3-Dimensional Digital Terrestrial Television
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DISTANCE LEARNING, MULTIMEDIA and VIDEO TECHNOLOGIES 3-Dimensional Digital Terrestrial Television RAFAEL G. AYESTARÁN1, JESÚS A. LÓPEZ1, VANESA LOBATO2, VÍCTOR M. PELÁEZ2, SONIA GARCÍA2 1Department of Electrical Engineering 2Department of R&D Universidad de Oviedo Fundación CTIC Campus Universitario Parque Científico y Tecnológico 33203 Gijón (Asturias) 33203 Gijón (Asturias) SPAIN SPAIN http://www.tsc.uniovi.es Abstract - A new Digital Terrestrial Television service based on transmission and visualization of 3D images is presented. This service has been designed to be suitable for domestic users without relevant increase of the final cost for the spectator, being the production of the programs what is modified to generate adequate 3D TV signals. The systems that make possible the implementation of the service have been prototyped and tested including the recording cameras and the visualization subsystem for the domestic environment. Some future development lines have also been defined, taking into account different parameters such as quality of service and final cost for the spectator. Key-Words – Digital Terrestrial Television, 3D image, Digital Video Broadcasting, services. 1 Introduction In the recent years, Digital Video Broadcasting 2 3D-Visualization (DVB), or Digital Television [1,2], is becoming the All of the many different 3D visualization systems standard for European broadcasting services that have been proposed in the literature [5,6] are (equivalently, ATSC, Advanced Television System based on the same principles. A 3-dimensional Committee, is the standard in USA and ISDB, perception of a scene is based on the observation of Integrated Services Digital Broadcasting, in Japan). two slightly different images taken by each eye. The Digital Satellite Television (DVB-S) and Digital human brain processes both images creating the Cable Television (DVB-C) are widely extended effect of depth that corresponds to the third between domestic users, and Digital Terrestrial dimension. Any 3D visualization system should Television (DVB-T or DTT) will soon replace analog present to each eye the corresponding image, and TV in most first-world countries. This scenario leads both images (left and right) must be obtained to the development of new services designed making somehow. The main difference between the existing use of the powerful characteristics of DVB: enhanced systems is typically the way in which both images are teletext services, multi-language broadcast, subtitling, presented: side-by-side layouts, alternate images or etc. In this paper we present a fully developed different light polarization, among others. service consisting on the broadcasting of three Most of the present techniques are not suitable for dimensional (3D) contents over a standard DVB DVB-T applications: side-by-side images require an platform. In particular, DVB-T features have been expert spectator; the use of different polarization for considered because of its increasing popularity in the two images cannot even be implemented in TV Spain and the proximity of the so-called “analog applications, because only one image should arrive to shut-down” planned for 2010. the visualization subsystem. Among the existing 3D Minimum monetary value of the domestic techniques, two have been chosen for evaluation visualization system is one of the major requirements purposes: anaglyphs and shutter glasses visualization. for the system designed in the present work. Most of the cost of the whole system is held in the production 2.1 Anaglyph images step where a full compliance with DVB-T standards Anaglyph images are used to provide a stereoscopic [3,4] must be achieved. 3D effect when viewed with two-color glasses (each lens with a chromatically opposite color, usually red ISSN: 1790-5109 146 ISBN: 978-960-474-005-5 DISTANCE LEARNING, MULTIMEDIA and VIDEO TECHNOLOGIES and cyan). Images are made up of two superimposed production studio, the transmission of a proper DVB- color layers with an offset between them to produce a T signal, and a domestic visualization scenario. depth effect. The picture contains two different The following sections describe in detail each filtered colored images, one for each eye. When subsystem and how it has been defined and viewed through the color glasses they reveal to each implemented. eye the correspondent image. The brain fuses both images into a three dimensional scene or 3.1 Camera positioning composition. The most important feature of a 3D recording system The use of a single transmitted image makes this is that it must record two images simultaneously. possibility suitable for DVB applications. The Some models of dual cameras have been developed colored glasses filter the image corresponding to each and are available for commercial use. A simpler eye. In fact, anaglyphs have been used previously in solution based on the use of two small adjacent analog TV 3D experiences. However, anaglyphs