GB2323232A - Boustrophedal image display generation - Google Patents

Abstract

The video display apparatus comprises a screen 10 which is divided into a matrix of display elements arranged in n rows of m elements. The individual elements are addressed by means of their coordinates, the top left-hand element being (1, 1) and so on. The screen 10 is mounted on the front face of a cathode ray tube (CRT) of broadly conventional design. Control circuitry (Fig 2) for the apparatus includes a control unit/interface (20), an EHT generator (30) for the CRT, and a power supply unit (40). The control unit/interface (20) is connected to a position counter (50) (which controls the position of the point of illumination in each row of the screen) and a line counter (60). The position counter (50) is connected via a first digital-to-analog converter (DAC) (52) to a line scanning coil (54). The line counter (60) is connected via a second DAC (62) to a frame scanning coil (64). The elements are addressed in both forward and reverse scanning directions thus avoiding the use of flyback.

Description

Title - Video Display Generation This invention relates to a method of video display generation, and to video display apparatus operating in accordance with such a method.

The use of video display units, eg associated with computers etc, is becoming more and more commonplace in all aspects of modem life. As the applications of such units become more sophisticated the demands placed upon them, in terrns of operating parameters such as resolution, brightness, contrast etc, become more and more difficult to satisfy. In attempts to keep pace with requirements, the designs currently available have become more and more complex and costly to produce and service.

Conventional video display units utilise technology based on that employed in television. A transmitted television signal encodes the moving image as a sequence of frames. Each frame is displayed by scanning one or more beams from a cathode ray tube across the display screen, conventionally in a series of horizontal lines. When the beam reaches the end of the first line it is returned to the other side of the screen and begins scanning the next line, below the first.

When the last line is complete, the beam returns to the starting point and the next frame is displayed in the same manner. This approach necessarily involves line and frame synchronization since there is no direct link between the transmitter and the receiving units.

Such an approach requires the use of so-called flyback transformers to generate synchronization pulses and to move the beam back across the screen following completion of each line, and back to the starting point following completion of each frame.

Whilst the application of such technology has proven acceptable for television and video display units in the past, the increasing demands now placed upon video display units are such that the disadvantages associated with known methods of video display generation lead to unacceptable performance. There is therefore a need for an alternative approach.

There has now been devised a new method of display scan generation, and display apparatus operated in accordance with that method, which overcome or substantially mitigate the disadvantages of the prior art.

According to a first aspect of the present invention, there is provided a method of generating a video display on a screen subdivided into a matrix of discrete display elements arranged in n rows of m elements, which method comprises activating the m discrete elements of a first row of display elements in sequence, and activating the m discrete elements of a second row of display elements in reverse sequence.

Preferably, all n rows of the screen are scanned in alternating sequence, ie for horizontal line scanning the first row may be scanned left-to-right, the second row right-to-left, the third row left-to-right, and so on.

Conveniently, the discrete display elements are addressed sequentially, position and line counters being provided and incremented (or decremented) as the display is generated. Thus, again for horizontal line scanning, the line counter may initially be set to I and the position counter incremented as follows 1,2,3,4 m to generate the first line of the display.

The line counter may then be incremented to 2 and the position counter decremented as follows: m, (m-l), (m-2), ...... 3, 2, 1 to generate the second line of the display.

This alternating process is repeated until the final line is scanned with the line counter set to n.

Most preferably, alternating frames are also generated in alternating fashion, ie at completion of a first frame, the display generation process is preferably reversed, the line counter being preferably decremented to (no1), and then (n-2), (n-3), ... etc at the end of each successive line.

According to a second aspect of the invention, there is provided apparatus for the generating a video display, said apparatus comprising a screen subdivided into a matrix of discrete display elements arranged in n rows of m elements, means for activating the m discrete elements of a first row of display elements in sequence, and means for activating the m discrete elements of a second row of display elements in reverse sequence.

