BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     This invention relates to video display.  
         [0003]     2. Description of the Prior Art  
         [0004]     In a video display system, for example, a computer-based video display system, it is often difficult for a user to know what video material is available for viewing without wasting a lot of time manually searching through the material.  
         [0005]     It has been proposed to use so-called representative images (often called “thumbnails” or “keyframes”) to indicate the content of a piece of video material. A representative image is often taken from a fixed point within a piece of material, for example, the first frame. In a long piece of material, such a single image may not provide a good indication of the overall content of the material. In particular, the first image of a sequence may be invalid—for example, a blank image or a test pattern.  
         [0006]     To address this problem, it has been proposed that multiple representative images could be used. The paper “A hierarchical keyframe user interface for browsing video over the internet”, M. Guillemot et al, IDIAP-COM 03-02, August 2003 discloses an arrangement whereby the user may select one or two levels of increased detail, each providing a greater number of representative images.  
       SUMMARY OF THE INVENTION  
       [0007]     This invention provides a video display apparatus for displaying a catalogue of one or more candidate video items for replay, each video item being represented in the catalogue by a catalogue entry having at least one displayed representative image; the apparatus comprising:  
         [0008]     a user control device operable to resize a displayed catalogue entry by a select-and-drag operation; and  
         [0009]     means responsive to a resizing of a catalogue entry to select a number of distinct representative images, for display in respect of that video item, so that the number displayed increases with increasing size of the catalogue entry while the display size of each representative image stays substantially constant with respect to changes in the catalogue entry size.  
         [0010]     In embodiments of the present invention, with just one, quick, interaction a user can interrogate the content of a video item to a degree where they are satisfied that they have seen enough to make a decision to view the video item.  
         [0011]     As the user expands the catalogue entry, the system intelligently fills the space with more representative images for that video item. The more the user expands the catalogue entry the more information they see. This expandability allows the user to see as much as they need to make a decision as to whether the media is what they are looking for or not. When they have seen enough they simply end the select-and-drag operation (e.g. lift their finger off the mouse) and move on to the next operation.  
         [0012]     The invention allows the user to interrogate the catalogue quickly without having to open a further screen or panel within the interface (e.g. “More Info”, “Details”, “storyboard”, etc.).  
         [0013]     The Guillemot et al paper presents a catalogue list to the user. Next to each representative image is a “+” button. The user has to click the “+” button to see a storyboard of the item that the representative image represents. Next to each further image is a further “+” button which the user clicks to present a shot breakdown below the further image. It should be noted that:  
         [0000]     (a) this requires 3 interactions to interrogate a single item and it is a potentially slow process.  
         [0000]     (b) the “+” button is similar to a “more info” or “storyboard” button and does not appear to add any benefits over and above a conventional storyboard.  
         [0000]     (c) the number of representative images that the system displays to the user is fixed so the user does not have a choice as to when they have seen enough.  
         [0014]     The present invention addresses these drawbacks with an advantageously elegant, flexible and convenient user interface arrangement allowing the user to vary the amount of information he sees with a simple select-and-drag operation.  
         [0015]     Further respective aspects of the invention are defined in the appended claims. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0016]     The above and other 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:  
         [0017]      FIG. 1  schematically illustrates a video replay system;  
         [0018]      FIG. 2  schematically illustrates a display screen;  
         [0019]      FIGS. 3A  to  3 D schematically illustrate a resizable catalogue entry;  
         [0020]      FIG. 4  schematically illustrates a set of representative keyframes; and  
         [0021]      FIGS. 5A  to  5 E schematically illustrate another set of representative keyframes.  
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0022]      FIG. 1  is a schematic diagram of an video replay system based around a general-purpose computer  10  having a processor unit  20  including disk storage  30  for programs and data, a network interface card  40  connected to a network  50  such as an Ethernet network or the Internet, a display device such as a cathode ray tube device  60 , a keyboard  70  and a user input device such as a mouse  80 . The system operates under program control, the programs being stored on the disk storage  30  and provided, for example, by the network  50 , a removable disk (not shown) or a pre-installation on the disk storage  30 .  
         [0023]      FIG. 2  schematically illustrates a display screen, for example as displayed on the display  60 . For clarity, not all features of the display screen are necessarily shown, but the significant ones are; a player window  100 , video player controls  110  and a catalogue area  120  containing representative key frames (images)  130 .  
         [0024]     Each representative key frame  130  corresponds to a different respective piece of video material. The key frame may be, for example, the first image of the corresponding video item or could be derived as a “most representative” image by a statistical technique such as an analysis of hue histograms. Such techniques are known and will not be documented further in the present description.  
         [0025]     The user may select an item of the video material by placing the mouse pointer on the key frame  130  and making a single “click”. This would cause the first frame of the selected video item to be displayed in the replay window  100 , in a “paused” fashion. Replay can then be initiated by selecting a play control from the controls  110 .  
         [0026]     Alternatively, a “double click” on a key frame  130  causes playback of the corresponding video item to be started (from the beginning) in the view out window  100 .  
         [0027]     Each entry (key frame) in the catalogue  120  is resizable.  FIGS. 3   a  to  3   d  schematically illustrate a resizable catalogue entry and the purpose behind the resizing technique.  
         [0028]     Referring to  FIG. 3A , a key frame  130  is shown. To allow this key frame to be followed throughout  FIGS. 3A  to  3 D, the key frame is labelled as a key frame (A).  
