 304 SEER/5% SYMBOL LOAD DOT PULSE SHIFT TV BLANK DELAY AR REGISTER SERIAL VIDEO LINES PULSE OUTPUT DOT CLOCK PULSES 302 HIGH RESOLUTION RM Affl CHARACTER GENERATOR WITH SYMBOL EDGING DEVICE 5 T 32 x 32 MATRIX MATRIX SYMBOLS SYMBOLS F/G'. 2B F/G. 3L9

2(50 ec) DOTS (minim uni) i 2 TV LINES PER FRAME (minimum) H6. 30

MONOCHROME EDGE KEY VIDEO VIDEO US. Patent Nov. 4, 1975 Sheet 4 of5 3,918,039

CLOCK TIMING so NANOSECONDS 5o NANOSECONDS TTI IT- DOT CLOCK l I I PHASE A CLOCK f I FL ['1 Fl I- PHASE B CLOCK FL FL ['1 F] H PHASE 0 CLOCK I L T1 I I FI I I PHASE 0 CLOCK I' I I L I I I L I I VIDEO SHIFT REGISTER LOAD TIMING SYMBOL DISPLAY SYMBOL I SYMBOL 2 SP E 32 pu sEs 32 PULSES- PHASE A CLOCK JUL--- LOAD DOTS PULSE I' I US. Patent Nov. 4, 1975 Sheet 5 of5 3,918,039

PHASEA CLOCK Fl FL FL PHASE B CLOCK n n n PHASE 0 CLOCK Fl Fl FL PHASE 0 CLOCK 1 1 L VIDEO A DOT PULSE l 1 vmeo A DOT PULSE FL VIDEO AI 0R A2 DOT PULSE J L VlDEO Al' 0R A2 DOT PULSE L VIDEO B DOT PULSE l l VIDEO B DOT PULSE VIDEO Bl 0R B2 DOT PULSE l" l VIDEO Bl 0R B2 DOT PULSE l VIDEO (2 DOT PULSE I' L VIDEO (2' DOT PULSE Fl VIDEO Cl 0R c2 DOT PULSE VIDEO cl OR 02' DOT PULSE 1 VIDEO D DOT PULSE I l VIDEO 0' DOT PULSE FL VIDEO 0| 0R D2 DOT PULSE J l VIDEO 0| OR 02' DOT PULSE FL TIMING DIAGRAM-VlDEO OUTPUT PULSES F/6. 6

HIGH-RESOLUTION DIGITAL GENERATOR OF GRAPHIC SYMBOLS WITH EDGING This invention relates to the digital generation of video signals manifesting characters or other graphic symbols and, more particularly, the digital generation, in a manner suitable for television broadcasting, of video signals manifesting high resolution graphic symbols with edging.

For many purposes, such as in a conventional video terminal, the display on a television monitor of relatively low resolution graphic symbols without edging is perfectly acceptable. By way of example, in most video terminals, each symbol is composed of a dot matrix of only 5 X7 dots. While this resolution is sufficient to provide intelligibility of a displayed message composed of such character symbols, it is insufficient to meet the high resolution requirements of broadcast television. To provide the high resolution which is most desirable in broadcast television, each character or other graphic symbol should be composed of a much larger dot matrix, such as a 32 X32 dot matrix for example.

The clock rate, (in the order of 5 MHZ) required for the digital generation of low resolution graphic symbols without edging (such as employed in conventional video terminals) is compatible with the switching speeds of standardly available shift registers and the other standard elements of video-signal digital generators. Further, 5 MHz is compatible with the video passbands of television monitors and standard television sets. However, the clock rate (in the order of MHZ) required for the digital generation of high resolution graphic symbols with edging is higher than the switching rates of standard shift registers and the other standard elements of a digital generator of high resolution graphic symbols with edging. In addition, a 20 MHz clock rate provides a dot duration of only 50 nanoseconds which, due to the video bandwidth and response time of a standard television set, is much below the approximately 150 nanosecond minimum required to maintain symbol brightness in both black-and-white and color television sets, and is even further below the minimum of approximately 200 nanoseconds required to obtain satisfactory symbol color saturation in color television sets. For these reasons. in the past, generators of high resolution graphic symbols with edging for use in television broadcasting were not completely digital in construction, but required expensive analog elements which were capable of operating effectively at a high clock rate (in the order of 20 MHZ).

