GB2348764A - Video wipe generator for random wipe effect - Google Patents

Abstract

A signal generator for use in a video wipe generator for generating a wipe 'solid'. The signal generator generates a solid which comprises an array of tiles having random amplitudes. The horizontal and vertical dimensions of the tiles are variable and may be randomly variable. The dimensions may be one pixel. The horizontal and vertical dimensions are defined by Hsize (10, fig.5) and Vsize (12) generators which define the boundaries of the tiles. The generators (10) and (12) include pseudo random number generators (PRB3 and 4) for randomising the dimensions. They control another pseudo random number generator (14) which defines the random amplitudes (PRB1) of the tiles. The tiles may flicker at an adjustable rate defined by the comparison (20) of a flicker rate (FR) control signal and a pseudo random number (PRB2) produced by another pseudo random number generator (18).

Description

SIGNAL GENERATOR The present invention relates to a signal generator for use in a video wipe generator. Such a wipe effect generator is used in a vision mixer for wiping between two video sources Reference will now be made to Figures 1 to 3 of the accompanying drawings which show the background to the present invention.

Figure 1 illustrates a known simple wipe between two video sources X and Y.

As the wipe proceeds as indicated by arrow W, video X is replaced across the display by video Y (or vice versa). The effect of the wipe is achieved by mixing the video sources X and Y according to KX + (1-K) Y, where K is a keying signal. The keying signal is derived from a'solid'. A solid is an electrical signal representing a threedimensional surface. It may comprise a linear ramp or a combination of linear ramps.

It may represent a curved surface. In the present specification a solid is described which has a random amplitude. The derivation of the keying signal will be explained with reference to Figures 2 and 3.

Figures 2A illustrates a known example of a solid 125 which is a simple ramp.

As shown in Figure 2, a clip level 142 is defined. It will be appreciated that over a field or frame, the clip level 142 is defined. It will be appreciated that over a field or frame, the clip level 142 defines a plane referred to herein as the clip plane 142. The keying signal K is in known manner, derived from the solid key by applying high gain to the solid and limiting the result, as shown in Figure 2B. The keying signal has two levels 0 and 1. The transition between the levels occurs where the solid intersects the clip plane 142. The position of the intersection is varied, to produce the wipe, by adding an offset to the solid.

Figure 3 is a schematic block diagram of a wipe generator of a vision mixer comprising a solid generator, a clip element, a gain element, a limiter and a mixer which mixes video sources X and Y in dependence upon the keying signal K. The solid produces a solid, for example a ramp as shown in Figure 2A. The clip element applies an offset tot he ramp to vary the intersection of the ramp with the clip plane 142 as shown in Figures 2A to 2C. Gain is applied to the offset ramps, in the gain element and the result limited in the limited to produce the signal K. The amount of gain applied may be varied as shown in Figure 2B: that varies the slope of the transition between the limit values of the keying signal K.

The mixer mixes the video sources X and Y according KX + (1-K) Y. Thus if K = 1 the output is X, if K = 0 the output is Y. If the gain applied to the solid is unity and the dip offset is zero, the solid and the key signal are identical.

The example of Figures 1 and 2 for ease of explanation refer to a solid, a ramp, which varies as a function of only pixel position h along a line to produce a simple wipe effect. It will be appreciated that it is possible to produce solids which vary as a function of both h and v co-ordinates in a picture, where v is a line number to produce more complex wipe effects.

It is also known to produce other solids which are not derived from ramps. The keying signal K is derived from such solids in the same way as described above. The present invention is concerned with the generation of solids having a random amplitudes and which allow the production of new wipe effects.

According to the present invention, there is provided a signal generator for use in a video wipe generator, the signal generator producing a solid representing a plurality of contiguous rectangular tiles defined by horizontal and vertical boundaries, the generator comprising means for producing width signals indicating on each video line a plurality of vertical boundaries, means for producing height signals indicating a plurality of horizontal boundaries on respective video lines, and a pseudo random number generator a) responsive to the width signals to repeatedly produce, between successive height signals, the same sequence of pseudo random numbers, and b) responsive to the height signals to change the sequence of pseudo random numbers.

