GB2348768A

GB2348768A - Video wipe signal generator with dual gain key signal

Info

Publication number: GB2348768A
Application number: GB9908243A
Authority: GB
Inventors: Jonathan Mark Greenwood; James Hendrie Mcintyre
Original assignee: Sony United Kingdom Ltd
Current assignee: Sony Europe Ltd
Priority date: 1999-04-09
Filing date: 1999-04-09
Publication date: 2000-10-11
Anticipated expiration: 2019-04-09
Also published as: GB2348768B; GB9908243D0; JP2000324392A

Abstract

A signal generator is used to produce a signal for producing a video wipe effect. The signal generator selectively applies two different gains, K<SB>1</SB> and K<SB>2</SB>, to the key signal in dependence upon whether the wipe solid (125, fig.5) is less than or greater than a clip level, (142, fig.5). The effect is to produce a wipe sequence comprising two transition regions (200 and 205, fig.4) between the areas displaying videos X and Y. Each transition region contains a different mix of video signals X and Y.

Description

Signal Generator The present invention relates to a key signal generator for use in a video wipe generator. Such a wipe 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 invention.

Figure I 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 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 co-ordinate system representing a curved surface. This will be explained with reference to Figures 2 and 3.

Figure 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 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 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 generator produces a solid, for example a ramp as shown in Figure 2A. The clip element applies an offset to the 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 limiter 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 to 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 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 desired to produce new wipe effects.

According to one aspect of the present invention there is provided a key signal generator for use in a video wipe generator and including an input for receiving a solid, and means for selectively applying a first gain or a second gain to the solid in dependence upon the relationship between the value of the solid and the value of a reference level to produce the key signal.

According to another aspect of the present invention there is provided a key signal generator for use in a video wipe generator and including, an input for receiving a solid, means coupled to the input for comparing the solid with a reference level to produce a control signal having a first value if the value of the solid is less than the reference level and second value if the value of the solid is greater than the reference level, and means for selectively applying either a first gain or a second gain to the solid in dependence upon the control signal to produce the key signal.

According to a further aspect of the present invention there is provided a key signal generator for use in a video wipe generator and including an input for receiving a solid, the solid being represented in a digital 2's compliment format, and means for selectively applying a first gain or a second gain to the solid in dependence on the most significant bit of the solid to produce the key signal.

The key signal generator of embodiments of the invention provides different gains either side of the clip level. Thus different visual effects can be provided either side of the clip in the region of mixing of the two video sources in a wipe.

For a better understanding of the present invention, reference will now be made by way of example to the accompanying drawings in which: Figure 1 illustrates a wipe; Figure 2 illustrates a solid together with a key signal; Figure 3 is a schematic block diagram of a wipe generator; Figure 4 illustrates an example of a wipe in accordance with an embodiment of the present invention; Figure 5 illustrates example signals required in order produce the example wipe in accordance with an embodiment of the present invention; Figure 6 illustrates a schematic block diagram showing a wipe generator in accordance with an embodiment of the present invention; and Figure 7 illustrates a schematic block diagram showing a wipe generator in accordance with a further embodiment of the present invention.

With reference to Figure 4, an example of a wipe effect between two video sources X and Y is shown in accordance with an embodiment of the present invention.

As the wipe effect proceeds, as indicated by arrow W, video X is replaced across the display by video Y at a transition line 105. The transition line 105 occurs at the junction of the solid 125 with the clip plane 142 as shown in Figure 2. Region X, displaying video X is separated from region Y, displaying video Y by a first transition region 200 and a second transition region 205. The first transition region 200, separating region X from the second transition region 205 and adjacent to the transition line 105 and a first transition boundary 210, contains a first mix of video sources X and Y according to KIT + (1-kil) Y. The second transition region 205, separating region Y from the first transition region 200 and adjacent to the transition line 105 and a second transition boundary 215, contains a second mix of video sources X and Y according to K2X + (1-K2) Y, where Kl X K2.

It will, of course, be appreciated that for illustrative purposes this example is based on a wipe using a single ramp solid, but that the wipe effect can also be achieved using more complicated solids formed, for example, from a combination of two or more ramps. Also, it will be appreciated that in other embodiments video Y could be replaced by video X, and that the wipe could proceed in any desired direction.

As shown in Figure 5B, the wipe effect is achieved by providing a key signal K derived from a solid 125 as shown in figure SA which has a first gain K, below the clip plane 142, before the transition line 105 and a second gain K2 above the clip plane 142, after the transition line 105. The result is limited as described earlier. The mixing of the video sources according to K (X) + (1-K) Y is shown in Figure 5C where K is the value of the key signal K, 0 s Ks 1. In the area X, bounded by the first transition boundary 210, video X is displayed. In the area Y, bounded by second transition boundary 215, video Y is displayed. In the first transition region 200 bounded by the transition line 105 and the first transition boundary 210, the first mix of video sources X and Y is displayed. The first mix is dependent on the first gain K,. In the second transition region 205 bounded by the transition line 105 and the second transition boundary 215, the second mix of video sources X and Y is displayed. The second mix is dependent on the second gain K2.

It will, of course, be appreciated that the size of the first transition region 200 and the second transition region 205 may be varied to any appropriate value by varying the first gain K, and the second gain K2.

