Video signal generator with a low clock rate

Abstract: A video signal generating apparatus comprises a first microprocessor (10) including a memory (16) for receiving and storing in non-real time instructions for the generation of a range of video signals, such as test patterns, digital multi-effect keys or wipe patterns for a digital switcher, and a signal generator (14) for reading the instructions and generating a selected required video signal in real time. The video signal is generated in a demultiplexed manner at a relatively low clock rate.

Description: This invention relates to video signal generating apparatus. In complex digital video processing systems which are currently being developed, there is a requirement to generate various video signals such as test patterns, digital multi-effects (DME) keys and wipe patterns for digital switchers. Such video signals have a wide range of complexity, but to provide apparatus to generate even the simplest signals may require a considerable amount of hardware design; while it may be impractical to provide apparatus to generate more complex signals, due to constraints on equipment size or cost. Consequently implementations are usually compromised, resulting in inflexibility or apparatus of limited application. UK Patent Specification GB-A-O 898 779 discloses a digital arbitrary function generator having a first store which holds digital numbers proportional to the gradients (ramp rates) of straight lines forming an approximation to the desired function, a second store which holds digital numbers specifying values of the variable at which a change from one such gradient to another is required, and a control unit which causes a gradient number to be emitted from the first store when the value of the variable reaches one of the values held in the second store. According to the present invention there is provided a video signal generating apparatus comprising: input means for providing data relating to an output video signal to be generated and representing at least one signal ramp start pixel address, a signal start level at the signal ramp start pixel address, and a signal ramp rate value indicating how the signal level is to change after the ramp start pixel address; a plurality of adder means for adding respective offset values to the signal start level to produce respective output signals; start value modification control means responsive to the signal ramp start pixel address and the signal ramp rate value to generate said offset values corresponding in number to the number of said adder means; a plurality of accumulator means for accumulating the output signals of said adder means from the signal ramp start pixel address in dependence on the signal ramp rate value, so as to generate plural video signals; and combiner means for combining the generated plural video signals so to generate said output video signal. Embodiments of the invention can provide apparatus having advantages in flexibility, cost and power consumption over known apparatus. The invention will be now be described by way of example with reference to the accompanying drawings, throughout which like parts are referred to by like references, and in which: Figure 1 is a block diagram of one embodiment of video signal generating apparatus according to the present invention; Figure 2 is a block diagram of a signal generating circuit in Figure 1; Figure 3 is a block diagram of an accumulator in Figure 2; and Figures 4 to 7 are schematic diagrams for explaining the operation of the embodiment of Figure 1. Referring initially to Figure 1, there is shown a video signal generating apparatus 1 embodying the invention. Control data are supplied to a controlling microprocessor 10 through a control interface 12 in non-real time. The control data relates to a required high definition video signal to be generated, which may, for example, be a ramp signal, a colour bar signal, some other test signal, a DME key or a wipe pattern. The controlling microprocessor 10 calculates the necessary data for the required video signal to be generated in dependence on the control data, the necessary data being, in the case of a ramp signal, line address data, pixel address data, ramp increment data, ramp start data, ramp up/down data and 5-bit, for example, control data relating to every video field or frame of the required video signals. These data are written in a common memory 16 in the controlling microprocessor 10. These data for a field/frame (N) are computed during the preceding field/frame (N-1) and supplied to a further microprocessor forming a signal generating circuit 14. These data for the field/frame (N) are then processed by the signal generating circuit 14 during the field/frame (N) to generate the required video signal. The signal generating circuit 14 is as shown in Figure 2, and comprises an interface 18 which receives the line address data, the pixel address data, the ramp increment data, the ramp start data, the ramp up/down data and the 5-bit control data from the memory 16. A first adder 20, a second adder 22, a third adder 24 and a fourth adder 26 are provided, to which the ramp start data from the interface 18 and an output signal of a start value modification control means 28 are supplied. Each adder 20, 22, 24 and 26 adds the output signal from the start value modification control means 28 to the ramp start data and supplies the added data to registers 30, 32, 34 and 36, respectively. Accumulators 38, 40, 42 and 44 are provided, to which output signals from the registers 30, 32, 34 and 36 are supplied. Each accumulator 38, 40, 42 and 44 accumulates the output