Such a generator allows the production of a solid in the form of rectangular tiles having random amplitudes, thus allowing a random wipe to be performed.

In an embodiment of the invention, the width of each tile may be fixed or random. Preferably the height of each row of tiles may be fixed or random. The random tile widths are defined by a pseudo random number generator. The random tile heights are defined by another pseudo random number generator.

A selector allows the selection of fixed or random width. Another selector allows the selection of fixed or random height.

The use of pseudo random number generators allows the same sequence of numbers to be generated repeatedly when seeded with a preset number. This allows the tiles to have heights of a plurality of lines and yet have the same sequence of random widths on each line. Likewise the rows of tiles can be repeatedly produced having the same sequence of random heights.

Tiles can be made to flicker. This is done by replacing a current tile by another tile at random times defined by yet another pseudo-random noise generator. The other tile is, in an embodiment of the invention, a tile stored in a frame store.

Tile signals may be mixed and thus filtered. In embodiments of the invention, a current tile may be mixed with a frame delayed tile, a current line may be mixed with a previous line; and/or pixels on a line may be mixed with delayed pixels of the same line. The resultant filtering is non-symmetrical 11R filtering. In a preferred embodiment, any of these mixing filtering effects can by passed.

For a better understanding of the present invention, reference will now be made by way of example to the accompanying drlwings in which: Figure 1 illustrates a wipe; Figure 2 illustrates a solid together with a key signal; Figure 3 illustrates a schematic block diagram showing a wipe generator; Figures 4A to C illustrate"tiles"produced in accordance with the invention; Figure 4D shows a row of tiles of Figure 4B with random amplitudes; Figure 5 is a schematic block diagram of a solid generator for generating the tiles of Figure 4; Figure 6 is a schematic block diagram of the mixing and filter block of Figure 5 ; Figure 7 is a schematic block diagram of the H size generator of Figure 5; Figure 8 is a schematic block diagram of the V size generator of Figure 5; Figure 9 is a schematic block diagram of the PRB 1 of Figure 5; and Figure 10 is a schematic block diagram of the PRB2 of Figure 5.

For the purpose of this illustrative description, it is assumed that progressively scanned frames are used.

The illustrative system of Figures 5 to 9 is a solid generator. The generator can produce various solids comprising"tiles"as shown for example in Figures 4A to 4C.

The tiles have fixed or random heights where"height"is the number of horizontal lines occupied by a tile, and fixed or random widths where"width"is the number of pixels along a line. The tiles have an amplitude which is random, as shown for example in Figure 4D where amplitude is the magnitude of the solid in the direction perpendicular to the plane of the frame. As a clip plane is moved through the solid it intersects the tiles at the random amplitudes of the tiles to produce a random wipe effect.

As will be discussed hereinafter, various other effects can be produced.

The tiles of Figure 4 may be made to flicker at an adjustable flicker rate. The flicker is created by replacing the current amplitude of the tile by a new amplitude produced by generator PRB 1.

A tile of one frame may be mixed with the corresponding tile of the previous frame. A pixel of a line may be mixed with another pixel of the same line or an adjacent line. This creates IIR non-symmetrical filtering.

Tile Generation Referring to Figure 5, an H size generator 10, which is shown in more detail in Figure 7, defines the width of a tile. The width may be fixed or random as determined by a control signal HSEL. The fixed width is defined by a signal Hsize. The random width is generated by a pseudo random number generator PRB3 in the Hsize generator. The tile width is defined by a width control signal HWIDTH produced by the generator 10.

A Vsize generator 12, which is shown in more detail in Figure 8, defines the height of a tile. The height may be fixed or random as determined by a control signal VSEL. The fixed height is defined by a signal Vsize. The random height is generated by a pseudo random number generator PRB4 in the Vsize generator. The tile height is defined by a height control signal VWIDTH produced by the generator 12.

