Processing system for video source identification signals

Abstract: In the processing of digital video signals there is provided in association with each signal an accompanying tally signal which provides an instantaneous identification of one or more signal sources from which the information contained in each pixel of a picture image has originated. The format of the tally signal may enable processing thereof to identify all signal sources contributing to a particular image area, to pixels of a mixed image or to any given field or frame of a video image signal. The signal may be encoded in the format of the digital chrominance signal component of a colour picture signal and combined with a conventional key signal which is encoded in the format of a digital luminance signal so that the combined signal has the format of a colour picture signal.

Description: In television production it is common to use several cameras and other picture sources to produce one scene, combining the pictures from the cameras and other sources to create a finished program. The process of combining the pictures is performed by a variety of electronic devices, commonly known as vision mixers and digital video effects equipment (DVE). Such an arrangement is shown in EP-A-0239262 which describes a method of processing digital video signals wherein a plurality of input video signals derived from corresponding signal sources are mixed to provide an output video signal, the frames of which each contain a picture area or areas derived from one or more of said input video signals. It is desirable, during such a production, to be able to indicate, to the performers and the production staff, which picture sources are currently providing the pictures which make up the outgoing program. This is commonly done by means of "Tally Indicators" which are coloured lights mounted in various positions, often on the cameras themselves, and by tally indications built in to other types of equipment. It is desirable to have these indicators respond automatically to the controls used to select the picture sources, so that when the operator selects a source then the appropriate tally indication will be turned on at once. This may be achieved simply when only one picture is present in the outgoing program. However, in current production practice digital video effects equipment may be used to create complex composite pictures in which contributions from many sources may be present. This is shown in figure 1 in which three cameras 4,5,6 are obtaining images of three scenes 1,2,3 and a caption generator 7 is providing the word "SPORTS" and associated graphics. These are combined by the DVE and vision mixer 8 to produce the programme 9 which is seen on the monitor 10. The picture of the bicycle and the racing car are present in the output, so the tally indications are set for cameras 4 and 5, the caption is present so the tally is set for the caption generator. The picture from the camera 6 looking at the skis is not currently being used so its tally indication is not set. In the drawing the tally indications are represented by lights on top of the signal sources, but other forms of display are also commonly used. Whereas such an arrangement enables signal sources contributing to a mixed output signal to be indicated directly in a visual manner, the present invention stems from the appreciation that it would be advantageous to associate tally signals with input signals derived from the signal sources in such a manner that when the input signals are mixed those input signals that contribute to an output signal at any given time can be identified. It is known, see US-A-4994916 to encode identification information on to a video signal to enable the video signal to be correlated to a given signal source. Such an arrangement is not, however, applicable to a single video signal derived from multiple sources. Thus an object of the present invention is to provide a means by which an accurate tally indication can be given, which will reliably mark all input signals which contribute in any way to the current output. The object is achieved by a method and apparatus as claimed in the independent claims. The dependent claims relate to embodiments thereof. Advantageously the tally signal is provided in such a format that a common signal may carry the identities of a plurality of picture sources. This signal may then be decoded frame by frame at the final picture stage to identify all sources contributing to each frame of the picture. According to one embodiment of the invention a key signal accompanying the picture signal is encoded as a monochrome picture signal but provided in the format of a colour picture signal, and the unused colour difference component of the coded key signal is encoded to provide the tally signal. The invention also provides apparatus for carrying out the above process. This may include, for example, means for selecting a video signal from a plurality of signal sources and for providing a key signal including the tally signal, apparatus for selectively combining video signals from a number of sources and correspondingly providing coded key/tally signals identifying the combination of signal sources, or means for decoding the composite key signals and providing from the tally signals included therein an indication of the original signal sources. Such an indication may be visual or may be of the nature of a control signal. This control signal could for example be used to prevent an original picture source from being interfered with when it has been selected by a later processing stage for inclusion in the final picture. It is common practice to pass television signals between different items of equipment as either parallel or serial digital signals conforming to European Broadcasting Union recommendation 656, or to subsequent revisions of the recommendation This standard allows for a high definition monochrome signal and two lower definition colour difference signals within one digital data stream carried by one cable. It is also common practice to associate a key signal with a picture signal, in order to indicate transparent areas of the picture behind which a background picture can be seen. This signal is commonly encoded as a monochrome picture signal, in which white represents solid picture, black represents transparency, and intermediate levels of grey represent partial transparency. If this key signal is transmitted from one unit to another as a digital data stream then the part of the stream which would, in a picture, represent the colour difference signals is, in the case of a key signal, unused. The present invention can make use of this unused capacity in the data transmission to transfer information about the picture sources which are currently in use. The invention is illustrated by way of example in the accompanying drawings, in which: Figure 1 is a diagrammatic view of a known television signal processing system, Figure 2 is