Handbook of Multimedia for Digital Entertainment and Arts- P16 pdf

448 W. H ¨urst capabilities of handheld devices is a difficult task that is yet unsolved. In the remainder of the article, we summarize our ongoing work in developing better in- terfaces that offer a richer browsing experience and therefore better usability of mobile video. A Short Review of Video Browsing Techniques for Larger Displays When browsing video, for example, to get an overview of the content of a file or to localize a specific position in order to answer some information need, there are normally two major problems. First, video is a continuous medium that changes over time. With a static medium such as text, people always see some context at a time and can decide themselves at which speed they look at it. In contrast to this, for video only a single frame of a sequence of time-ordered frames is shown for a time slot that depends on the playback speed (e.g. 1=25 sec for a typical video play- back rate). Second, there is often not much meta-information available to support users in their search and browsing tasks. Again, think about browsing the pages of a book. Besides the actual content, there is meta-information encoded, for exam- ple, in the header and footer. Spatial information such as the separation in different paragraphs illustrates related parts with regards to content. Headlines give a short summary of the following content. Different font styles, such as bold face or italic, are used to highlight important information, and so on. In addition, higher level meta-information exists such as an abstract printed on the cover of the book, the content list at its beginning, etc. All of this meta-information supports users in vari- ous browsing task. For video however, comparable information is usually missing. Not surprisingly, most existing research in digital video browsing tries to make up for this lack of meta-information by automatically extracting comparable infor- mation from videos and representing it in an appropriate way that supports users in their browsing tasks (cf. Figure 1). For example, automatic segmentation techniques are often used to identify content-related parts of a video [13, 17]. This structure in- formation can be displayed and used for navigation (e.g. jumping from scene to scene using dedicated buttons) in order to make up of the missing structure infor- mation encoded in paragraphs and spaces between them in printed text. Single key frames can be extracted from a scene and represented as a storyboard, that is, a visual arrangement of thumbnails containing the key frames where the spatial order represents the temporal alignment in the video [4, 16]. This static representation can be used to get a rough idea of the video’s content, similarly to the content list in a book. One variation, so called Video Mangas, represent different scenes in a comic book style where thumbnail sizes depend on the relevance of the related scene, thus resembling the hierarchical structure of a content list [2, 18]. Another variation of storyboards, so called video skims or moving storyboards pay tribute to the dy- namic nature of video. Here, the static thumbnail representation is replaced with a short video clip that offers a glimpse into the related scene [3]. On a higher level, 20 Video Browsing on Handheld Devices 449 KEYFRAMES Single frames from a scene that represent its content STORYBOARD Spatial arrangement of thumbnails representing temporally ordered scenes VIDEO MANGA Comic book like representation of thumbnails indicating scenes with different relevance TRAILER Automatically generated video summary VIDEO BROWSING comparable concepts AUTOMATICALLY GENERATED META-INFORMATION … SEGMENTATION Automatically generated content-related scenes classified based on low level features (e.g. histogram changes due to camera cuts) PARAGRAPHS AND SPACES Indicate structure and units that are related in terms of content CONTENT LIST Gives high level info about content and structure of the book HEADLINES AND PAGE HEADERS Give high level information about the following content SPECIAL FONT STYLES Highlight words of particular interest ABSTRACT ON BOOK COVER Gives high level content description TEXT BROWSING Fig. 1 Comparing content-based video browsing approaches with text skimming automatically generated trailers offer a high level overview of a video’s content and can thus be compared to the abstract often found on the back side of a book’s cover [11]. Because all of these approaches are based on the actual structure or content of a file, we will subsequently refer to them as content-based approaches. Figure 1 sum- marizes how they relate to text browsing thus illustrating the initial claim that most of the work on video browsing aims at making up for the missing meta-information commonly available for text. The usefulness of such content-based approaches for video browsing has been confirmed by various evaluations and user studies. However, when browsing text, people do not only look at meta-data, but also skim the actual content at different speeds and levels of detail. For example, when grabbing a new book, they often skim it in flip-book style in order to get a rough overview. They browse a single page by quickly moving their eyes over it and catch a glimpse of a few single words allowing them to get a rough idea of the content. If they run over something that might be of particular interest, they quickly move their eyes back, read a few sentences, and so on. Hence, they skim text by moving their eyes over the content at different speeds and in random directions. Their visual perception allows them to make sense of the snatches of information they are picking up by filtering out irrelevant information and identifying parts of major interest. Unfortunately, such intuitive and flexible ways