The Hsize Generator 10 and the Vsize Generator 12 control a pseudo random number generator PRB 1 (14) which is shown in more detail in Figure 9. The generator PRB1 produces a number representing the amplitude of a tile for a duration of the HWIDTH and VWIDTH control signals. A new number PRB 1 is produced each time HWIDTH and VWIDTH are set. The number is held constant over the width and height of the tile defined by HWIDTH and VWIDTH.

The number PRB1 for a tile is coupled (after optional further modification which will be described hereinbelow) as a number PRB to a mixing and filtering system 16. The mixing and filtering system 16 is shown in more detail in Figure 6.

The system 16 comprises a series of mixers 161,162,163. Any of the mixers 161, 162,163 may be disabled by a signal BYPASS so that the signal is not modified by that mixer.

Each mixer mixes a signal A at its input with a delayed version B of its output according to KA + (I-K) B where 0SKE1. The delay applied to the output of at least one mixer is variable by a control signal NDELAY. The mixing and filtering system 16 also controls the overall gain applied to the output signal thereof by means of a gain control signal K4. The mixing and filtering system provides non-symmetrical IIR filtering.

Referring again to Figure 5, a second pseudo random number generator PRB2 (18) is provided. Generator PRB2 is similar to generator PRB1. It produces a pseudo random number PRB2 which is fixed for the duration of a tile. A comparator 20 compares PRB2 with a threshold value FR denoted'flicker rate'. A selector 22 selects either the current value of PRB1 produced by generator PRB1 14, or the delayed output of one of the mixers of the mixing and filtering system 16, in dependence on the comparison. This has the effect of flickering a tile. In the examples of Figures 5 and 6 the delayed output is delayed by at least one frame.

Horizontal Tile Size Referring now to Figure 7, the control of horizontal tile size will be described (assuming the vertical tile height is fixed).

A signal HSEL determines whether the horizontal tile width is fixed or random. If the tile width is fixed a selector 30 selects an input HSIZE which receives a signal HSIZE defining the fixed tile width. If the tile width is random, the selector 30 selects a signal HSIZE~PRB produced by a pseudo random number generator 32 (HSIZE PRB GEN).

Assume that a fixed tile width is selected, and the selected fixed tile width is within limits allowed by a limiter 42. The fixed tile width HSIZE is applied to one input of a comparator 34 by a selector 40.

A counter 36 counts pixels along a line. Its count is applied to the second input of the comparator 34. When the two counts are equal the comparator produces a pulse HTWIDTHP which resets the counter 36 and also indicates the start of a new tile. The counter 36 is reset also at the beginning of each line by pulse IP-H. IP-H and the output of the comparator are applied to the reset input R of the counter 36 via an OR gate 38.

The value HSIZE is applied to the comparator 34 continuously for a whole frame when the fixed tile width is selected.

The same value HSIZE may be applied to the comparator 34 and reapplied to the register 48 and to the generator 32 at the beginning of every line of a frame. That produces the effect shown in Figure 4C of random tile widths repeated on all lines of frame.

If the tile width is random, the signal HSEL selects the input HSIZE PRB of the selector 30. The HSIZE PRB signal is a random number produced by the generator 32. HSIZE PRB is applied to one input of a selector 40 and also to the limiter 42. The limiter 42 receives a limit value HRANGE specifying both the maximum and the minimum values of the tile width 40. If the value is outside the limits defined by HRANGE then the limiter applies a limit value to the selector 40.

Selector 40 then selects the limit value or the HSIZE PRB if it is within the limits.

The selected value is compared in comparator 34 with the count of the counter 36 to produce the pulse HTWIDTHP which defines the end of the tile and resets the counter via the OR gate 38. The OR gate also receives the IP~H pulse at the beginning of each line to reset the counter at the beginning of the line.

To initiate the generation of the random number HSIZE-PRB, at the beginning of the first line of a first frame, as indicated by IPV AND IP-H in gate 44, the generator 32 is seeded with a value HSIZE which causes it to produce a pseudorandom number HSIZE~PRB dependent on the seed value. At the same time, at the beginning of the frame as indicated by IP-V the initial number HSIZEPRB is loaded via a selector 46 into a register 48 as a value HLNFBD.