have cameras imitating the human visual caption system two major drawbacks. On the one hand, the treatment has been designed as a prototype. These two images of the color information in the receiver is critical so must be captured taking into account the properties of that ghosting effects could arise if the reproduced human vision, so an exhaustive trigonometric study colors do not match the glasses lenses colors. of the recording system is required to determine the Furthermore, the color information of the resulting correct position of the two cameras in order to create 3D image is distorted by the colored lenses a realistic stereoscopic effect. decreasing the final quality of service (QoS). On the other hand, anaglyph-based systems present an extremely low price for the final user which represents their most important advantage. 2.2 Shutter glasses Another 3D technique that is becoming popular in computer applications is the use of shutter glasses for stereoscopic visualization. In this technique, the images corresponding to each eye are combined using different time slots (usually alternative frames or lines) and the LCD lenses of the glasses become dark and transparent alternatively and in synchronization with the frame rate (or the display refresh rate). In this manner, each eye only receives its corresponding image. This technique is also implemented using different time slots for alternative fields, instead of frames, for the two images. In both implementations, Fig. 1. Camera layout for 3D recording. flickering is not noticeable for sufficiently high refresh rates. In the general case depicted in Fig. 1, two cameras The main advantage of this technique is that it is (left and right) record two images. The distance not affected by ghosting and it does not distort the between cameras is 2a, the principal object (PO) is color information. However, at conventional TV placed at a distance D from the plane of the cameras, refresh rates, the effective frame rate is reduced by a and its position is considered to be the origin. A factor of 2 which is enough to show flickering. secondary object (SO) is placed at a position defined Additionally, the price of the system for the domestic as (d,h). At this point, the goal is to determine the user is greater than anaglyph-based solutions, virtual distance A that must be considered to properly although cheap viewing systems can be found with an represent the real positions of the two objects. This equivalent cost to digital television decoders. parameter will be used to relate all the distances involved in the recording process and hence to select a proper position for the cameras. It is worth 3 Definition and implementation mentioning that parallel camera geometry may be A complete prototype of the 3D-DTT service has selected as a particular case of the general geometry. been designed and implemented including the The following relations determine the position of recording and processing of 3D images in the any object in a 3D scene so that each camera records ISSN: 1790-5109 147 ISBN: 978-960-474-005-5 DISTANCE LEARNING, MULTIMEDIA and VIDEO TECHNOLOGIES the same image that the corresponding eye would distances, similar to the distance between human perceive. For example, considering the right camera eyes. Professional or domestic cameras cannot be in Fig. 1, the following relations can be easily stated: placed so closely because of their dimensions, so a solution based on two webcams has been considered. 22 ADa=+tan(α ) (1) Resolution: Most of the available webcams have −−11⎛⎞ad ⎛− a ⎞ lower resolutions than DVB-T standards. Although α =+tan⎜⎟ tan ⎜ ⎟ (2) ⎝⎠DD ⎝+ h ⎠ post-processing could be performed, some high resolution cameras can be obtained at a reasonable Substituting (2) in (1): price. ah+ Dd Price: The academic purpose of the prototypes ADa=+22 (3) imposes low cost solutions even in the production DD()(+− h ad − a) studio. where the distance A is expressed in terms of known All these conditions have been taken into account parameters. The maximum value of the angle α to choose two high-resolution webcams Logitech depends on the characteristics of the camera and it Quickcam® Pro 9000, with resolution up to defines the maximum value for the virtual distance, 1600×1200 pixels (fixed to 720×576 for DTT Amax. The horizontal distance P between SO position applications), 30 fps, 24 bits/pixel, small dimensions and O (center of the scene) may be derived as and a price around 100 €. Of course, the resulting follows: recording system does not comply with professional specifications, but its performance is adequate for a AahD+ d1 system with academic purposes. PP== P max ADDhadamax ()()tan(+− − α ) max max 3.3 Image processing tool (4) The recording system provides two images that must be processed and combined into a single 3D image to where P represents the maximum horizontal max be transmitted. A software tool has been developed to distance between SO and O, and hence 2P is the max deal with such processing.