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ICT Project 3D VIVANT– Deliverable 2.3 Contract no.: 248420 User Acceptance Validation Plan These will set certain standards in terms of what the user expects with respect to e.g., colour, resolution, brightness, contrast, etc., which the project results will have to meet. Although this may sound like a challenge, comparison with other technologies may also show advantages, such as independence from the need to wear special glasses, etc. The following two sub-sections will outline features of 3D technologies suitable for comparison tests. Nevertheless, since the 3D holoscopic technology is in its infancy, the tests envisaged in the project should be considered more as useful guidelines for the future developments of this technology rather than competitive comparisons aimed to persuade about the need of giving up any other existing 3D visual technology. Consequently, the methods and approaches reported in the aforementioned publications will be practiced as required in order to obtain valid results, but it is assumed that they may have to be relaxed when deemed necessary. In this case the corresponding WP7 deliverables will mention the actual modifications with respect to the standardized rules. User Acceptance Tests on 3D holoscopic video content will primarily be conducted with questionnaires comprised of closed questions to explore limits of quality acceptance and open questions to allow for individual input. For a detailed description of the tests, see Section 4.1. 2.2.1 Stereoscopic 3D Most of the currently available 3D technologies are based on stereoscopic images. In this approach, one image is produced for each eye and delivered to the appropriate eye during playback. The separation of the images is usually done using special 3D glasses, for home users usually with activeshutter or polarised glasses. For the production of live-action stereoscopic content, stereo setups of two cameras in mirror or sideby-side rigs are used. This requires a high degree of accuracy when setting up the cameras since the cameras have to be accurately aligned and work exactly frame synchronously. In addition, to achieve good results, the properties of the lenses also have to match perfectly. One of the main disadvantages of the stereoscopic method is the need to wear some kind of special 3D glasses. Moreover, in stereoscopic viewing, the eyes’ convergence and accommodation do not work in unison in contrast to normal human viewing. This leads to eye fatigue and in some cases even to headaches. Another shortcoming of stereoscopic 3D is the dependency on the viewing angle. Since only two different perspectives are present, a sideways movement of the observer results in a sideways shear of the stereoscopic image. 2.2.2 Multiview Auto-stereoscopic 3D Auto-stereoscopic approaches are generally based on the same principles as the stereoscopic 3D. But in contrast to the classical stereoscopic 3D, for the multiview auto-stereoscopic case a larger number of perspectives (views) are used. To view the content, mostly LCD-based displays with lenticular lenses are used. They distribute the multiple views horizontally across the entire field of view of the display. Depending on the position, every viewer can see exactly one pair of these views, a stereoscopic image pair. The main advantage of auto-stereoscopic displays is that the viewer does not need glasses and that a larger area of parallax can be shown. With a larger number of different views, the effect of shear distortion can also be reduced. The main disadvantage, on the other hand, is that the more views a display offers the more the resolution is reduced in comparison with 2D of stereoscopic 3D systems. Unless intermediate view interpolation or extrapolation is used, in general, for the production of content for auto-stereoscopic displays the number of cameras required is the same as the number of views offered, normally at least five to nine. This significantly increases the effort and expenditure, 01.09.11 10
ICT Project 3D VIVANT– Deliverable 2.3 Contract no.: 248420 User Acceptance Validation Plan especially for live events, because, as is the case for stereoscopic 3D, here the cameras must also be exactly aligned and synchronised. Even though auto-stereoscopic displays do not offer a large parallax area, the viewer appears to be able to look around objects. However, the number of viewing positions and the resulting stereo pairs is limited. In this case, the shear distortion effect is reduced but still detected in each stereo pair. Nevertheless, if the viewer moves around in front of the display, jumps in the picture can be detected when the viewing angle changes. This phenomenon is called flipping. A further disadvantage of the auto-stereoscopic process is the missing vertical parallax. As the views can only be separated horizontally, no vertical parallaxes can be displayed. The result is that a viewer can appear to look left and right around an object but not over or under it. More recently, a combination of conventional 2D video capture with depth map generation has been used for the capture and processing of multiview auto-stereoscopic 3D content. However, the display of multiview auto-stereoscopic 3D content relies upon the brain to fuse the two disparate images to create the 3D sensation. A particularly contentious aspect for entertainment applications is the human factors issue. For example, in stereoscopy, the viewer needs to focus at the screen plane while simultaneously converging the eyes to different locations in space producing unnatural viewing (Yamazaki et al., Lambooij et al. 1989). This can cause eye-strain and headaches in some people. Consequently, content producers limit the depth of scene to be viewed to minimise this problem. With recent advances in digital technology, some human factors which result in eye fatigue, such as limits in head movement in the case of circulate/linear polarized glasses systems, etc., have been eliminated. However, some intrinsic eye fatigue factor, like a mismatch in convergence and focus, will always exist in stereoscopic 3D technology (Onural et al., Benton, Honda 2006). Furthermore, due to the lack of perspective continuity in 2D view systems, objects in the scene often lack solidity (cardboarding) and give rise to an ‘unreal’ experience. For the 3D video quality assessment of stereoscopic videos, most researchers employ subjective testing (De Silva et al., Hewage et al., Leon et al.2010) focusing mainly on depth perceived by the users on autostereoscopic displays and the sensitivity of the observers to the changes in depth in a 3D video scene (De Silva 2010). Most of the 3D video user perception studies relate to the design and evaluation of 3D stereoscopic and multiview video systems based on different coding parameters. In the majority of these studies, subjective testing using a qualitative methodology with no more than 15 users has been employed (Kalva et al. 2006; Saygili et al. 2009; Knorr et al. 2008; Olsson and Sjostrom 2010). In some of these research studies, different types of video systems were compared by the users in terms of various system parameters and user perception of stereoscopic versus multiview video (Knorr et al.2008; Olsson and Sjostrom 2010). Most of the results suggest that, for stereoscopic and multiview video, the bit rate and the content of the original 3D image form the factors that most significantly affect the perceived 3D image quality (Kalva et al. 2006; Knorr et al. 2008; Olsson and Sjostrom 2010; Reis et al. 2007). In terms of multiview 3D video, it is also noted that users prefer less apparent depth and motion parallax when being exposed to compressed 3D images on an autostereoscopic multiview display (Olsson and Sjostrom 2010). Furthermore, it was found that motion and complexity of the depth image have a strong influence on the acceptable depth quality in 3D videos (Leon et al. 2008). 2.2.3 Data Collection Methods The following data collection methodologies will be employed to gather information on the users’ perceived quality of the project’s video content: • Questionnaires – Comprising of both closed and open ended questions. • Interviews – Semi-structured (prepared and spontaneous questions) interviews comprising of a selected user sample and one/two interviewees. 01.09.11 11
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