The comparator 34 compares the initial value HSIZE-PRB of the first tile with the count in counter 36 as described above. When the values are equal pulse HTWIDTHP is produced indicating the start of the next tile and resetting the counter.

HTWIDTHP is supplied to the generator 32 by an OR gate 50 and the generator produces the next pseudo-random number HSIZE-PRB in its sequence. That number is applied via selectors 30 and 40 to comparator 34 to define the width of the next tile.

A sequence of pseudo random numbers defining tile widths is produced by generator 32 until the end of a line.

At the end of the first line, the generator 32 is loaded again with the seed value HLNFBD stored in register 48. The process repeats along the next line, with the same sequence of pseudo random numbers as on the first line.

The process repeats line-by-line until the fixed tile height VSIZE has been achieved. The vertical tile size generator then produces a pulse VTWIDTHP which is applied to the generator 32 via the OR gate 50 and causes the generator 32 to produce a new pseudo-random number which is loaded into the register 48 as a new seed value.

The process repeats until the end of the frame. At the beginning of the next frame the original seed value HSIZE is loaded again and the same pseudo random pattern of tiles produced.

Vertical Tile Size Figure 8 shows an example of the vertical tile size generator 12. The operation of the generator 12 is similar to that of the horizontal tile size generator 10.

A signal VSEL determines whether the vertical tile height is fixed or random.

If the height is fixed, a selector 56 selects an input VSIZE which receives a signal VSIZE defining the tile height in lines. If the tile height is random, the selector 56 selects a signal VSIZE-PRB produced by a pseudo-random number generator 58 (VSIZE PRB GEN).

Assume that a fixed tile height is selected and the selected fixed tile height is within allowed limits. The fixed tile height VSIZE is applied to one input of a comparator 60.

A counter 62 counts line pulses IP-H. Its count is applied to the second input of the comparator 60. When the two counts are equal the comparator 60 produces the pulse VTWIDTHP which resets the counter 60 and also indicates the start of a new tile. The counter 62 is reset also at the beginning of each frame by pulse IP-V. IP-V and the output of the comparator 60 are applied to the reset input R of the counter 62 via an OR gate 64. (Pulse VTWIDTHP is also supplied to the horizontal tile size generator of Figure 7.) The value VSIZE is applied to the comparator 60 continuously for a whole frame when the fixed tile height is selected.

If the tile height is random, the signal VSEL selects the input VSIZE PRB of the selector 56. The VSIZEPRB signal is a pseudo random number produced by the generator 58. VSIZEPRB is applied to one input of a selector 66 and also to a limiter 68. The limiter 42 receives a limit value VRANGE specifying the maximum and minimum values of the tile height 66. If the value is outside the limits defined by VRANGE then the limiter applies a limit value to the selector 66. Selector 66 then selects the limit value or the VSIZE PRB if it is within the limits.

The selected value is compared in comparator 60 with the count of the counter 62 to produce the pulse VTWIDTHP which defines the end of the tile and resets the counter via the OR gate 64. The OR gate 64 also receives the IP~V pulse at the beginning of each frame to reset the counter at the beginning of the frame.

To initiate the generation of the random number VSIZE PRB at the beginning of a frame, as indicated by IP~V, the generator 58 is loaded with the value VSIZE which acts to seed the generator 58 to cause it to produce an initial pseudo random number VSIZE-PRB dependent on VSIZE.

The comparator 60 compares the initial value of VSIZE-PRB of the first row of tiles with the count in counter 62 as described above. When the values are equal pulse VTWIDTHP is produced indicating the start of the next row of tiles and resetting the counter. VTWIDTHP is supplied to the EN input of generator 58 and the generator produces the next pseudo-random number VSIZE-PRB in its sequence. That number is applied via selectors 56 and 66 to comparator 60 to define the height of the next row of tiles. A sequence of pseudo random numbers defining heights of the rows of tiles is produced by generator 58 until the end of the frame.