In accordance with the principles of the present invention, there is disclosed and claimed a completely digital generator of high resolution graphic symbols with edging. This is accomplished by providing fourphase television video signals, each at a relatively low clock rate and then using these four-phase TV video signals for deriving the required high-clock rate output video signals from the digital generators.

These and other features of the present invention will become more apparent from the following detailed de scription taken together with the accompanying drawing, in which:

FIG. I is a block diagram of a typical prior art television broadcast display control system, of a type which provides the display of graphic symbols.

FIG. 2a is a block diagram of a typical low resolution prior art digital character generator, and FIG. 2b illus- 2 trates a typical low resolution character generated by the generator of the type shown in FIG. 2a;

FIG. 3a is a block diagram ofa typical high resolution prior art character generator with a symbol edging device. FIG. 3b is a dot matrix of a high resolution charac ter without edging, and FIG. 30 shows a typical high resolution character with edging;

FIG. 4 is a block diagram of a graphic symbol digital video signal generator embodying the present invention;

FIG. 5 is a timing diagram of the clock and load pulses employed in FIG. 4, and

FIG. 6 is a timing diagram of the video output pulses derived by the video signal generator of FIG. 4.

Referring now to FIG. I, there is shown. in generalized form, a television broadcasting display control system of the type which includes a graphic symbol digital video signal generator. Specifically, as shown in FIG. 1, picture video signal source applies one or more picture video signals as one or more inputs to composite video signal derivation means 102 over picture video connection I04. The picture video signals may be generated locally from one or more television cameras, video recorders, etc. or. as in the case ofa network program, one or more of the picture video signals may originate at a distant point. In any case, any and all of these picture video signals may be applied as inputs to composite video signal derivation means I02 over connection 104 at the same time.

Horizontal drive and vertical drive signals from picture video source I00 are applied over respective connections I06 and 108 as sync inputs to symbol display timing and color control means 110. Symbol display timing and color control means 110 applies timing control signals to a plurality of inputs of graphic symbol digital signal generator 112 over timing control connection I I4. Graphic symbol digital video signal generator 112 applies one or more symbol video signals as an input to composite video signal derivation means 102 over connection 116. If the television broadcast is in color, symbol display timing and color control means 110 applies color control signals to composite video signal derivation means 102 over connection 118. Of course, if the television broadcast is to be in black-andwhite. both the color control portion of 110 and color control connection I18 may be omitted.

As is known in the television broadcast art, each of the blocks I00, 102, I10 and 112 may include the various switches and control means which are manually operated to provide the desired picture video, symbol video and color control input to composite video deri vation means I02 and to provide the desired composite video signal output from composite video signal derivation means 102. For instance, as is known in the television broadcast art, composite video signal derivation means I02 may include suitable video keyers and mixers for selectively combining the video signal input thereto over connection I04 and 116 in any desired manner to provide the television frame format manifested by the composite video signal output therefrom. For example, picture video signals may be selectively combined to provide a so-called split screen" format, or symbol video signals may be superimposed on top of a picture video signal or. in the alternative, a video may be employed to "key out" from the picture the area in a television frame in which a symbol is located. Thus, a television broadcast display control system provides great versatility in forming the composite video signal 3 which actually is broadcast by the television transmitter.

