Abstract:
A wipe pattern comprises a series of horizontal rows, R0-R4. As the wipe proceeds first video Y in a row is replaced by second video X. The wipe proceeds from row to row. The wipe may progress from left to right from the top row to the bottom or from right to left from the bottom row to the top. An alternative wipe pattern comprises vertical rows. In another alternative, the wipe in one row begins before the wipe of the preceding row ends.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     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 
     2. Description of the Prior Art 
     Reference will now be made to FIGS. 1 to  3  of the accompanying drawings which show the background to the present invention. 
     FIG. 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’. This will be explained with reference to FIGS. 2 and 3. 
     A solid is an electrical signal representing a three dimensional surface of a desired shape. It may comprise at least one ramp signal and typically comprises a combination of at least two ramp signals which themselves may be modified. It may also comprise a signal defined by a polar coordinate system representing a curved surface. 
     FIGS. 2A illustrates a known example of a solid  125  which is a simple ramp. As shown in FIG. 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 by applying high gain to the solid and limiting the result, as shown in FIG.  2 B. 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. 
     FIG. 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 generator produces a solid, for example a ramp as shown in FIG.  2 A. The clip element applies an offset to the ramp to vary the intersection of the ramp with the clip plane  142  as shown in FIGS. 2A to  2 C. 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 FIG.  2 B: 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 clip offset is zero, the solid and the key signal are identical. 
     The example of FIGS. 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. 
     The present invention is concerned with the generation of a solid which allows the production of new wipe effects. 
     SUMMARY OF THE INVENTION 
     According to the present invention, there is provided a solid generator for use in a vision mixer comprising, 
     means for producing ramp signals within each video field or frame, each ramp signal having an amplitude which increases in a predetermined direction, 
     means for producing an offset signal, the offset signal having a value mV where m=1 to M where M≧2 mV being fixed for each set m of n ramp signal where n&gt;2 and 
     means for adding the ramp signal to the offset signal to produce the solid. 
     Such a signal generator produces a solid which allows the production of a wipe effect which is believed to be novel per se. The wipe effect comprises bands which progress across a frame as the wipe proceeds. Consecutive bands have start times which differ by controllable amount. The bands may be contiguous or spaced apart. The bands may be confined to an area of a frame, or may occupy the whole frame. The wipe may proceed in the line direction or the frame direction. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above and other objects, features and advantages of the invention will be apparent from the following detailed description of illustrative embodiments which is to be read in connection with the accompanying drawings, in which: 
     FIG. 1 illustrates a wipe; 
     FIG. 2 illustrates a solid together with a key signal, 
     FIG. 3 is a schematic block diagram of a wipe generator; 
     FIGS. 4A and B illustrate two wipe patterns in accordance with the present invention; 
     FIG. 4C shows another wipe pattern in accordance with the invention, 
     FIGS. 5A to C are waveform diagrams illustrating the “solid” which allows the production of the wipe pattern of FIG. 4A; 
     FIG. 6 is a schematic block diagram of an embodiment of a signal generator according to the present invention; 
     FIG. 7 illustrates a modification of the signal generator of FIG. 6 or  9 ; 
     FIGS. 8A to C illustrate another wipe pattern in accordance with the present invention and wave forms allowing the production of the pattern; and 
     FIG. 9 is a schematic block diagram of an embodiment of another signal generator according to the invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The following description assumes a frame is progressively scanned. 
     Referring to FIG. 4A, an illustrative wipe pattern in accordance with the present invention comprises a horizontal band  1  of a video from a source Y which progressively moves across a frame video of source X in the direction of arrow W. Further bands  2  to  4  and  5  follow band  1  with a delay. 
     The delay between the bands may be selected. For example band  2  may start only when band  1  has progressed to very near the right hand edge of the frame. The widths of the bands is selectable. The direction of the wipe may be reversed. 
     As shown in FIG. 4B the bands  1  to  4  may be vertically spaced. 