Figure 6 shows an embodiment of the gain stage 100 in accordance with the present invention of the key generator of Figure 3. The gain stage 100 comprises an input for receiving a solid 125, a comparator 140 for comparing the solid 125 with the clip plane 142 to produce a comparison signal 145, a selector 150 for selectively outputting the solid 125 to either one or the other of its outputs in dependence on the comparison signal 145, a first multiplier 300 for adjusting the amplitude of the solid 125 in dependence on the first gain K, to produce first modified solid 127, a second multiplier 310 for adjusting the amplitude of the solid 125 in dependence on the second gain K2 to produce a second modified solid 129, a combiner for combining in a logical OR manner the first modified solid 127 and the second modified solid 129.

In order to produce the key signal K as shown in Figure 5B, the solid 125 is presented to the input of the first multiplier 300 and to the input of the second multiplier 310. Signals presented to the first multiplier 300 are amplified in dependence on the first gain K, to produce a first modified solid 127. Signals presented to the second multiplier 310 are amplified in dependence on the second gain K2 to produce a second modified solid 129. The first modified solid 127 and the second modified solid 129 are presented as inputs to the selector 150. The selector 150 is operable to present the first modified solid or the first modified solid at its output.

The selector 150 is controlled by the comparison signal 145 produced by the comparator 140. The comparator 140 compares the solid 125 against the clip plane 142. In this embodiment, in cases where the value of the solid 125 is less than the value of the clip plane 142 the comparison signal 145 is set to logical'0'and the selector 150 outputs a key signal K representative of the first modified solid 127.

Conversely, where the value of the solid 125 is greater than the value of the clip plane 142 the comparison signal 145 is set to logical'1'and the selector 150 outputs a key signal K representative of the second modified solid 129. Thus a key signal K, with the characteristics shown in Figure 5B is achieved.

It will be appreciated that the characteristics of the key signal K, and with it the wipe effect, can be varied by altering the values of the first gain K, and/or the second gain K2, and that the solid 125 may be more complicated than the simple illustrative example used above. Further, it will be appreciated that the selector 150 could be arranged such that the key signal K comprises the second modified solid 129 selected to be below the clip plane 142, with the first modified solid 127 selected to be above the clip plane 142.

Figure 7 shows a preferred embodiment of the gain stage 100 in accordance with the present invention. The gain stage 100 comprises an input for receiving a solid digitally represented an a 2's compliment format 125, a selector 150 for selectively outputting a gain value representative of either K, or K2 in dependence on the most significant bit (MSB) of the solid 125, and a multiplier 320 for adjusting the amplitude of the solid 125 in dependence on the gain value presented by a selector to produce key signal K.

In order to produce the key signal K as shown in Figure 5B, the selector 160 outputs a gain value representative of either K, or K2 in dependence on the MSB of the 2's compliment solid 125. In this embodiment, where the value of the MSB is a logical '1'indicating that the value of the solid 125 is less than the clip plane 142, selector 160 is arranged such that the gain value K, is presented to the multiplier 320 and the resultant key signal K is representative of the first modified solid 127. Where the value of the MSB is a logical'0'indicating that the value of the solid 125 is higher than the clip plane 142, selector 160 is arranged such that the gain value K2 is presented to the multiplier 320 and the resultant key signal K is representative of the second modified solid 129. Thus a key signal K, with the characteristics shown in Figure 5B is achieved.

It will be appreciated that the characteristics of the key signal K, and with it the wipe effect, can be varied by altering the values of the first gain K, and/or the second gain K2, and that the solid 125 may be more complicated than the simple illustrative example used above. Further, it will be appreciated that the selector 160 arrangement could be such that the key signal K comprises the second modified solid 129 selected to be below the clip plane 142, with the first modified solid 129 selected to be above the clip plane 142.

Claims

CLAIMS 1. A key signal generator for use in a video wipe generator and including: an input for receiving a solid; and means for selectively applying a first gain or a second gain to the solid in dependence upon the relationship between the value of the solid and the value of a reference level to produce the key signal.
2. A key signal generator for use in a video wipe generator and including: an input for receiving a solid; means coupled to the input for comparing the solid with a reference level to produce a control signal having a first value if the value of the solid is less than the reference level and second value if the value of the solid is greater than the reference level; and means for selectively outputting either the solid with a first gain applied or the solid with a second gain applied in dependence upon the control signal to produce the key signal.
3. A key signal generator as claimed in claim 1 or 2 wherein the selection means outputs the solid with the first gain applied when the value of the solid is less than the reference level and outputs the solid with the second gain applied when the value of the solid is greater than the reference level.
4. A key signal generator as claimed claims 1, 2 or 3 further comprising means coupled to the said input for generating the solid.
5. A key signal generator as claimed in any one of claims 1 to 4 wherein the first gain and the second gain are adjustable.
6. A key signal generator for use in a video wipe generator and including: an input for receiving a solid, the solid being represented in a digital 2's compliment format ; and means for selectively applying a first gain or a second gain to the solid in dependence on the most significant bit of the solid to produce the key signal.
7. A key signal generator as claimed in claim 6 wherein the selection means outputs the solid with the first gain applied when the value of MSB of the solid is set at logic'1'indicative of the value of the solid being less than the reference level and the solid with the second gain applied when the value of MSB of the solid is set at logic '0'indicative of the value of the solid being greater than the reference level.
8. A key signal generator as claimed claims 6 or 7 further comprising means coupled to the said input for generating the solid.
9. A key signal generator as claimed in claim 6,7 or 8 wherein the first gain and the second gain are adjustable.
10. A key signal generator as claimed in any preceding claims comprising a clip circuit connected to the said input for supplying a clipped solid thereto, and a mixer coupled to the said output via a limiter for mixing two video sources X and Y according to the equation KX + (K-1) Y where K is the key signal.
11. A key signal generator substantially as hereinbefore described with reference to Figure 3 as modified by Figures 6 or 7.