Both the vertical and horizontal tile size generators may be set to produced fixed size tiles. Both may be set to produce random size tiles. One may be set to produce fixed size tiles and the other random size tiles.

Pseudo Random Number Generation Figure 9 shows an example of the pseudo random number generator PRB1 (14) which generates the tile amplitudes as shown in Figure 4D. The generator allocates an amplitude to each tile as defined by the horizontal and vertical tile size generators 10 and 12 of Figures 5,7 and 8.

Before the beginning of a frame a seed value SEED is loaded into a frame feed back register FFBREG 70 via a selector 72. The seed value is then loaded into a pseudo random signal generator 74 via another selector 76 in response to the pulse IP V at the beginning of the first line as indicated by IP-H.

The seed value is also stored in a line feed back register 78 at the beginning of the frame as indicated by IP-V. For the first tile on the first line of the frame, the seed value is output as pseudo random value PRB1 which indicates the amplitude of the current tile. As the horizontal end of that tile as indicated by HTWIDTH, applied via OR gate 80 the random signal generator 74 produces another value PRB 1. For each successive HTWIDTH pulse, along the first line, the generator 74 produces another value PRB 1. At the beginning of the next line, as indicated by IP-H the seed value is loaded from the line feedback register 78 into the random signal generator 74 again via selector 76. That generator 74 produces the same sequence of numbers on each line because it has the same start value on each line. That process repeats until the vertical tile end signal VTWIDTH is produced. VTWIDTH applied via OR gate 80 causes the random signal generator 74 to produce a new start value of PRB 1 for the first line and tile of the next row of tiles. The new value of PRB 1 is also loaded into the line feed back register 78 in response to VTWIDTH applied to register 78 via an OR gate 82.

The process repeats for each row of tiles until the end of the frame. At the beginning of the next frame, register 70 seeds the initial value of SEED into generator 74 to enable the same sequence as in the previous frame to repeat.

If the tile size is zero, the random generator PRB 1 produces a new value on every pixel.

Flicker Figure 10 shows an example of the pseudo random number generator PRB2 (18) which controls the flicker of tiles.

A pseudo random number generator 86 produces pseudo random numbers PRB2 which are compared with numbers FR representing flicker rate in the comparator 20 (see also Figure 5). At the beginning of the first line (as indicated by IP-H) of a frame, (as indicated by IP~V) the generator 86 is loaded via a selector 90 with a seed value from a feedback register FFBREG 88. The value PRB2 is also loaded into a line register 92 at the same time. For the first line of the first row of tiles, the generator 86 produces a succession of values PRB2 in response to the tile end pulses HTWIDTH applied for the generator via OR gate 94. At the beginning IPH of each successive line the value LNFBD stored in register 92 is reloaded into the generator 86 so the same sequence of pseudo-random numbers is repeated.

When the vertical tile end signal VTWIDTH occurs the process repeats but with a new start value PRB2 produced in response to VTWIDTH. That new value is loaded into register 92 in response to VTWIDTH which is applied to register 92 via an OR gate 96.

The process continues for each row of tiles until the end of the frame.

At the beginning of the next frame, the random generator 86 is re-seeded with the value stored in register 88. This value may be the same as the previous seed value.

A frame counter 98 counts frame pulses FRMP and a comparator 100 compares the count with a reference value FRDEL. If they are equal, a new value of PRB2 is loaded into the register 88. Thus the sequence of numbers produced by generator 86 may stay constant for a number of frames defined by FRDEL.

Filtering Referring to Figure 6, an example of the mixing and filtering circuit 16 is shown.

The circuit 16 comprises mixers 161,162 and 163 each of which mixes an input signal A with an input signal B according to KA + (I-K) B.

Signal B is a delay version of signal A. K is defined by a control signal K1, K2 or K3 where 0 < K < 1. Mixers 161,162 and 163 are connected in series. Each mixer may be bypassed as controlled by a BYPASS signal.

