Abstract:
A digital video effects apparatus is arranged to generate a digital video effect by interpolating the values of parameters governing the effect, according to a given function, between time points corresponding to selected frames of a video signal and at which the parameters are fixed at selected values. The apparatus is organised in such a manner that the values of parameters are stored in exclusive timelines enabling the time points at which the parameter values are fixed to be adjusted without reference to other parameters governing the same video effect.

Description:
BACKGROUND OF THE INVENTION 
     This invention concerns the processing of digital video images and relates more especially to an improved method and means for achieving digital video effects. 
     It is well known to effect the transformation of a digital video image in such a manner that image information from one video source can be combined with that from another in order to achieve a variety of special effects. For example a frame containing a first image can be caused to move around within the frame of a second image by defining a desired trajectory within the second image frame. By defining parameters such as position, size, rotation and border size of the moving image further effects can be achieved. As will be understood by one skilled in the art of video editing such effects require the selection and manipulation of many different image parameters as made available for control in any given digital video effects apparatus. Effects such as turning pages, trails, textures, 3-D solid shapes, chroma keys, wraps, defocus, and shatters can all be achieved, and in a typical apparatus as many as four hundred different image parameters may be available for control by the editor. To edit such parameters for each frame of a moving image would be extremely labour intensive, and therefore in known digital effects apparatus controls are provided to enable the editor to set the values of selected parameters at critical points in the running time of a scene involving a given effect. Between the critical points at which the parameters are fixed, the values of the parameters are interpolated by the digital video effects apparatus in order to produce the desired course of the relevant effect. Such interpolation need not necessarily by linear but may proceed according to a function that has itself been defined by selection of an appropriate parameter. 
     This process is known as keyframe editing and virtually all currently used digital video effects apparatus are based on this system. The system does however have disadvantages in that unless the editing of a desired effect is very carefully planned in advance difficulty may arise when a sequence of events defined by consecutive keyframes is to be modified. This is because when a keyframe has been defined during the editing process the values of the parameters defined thereby have been fixed in the manner of a snapshot and thus the keyframe defines a limit of particular stage of interpolation for all parameters set thereby. If it should be desired to change the value of one parameter of a keyframe in order to vary a selected effect, for example, it my not therefore be possible to avoid undesirable changes in the course of interpolation of this parameter because the values of this parameter have been fixed by adjacent keyframes that may have been inserted only with the intention of governing the interpolation of other parameters. For this reason the editing of an existing stored effect may require laborious revision of many adjacent keyframes in order to achieve a desired charge. 
     SUMMARY OF THE INVENTION 
     There is therefore a requirement for a digital video effects apparatus that allows editing of effects to be achieved in a simpler, more versatile and intuitive manner than has hitherto been possible and it is an object of the invention to provide an answer to this problem. 
     In accordance with one aspect of the invention there is provided a method for processing a digital video image to provide a desired video effect, which comprises selecting values of parameters that are to govern the course of said effect during the time period of the corresponding scene to be displayed, storing the said values of said parameters with reference to time, at defined points in said time period spaced from one another in such a manner that the desired course of each said parameter can be interpolated from the stored values for the reproduction of video image frames occurring between the defined point of said time period, and causing said stored values to be retrieved and interpolated by a digital video effects apparatus during reproduction of a digital video signal in order to display the desired effect, characterised in that the values of each of at least some of said parameters are stored independently of other parameters in a timeline exclusive to that parameter, whereby the position of the defined point at which said value is stored in the timeline, and/or the value of the parameter stored at said point can be adjusted independently of the other parameters. 
     The invention further provides a digital video effects apparatus for use in said method. Such an apparatus may provide conventional video effects but is organised in such a manner as to enable independent selection and storage of values of parameters governing the effects to be achieved in order to obtain the advantages of the method defined above. The apparatus is further organised to enable retrieval and interpolation of the stored values in such a manner that the signals ultimately derived for reproduction of the effect are comparable with those provided in the conventional apparatus operating on the keyframe basis and therefore the hardware required for reproduction of the effect will not be described further. 
     It will be appreciated that given defined requirements for the provision of manual controls for selection and storage of data, for a corresponding display for organising the data to be stored and for the manner in which data is to be stored and retrieved, it will be within the routine skills of one versed in the art to provide corresponding software to enable the required functions to be achieved. Thus the invention lies not in any resultant software programme that may be so derived and that will not therefore be further described in detail, but in the functional interrelationship of features provided by the machine embodying such software. 