Referring now to FIG. 2a, there is shown certain elements of the low resolution prior art character generator of the type employed in video terminals. Character generator memory 200 typically stores 64 different alphanumeric symbols. Each symbol may be stored in a dot matrix having an overall size of 8X8, of which the symbol itself occupies a 5X7 portion. This is exemplified for the symbol R, illustrated in FIG. 2b. It will be noted that the low resolution of 5X7 dots for the symbol itself greatly affects the appearance of diagonal portions of the symbol.

As shown in FIG. 20, character generator memory 200, which is usually a ROM, receives a 9 bit character generator address, which is composed of a 6 bit symbol code (such as the ASCII code) and a three bit TV scan line code. The 6 bit symbol code defines the particular one of the 64 storage symbols, such as the symbol R, to be read out, while the three bit TV scan-line code defines the particular one of the eight consecutive raster scan lines occupied by a row of characters then being scanned. In response thereto, character generator memory 200 loads eight-bit shift register 202 (which serves as a paralleI-to-serial converter) with an appropriate group of eight binary bits. More specifically, if the symbol being read out is an R and the TV scan line designated by the three bit code is either the first or fourth scan line, the eight bit dot pattern code for the symbol R which loads eight bit shift register 202 is l l l [0000, as shown in FIG. 2b. Similarly, as shown in FIG. 2b, this eight bit dot pattern code for the symbol R is 10001000 for each of the second, third and seventh TV scan lines; while this eight bit pattern code is ll00000 for the fifth TV scan line and is l00l0000 for the sixth TV scan line. To provide a space between wymbols occupying different rows of symbols on the television display, the eight bit dot pattern code for the eighth TV scan line is always 00000000.

Eight-bit shift register 202 is loaded in response to the receipt of a load dot pulse input from an associated timing control means. The loaded eight bit dot pattern code in eight-bit shift register 202 is then read out serially in response to applied dot clock shift pulses. The rate of these dot clock pulses is normally in the order of MHz, so that each successive dot has a duration in the order of 200 nanoseconds, which is within the video bandwidth capabilities of standard commercial television sets. As further shown in FIG. 2a, the serial video pulse output from eight-bit shift register 202 is added to W horizontal and vertical sync signals and a TV blanking signal in video mixer amplifier 204, from which the symbol video output of the character generator is obtained.

For television broadcast purposes, the relatively low resolution provided by 5X7 matrix symbols, shown in FIG. 2b, is insufficient. Instead, relatively high resolu tion 32x32 matrix symbols, such as shown in FIG. 3b, are required for broadcast television. In FIG. 3b, the width of each line of the symbol R still has a duration of 200 nanoseconds, so that it is within the video bandwidth capabilities of a standard television set. However, as shown in FIG. 3b, the high resolution capability is achieved by employing a dot duration for the dot matrix of only 50 nanoseconds, so that the 200 nanosecond width of each line of the symbol R in FIG. 3b is provided by four consecutive 5O nanosecond dots 4 (rather than a single 200 nanosecond dot as in FIG. 2b).

Furthermore, in the case of broadcast television, it is often desired to display a high resolution symbol with edging, in the manner shown for the symbol E in FIG. 3c. As indicated in FIG. 3c, the minimum width of the edging may be only I00 nanoseconds, i.e. 2 consecutive dots of 50 nanoseconds each. In the past, in order to provide symbols with edging, such as shown in FIG. 3c, required high resolution character generators with an analog symbol edging device of the type shown in FIG. 3a.