for data browsing are not possible for a dynamic medium such as video. Due to its continuous nature, people can not 450 W. H ¨urst VIDEO BROWSING . For video, only one information unit (frame) is visible per time unit. Its context (i.e. information encoded in consecutive frames making up a scene) arises when users modify playback speed (top) or directly manipulate the currently visible part of the video by directly accessing the related position along the timeline using a slider 2x 2x Modification of playback speed (e.g. fast forward) Slider for scrolling along the timeline FLIP-BOOK STYLE SKIMMING Getting a quick overview of the content by flipping through the pages TEXT BROWSING . When looking at printed text, people always see some context (spatially arranged words and meta-information) and decide by themselves at which speed they process the visual information CROSS-READING Moving your eyes at various speeds and in random direction over the static arrangement of words Fig. 2 Comparing timeline-based video browsing approaches with text skimming move their eyes spatially over a video. However, comparable to how readers are able to make sense of the snatches of information they grasp when moving their eyes quickly over a printed text, the visual perception of the human brain is able to classify certain parts of the content of a video even if played back at higher speeds or in reverse direction. We call video browsing approaches that try to take advantage of this characteristic subsequently timeline-based approaches. In related techniques, users control what part of the video they see at a particular time by manipulating the current position on the timeline. This is comparable to implicitly specifying which part of a text is currently seen by moving ones eyes over the printed content. Figure 2 illustrates how such temporal movements along the timeline when skim- ming a video relate to spatial movements of your eyes over printed text. The most obvious approach to achieve something like this is to enable users to manipulate playback speed. This technique is well known from analog VCRs where fast for- ward and backward buttons are provided to skim forward or backward. Since digital video is not limited by the physical characteristics of an actual tape, but only by the time it takes to decode the encoded signal, we are usually able to provide users with a much larger variety of different browsing speeds. Alternatively to manipulation of playback speed, people can often also navigate a video by dragging the thumb of a slider representing the video’s timeline. If visual feedback from the file is pro- vided in real-time, such an approach can be used to quickly skim larger parts of a file, abruptly stop and change scrolling speed and direction, and so on, thus offering more flexibility than modification of replay speed. On the other hand, increasing or decreasing playback speed seems to be a better and more intuitive choice when users want to continuously browse larger parts of a document at a constant speed or if the information they are looking for is encoded into the temporal changes of an object in the video. Both approaches enable users to perceive visual information from a video in a comparably flexible way to moving their eyes over text when browsing the con- tent of a book. It should also be noted that in both cases, browsing of static media such as text as well as dynamic media such as video, the content-based browsing approaches summarized in Figure 1 also differ from the timeline-based ones illus- trated in Figure 2 in a way that for content-based approaches, users generally browse some meta-data that was preprocessed by the system (e.g. headlines or extracted 20 Video Browsing on Handheld Devices 451 key frames), whereas for timeline-based approaches, they usually manipulate them- selves what part of the content they see at a particular point in time (either by moving their eyes over text at random speed or by using interface elements to manipulate the timeline of a video). Hence, none of the two concepts is superior to the other but they both complement each other and it depends on the actual browsing task as well as personal preference which approach is preferred in a particular situation. Mobile Video Usage and Need for Browsing Even though screen sizes are obviously a limiting factor for mobile video, improve- ments in image quality and resolution have recently led to a viewing experience that in many situations seems reasonable and acceptable for users. In addition, tech- niques for automatic panning and scanning [12] and adequate zooming [10]offer great potential for video viewing on handhelds although they have not made it to the market yet. Recent reports claim that mobile video usage, although still being small, is facing considerable rates of growth with “continued year-over-year growth of mobile video consumption” 1 . Observing that mobile video finally seems to take of, it is interesting to notice that so far, most mobile video players only offer very limited browsing function- ality, if supported at all. Given that we can assume that established future usage patterns for mobile video will differ from watching traditional TV (a claim shared by Belt et al. [1]), one might wonder if intensive mobile video browsing might not be needed or required by the users. Indeed, a real-life study on the usage of mo- bile TV presented by Belt at al. [1] indicated little interest in interactive services. However, the authors themselves claim that this might also be true do to a lack of familiarity with such advanced functions. In addition, the study focused on live TV where people obviously have different expectations for its consumption on mobiles. In contrast to this, the study on the usage of mobile video on handheld devices presented by O’Hara et al. [14] did report