signal from the register 30, 32, 34 or 36 under control of a ramp start controller 46, a bit shift controller 48, a register control sequencer 50 and the ramp up/down data. Each accumulator 38, 40, 42 and 44 outputs demultiplexed phase 0 data, phase 1 data, phase 2 data and phase 3 data of the ramp signal to be generated. A first signal path comprises the adder 20, the register 30 and the accumulator 38. A second signal path comprises the adder 22, the register 32 and the accumulator 40. A third signal path comprises the adder 24, the register 44 and the accumulator 42. A fourth signal path comprises the adder 26, the register 36 and the accumulator 44. The start value modification control means 28 generates offset data for the first, second, third and fourth signal paths according to the pixel address data and the ramp increment data from the interface 18, and supplies these offset data to the adders 20, 22, 24 and 26. The bit shift controller 48 multiplies the ramp increment data received from the interface 18 through a register 52 by four, by shifting the bits of the ramp increment signal, and supplies a multiplied ramp increment signal to the accumulators 38, 40, 42 and 44, so as to control the gradient of the ramp signal to be generated. The ramp start controller 46 is a counter which is reset at the beginning of each video field/frame in dependence on a field/frame based control signal. Then the ramp start controller 46 counts scan lines and pixels. The ramp start controller 46 controls the accumulators 38, 40, 42 and 44 in order that the ramp start data are loaded from the registers 30, 32, 34 and 36 into the accumulators 38, 40, 42 and 44 when the count value equals the line address and pixel address designated. On the next clock cycle, the accumulators 38, 40, 42 and 44 begin to add the multiplied ramp increment signal from the bit shift controller 48 to the output signals from the registers 30, 32, 34 and 36 to generate a ramp signal. The ramp start controller 46 controls the accumulators 38, 40, 42 and 44 in order that next ramp start values are loaded from the register 30, 32, 34 and 36 into the accumulators 38, 40, 42 and 44 when the count value equals the next pixel address memorized in a register 54. Then the accumulators 38, 40, 42 and 44 begin to add the next multiplied ramp increment signal from the bit shift controller 48 to the next output signal from the registers 30, 32, 34 and 36 to generate the next ramp signal. If the ramp value reaches the maximum (for example, white) or minimum (for example, black level) allowed value, the accumulation operation ends. Ramp up/down data from the interface 18 are supplied to the accumulators 38, 40, 42 and 44 through a register 56. The accumulating direction of the accumulators 38, 40, 42 and 44 is controlled according to the ramp up/down data. If the accumulation direction is the up direction, then the gradient of the generated ramp signal is positive. On the other hand, if the accumulation direction is the down direction, then the gradient of the generated ramp signal is negative. A signal indicating all the data necessary to specify a ramp signal is supplied to the register control sequencer 50. The register control sequencer 50 controls the registers 30, 32, 34, 36, 52, 54 and 56, so that the data necessary to specify a ramp signal are sequentially memorized in the registers 30, 32, 34, 36, 52, 54 and 56, and are sequentially read out therefrom in dependence on that signal. Each register 30, 32, 34, 36, 52, 54 and 56 may be a first-in-first-out memory. Referring to Figure 3, the accumulators 38, 40, 42 and 44 will be explained. Since they are all the same, only the accumulator 38 will be explained here. There is provided a register 58 which receives the output signal from a switch 60. The switch 60 selectively supplies an output signal from the register 30 and an adder 62 to the register 58 in dependence on an output signal from the ramp start controller 46. There is provided a inverting means 64 which takes the 2's complement of the output signal from the bit shift controller 48. A switch 66 selectively supplies an output signal from the bit shift controller 48 and an output signal from the inverting means 64 to the adder 62 in dependence on the ramp up/down signal. The adder 62 adds the output signal from the switch 66 to the output signal from the register 58. The operation of the register 58 is controlled by the register control sequencer 50. The signal memorized in the register 58 is supplied as the phase 0 output signal. The operation of the ramp signal generating apparatus will now be described with reference to Figure 4. In Figure 4, a solid line S is a ramp signal to be generated at video line m. In this case, the operator inputs a first set of data, namely, the video line address 'm', the ramp start value 'a', the ramp start pixel address '6', the ramp increment data 'x', and a second set of data, namely, the video line address 'm', the ramp end value 'i', the ramp end pixel address '14', and the subsequent ramp increment data '0', to the microprocessor 10 through the keyboard 12. The microprocessor 10 supplies these data to the ramp signal generating circuit 14 via the interface 18. In Figure 2, the ramp start value 'a' from the interface 18 is supplied to the adders 20, 22, 24 and 26. The start value modification control means 28 generates start value modification values '2x', '3x', '0', 'x' according to ramp increment data 'x' and ramp start pixel address '6', and supplies the start value modification values '2x', '3x', '0', 'x' to the adders 20, 22, 24 and 26, respectively. The bit shift controller 