     A preferred embodiment of the invention will therefore be described in these terms below. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a diagram illustrating the concept of a digital video effect produced using a known keyframe-based apparatus and an attendant disadvantage thereof; 
     FIG. 2 is a diagram illustrating the concept embodied in a method and apparatus in accordance with the present invention; 
     FIG. 3 is a diagram illustrating the production of a digital view effect by means of the invention; 
     FIG. 4 is a diagram illustrating a graphic display provided by an apparatus in accordance with the invention and enabling the selecting and entry of data; 
     FIG. 5 is a corresponding view of an apparatus embodying the graphic display and showing an appropriate manual control panel for use therewith; 
     FIGS. 6A and 6B are diagrams illustrating examples of the entry of data utilising the apparatus of FIGS. 4 and 5; 
     FIG. 7 is an illustration of a graphic display showing the trajectory path of an effect in accordance with FIGS. 6A and 6B; 
     FIG. 8 is a view similar to FIG. 6B showing an adjustment of the parameters governing the trajectory shown in FIG. 7, and 
     FIG. 9 is a graphic display illustrating the corresponding modifications of the trajectory. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to FIG. 1, there is shown in FIG. 1A a diagrammatic depiction of a video screen represent by the rectangle  1 , within which is to be depicted the moving image of a picture derived from another source and enclosed within a rectangle  2  to be moved within the image are of the rectangle  1 . Assuming that the rectangle  2  is to be given a trajectory simulating a bounce, as indicated by the lines  3  and  4 , in the known keyframe editing process there will be inserted at the relevant point in time a keyframe defining parameters including the X and Y positions of the rectangle  2  as shown in the top left hand corner of the frame  1 , a keyframe defining the X and Y positions of the frame  2  at the lower edge of the frame  1 , as indicated at  2 ′, and a further keyframe including the X and Y parameters of the frame  2  when at the right hand edge of the frame  1 , as indicated by  2 ″. The parameters for intermediate positions of the frame  2  during movement between the three positions defined by the respective keyframes will be interpolated from the values defined by the keyframes according to appropriate functions that may also be stored as parameters of the relevant keyframe. Such a process is well known to one skilled in the art. 
     Assume now that it is desired that during movement of the frame  2  from the position  2 ′ to the position to  2 ″,the frame  2  is to be provided with a border. To achieve this effect a further keyframe is inserted at the point where the border is to be formed, as indicted by the broken lines  2 ′″, in order to introduce into the keyframe the parameter appropriate to the formation of a border. Since, however, each keyframe fixes all of the relevant parameters of the effect, the provision of the fourth keyframe will have the effect not only of introducing a boundary at point  2 ′″, but also of fixing the other parameters, including the X and Y positions of the border  2  at this point. Assume now that it is desired to vary the trajectory of the bounce shown in FIG. 1A by altering the X parameter of the position  2 ′ of the rectangle  2  to move this to the right. As shown in FIG. 1B, because of the presence of the additional keyframe at point  2 ′″, the resultant effect will not be that the bounce will proceed smoothly from the new position  2 ′ to the position  2 ″, because the X and Y parameters of the frame  2  have been fixed at point  2 ′″, and therefore the interpolation of the trajectory indicated by line  4  must proceed through this point as illustrated in FIG.  1 B. This characteristic is inherent in keyframe-based digital video effects apparatus and represents a significant disadvantage. 
     Referring now to FIG. 2, there is shown the concept of the storage of effects parameters in accordance with the invention. In FIG. 2 the boxes  5 ,  6  and  7  represent what will hereinafter be referred to as ‘timelines’, and a separate timeline is provided for each relevant parameter of the effect. Thus, the timeline indicated by the box  5  represents the border parameter introduced at position  2 ′″ of FIG. 1, the timeline represented by box  6  represents the Y parameter defining the position of the rectangle  2  and the box  7  represents the timeline defining the X parameter covering the position of the rectangle  2  in FIG.  1 . 
     In each timeline the horizontal axis represents the time period of the effect to be achieved and the vertical axis represents the value of the parameter stored therein. It will be appreciated that the parameter values are stored only at points of transition of the graphic lines, the lines themselves representing the fact that the values are interpolated between the points of transition. thus, for the timeline  5 , the value of the border parameter is stored only a position  5 ′, for the timeline  6  the value of the Y parameter is stored only at the points  6 ′,  6 ″ and  6 ′″ and for the timeline  7  the values of the X parameter are stored only at the beginning and end of the timeline at the points  7 ′ and  7 ″. Therefore, because of the manner in which the parameter values are stored in the independent timelines, a transition of a parameter can occur in its own timeline without fixing the parameters of related timeline. 
     The effect of this is illustrated in FIGS. 3A and 3B, wherein FIG. 3A corresponds to the situation in FIG.  1 B and illustrates that because the introduction of the border at position  2 ′″ is governed only by the value in timeline  5  of FIG. 2, smooth interpolation of the X and Y positions of the frame  2  can be effected between the positions  2 ′ and  2 ″. Likewise, if the value of the Y parameter is changed to move the position of the rectangle  2  away from the lower edge of the image frame  1 , as illustrated in FIG. 3B, new trajectories  3  and  4  can be interpolated from the stored values without requiring further adjustment of the associated timelines. 
     FIGS. 4 and 5 illustrate respectively a graphic display and associated manual controls that enable storage of data in accordance with the novel concept referred to above. 