Referring now to FIG. 3a, character generator memory 300, which like character generator memory 200 may be ROM, stores each of 64 symbols in a 32x32 dot matrix. Each of the 64 symbols is selected by the binary address of a six-bit symbol code applied as an input to character generator memory 300. Character generator memory 300 is further addressed by a five-bit TV scan line code applied as an input thereto for the purpose of selecting the particular one of the 32 rows of the selected dot matrix in accordance with the particular one of 32 consecutive TV scan lines then being scanned. In response thereto, character generator memory 300 derives as an output a 32 bit dot pattern code defining the symbol dot pattern of the selected row for the selected symbol. In response to a load dot pulse applied to 32 bit shift register 302, the 32 bit dot pattern code from character generator memory 300 is loaded in parallel into 32-bit shift register 302. In response to dot clock pulses applied as shift pulses 32-bit shift register 302 at a relatively high rate of about 20 MHz, a serial video pulse output is obtained from 32 bit shift register 32. This serial video pulse output is added to TV horizontal and vertical sync signals and a TV blanking signal in mixer 304. Although, as so far described, the high resolution prior art character generator of FIG. 3a is digital in construction, it requires a more expensive nonstandard shift register capable of operating at 20 MHz, rather than a relatively inexpensive standardly available shift register operating at 5 MHz employed in the low resolution prior art character generator of FIG. 20. Furthermore, if symbol edging of the type shown in FIG. 3c is desired, the output from mixer 304 must be passed through an edging device, such as symbol edger delay lines 306, to produce the symbol video outputs. Due to the high frequency (20 MHz) requirement of the final video output stages, symbol edging, as shown in FIG. 3c, is perfonned by symbol edger 306 using expensive analog circuitry, which includes delay lines.

The present invention, embodied in the graphic symbol digital video signal generator of FIG. 4, provides a technique for generating high resolution digital symbols with edging, which does not require a 32 bit, 20 MHz output shift register and in which it is possible to provide an inexpensive digital (rather than analog) symbol edging using off-the-shelf 5 MHz digital shift registers instead of analog circuitry including delay lines.

FIG. 4 illustrates an embodiment of graphic symbol digital video generator 112 of FIG. 1, which incorporates the present invention. As is conventional in graphic symbol digital video signal generators, there is included keyboard 400, data input output control logic 402 and display refresh memory 404. Block 400, 402, and 404 cooperate in a manner known in the art to store in display refresh memory 404 the characters making up the message to be displayed. Specifically,

each character of the message is manifested by a six-bit word symbol code. This six-bit word symbol code corresponding to each character in the message is stored within display refresh memory page 404 at a location thereof which corresponds to the display position of that character in the format of the displayed message. as is conventional.

In a manner known in the art, the readout of memory page 404 is synchronized by a display refresh address word timing control signal applied thereto over connection 114 to read out in sequence the entire stored page of six-bit word symbol codes in synchronism with the raster scan of each successive television frame.

The six-bit word symbol code output from display refresh memory 404 and a five-bit television scan line code applied from timing control connection 114 are applied as inputs to character generator memory 406, which is identical in all respects to character generator memory 300 of FIG. 3a.

The output from character generator memory 406 consists of a 32-bit parallel dot pattern, each bit of which appears on a separate lead of connection 408. In response to a load dot pulse from timing control con nection 114, bits 1, S, 9, l3. 17, 21, and 29 of the 32-bit parallel dot pattern carried by the corresponding leads of connection 408 are loaded into eight-bit phase A shift register 410. In a similar manner, bits 2, 6, 10, 14, 18, 22, 26 and 30 are loaded into eight-bit phase B shift register 412, bits 3, 7, ll, 15, 19, 23, 27 and 31 are loaded into eight-bit phase C shift register 414, and bits 4, 8, l2, 16, 20, 26, 28 and 32 are loaded into eight-bit phase D shift register 416.

Phase A shift register 410 receives phase A clock pulses from timing control connection 114, which occur at a given relatively slow rate, such as 5 MHz. In a similar manner, phase B shift register 412 receives phase B clock pulses, phase C shift register 414 receives phase C clock pulses and phase D shift register 416 receives phase D clock pulses. Each of phase B, D and D clock pulses occur at the same relatively slow given rate, such as 5 MHz, as the phase A clock pulses. However, as shown in FIG. 5, the respective phase A, phase B, phase C and phase D clock pulses (which are each 50 nanoseconds in duration) are phase delayed with respect to each other. Specifically, the leading edge of phase D clock pulse occurs coincidentally with the lagging edge of the preceding phase A clock pulse; the leading edge of a phase C clock pulse occurs coincidentally with the lagging edge of preceding phase C clock pulse; the leading edge of a phase D clock pulse occurs coincidentally with the lagging edge of the preceding phase C clock pulse and the leading edge of a phase A clock pulse occurs coincidentally with the lagging edge of the preceding phase D clock pulse. Thus, the durations between the leading edges of two successive pulses of the same phase is 200 nanoseconds (i.e., the clock pulses occur at a frequency of 5 MHz.).