     The wipe pattern is shown in FIGS. 4A and B as occupying the whole of a frame. The pattern may be restricted to a restricted area of the frame as shown in FIG.  4 C. 
     The inventors have termed wipe patterns, such as those shown in FIG. 4, “karaoke wipes” because they resemble displays produced by karaoke machines. 
     FIGS. 5A to C show waveforms used to generate the wipe pattern of FIG.  4 A. FIG. 5A shows repeated horizontal ramp waveforms each having a duration of one horizontal line interval  1 H. The number of lines is equal to the number of active lines of a frame. 
     The lines are grouped into bands,  1  to  5  in FIG.  5 A. Any suitable number n of bands may be chosen. The number of lines per band is L/n. 
     FIG. 5B shows a stepped waveform. The waveform is shown in FIG. 5B as stepping up from left to right. In terms of the video frame the waveform steps up from top to bottom of the frame. Each step has a duration of L/n lines coincident with the bands  1  to  5 . The waveform of FIG. 5A is added to the waveform of FIG. 5B to produce the waveform of FIG. 5C which represents the ‘solid’ defining the wipe pattern of FIG.  4 A. 
     The clip plane CP is shown at CP in FIG.  5 C. By varying the offset between the solid and the clip plane in the direction of arrow W in FIG. 5C, the wipe proceeds in the direction W shown in FIG.  5 C. 
     FIG. 6 is a schematic block diagram of an illustrative digital signal generator for producing the waveforms of FIGS. 5A to C and thus the wipe patterns of FIGS. 4A to C. Pixels along lines H are essentially defined by clocks of a pixel clock  42  synchronised to the lines H. 
     Referring initially to FIGS. 4A,  5 C and  6 , a horizontal counter  10  counts pixels in the horizontal direction along a video line from reception of a signal Hstart. Assume H start is at the beginning of each line. The count of the counter  10  then represents the ramp shown in FIG.  5 A. The counter is reset by Hstart at the beginning of each line and thus produces the repeated ramps of FIG.  5 A. 
     A row counter  12  is preloaded with a value RowHgt stored in a register  14  and representing the number of lines L/n in a band. The counter  12  counts down in response to each line H. When the count reaches 0 indicating the end of a band an accumulator  16  is enabled and the value in the accumulator incremented by an increment Inc stored in a register  18 . The increment Inc represents the delay in pixels between successive bands and is indicated by Inc in FIGS. 4C and 5B. The maximum value is one line interval IH and the minimum value is zero. 
     The count of 0 in row counter  12  also reloads RowHgt into the counter  12  and the counting down repeats for the next band. 
     The output of the accumulator (FIG. 5B) is added to the output of the horizontal counter  10  (FIG. 5A) in an adder  20  to produce the solid of FIG.  5 C. 
     At the beginning of the next frame, in the case of FIG. 4A, the accumulator  16  is cleared to zero by a signal Vstart. The accumulation process then repeats on the next frame. 
     Referring to FIG. 4C, the wipe pattern, i.e. the solid, may be restricted to an area A. The start position of the area A is defined by the signals Hstart and Vstart. 
     A value Hstart is stored in a register  22 . The value Hstart represents the number of pixels from the left hand edge of the frame in the line direction of the top left corner of the area A. The value Hstart is loaded into a counter  24  at the beginning of each line. The counter  24  counts down and at zero count enables the counter  10  to count pixels. 
     A value Vstart is stored in a register  26 . Value Vstart represents the number of lines from the top of the frame to the top of the area A. Vstart is loaded into a counter  28  at the beginning of each frame. The counter  28  counts down in response to lines H and at count zero the counter  10  is enabled to count pixels. 
     A horizontal comparator  30  compares the count of the horizontal counter  10  with a value Width stored in a register  32 . The value Width represents the horizontal width in pixels of the area A. When the count is less than Width the comparator  30  outputs logic ‘1’. 
     A vertical counter  34  enabled by Vstart counts lines H, of the area A. A comparator  36  compares a value Height, stored in a register  40 , representing the height in lines of the area A, with the count of counter  36 . When the count is less than Height, the comparator  36  outputs logic ‘1’. 