     In FIG. 4, the graphic image shown will be represented on the screen of the video monitor  1  of the apparatus of FIG. 5, when the apparatus is set in an appropriate control mode. The horizontal bands  10  indicated in the upper region of the screen of FIG. 4 represent timelines equivalent to those of FIG. 2, whereas the vertical shaded are  11  common to the timelines represents a play head that can be moved horizontally along the timelines for positioning events within the timelines, making selections for editing and indicating progress of sequence runs. The head  11  can be positioned horizontally by entering numerical data, or can be positioned manually using a T-bar control  12  as illustrated in FIG.  5 . 
     The horizontal panels  13  in the right hand area of the screen represent vector menus that provide access to corresponding ranges of effects parameters to be allocated to the timelines  10  for editing. These menus may be selected by menu selection keys  14  indicated on the right hand side of the screen  1  in FIG. 5, and the groups of menus indicated at  13  can be toggled to select further groups of menus by means of a select key  15  also indicated in FIG.  5 . 
     the rectangular areas  16  at the lower edge of the display of FIG. 4 are allocated to parameters of the respective timelines  10  and are also assigned to correspondingly positioned manually adjustable controls  17  and control keys  18  enabling the setting of the values of the respective parameters at the point designated by the play head  11 . The areas  16  also indicate the parameter values at this position. 
     Thus, the entry of parameter values in given timelines to achieve any desired effect can be achieved in a simple and versatile manner by toggling the menus  13  to find the required effect, selecting the appropriate menu and associated timelines via keys  14  and entry of the relevant values using T-bar  12  and controls  17  and  18 , or by entry of numeric valves using a key pad  19  as shown in FIG.  5 . The keys  20  in FIG. 5 are provided to enable a variety of timeline editing functions such as cutting, copying and pasting, and further keys are provided for multi-channel control in known manner and for positioning, locating and selecting events on the timelines. A take key  21  shown in FIG. 5 is further provided for running the sequence of selected effect. 
     It will be appreciated that in addition to the graphic display illustrated in FIG. 4, the screen  1  of the apparatus of FIG. 5 can show a representation of the effect itself, and live manipulation of picture size, position and rotation of an image area to be represented by the effect can be achieved using a joystick  22 . 
     An example of an editing effect that can be achieved by the apparatus of FIGS. 4 and 5 will now be described in further detail with reference to FIGS. 6-9, which illustrate the editing of a bounce effect. 
     In FIG. 6A the lower shaded area represents two timelines of a graphic display as shown in FIG. 4, in the lower of which is entered the values of the Y parameter of an image area which is to be shown as bouncing. In the upper part of FIG. 6A are shown representations of the display monitor indicating corresponding Y positions of the image area at the respective positions of events determined by the entry of data in the Y timeline. Thus, starting from the left hand end of the Y timeline, an initial Y value is set at the point  30  using the joy stick  22 , a control knob  17 , or the numeric key pad and the respective data entry key  18 . The play head of the graphic display is now moved forward to position  31  using the T-bar  22  or numeric key pad  19 , and the next value for the parameter Y is entered. Further values of the Y parameter can be entered in a similar manner, or, the area between positions  30  and  31  can be selected as indicated at  32 , copied and pasted at a further position  33  of the timeline. This process can be repeated to define as many up/down moves as desired. 
     Referring to  6 B, values for the X parameter can similarly be entered in the upper one of the two timelines as indicated, the areas above the beginning and end of the upper timelines showing the corresponding X and Y positions of the image area to be moved, in as similar manner to FIG.  6 A. 
     FIG. 7 shows a graphic representation of the trajectory on a video screen of the effect defined by the timelines as shown in FIG.  6 B. It will be appreciated that the sinusoidal curve of FIG. 7 results form the fact that interpolation of the values of the Y parameter is not linear but proceeds according to a function defined by a further selected parameter. The straight lines between the values of the Y timeline merely indicate that interpolation will occur and do not represent the actual values of the Y parameter that will be interpolated. Of course, the Y parameter could be arranged to be interpolated linearly, in which case the trajectory of FIG. 7 would alter to a simple triangular form. 
     It will be appreciated from the above description that versatile editing of the parameters contained in individual timelines can be achieved. For example, as shown in FIG. 8, by stepping through the consecutive parameter values in the Y timeline, for example by using previous and next keys of the key board to step the play head through the timeline events, the values of the Y parameter can be adjusted. In this case a gradually decreasing bounce is defined as shown in FIG. 9, the trajectory being defined by the adjusted parameter values shown in the Y timeline of FIG.  8 . 
     Further adjustments of the timelines may be achieved by means of other editing functions that can be made available via the key board of the device of FIG.  5 . For example, the timelines can be compressed or extended in the horizontal direction to vary the timing of the events represent therein. By compressing the timelines of FIG. 8, the bounce depicted in FIG. 9 could be made to end within the image area of the video frame instead of extending over the right hand margin as illustrated in FIG.  9 . 
     It will thus be appreciated that the method and apparatus in accordance with the invention enables versatile editing of digital video effects in a novel and advantageous manner not hitherto available in known arrangements.