Mixer 161 is associated with a frame store 165 which stores the previous output of mixer 161 delayed by one frame period or more. The signal B produced by the frame store 165 is fed to input B of the mixer 161 and also to the selector 22 of Figure 5 for producing the flicker effect. The mixing is controlled by mix control signal K 1.

Mixer 162 is associated with a delay 166 which delays the output of the mixer 162 by N clock cycles (i. e. pixels) as controlled by a control signal NDELAY. The mixing is controlled by mix control signal K2.

Mixer 163 is associated with a line store 167 which delays the output of the mixer 163 by one line period. The mixing is controlled by mix control signal K3.

A gain control circuit 164 is controlled by a gain control signal K4. The circuit 164 is in series with the mixers 161,162,163 and outputs the random solid to, for example, a key generator as shown in Figure 3. K4 is set so that the overall gain through the mixing and filtering circuit 16 is unity. In embodiments of the circuit 16, the gain applied in each of the mixers 161 to 163 is less than unity. Therefore K4 is greater than unity.

Referring to Figure 5, the solid generation system is controlled by a control system 100 which is also an operator interface. The system 100, under the control of an operator, sets the various control signals applied to the circuits of Figures 5 to 10.

The solid generation system may be controlled so as to produce a fixed set of solids, from which the operator selects.

Although the invention has been described with reference to a progressively scanned frame, it may be applied to interlaced fields.

Claims (19)

1. A signal generator for use in a video wipe generator, the signal generator producing a solid representing a plurality of contiguous rectangular tiles defined by horizontal and vertical boundaries, the generator comprising means for producing width signals indicating on each video line a plurality of vertical boundaries means for producing height signals indicating a plurality of horizontal boundaries on respective video lines, and a pseudo random number generator a) responsive to the width signals to repeatedly produce, between successive height signals, the same sequence of pseudo random numbers, and b) responsive to the height signals to change the sequence of pseudo random numbers.

2. A generator according to claim 1, comprising means for defining a fixed width between vertical boundaries.

3. A generator according to claim 1 or 2, comprising means for defining a random width between vertical boundaries.

4. A generator according to claims 2 and 3 comprising means for selecting one of the fixed width and the random width.

5. A generator according to claim 3 or 4, wherein the means for defining the random width comprises a pseudo random number generator.

6. A generator according to claim 5, wherein the pseudo random number generator of the width defining means produces on each video line between successive height signals the same sequence of pseudo random numbers representing the widths.

7. A generator according to any preceding claim comprising means for defining a fixed height between horizontal boundaries.

8. A generator according to any preceding claim comprising means for defining a random height between horizontal boundaries.

9. A generator according to claims 7 and 8 comprising means for selecting one of the fixed height and random height.

10. A generator according to claim 8 or 9, wherein the means for defining a random height comprises a pseudo random number generator.

11. A generator according to claim 10, wherein the pseudo random number generator of the height defining means produces a sequence of pseudo random numbers representing the heights between horizontal boundaries.

12. A generator according to any preceding claim comprising means for causing the tiles to flicker.

13. A generator according to claim 12, wherein the flicker causing means comprises a pseudo random number generator.

14. A generator according to claim 13, wherein the flicker causing means comprises a frame store for storing a frame of tiles, selecting means for selecting the said stored frame or the current frame of tiles, means for comparing pseudo random numbers generated by the pseudo random numbers generator of the flicker causing means with a selected number representing a desired flicker rate and selecting the said stored frame or the said current frame in accordance with the comparison.

15. A signal generator according to claim 14, further comprising means for mixing the said current frame with the said stored frame.

16. A generator according to any preceding claim, comprising means for delaying pixels of a video line by N pixels and means for mixing the delay pixels of the video line with undelayed pixels of the video line.

17. A generator according to any preceding claim comprising a line delay, and means for mixing a current line with the delayed line.

18. A generator according to any preceding claim in combination with a key generator.

19. A signal generator substantially as hereinbefore described with reference to Figure 5 optionally together with Figure 6,7,8,9 and/or 10.