The respective video A, video B. video C and video D output from respective shift register 410, 412, 414, and 416, in response to being shifted by the respective phase A, B, C and D clock pulses applied thereto, are applied over connection 418 as respective inputs to video dots shaping and phasing flip flops 420. In addition, the respective video A, video B, video C and video D signals are applied as inputs to 1 TV line delay logic 422 (which consists of four shift registers, each having a capacity of 256 bits). Block 422 also receives phase A 6 and phase C clock shift pulses, which operate in a manner to be described below in connection with FIG. 6.

The output from 1 TV line delay logic 422, which consists of video signals A1, B1, C1 and D1, is applied as second inputs to video dot shaping and phasing flip flops 420 over connection 424, and is also applied as inputs to 1 TV line delay logic 426. Block 426, like block 422, comprises four 256 bit shift registers, which have phase A and phase C clocks applied as shift pulses thereto. The function performed by delay logic 426 also will be described below in connection with FIG. 6.

The outputs from one TV line delay logic 426, which consists of video signals A2, B2, C2 and D2, are applied as third inputs to video dot shaping and phasing flip flops 420 over connection 428. Video clot shaping and phasing flip flops 420 also has phase A, B, C and D clocks applied as inputs thereto. as shown.

Delay logic 422, delay logic 426 and video dot shaping and phasing flip flops 420 cooperate to effectively convert the relatively low resolution (5 MHZ) video signals A, B, C and D appearing at the respective outputs of shift registers 410, 412, 414 and 416 into relatively high resolution (20 MHz) video signals appearing at the output of video dot shaping and phasing flip flops 420. More specifically, referring to the timing diagram shown in FIG. 6, each video A dot pulse has a duration of 200 nanoseconds and has its leading edge in time coincidence with the leading edge of the phase A clock. In video dot shaping and phasing flip flops 420, each video A dot pulse is sampled during the occurrence of a phase-D clock pulse, to provide a 50 nanosecond video A dot pulse which occurs in time coincidence with a phase D clock. In a similar manner, each 200 nanosecond video B dot pulse is sampled during the occurrence of a phase A clock to provide a 50 nanosecond video B dot pulse in time coincidence with the the phase A clock; each 200 nanosecond video C dot pulse is sampled during the occurrence of a phase B clock to provide a 50 nanosecond video C dot pulse in time coincidence with the phase B clock, and each 200 nanosecond video D dot pulse is sampled during the occurrence of a phase C clock to provide a 50 nanosecond video D' dot pulse in time coincidence with the phase C clock.

Essentially, one TV line delay logic 422 and one TV line delay logic 426 together form a center-tapped delay means which provides an overall delay of 512 successive shift pulses for each respective one of the video A, video B, video C and video D signals loaded into the input of 1 TV line delay logic 422. Furthermore, since logic 422 cannot be loaded and shifted at the same time, there is provided a phase delay between the loading of the first stage of the four shift registers of delay logic 422 and the shifting of both these four shift registers and the corresponding four shift registers of delay logic 426. Specific ally, both the A and B shift registers of both blocks 422 and 426 are shifted in response to a phase C clock applied thereto, while both the C and D shift registers of both block 422 and 426 are shifted in response to a phase A clock applied thereto This is illustrated in the timing diagram of FIG. 6, wherein the leading edge of the video Al, A2, B1, and B2 200 nanosecond dot pulses occur in time coincidence with the leading edge of a phase C clock, although the leading edge of the video A dot pulse itself occurs in time coincidence with the leading edge of the preceding phase A clock and the leading edge of the video B dot pulse itself occurs in time coincidence with the preceding phase B clock. In a similar manner, the leading edge of the C1, C2, D1 and D2 dot pulses occur in time coincidence with a phase A clock, although the leading edge of the video C dot pulse itself occurs in time coincidence with the preceding phase C clock and the leading edge of the D dot pulse itself occurs in time coincidence with the preceding phase D clock.