The apparatus preferably further comprises address means including a line counter and a position counter for selectively addressing one of the discrete display elements, and means for incrementing or decrementing the line and position counters.

The discrete display elements are preferably simply distinct regions of the display screen, eg regions surrounding spatially separated points on the screen.

Although described above principally in connection with horizontal line scanning (and vertical frame scanning), the invention may be applied in other modes, eg vertical line scanning and horizontal frame scanning.

The method and apparatus of the invention offer numerous advantages over conventional video display methods and apparatus. Many of these advantages are derived from the fact that the video display can be generated entirely by movements of just one increment, either by incrementing/decrementing the position counter along each line or incrementing/decrementing the line counter at the end of each line.

The apparatus of the invention may also require fewer components than a conventional system.

The clock and memory addressing circuitry can be constructed easily, and the scan drive can be generated using digital-to-analog converters to create triangular drive waveforms which may then be amplified and applied to the scan coils. At all stages, DC coupling may be used, thereby eliminating the need for capacitors, in particular unreliable electrolytic capacitors.

Another advantage is that a single printed circuit board may be used to drive any size of cathode ray tube display, eg using a simple system of gain control on the output amplifier to adapt the system to different sizes. Also, by separating the scan circuitry from the circuitry for EFIT generation, different scan rates can be achieved simply by changing the scan step size, which may be done by software.

As the display is generated in small discrete steps and there are no flyback surges between lines, the design of the scan coils can be optimised for maximum sensitivity, leading to greater efficiency coupled with a reduction in drive power.

Because the position of the spot is known at all times (by virtue of the known position counter and line counter values), it is possible to enhance the quality of the image, enabling digital correction of focus, convergence, linearity and pincushion distortion.

A further significant advantage relates to security. With known display units, the flyback pulses can be detected externally and used to pick up information displayed on the screen. In the present invention, although a flyback transformer may be used to generate the EHT and focusing voltages its oscillator may be free-running, which will prevent attempts to view the display by synchronization onto the radiated flyback pulses.

In conventional display systems, the illumination spot is constantly moving. This leads inevitably to some smearing of the spot, and also requires high EHT voltage to achieve the desired brightness. In the present invention, by contrast, the spot is stationary at each moment of illumination. This reduces the EHT required to attain the required level of brightness, and also eliminates smearing of the image.

The invention will now be described in greater detail, by way of illustration only, with reference to the accompanying drawings, in which Figure 1 shows several schematic views of a video display screen operated in accordance with the invention; and Figure 2 shows a schematic block diagram of control circuitry for apparatus according to the invention.

Referring first to Figure 1, in a video display apparatus according to the invention, a screen (generally designated 10) is divided into a matrix of display elements arranged in n rows of m elements. The individual elements are addressed by means of their coordinates, the top left-hand element being (1,1) and so on. For simplicity, an 8 x 8 array of display elements is shown in the drawings; in reality the size of the array for most applications would of course be considerably larger.

The screen 10 is mounted on the front face of a cathode ray tube (CRT) of broadly conventional design. Referring to Figure 2, control circuitry for the apparatus includes a control unit/interface 20, an EHT generator 30 for the CRT, and a power supply unit 40. The control unit/interface 20 is connected to a position counter 50 (which controls the position of the point of illumination in each row of the screen) and a line counter 60. The position counter 50 is connected via a first digital-to-analog converter (DAC) 52 to a line scanning coil 54. The line counter 60 is connected via a second DAC 62 to a frame scanning coil 64.

A video display is generated by illuminating the display elements in sequence ("illumination" in this context meaning irradiation of the display element with a beam of radiation from the CRT). Each display element can be addressed according to its coordinates and illuminated individually. First, with both position and line counters 50,60 set to 1, the element (1,1) is illuminated. The position counter 50 is then incremented (to 2) and the point of illumination is moved to the next element (1,2). Succeeding elements (1,3), (1,4), (1,5) ... are illuminated until the point of illumination reaches the display element (1,8) at the end of the first line. The line counter 60 is then incremented (to 2) to move the point of illumination to the element (2,8) and the position counter 50 is progressively decremented to move the point of illumination back along the second line. Once the point of illumination reaches the element (2,1), the line counter 60 is once again incremented to move the point of illumination to the third line, whereupon the position indication 50 is once again incremented (see Figure Lea).