several mobile usage scenarios and sit- uations that already included massive video browsing or would most likely profit from improved navigation functionality. For example, in one case, a group of four kids gathered around on PSP (Sony’s PlayStation R Portable) in order to watch and talk about the scenes of their favorite movie that each of them liked the most. Such an activity does not only require massive interaction to find the related scene, but also continuously going backwards in order to replay and watch particular parts again to discuss them or because they have not been well perceived by some of the 1 The quote was taken from an online article from November 4, 2008, that was posted at http:// www.cmswire.com/cms/mobile/mobile-video-growing-but-still-niche-003453.php (accessed Feb 1, 2009) and discussed a related report by comScore. On January 8, 2009, MediaWeek reported comparable arguments from a report issued by the Nielsen Company, cf. http://www.mediaweek. com/mw/content display/news/media-agencies-research/e3i746 3e6c2968d742bad51c7faf7439 adc (accessed Feb 1, 2009). 452 W. H ¨urst participants due to the small screen size. Ojala et al. [15] present a study in which several users experimented with multimedia content delivered to their device in a stadium during hockey games. According to their user study, the “most desired con- tent was video footage from the ongoing match”. Reasonable applications of such data streams would be to get a different view of the game (e.g., a close up of the player closest to the puck that complements the overview sight of the hockey field they have from their seat) but also the opportunity to re-watch interesting scenes (e.g. replays of goals or critical referee decisions) – a scenario that would require significant interaction and video browsing activity. At this rather early stage of video usage on handhelds, we can only speculate what kind of browsing activities users would be willing and interested to really do on their mobiles once given the opportunity. However, the examples given above demonstrate that there are indeed lots of scenarios where users in a mobile context would be able to take advantage of advanced browsing functionality, or which would only be feasible if their system offers such technologies in an intuitive and useful way. In the following section, we present an example that is related to the study in a hockey stadium done by Ojala et al. [15] but extends the described scenario to a fictional case illustrating the possibilities advanced browsing functionalities could offer in order to increase the mobile video user experience. Timeline-Based Mobile Video Browsing and Related Problems In order to motivate the following interface designs and illustrate the most crit- ical problems for timeline-based mobile video browsing, let’s look at a simple example. Assume you are watching a live game in a soccer stadium. The game is also transmitted via mobile TV onto your mobile phone. In addition, live streams from different cameras placed in the stadium are provided. Having a large stor- age space (common newer multimedia smart phones already offer storage of up to 16GB, for example), you can store all these live streams locally and then have instant access to all videos on your local device. The study related to hockey games pre- sented by Ojala et al. [15] (cf. previous section) confirmed that such a service might be useful and would most likely be appreciated and used intensively by many sports fans. But what kind of browsing functionality would be necessary? What could and would many people like to do (i.e. search or browse for)? We can think of many in- teresting and useful scenarios. For example, it would be good to have some system generated labels indicating important scenes, goals, etc. that users might want to browse during halftime. During the game, people might want to quickly go back in a video stream in order to review a particular situation, such as a clever tactical move leading to a goal or an offside situation, a foul, a critical decision from the referee, etc. In the latter case, it can be useful to be able to navigate through the video at a very fine level of detail – even frame by frame, for example to identify the one single frame that best illustrates if a ball was indeed outside or not. Such a scenario would require easy and intuitive but yet powerful and ambitious browsing functionality. 20 Video Browsing on Handheld Devices 453 For example, people should be able to quickly switch between browsing on a larger scale (e.g. to locate a scene before the ball went outside of the playfield) and very sensitive navigation along the timeline (e.g. to locate a single frame that illustrates best which player was the last to touch it). It is also important to keep in mind that the related interactions are done by a user who is standing in a soccer stadium (and probably quite excited about the game or a questionable decision by the referee) and thus neither willing nor able to fully concentrate on a rather complex and sensitive interaction task. Given the small form factor and the limited interaction possibilities of handheld devices this clearly makes high demands on the interface design and the integration of the offered browsing functionality. Obviously, the content-based approaches known from traditional video brows- ing could be quite useful for some higher level semantic browsing, for example when users want to view all goals or fouls during halftime. For a more advanced interaction, for example to check if a ball was outside of the field or not, timeline- based approaches seem to be a good choice. For example, by moving a slider thumb quickly backwards along the timeline, a user can identify a critical scene (e.g. an offside) that is then further explored in more detail (e.g. by moving the slider