Thus, the overall delay between the occurrence of an A1 or C1 200 nanosecond dot pulse on connection 424 with respect to the occurrence of the corresponding video A and video C dot pulses on connection 418 is actually I nanoseconds greater than one TV line delay, while in the case of the video B1 and video D1 dot pulses this delay is actually 50 nanoseconds greater than one TV line delay. In a similar manner, the actual delay of the A2, B2, C2 and D2 video dot pulses on connection 428 is either 50 or 100 nanoseconds greater than a two TV line delay with respect to the corresponding video A, video B, video C and Video D dot pulses applied to connection 418.

Despite the 50 or 100 nanosecond phase delay of the 200 nanosecond video dot pulses appearing on connections 424 and 428 with respect to the corresponding 200 nanosecond dot pulses appearing on conductor 418, the sampling of these video dot pulses in video dot shaping and phasing flip flops 420 is such that the 50 nanosecond video A1 and A2 dot pulses occur in time coincidence with a video A dot pulse, the 50 nanosecond video B1 and B2 dot pulses occur in time coincidence with a video 8' dot pulse, the 50 nanosecond video C1 and C2 dot pulses occur in time coincidence with a video C dot pulse and the 50 nanosecond video D1 and D2 dot pulses occur in time coincidence with a video D dot pulse. This is illustrated in the timing diagram of FIG. 6, which shows that the 200 nanosecond video A1 or A2 dot pulse, as well as the 200 nanosecond video A dot pulse, is sampled by a phase D clock; the 200 nanosecond B1 and B2 dot pulses, as well as the 200 nanosecond video B dot pulse, is sampled by a phase A clock; the 200 nanosecond video C1 and C2 dot pulses, as well as the 200 nanosecond video C dot pulse, is sampled by a phase B clock, and the 200 nanosecond video D1 and D2 dot pulses, as well as the 200 nanosecond video D pulses, is sampled by a phase C clock.

As further shown in FIG. 4, all the video A, B, C and D signals are applied through OR gate 430 as a first input to 2 dot delay logic 436. Similarly, all the video A] B l Cl and D1 signals are applied through OR gate 432 as a second input to 2 dot delay 436 and all of the video A2, video B2, video C2 and video D2 signals are applied through OR gate 434 as a third input to 2 dot delay logic 436. In addition, the output from OR gate 430 represents the V signal (the video signal with no dot delay and no TV line delay). In a similar manner, the output from OR gate 432 represents the V signal (the video signal with no dot delay and one TV line delay) and the output from OR gate 434 represents the V signal (the video signal with no dot delay and two TV line delay).

2 dot delay logic 436, in response to a 50 nanosecond clock applied thereto, provides a two dot (100 nanosecond) delay in each of its three inputs to thereby provide three corresponding outputs represented by the V V and V signals. The three output signals from 2 dot delay logic 436 are also applied as inputs to 2 dot delay logic 438, which, in response to 50 nanosecond clock pulses applied thereto, provides an additional two dot nanosecond) delay. This results in corresponding output signals represented by output V V V appearing at the output of 2 dot delay logic 438.