48 multiplies the ramp increment data 'x' by '4'. The ramp start controller 46 controls the switch 60 of the accumulators 38, 40, 42 and 44 in order that the added ramp start values are loaded from the registers 30, 32, 34 and 36 into the registers 58 (Figure 3) when the count value equals the video line address and the pixel address designated. On the next clock cycle, the adder 62 adds the non-inverted signal of the bit shift controller 48 to the output signal from the register 58. The switch 60 then supplies the output signal of the adder 62 to the register 58 under control of the ramp start controller 46. This accumulating operation is continued until the count value reaches the ramp end pixel address (on a next ramp start pixel address). When the count value reaches the ramp end address, the next ramp start value 'i' from the interface 18 is supplied to the adders 20, 22, 24 and 26. The start value modification control means 28 generates start value modification values '0', '0', '0', '0' according to the next ramp increment data '0' and the next ramp start pixel address '14', and supplies the start value modification values '0', '0', '0', '0' to the adders 20, 22, 24 and 26. The bit shift multiplier 48 multiplies the next ramp increment data '0' by '4'. Then the ramp start controller 46 controls the switch 60 of the accumulators 38, 40, 42 and 44 in order that the next added ramp start values are loaded from the registers 30, 32, 34 and 44 into the register 58, when the count value equals the next pixel address '14'. On the next clock cycle, the adder 62 adds the non-inverted signal of the bit shift controller 48 to the output signal from the register 58. The switch 60 then supplies the output signal of the adder 62 to the register 58 under control of the ramp start controller 46. This accumulating operation is continued until the count value reaches the next ramp start pixel address. Thus phase 0 output signal values 'c=a+2x', 'g=c+4x' and 'i' are sequentially outputted from the accumulator 38. Phase 1 output signal values 'd=a+3x', h=d+4x' and 'i' are sequentially outputted from the accumulator 40. Phase 2 output signal values 'a=a+0', e=a+4x' and 'i' are sequentially outputted from the accumulator 42. Phase 3 output signal values 'b=a+x', 'f=b+4x' and 'i' are sequentially outputted from the accumulator 44. Then these output signals from the accumulators 38, 40, 42 and 44 are combined by a combiner 68, so as to generate the ramp signal represented by the solid-line S. In another case, if the operator inputs the following data through the keyboard 12 to the microprocessor 10, a signal such as a colour bar signal T as indicated in Figure 5 can be generated by the signal generating circuit 14. A first set of data are a video line address 'm', a start value 'i', a start pixel address '0', and ramp increment data '0'. A second set of data are a video line address 'm', a start value 'g', a start pixel address '2', and ramp increment data '0'. A third set of data are a video line address 'm', a start value 'e', a start pixel address '4', and a ramp increment data '0'. A fourth set of data are a video line address 'm', a start value 'c', c start pixel address '6', and ramp increment data '0'. A fifth set of data are a video line address 'm', a start value 'a', a start pixel address '8', and ramp increment data '0'. If the operator inputs the following data through the keyboard 12 to the microprocessor 10, a saw tooth signal U as indicated in Figure 6 can be generated by the signal generating circuit 14. A first set of data are a video line address 'm', a start value 'a', a start pixel address '1', and ramp increment data 'x/2'. A second set of data are a video line address 'm', a start value 'a', a start pixel address '9', and ramp increment data 'x/2'. If the operator inputs the following data through the keyboard 12 to the microprocessor 10, a signal V as indicated in Figure 7 can be generated by the signal generating circuit 14. A first set of data are a video line address 'm', a start value 'a', a start pixel address '1', and ramp increment data '2x'. A second set of data are a video line address 'm', a start value 'd', a start pixel address '5', and ramp increment data 'x'. A third set of data are a video line address 'm', a start value 'c', a start pixel address '9', and ramp increment data 'x/2'. A fourth set of data are a video line address 'm', a start value 'a', a start pixel address '13', and ramp increment data '2x'. A fifth set of data are a video line address 'm', a start value 'a', a start pixel address '17', and ramp increment data '0'. The ramp signal so generated may be used as a key signal in a DME device, and allows keys to be generated with fully anti-aliased edges. The output signals of the accumulators 38, 40, 42 and are further processed into a multiplexed channel by the combiner 68 (Figure 2). Thus the embodiment can generate a range of required video signals with complete control over the start and end values and the gradients. By executing a sequence of ramps and flat portions on a video line by line basis, a required video signal can be constructed. Anti-aliased DME keys may be produced by generating ramps with critical gradients at key edges. Moreover, the hardware construction is simple. When using a demultiplexed signal generating apparatus as described, for example with four signal paths (phase 0, phase 1, phase 2, phase 3), the data processing can be carried out at a quarter clock rate on four demultiplexed component signals. Therefore it is possible to generate a signal for a high definition video system at a relatively low clock rate.