         [0029]     Using a mouse pointer  160 , the user may “grab” (click-and-hold) the key frame  130  and resize it. This does not actually change the size or position of the initial key frame A, but opens up a window, area or box  150  (referred to as “box”, though without necessarily limiting it to a rectangular shape) which, as it expands, accommodates more key frames.  
         [0030]     So, in  FIG. 3B , a further key frame  132  (labelled as “B”) has been accommodated. In  FIG. 3C , the box  150  has been expanded to the extent that two further key frames  134  and  136  (“C” and “D”) are accommodated. In  FIG. 3   d , the box  150  has been changed in shape so that two further key frames  138  and  140  are accommodated. Note that these are labelled as “E” and “F”, although they could in fact be the key frames “C” and “D”. However, they need not be the same as “C” and “D”.  
         [0031]     In general, throughout this process, once a key frame has been displayed at a certain display position relative to the initial key frame  130 , it remains displayed there as long as the box  150  is large enough still to accommodate it.  
         [0032]     Preferably, key frames are added only as entire key frames. As is to say, as the box  150  is expanded, when it passes a threshold size which is large enough to accommodate 1 or more further key frames, those one or more further key frames are added at a single step. That is to say, partial key frames are not displayed. However, the opposite is of course possible, so that as the box expands by a small amount, a corresponding small amount of a newly revealed key frame or key frames is displayed.  
         [0033]     The origins of the key frames “B to F” will be described with reference to  FIGS. 4 and 5  below.  
         [0034]     Referring back to  FIG. 2 , it can be seen that for at least some of the key frames  130 , as a box  150  is expanded away from the key frame it may obscure other important parts of the display. However, in the present embodiment as soon as one of the key frames is selected to initiate replay, the box  150  disappears and so the viewer window may be seen once again.  
         [0035]     The key frames revealed as the box  150  is expanded come from different parts of the video item. Thus, as the box expands, and increasing impression of the overall content of the video item is given to the user. Also, given that each key frame has a corresponding temporal position within the video item, it is preferred that as a key frame is selected (by a single click or a double click operation as described above), video replay is set up or initiated with effect from the temporal position corresponding to that key frame. So, the key frames provide links into different temporal positions within the video material. Again, this can be very useful to the user trying to navigate rapidly through pieces of video material.  
         [0036]     In principle, any number of key frames may be displayed using this technique. Of course a limitation is the image size available on the display screens  60  when compared with the size of a key frame. Preferably the key frames remain the same size as the box  150  expands, as is to say, the number of key frames increases but the size of each key frame neither increases nor decreases.  
         [0037]      FIG. 4  schematically illustrates a set of representative key frames derived from a video material item. The video item is represented by a horizontal bar  200 , with time running in a horizontal direction. Vertical bars  210  schematically illustrate scene changes within the video material, as detected by a known scene change detection algorithm. The scene changes to 10 according divide the video item  200  into respective segments, and a key frame G . . . L is derived in respect of each individual scene. (This could be, for example, the centre frame of each scene or, for example, a “most representative” frame of each scene as described above).  
         [0038]     A ranking order is associated with the key frames G . . . L. This order provides that one of the key frames (for example the key frame from the first scene-G-) is selected to be the single key frame  130  displayed in the catalogue  120 . After that, an order is associated with the key frames so that as the box  150  is expanded, key frame are displayed in the successive order. The order can be, for example, such that the key frames are ranked in order of scene length, or scene position within the material etc). Of course, if there are insufficient scenes within the material to provide the number of key frame which can be displayed, then multiple key frame can be derived from each scene, for example by taking spaced apart frames within a scene.  
         [0039]     Another technique for deriving the key frames for display is shown in  FIGS. 5A  to  5 E. Here, a first key frame, M, is taken as the first frame of the video material. In  FIG. 5B , a second key frame, N is taken as the last frame of the material. When a third key frame, O is required, it is taken as the middle (or nearest to middle) key frame of the material.  
         [0040]     In  FIGS. 5D and 5E , it can be seen that various options now present themselves. When a fourth key frame is required, one option is to subdivide the gap between two existing key frames, to provide a new key frame P. This means that a next key frame position would be the position  220  in  FIG. 5D . This arrangement has the advantage that already-displayed key frames are not altered by the addition of a new key frame P. However, an alternative is shown in  FIG. 5E , where at each stage, as one or more new key frames are added, the key frame are shuffled so that they are equi-spaced in time within the video material. T his means that the previous key frame O from  FIG. 5C  stops being displayed and instead new key frames O′ and P′ are provided. This has the advantage that at any stage the key frames which are displayed on the screen are equi-spaced and therefore should give a particularly good representation of the content throughout the video material.  
         [0041]     The invention may be embodied in software, programmable hardware (e.g. FPGA, ASIC), hardware or a combination of these. In the case of a software component, the invention also includes a providing (e.g. storage, transmission) medium by which such software is provided.  
         [0042]     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.
A video display apparatus for displaying a catalogue of one or more candidate video items for replay, each video item being represented in the catalogue by a catalogue entry having at least one displayed representative image comprises a user control device operable to resize a displayed catalogue entry by a select-and-drag operation; and means responsive to a resizing of a catalogue entry to select a number of distinct representative images, for display in respect of that video item, so that the number displayed increases with increasing size of the catalogue entry while the display size of each representative image stays substantially constant with respect to changes in the catalogue entry size.