As further shown in FIG. 4, eight of the nine output signals from OR gates 430, 432 and 434 and 2 dot delay logic blocks 436 and 438 are applied as inputs to OR gate 440. In particular, signals V V V V,,,, V V V and V are applied as inputs to OR gate 440, while the remaining one of these nine signals, V is applied as an input to an inverter 444 and as an input to signal mixer 446. Horizontal and vertical TV sync signals and a TV blanking signal are applied as additional inputs to signal mixer 446.

The output of OR gate 440 is applied as a first input to AND gate 442, while the output from inverter 444, manifesting V is applied as a second input to AND gate 442.

The symbol video present on connection 1 16 consists of two separate component video signals. The first of these two separate component video signals is the edge key video signal which appears at the output from AND gate 442 and the second of these separate component video signals is the monochrome video signal which appears at the output of signal mixer 446. As shown in FIG. 1, the edge key video signal and the monochrome video signal, which together form the symbol video output present on connection 116, are applied as control inputs to composite video signal derivation means 102.

It will be seen that the edge key video signal is derived in response to the presence of any one or more of the eight signal inputs to OR gate 440, if and only if signal V is then absent.

As is known, each frame of a television picture is made up of two interlaced raster-scan fields. When the video signal A, B, C and D present on connection 418 correspond to the first (top) television scan line of a row of symbols to be displayed during a given rasterscan field, no signal is present on connection 424 and, hence, output signal V, (along with output signals V and V is absent. Similarly, two TV scan lines after the video A, B, C and D signals corresponding to the last (bottom) television scan line of a row of symbols to be displayed during a given raster-scan field, video A2, B2, C2 and D2 signals are present on connection 428, but no video signals are present on either connection 418 or connection 424. Therefore, in this case, signals V V and V are applied to OR gate 440, but signal V is absent. During all intermediate scan lines of a display signal, the V signal is present, except for the first two dot periods I00 nanoseconds) of the scan of that symbol, when none of the output signals V V V V, V nor V is present, and during the last two dot periods 100 nanoseconds) of the scan of that symbol, when none of output signals V V V V V nor V is present. Thus, because of the fact that a television frame is made of two interlaced raster-scanned fields, the generation of the edge key video signal corresponds to the edge key video portion of FIG. 3c, while the generation of the monochrome video signal corresponds to the monochrome video portion of FIG.

The edge key video signal and/or the monochrome video signal component of the symbol video may be made use of in various ways within composite video signal derivation means 102. For instance, the edge key video signal alone may be used to "key out" the picture video. In this case, the picture video would appear both outside the symbol and within the monochrome" video portion of the symbol. A second example would be to OR together the monochrome video signal and the edge key video signal to key out" the picture video. in this case, the symbols would appear as black" block symbols within the picture field. However, if the monochrome video signal, besides being combined with the edge key video signal for keying out" purposes, is also employed to gate in a selected color into the mixed composite video signal, the monochrome video portion of the symbol will appear in the selected color within a black" edging. Further, the combined edge key video signal and monochrome video signal, beside being used for key out purposes, may also be used for selecting a second color, In this later case, the monochrome video portion of the symbol will appear in the first color within an edging having the second color. Besides these various examples, other ways of using either or both the edge key video signal and the monochrome video signal may occur to the controller of a television broadcast display control system. In any case, it is the generation of the separate edge key video signal and monochrome video signal by the techniques embodied in generator 112 of FIG. 4, and not the various ways of employing these two components of the symbol video within composite video signal derivation means 102, which forms the novel subject matter of the present invention,