thumb back and forth in a small range in order to identify a frame confirming that it was indeed an offside). However, one significant problem with this approach is that sliders do not scale to large document files. Due to the limited space that is available on the screen, not every position from a long video can be mapped onto a position on the slider. Thus, even the smallest possible movement of a slider’s thumb (i.e. one pixel on the screen) will result in a larger jump in the file, making it impossible to do a detailed navigation and access individual frames. In addition, grabbing and manipulating the tiny icon of a slider’s thumb on a mobile is often considered hard and unpleasant. Interfaces that allow users to browse a video by manipulating its playback speed often provide a slider-like interaction element as well in order to let users select from a continuous range of speed values. Although the abovementioned scaling problem of sliders might appear here as well, it is usually less critical because normally, not that many values, that is, levels of playback speed need to be mapped to the slider’s length. However, the second problem, that is, targeting and operating a very tiny icon during interaction remains (and becomes especially critical in situations such as standing in a crowded soccer stadium). In the following, we will present different interface designs for handheld de- vices that deal with these problems by providing an interaction experience that is explicitly optimized for touch screen based input on mobiles. The first four ap- proaches realize timeline-based approaches – both navigation along the timeline at different levels of granularity and skimming the file by using different playback rates (cf. Fig. 2) – whereas the fifth approach presents a content-based approach that also takes into account another important characteristic we often observe in mobile scenarios: that often, people only have one hand available for operating the device. Research on interfaces for mobile video browsing is just at its beginning and an area of active investigation. The question of how both interaction concepts can seamlessly be integrated into one single interface is yet unanswered and thus part of our ongoing and future research. 454 W. H ¨urst Implementation All interfaces presented in the next two sections are optimized for pen-based inter- action with a touch sensitive display. Touch screen based interaction has become an important trend in mobile computing due to the tremendous success of the iPhone. So far, we restricted ourselves to pen-based operation in our research, although some of the designs presented below might be useful for finger-based interaction as well. All proposed solutions have been implemented on a Dell AXIM TM X51v PDA which was one of the high end devices at the time we started the related projects. Meanwhile, there are various other mobile devices (PDAs as well as cell phones) offering similar performance. Our Dell PDA features an Intel XScal, PXA 270, 624 MHz processor, 64 MB SDRAM, 256 MB FlashROM, and an Intel 2700g co- processor for hardware-side video encoding. The latter one is particularly important for advanced video processing as it is required by our browsing applications. The de- vice has a 3.7-inch screen with a resolution of 640480 pixels and a touch sensitive surface for pen-based operation. Our interfaces have been implemented in CCCon the Windows Mobile 5 platform on top of TCPMP (The Core Pocket Media Player) which is a high-performance open source video player. The implementation was based on the Win32 API using the Graphics Device Interface for rendering. For all approaches we present below, audio feedback is paused when users start browsing the visual information of a video stream. We believe that there are lots of situations where approaches to browse the audio stream are equally or sometimes maybe even more important than navigation in the visual part of a video. However, at the time we started these projects, technical limitations of the available devices prevented us from addressing related issues. With newer, next generation models, this issue certainly becomes interesting and therefore should be addressed as part of future work (cf. the outlook at the end of this article). All our implementations have been evaluated in different user studies. In the following, we will only summarize the most important and interesting observations. For a detailed description of the related experiments as well as further implementation details and design decisions we refer to the articles that are cited in the respective sections. Flicking vs. Elastic Interfaces As already mentioned in the introduction, the iPhone uses a technique called flick- ing to enable users to skim large lists of text, for example all entries of your music collection. For flicking, users touch the screen and move their finger in the direction they want to navigate as if they want to push the list upwards or downwards. Upon releasing the finger from the screen, the list keeps scrolling with a speed that slowly decreases till it comes to a complete stop. The underlying metaphor can be explained with two rolls each of which holding one end of the list (cf. Figure 3). Pushing the rolls faster increases scrolling speed in the respective direction. Releasing the finger 20 Video Browsing on Handheld Devices 455 Left: Flicking your finger over the touch screen starts scrolling of the content in the same direction. After a while, scrolling slows down and comes to a complete stop simulating the frictional loss of two rolls that wind the document. Right: Moving you finger over the screen without flicking it results in a similar movement of the document’s content. However, instead of scrolling automatically, the content is not “pushed” but directly follows the movements