     An AND gate  38  is enabled by the logic ‘1’s from both of the comparators  30  and  36  to pass the solid which is output from adder  20 . 
     The values Hstart, Vstart, Width, Height, RowHgt, and Inc stored in the registers  22 ,  26 ,  32 ,  40 ,  14  and  18  may be varied, using a control processor  40 . 
     FIG. 4B shows a wipe pattern in which bands  1  to  4  are spaced apart. One way of achieving that is to apply a logic ‘O’ to the AND gate  38  for the lines corresponding to the spaces. FIG. 7 shows one example of a modification of FIG. 6 for achieving that. A comparator  44  compares a value Space stored in a register  46  with the value of the count in the Row Counter  12 . If the value of the count is less then or equal to Space, the comparator outputs logic 0 to the AND gate  38 . 
     FIG. 8A illustrates one example of a Karaoke wipe pattern which wipes vertically. 
     FIGS. 8B and C illustrate waveforms involved in producing the wipe pattern of FIG.  8 A. 
     As shown in FIG. 8C, a ramp waveform is produced in the vertical direction. The ramp has the form R=Bv, where v is line number, and B is the slope of the ramp. 
     The columns C 1 -C 3  . . . Cn of the wipe are defined by a stepped waveform as shown in FIG.  8 B. The waveform occurs on each line and each step has a width of h pixels. The delay between adjacent columns C is defined by the increment Inc between the steps. 
     FIG. 9 shows an illustrative signal generator for producing the vertical wipe pattern of FIG.  8 A. It operates in very similar fashion to the generator of FIG.  6 . 
     Once enabled by a signal Vstart, a line counter  50  counts lines H to produce the ramp waveform R=Bv of FIG.  8 . 
     A column counter  52  is loaded with a count ColWid, stored in a register  54  and counts down in response to pixels along each line. When the count reaches 0, an accumulator  56  is enabled and the value in the accumulator incremented by the increment Inc, which is stored in a register  58 . The counter  52  is also reloaded with ColWid. The accumulator  56  and the counter  52  are reset by a signal Hstart. 
     The outputs of the line counter  50  and the accumulator  56  are added in an adder  60 . The output of the adder  60  is solid which allows the production of the wipe pattern of FIG.  8 A. 
     The foregoing assumes that the wipe pattern occupies an entire frame. The wipe pattern may be restricted to an area A similar to that shown in FIG.  4 C. The vertical position of the are A is defined by the value Vstart in a register  62 . A counter  64  is preloaded with Vstart and counts down in response to lines H beginning at the start V of the frame. When the count is zero counter  50  is enabled. 
     Similarly counter  52  is enabled by an H counter  66  which counts down in response to pixels from the beginning of each line. The counter is preloaded with value Hstart stored in a register  68 . 
     The height and width of area A are controlled by comparators  70 ,  72 . Comparator  70  compares a value Height stored in a register  74  with the count in the counter  50 . Comparator  72  compares a value Width stored in a register  76  with the count of a counter  80  which counts pixels when enabled by Hstart. The comparator operate, and disable AND gate  78 , in the manner described with reference to FIG.  6 . 
     The values stored in the registers  54 ,  58 ,  62 ,  68 ,  74 ,  76  may be selected as discussed with reference to FIG.  6 . The columns may be spaced in the same way as shown in FIG. 7, with the row counter  12  and Row Hgt register  14  of FIG. 7 replaced by the Column counter  52  and Col Wid register  54  of FIG.  9 . 
     Although the invention has been described wit reference to a progressively scanned frame, it may be applied to interlaced fields. 
     Although illustrative embodiments of the invention have been described in detail herein with reference to the accompanying drawings, it is to be understood that the invention is not limited to those precise embodiments, and that various changes and modifications can be effected therein by one skilled in the art without departing from the scope and spirit of the invention as defined by the appended claims.