What is claimed is:

l. in a digital generator of graphic symbols with edging for display on a display device exhibiting a television raster scan, said generator being of the type which includes a character generator memory responsive to the application thereto of a first multibit symbol code and a second multibit scan line per symbol height code for deriving an m bit parallel dot pattern manifesting a selected scan-line portion of a selected symbol to be displayed; the improvement therein comprising:

a. a set of n shift registers each having k stages, wherein both n and k are plural integers and m is equal to the produce of n times k;

b. means for loading said k stages of each ordinal one of said n shift registers with the i, n-l-z', 2n+i, m-n+i ordinal ones of said hi bits, where i is the ordinal value of that ordinal one of said n shift registers;

c. means for applying as shift pulses to each respective one of said n shift registers a corresponding one of a set of n clocks, each of said n clocks consisting of a series of pulses each having a duration of t which occur at a repetition frequency substantially equal to 1/11], and each ordinal one of said set of n clocks being phase delayed by a time interval substantially equal to r with respect to the preceding one of said set of n clocks, to thereby produce a set of respective outputs of said n shift registers each pulse of which has a duration substantially equal to m,

d. first and second serially connected l television scan line delay logic means having the set of respective outputs of said n shift registers applied as respective inputs to said first line delay logic means for producing a first set of corresponding outputs from said first line delay logic means and a second set of corresponding outputs from said second line delay logic means,

e. video dots shaping and phasing flip flops having said set of respective outputs of said n shift registers applied as first inputs thereto, said first set of corresponding outputs applied as second inputs thereto, said second set of corresponding outputs applied as third inputs thereto, and said set of n clocks as fourth inputs thereto for sampling all of each separate group of corresponding ones of said first, second and third inputs with a different respective predetermined one of said set of n clocks, whereby said video dots shaping and phasing flip flops derives first, second and third output dot samples corresponding respectively to said first, second and third inputs thereto, with each dot sample having a duration t;

f. first and second serially connected dot delay logic means, each of which provides a delay substantially equal to a predetermined integral multiple oft, said first, second and third output dot samples being applied as inputs to said first dot delay logic means for producing a first set of corresponding outputs from said first dot delay logic means and a second set of corresponding outputs from said second dot delay logic means, and

g. output means including first means responsive to the presence of that given particular one of said first set of outputs from said first dot delay logic corresponding to said second output dot samples for deriving a monochrome video signal, and sec ond means responsive to the absence of said given particular one of said first set together with the presence of at least another of said first set, any of said first, second and third output dot samples. or any of said second set of corresponding outputs from said second dot delay logic means for deriving an edge key video signal.

2. The generator defined in claim 1, wherein m is 32,

n is four, k is eight, and t is 50 nanoseconds, whereby l/nz is five megahertz and nt is 200 nanoseconds.

3. The generator defined in claim 2, wherein said graphic symbols are for display on a display device exhibiting a television raster scan for a frame consisting of two interlaced raster-scan fields, and wherein said predetermined integral multiple of l' is two, whereby each of said first and second dot delay logic means provides a delay of one-hundred nanoseconds.

4. The generator defined in claim l, wherein each of said first and second serially connected 1 television scan line delay logic means includes a second set of n shift registers individually corresponding to each of the n shift registers of said first mentioned set, each of said second set of n shift registers having a given number of stages which is equal to the number of pulses in the series of any one of said It clocks which occur during any one complete television scan line, means for loading the first stage of each of the n shift registers of said first 1 television scan line delay logic means with the output of the corresponding one of the u shift registers of said first-mentioned set, and means for applying as shift pulses to each respective one of said n shift registers of said second set of both said first and second 1 television scan line delay logic means a preselected one of said It clocks which is different from the clock applied as shift pulses to the corresponding one of the first-mentioned set of n shift registers, but which results in the respective outputs from the corresponding shift registers of said first-mentioned set and said second set of both said first and second serially connected 1 television scan line delay logic means all being simultaneously present during the occurrence of the sampling of the respective outputs of these corresponding shift registers by said 12 for combining said first, second and third output dot samples, each of said others of said first set and all of said second set, an AND gate having the output of said OR gate applied as a first input thereto, and an inverter for applying said given particular one of said first set of outputs as a second input to said AND gate, the output from said AND gate constituting said edge key video signal.

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Classifications
U.S. Classification345/469.1
International ClassificationG09G5/24
Cooperative ClassificationG09G5/24
European ClassificationG09G5/24