of your finger. FLICKING AND RELATED METAPHOR Fig. 3 Scrolling text lists on the iPhone by flicking By flicking their fingers over the touch screen, users can “push” the video along the timeline. Fig. 4 Applying flicking to video browsing causes scrolling to slow down due to frictional loss. If the user does not push the con- tent but the finger rests on the screen while moving it, the list can be moved directly thus allowing some fine adjustment. By modifying how often and how fast the fin- ger is flicking over the touch screen or by changing between flicking and continuous moving users can achieve different scrolling speeds thus giving them a certain vari- ety for fast and slow navigation in a list. Transferring this concept to video browsing is straightforward if we assume the metaphor illustrated in Figure 4. Although the basic idea is identical, it should be noted that it is by no means clear that we can achieve the same level of usability when transferring such an interaction approach to another medium, that is, from text to video. With text, we always see a certain context during browsing, allowing us, for example, to identify paragraph borders and new sections easily even at higher scrolling speeds. With video on the other hand, scene changes are pretty much unpredictable in such a browsing approach. This might turn out to be critical for certain browsing tasks. Based on an initial evaluation that to some degree confirmed these concerns, we introduced an indica- tion of scrolling speed that is visualized at the top of the screen during browsing. In a subsequent user study it turned out that such information can be quite useful in order to provide the users a certain feeling for the scrolling speed which is otherwise lost because of the missing contextual information. Figure 5 shows a snapshot of the actual implementation on our PDA. 456 W. H ¨urst Fig. 5 Implementation of flicking for video browsing on a PDA. The bar at the top of the display illustrates the current scrolling speed during forward and backward scrolling Our second interface design, which also enables users to navigate and thus browse through a video at different scrolling speeds, is based on the concept of elastic interfaces. For elastic interfaces, a slider’s thumb is not dragged directly but instead pulled along the timeline using a virtual rubber band that is stretched be- tween the slider thumb and the mouse pointer (or pen, in our case). The slider’s thumb follows the pointer’s movements at a speed that is proportional to the length of the virtual rubber band. A long rubber band has a high tension, thus resulting in a faster scrolling speed. Shortening the band’s length decreases the tension and thus scrolling slows down. Using a clever mapping from band length to scrolling speed, such interfaces allow users to scroll the content of an associated file at different levels of granularity. The concept is illustrated in Figure 6 (left and center). Simi- larly to flicking, transferring this approach from navigation in static data to scrolling along the timeline of a video is straightforward. However, being forced to hit the timeline in order to drag the slider’s thumb can be critical on the small screen of a handheld device. In addition, the full screen mode used per default on such devices prevents us from modifying the rubber band’s length at the beginning and the end of a file when scrolling backward and forward, respectively. Hence, we introduced the concept of elastic panning [5] which is a generalization of an elastic slider that works without explicit interface elements. Here, scrolling functionality is evoked by simply clicking anywhere on the screen, that is, in our case, the video. This ini- tial clicking position is associated with the current position in the file. Scrolling along the timeline is done by moving the pointer left or right for backward and for- ward navigation, respectively. Vertical movements of the pointer are ignored. The (virtual) slider thumb and the rubber band are visualized by small icons in order provide maximum feedback without interfering with the actual content. Figure 6 (right) illustrates the elastic panning approach. Photos from the actual interface on the PDA can be found in Figure 7. For implementation details of this approach we refer to [5, 9]. With both implementations we did an initial heuristic evaluation in order to identify design flaws and optimize some parameters such as appropriate levels for frictional loss and a reasonable mapping of rubber band length to scrolling speed. With the resulting interfaces, we did a comparative evaluation with 24 users. After making themselves familiar with the interface, each participant had to solve three 20 Video Browsing on Handheld Devices 457 Virtual slider thumb Pen position Large rubber band: fast scrolling Short rubber band: slow scrolling Scrolling speed Length of rubber band ELASTIC SLIDER INTERFACE ELASTIC PANNING Mapping rubber band length to scrolling speed Fig. 6 Elastic interface concepts: slider (left) and panning (right) Fig. 7 Implementation of elastic panning for video browsing on a PDA browsing tasks that required navigation in the file at different levels of granularity: First, on a rather high level (getting an overview by identifying the first four news messages in a new show recording), second, a more specific navigation (finding the approximate beginning of one particular news message), and finally, a very fine granular navigation (finding one of the very few frames showing the map with the temperature overview in the weather forecast). Flicking and elastic panning are comparable interaction approaches insofar as both can be explained with a physical metaphor – the list or tape on two rolls in one case vs. the rubber band metaphor in the other case. Both allow users to skim a file at different