a block diagram of an apparatus in accordance with the invention for generating tally signals, Figures 3 and 4 are block diagrams of apparatus in accordance with the invention for processing picture signals including such tally signals and Figure 5 is a block diagram of an apparatus in accordance with the invention for decoding tally signals. The apparatus of Fig 2 comprises an input selector and tally inserter. A number of picture inputs 11 and a number of key inputs 13 are supplied to the switches 12 and 14. A control signal derived from the operator controls 15 is used to control the switches to select one key and one video input. This control signal is also used to control the tally generator 16 which generates a colour difference word stream with all bits clear except for the most significant bit and a single bit selected by the control signal. The position of this bit within the word indicates which input is selected by the switches. An arbitrary correspondence can be set up by the operator between the selected source and the bit which is set to represent it. This signal is combined with the switched key signal in the combiner 17 to produce a mixed signal 19 which contains the luminance information of the key signal, and the tally information in the chrominance areas. The switched picture 18 information is passed on to subsequent stages of processing. The switches 12, 14 have been shown with four inputs, but a larger or smaller number of inputs could be used. Figure 3 shows the tally processing associated with a DVE. The picture information enters by the digital connection 20 and is placed in the store 21. It is extracted through the digital filter 22 under control of the shape generation system 24 and leaves on the digital connection 23. The key signal is similarly processed by the key path 25, 26, 27. Note that the DVE 20 to 27 is assumed to exist, and is of known type that will not be further described. As will be understood by one skilled in the art the store 21 stores pixel information relating to an area of the picture image that is to be transformed and 26 is a similar store for key information. The tally path, which is part of this invention, comprises the store 28 in which tally bits extracted from the incoming key 25 are stored. This store is then read into the tally combiner 29. This receives data from the area of the store which corresponds to the same area of the source picture as the area which is currently being used by the interpolators or digital filters 22 and 27. As will also be understood by one skilled in the art the picture signal to be processed by the DVE may include image information from different sources in the area defined in the stores 21 and 26. Therefore the store 28 will hold correspondingly different coded tally words generated as described with reference to Fig. 2 and inserted in the video signal for example by a mixer as described below. The tally combiner forms the logical OR of the tally words within the area which it is processing. The bits which are set in this word therefore indicate which sources have made contributions to the final output. The tally thus produced is reinserted into the key signal in the inserter 30, which is functionally identical to 17, in order to produce the output key 31. Figure 4 shows how the tally is processed through a mixer. In this example the mixer combines two signals which each comprise key and video to produce a picture which also comprises key and video. The operation of the mixer is described, but, apart from the addition of the tally processing feature of the invention, is of known type. The way in which the mixer operates is as follows. The picture information which is to appear as the front picture on the final output enters at 33 and its associated key at 32. This key is multiplied 38 by a local key 36, which is under the control of the operator and can be used to wipe or fade the picture. The resulting product is multiplied 40 by the picture information, and passes to the adder 46. The back picture entering at 35 and its key 34 are similarly dealt with at 37,41,42,43 and a mixed picture produced at the output 47. The back picture key is however reduced by the key multiplier 41 such that the front picture, when not transparent, will cause the back picture to be suppressed. The background key which passes from the key combiner 41 to the inserter 45 represents the solidity of the picture as a whole. If the incoming keys 32,34 are expressed as numbers K1 and K2 which are between 0 and 1 then the outgoing key may be obtained by the expression 1-((1-K1)(1-K2)). The tally path, which is part of this invention, indicates which sources are still visible at the output of the mixer. The tally gates 39,42 take in the actual key value which is used to multiply the associated video, and if this key value is non-zero then they pass the tally bits presented at their other inputs to their outputs. If the key value is zero then they produce zero at the outputs. The resulting tally words are then combined with a logical or gate 44 and reinserted into the key at 45 to produce the combined key and tally signal at output 48. Figure 5 shows the extractor which obtains the final value of the tally from the tally words. The tally words enter at 49 and are combined by the logical AND gate 51 within a mask word 50. The mask word is arranged to be all ones during the time when valid picture information is present, but all zeros during the blanking intervals. The resulting word passes to the gate 52 which, on every pixel, combines the contents of the latch 53 with the input from the AND gate, and passes the result to the latch to be delayed by one pixel time. The gate is arranged in such a way that it produces the logical OR of its inputs, except for one clock period during vertical blanking, when it produces zero to reset the latch for the next field. Between the end of one field of the picture and the latch being reset, the data in the latch is copied to the buffer 54. This data, which remains stable for a field, is then used to access the look up table 55 which is set up by the control system. This table is used to translate between the data in the buffer, and the identities of the picture sources providing the key and video signals which are in use. The result of this translation is presented at the tally outputs 56. Any suitable means may then be adapted to provide a visual display or other indication of information provided at the output 56. Although in the above description the latch 53 is reset for each field, it will be appreciated that the latch could be reset for alternate fields so that the information in the buffer 54 relates to a frame rather than a field. Where two or more parts of the invention are combined within one unit, it may be possible to pass the tally words from one stage to the next without reinserting them into the key. In this case a separate bus would be provided for the tally words and the inserters omitted.