Display of the first complete frame is complete when the point of illumination reaches the display element (8,1) (Figure lob). At that point the position counter 50 (which was decremented as the final line of the frame was scanned) is then incremented to move the point of illumination back along the lowest line ofthe display to begin display of a second frame (Figure inc). Display of the second frame continues by the reverse of the process by which the first frame was generated (Figure ld). Third and subsequent frames are generated by the same process.

Claims (20)

1. A method of generating a video display on a screen subdivided into a matrix of discrete display elements arranged in n rows of m elements, which method comprises activating the m discrete elements of a first row of display elements in sequence, and activating the m discrete elements of a second row of display elements in reverse sequence.

2. A method according to claim 1 wherein all S rows of the screen are scanned in alternating sequence.

3. A method according to claim 1 or claim 2 wherein the discrete display elements are addressed sequentially.

4. A method according to claim 3 wherein position and line counters being provided and incremented (or decremented) as the display is generated.

5. A method according to claim 4 wherein, for horizontal line scanning, the line counter is initially set to l, and the position counter incremented as 1,2,3,4... . .. m to generate the first line of the display, the line counter is then incremented to 2, and the position counter decremented as m, (F-1), (m-2).... .. 3,2,1 to generate the second line of the display, and this alternating process is repeated until the final line is scanned with the line counter set to n.

6. A method according to claims 5 wherein alternating frames are generated in alternating fashion, such that at completion of a first frame, the display generation process is reversed, the line counter being decremented to (n-l), and then (n-2), (n-3), ... etc at the end of each successive line.

7. A method according to any one of the preceding claims wherein the line scanning is carried out vertically.

8. Apparatus for the generating of a video display comprising: a screen subdivided into a matrix of discrete display elements arranged in n rows of m elements, means for activating the m discrete elements of a first row of display elements in sequence, and means for activating the m discrete elements of a second row of display elements in reverse sequence.

9. Apparatus according to claim 8 further comprising address means including a line counter and a position counter for selectively addressing one of the discrete display elements, and means for incrementing or decrementing the line and position counters.

10. Apparatus according to claim 8 or claim 9 further comprising a clock and memory addressing circuitry.

11. Apparatus according to any one of claims 8 to 10 further comprising a scan drive and scan coils.

12. Apparatus according to claim 11 wherein the scan drive is generated using digital-to-analog converters to create triangular drive waveforms which may then be amplified and applied to the scan coils.

13. Apparatus according to any one of claims 8 to 12 wherein DC coupling is used.

14. Apparatus according to any one of claims 8 to 13 wherein the screen is mounted on the front face of a cathode ray tube.

15. Apparatus according to claim 14 wherein a single printed circuit board is used to drive any size of cathode ray tube display, said apparatus using a simple system of gain control on the output amplifier to adapt the system to different sizes.

16. Apparatus according to claim 14 or 15 further comprising control circuitry for the apparatus including a control unit/interface, an EHT generator for the cathode ray tube and a power supply unit.

17. Apparatus according to claim 16 wherein the control unit/interface is connected to a position counter for controlling the position of the point of illumination in each row of the screen and a line counter.

18. Apparatus according to claim 17 wherein the position counter is connected via a first digital-to-analog converter to a line scanning coil 54 and the line counter 60 is connected via a second digital-to-analog converter to a frame scanning coil.

19. A method of generating a video display on a screen as hereinbefore described with reference to the accompanying drawings.

20. Apparatus for the generating of a video display as hereinbefore described with reference to the accompanying drawings.