granularity levels by modifying the scrolling or playback speed – in the first case by flicking your finger over the screen with different speeds, in the second case by modifying the length of the virtual rubber band. In both cases it is hard, however, to keep scrolling the file at a constant playback speed similar to the fast forward mode of a traditional VCR due to the frictional loss and the effect of a slowing down slider thumb in result of a shorter rubber band. Despite these similar- ities, both concepts also have important differences. Dragging the slider thumb by pulling the rubber band usually gives people more control over the scrolling speed than flicking because the can, for example, immediately slow down once they see something interesting. In contrast to this, flicking always requires a user to stop first and then push the file again with a lower momentum. However, being able to do a fine adjustment by resting the finger on the screen is much more flexible, for ex- ample, to access single frames than using the slow motion like behavior that results from a very short rubber band. The most interesting and surprising result in the [...]... School of Software Shanghai Jiao Tong University, Shanghai, China e-mail: yangxubo@cs.sjtu.edu.cn B Furht (ed.), Handbook of Multimedia for Digital Entertainment and Arts, DOI 10.1007/978-0-387-89024-1 21, c Springer Science+Business Media, LLC 2009 471 472 O Bimber and X Yang Section “Application Examples” outlines different professional applications of projector-camera systems in commercial and research... Netherlands, April 2000, pp 185–192 3 M G Christel, A G Hauptmann, A S Warmack, S A Crosby, “Adjustable Filmstrips and Skims as Abstractions for a Digital Video Library,” Proceedings of the IEEE Forum on Research and Technology Advances in Digital Libraries, March 1999, pp 98 4 M G Christel, A S Warmack, “The Effect of Text in Storyboards for Video Navigation,” Proceedings of the Acoustics, Speech, and. .. Another issue that is typical for a mobile scenario and we have not addressed so far is that often people have just one hand free for operation of the device A typical example includes holding on to the handrail while standing in a crowded bus Our premise for the design discussed in this section was therefore to create an interface that can easily be operated with a single hand In contrast to the previous... who did not feel comfortable operating the device with one hand at all and some others expressed that they see a need for one-handed operation, think that it is useful, but only would take advantage of it if they have to Otherwise, they would always use both hands Therefore, the final design, although being optimized for one-handed operation, should also support interaction with both hands Figure 17 illustrates... number for corresponding color modula1 tions between pŒr;g;b and cŒr;g;b Once V3x3 has been measured, its inverse V3x3 can be computed to compensate for the color and intensity modulation on the surface Note, that in this case individual forward and inverse color mixing matrices 1 V3x3 and V3x3 exist for each pixel Different extensions to this simple linear color transformation, and a variety of acquisition... issues and approaches for interaction with projectordominant systems Interaction with Spatial Projector Spatial projectors are installed at fixed locations, and are either static, steerable or automated Static spatial projectors are the most common installations for virtual environment and for commercial usage, and recently are increasingly used for home entertainment systems A large number of interaction... Devices 465 some examples of the logged interactions Similar visualizations for the remaining participants as well as more detailed information about the experiments can be found in [8] The evaluation revealed some interesting and important observations for the final interface design First and most important, it proved that this way of holding and operating the device is feasible and that most users find... Effective Video Retrieval: Effective Cataloguing and Browsing,” Proceedings of the 6th ACM international conference on Multimedia, Bristol, United Kingdom, September 1998, pp 99–107 17 M A Smith, “Video Skimming and Characterization through the Combination of Image and Language Understanding Techniques,” Proceedings of the 1997 Conference on Computer Vision and Pattern Recognition (CVPR ’97), June 1997,... due to the small screen size, the common trade off for storyboards between overview and level of detail becomes even more critical Representing too many scenes results in a thumbnail size that is too small for recognizing any useful information Representing too few scenes can guarantee a reasonable thumbnail size but at the cost of a loss of overview of the whole file’s content Hence, we decided that... include museums installations, multimedia presentations at historic sites, on-stage projection in theaters, architectural visualization, visual effects for film and broadcasting, and interactive attraction installations for exhibitions and other public environments Finally, section “The Future of Projector-Camera Systems” gives a brief outlook of the technological future of projector-camera systems that . experience and therefore better usability of mobile video. A Short Review of Video Browsing Techniques for Larger Displays When browsing video, for example, to get an overview of the content of a file. seems reasonable and acceptable for users. In addition, tech- niques for automatic panning and scanning [12] and adequate zooming [10]offer great potential for video viewing on handhelds although. task. Given the small form factor and the limited interaction possibilities of handheld devices this clearly makes high demands on the interface design and the integration of the offered browsing