Claims: A method of processing digital video signals to provide a tally indication, wherein a plurality of input video signals derived from corresponding signal sources are mixed to provide an output video signal, the frames of which each contain a picture area or areas derived from one or more of said input video signals, characterised in that there is provided in association with each input signal a tally signal having a code identity individual to that input signal, and that upon mixing of the said input video signals the respective tally signals are combined to provide, in association with the mixed output video signal a combined signal that, for each said frame of the output video signal, contains the code identity or identities only of an input signal or those input signals from which is or are derived a picture area or picture areas present in the mixed output signal. A method as claimed in Claim 1, wherein the combining of said tally signals is controlled by key signals that determine the mixing of said picture signals in such a manner that the identity code of a given picture signal is present in the combined signal only at the instant that said picture signal is contributing to the picture of the mixed output signal. A method as claimed in Claim 1 or 2 wherein said tally signal is provided in such a format that a common signal carries the identities of a plurality of picture signals. A method as claimed in Claim 3, wherein said tally signals are decoded frame by frame, or field by field, at a final picture stage to identify all picture signals contributing to each frame of the output picture. A method as claimed in any one of Claims 1 to 4, wherein each input picture signal is associated with a signal encoded in the format of a colour picture signal the luminance component of said signal format providing a key signal relating to the picture signal and the chrominance component of said signal format providing the tally signal. An apparatus for providing a tally indication adapted to process digital video signals and comprising means to perform each of the steps of the method of any one of Claims 1-5, including means (12) for selectively combining picture signals from a number of sources and means (16) for providing, in association with the combined output picture signal an encoded tally signal identifying each source contributing to said output picture signal. An apparatus as claimed in Claim 6, wherein said means for selectively combining picture signals comprises first selector switching means (12) having a plurality of picture signal inputs in a single picture signal output and second selector switching means (14) having a plurality of key signal inputs and a single key signal output; said means (16) for providing said tally signal comprises a code signal generator controllable to generate any one of a number of predetermined code signals; and said apparatus further comprises control means (15) for controlling each of said first and second switching means (12, 14) to couple a selected input to the said output thereof and for controlling said code signal generator (16) to generate a corresponding one of said predetermined code signals. An apparatus according to Claim 7, further comprising combining means (17) coupled to the output of said second selector switching means (14) and to an output of said code signal generator (16) and arranged to combine signals received from said outputs. An apparatus according to Claim 8, wherein said combining means (17) is arranged to provide at an output (19) thereof a signal encoded in the format of a colour picture signal, with the signal received from said second selector switching means (14) provided in the luminance component of said format and the signal received from said code signal generator (16) provided in the chrominance component of said format. An apparatus for providing a tally indication, adapted to process a digital video signal including a digital picture signal together with an encoded tally signal provided by the apparatus of Claim 6, comprising means (20,25; 32,33; 34,35) for receiving said digital video signal and means (28,29,30; 39,42,44,45; 49-55) for processing said tally signal to provide an identification of each of the signal sources contributing to said picture signal.

Inventors: BARTON NICHOLAS, JONES ANTHONY RICHARD, LITTLEJOHN HUGH KENDAL, BARTON, NICHOLAS, JONES, ANTHONY RICHARD, LITTLEJOHN, HUGH KENDAL
Applicants: QUESTECH LTD, QUESTECH LIMITED
Application year: 1995
Main classification: H04N5
IPC codes: H04N5