Claims: A video signal generating apparatus comprising: input means (10, 12, 16) for providing data relating to an output video signal to be generated and representing at least one signal ramp start pixel address, a signal start level at the signal ramp start pixel address, and a signal ramp rate value indicating how the signal level is to change after the ramp start pixel address; a plurality of adder means (20, 22, 24, 26) for adding respective offset values to the signal start level to produce respective output signals; start value modification control means (28) responsive to the signal ramp start pixel address and the signal ramp rate value to generate said offset values corresponding in number to the number of said adder means; a plurality of accumulator means (38, 40, 42, 44) for accumulating the output signals of said adder means from the signal ramp start pixel address in dependence on the signal ramp rate value, so as to generate plural video signals; and combiner means (68) for combining the generated plural video signals so to generate said output video signal. Apparatus according to claim 1, wherein said input means (10, 12, 16) inputs up/down data representing the polarity of the signal ramp rate value. Apparatus according to claim 1 or claim 2, wherein each said accumulator means (38, 40, 42, 44) and each said adder means (20, 22, 24, 26) operates at 1/n clock rate, where n is the number of adder means. Apparatus according to claim 1, claim 2 or claim 3, comprising: signal start control means (46) for generating an accumulation start trigger signal according to the signal ramp start pixel address and a count value; and means (48) for generating a multiplied signal ramp rate value by multiplying the signal ramp rate value by n (where n is the number of adder means), said accumulator means (38, 40, 42, 44) accumulating the output signals of said adder means (20, 22, 24, 26) from the signal ramp start pixel address in dependence on the multiplied signal ramp rate value and the accumulation start trigger signal so as to generate said plural video signals. Apparatus according to claim 4, wherein each said accumulator means (38, 40, 42, 44) includes register means (58) for memorizing data, inverting means (64) for inverting the polarity of said multiplied signal ramp rate value, switch means (66) for selectively outputting the multiplied signal ramp rate value and the output signal of said inverting means (64) in dependence on an up/down signal, adding means (62) for adding the output signal of said switch means (66) to the output signal of said register means (58), and second switch means (60) for selectively supplying the output signal of said adding means (62) and the output signal of the associated said adder means to said register means (58) in dependence on the accumulation start trigger signal. Apparatus according to any one of the preceding claims, wherein said input means (10, 12, 16) comprises a microprocessor (10) and a memory (16), the microprocessor (10) being responsive to receipt in non-real time of instructions for the generation of said output video signal to generate, and write to the memory (16), during one field or frame of the output video signal, said data relating to the output video signal for the next field or frame. Apparatus according to claim 6, of which the components downstream of said input means (10, 12, 16) are constituted by a second microprocessor (14).

Inventors: CHOUHAN MUKESH, HEDLEY DAVID JOHN, TURNER ALAN, CHOUHAN, MUKESH, HEDLEY, DAVID JOHN, TURNER, ALAN
Applicants: SONY UK LTD, SONY UNITED KINGDOM LIMITED
Application year: 1993
Main classification: H04N5
IPC codes: H04N5, H04N17