9.4 3D Mobile

Due to keen competition in the smartphone market, companies try their best to equip their phones with different interesting functions to attract consumers. 3D technology is one of them. Thus, there are at least two 3D smartphones available commercially: LG Optimal and HTC EVO 3D. The main attraction points provided by these two phones are to capture and display 3D contents using a stereoscopic pair of cameras and an autostereoscopic display. Thus, a short description of HTC EVO 3D is given as a representative of current 3D mobile systems. Later, a discussion about the perception in mobile 3D display devices is also given.

9.4.1 HTC EVO 3D

In addition to the original features provided by HTC smartphones, HTC EVO 3D has been equipped with 3D stereoscopic features including 3D gaming, 3D photo and video capture, 3D photo and video viewing, and an easy 2D-to-3D switch. This smartphone can capture the world in 3D stereoscopic images and videos and the 3D stereoscopic images and videos can be viewed on the screen without the need for glasses. There are a few feature points for HTC EVO 3D:

• Screen: The screen is bright and clear. Although EVO 3D can capture and display 3D stereoscopic images or videos, none of the widgets runs in 3D. Currently, there is only one 3D app available in the store. Lack of 3D applications and content is still the main issue for 3D technologies. There is a 2D-3D switch which allows users to operate the phone in 2D mode.
• Camera: The stereoscopic pair of cameras is one of the specific feature points of HTC Evo 3D. When opening the capturing app, there is a button to switch between the 2D and 3D capturing modes. The phone should be held at the position of about the length of an arm to get a proper stereoscopic view of the world. When the phone is further away from the scene, the 3D effect is not obvious. When the phone is too close to the scene, the captured 3D content becomes ghosted and error-prone. At the right distance, the 3D effect is vivid and gives viewers a perfect 3D stereoscopic sense of the scene.
• Video: HTC Evo 3D becomes a powerful mobile 3D video camera that is able to shoot clean movies. The recommended 3D videos have a resolution up to 720p. The shooting videos are clean and the 3D effect can be more convincing if the foreground objects and background are on two obviously distinct depth planes. In the 3D video capturing mode, MPO or JPS file formats are available. A grid option helps the user line up distant and near objects in the frame.
• Media: Content is important for the popularity of a device. 3D content editing needs a proper medium to show the intermediate and final results. HTC Evo 3D provides a simple means for users to watch their own 3D content. It also provides functions to make their own 3D images and movies. Those 3D videos and photos must look convincing and interesting. YouTube provides a simple means to get 3D videos. Users can search for “YT3D” to find hundreds of 3D videos and EVO 3D allows users to watch them directly.
• More 2D applications and less 3D applications: Although HTC Evo 3D has the stereoscopic pairs of cameras and 3D autostereoscopic display, it does not provide any interesting 3D user interface out of its 3D abilities. For example, the phone cannot have the 3D profiles of the user's friends popping out on the screen when browsing through contacts. It does not provide 3D tele conference between two Evo 3D phones. The messaging system still uses traditional 2D methods without any 3D effects. Generally, 3D hardware advances much faster than 3D software. Therefore, it is easy to put the 3D hardware into a system but the corresponding applications and features are hard to come by to make the 3D system popular. Because HTC Evo 3D does not try to use as many 3D features as possible, it is hard to make 3D mobile phones popular.

Headaches and eye strain may be induced after watching 3D stereoscopic content for over 30 minutes.

9.4.2 Mobile 3D Perception

Because smartphones have become popular and mobile services are an important business, more advanced services are developed to fulfill the expectation of users. 3D services can use depth perception to enhance the naturalness of the displayed content and give viewers the feeling of being there [3–5]. Autostereoscopic displays provide the 3D effect without the need of glasses or other extra devices as discussed in Chapter 3 and also Section 9.1. Humans perceive the 3D world using a combination of different visual depth cues. Details about possible depth cues are discussed in Chapter 7. Depth cues are generally classified as binocular depth cues that need both eyes to perceive and monocular depth cues that can be perceived by a single eye. The perception of the binocular depth cues is independent of that of monocular depth cues [6]. Additionally, the depth range perceived by a viewer is highly accurate but quite narrow [7]. The process of perceiving depth is delicate and vulnerable to artifacts. The aim of mobile autostereoscopic 3D displays is to enhance the realism for viewers by giving extra depth perception. Because these autostereocopic technologies are still not mature, artifacts are induced in the delivery process. How the depth perception is affected by the delivery of binocular depth cues and monocular cues is important for the proper usage of mobile 3D autostereoscopic displays. Motion parallax and stereopsis are considered as the most important depth cues [8–10]. Binocular depth cues get better ratings on the accuracy and speed of depth perception than monocular cues do. Additional monocular depth cues (shadows, texture, focal depth) do not lead to better depth perception. This phenomenon might be an implication of the supremacy of stereopsis over monocular depth cues on portable displays. Furthermore, even though users do not have any reason to make an assumption of constant object size, the size is generally used as a depth cue for them. For example, when texture depth cues are not reliable, the size may be used as a strong auxiliary cue for depth judgment. This phenomenon also confirms the theory [8, 11–13] that the importance of depth cues can be seen as a weighted combination of the presented cues, based on their reliability in each situation. However, focal depth cues seem to get a low ranking in accuracy, efficiency, and acceptance. This finding may seem to be surprising and may be a topic for further exploitation. To summarize the above, binocular depth cues outperform the monocular ones in efficiency and accuracy on portable autostereoscopic displays. Additionally, an interesting topic for further exploitation would be how much monocular cues–such as strong perspective lines, textures and sizes–can facilitate the depth estimation task.

Another interesting issue is how compression artifacts affect depth perception. When few compression artifacts are induced in a 3D video, the depth perception contributes to the quality perception on mobile 3D autostereoscopic displays [14]. But when compression artifacts become noticeable, artifacts induced by compression seem to significantly affect depth perception on both the correctness of depth estimation and the depth estimation speed [8]. Especially, the depth estimation speed can be affected even by slight blockedness induced by compression. When the quality has few defects, the depth might be still perceived perfectly but when the defects increase, the accuracy of depth perception becomes affected further. The time needed to estimate the depth and the correctness of the depth estimation has a negative correlation. This indicates that if the depth estimation can be finished fast, the depth estimation results seem to be also most likely correct. The kind of effects on 3D videos can be easily understood: if lower quality affects the efficiency of depth perception, the binocular HVS might not have enough time to create a plausible 3D effect for objects. The binocular HVS is very vulnerable to losing the depth effect if artifacts are present.

3D stereoscopic technologies have been introduced into mobile devices and it is important to have proper content and applications to make 3D mobile devices popular. Therefore, researchers are trying to push 3D movies onto the 3D mobile devices. Motivation to use a mobile TV is to kill time while waiting, or to get hold of up-to-date news while on the move [15]. Therefore, users of mobile TV services prefer short clips such as news, music videos, YouTube videos and sports programs [16]. In contrast, motivation to use 3DTV is to be entertained and therefore realism and the feeling of being there [17, 18] seem to be the killer experiences. And the users normally expect to watch movies with special 3D effects [19] to experience the new feeling of presence and to explore the content sufficiently [20]. For the context of usage, 3DTV is used for entertainment in environments such as 3D cinemas and would like to use shared views, and the main situations for the usage of mobile TV are at work during breaks, while commuting, at home to create privacy, and in waiting or waste-time situations [15, 21, 22]. And additionally users would like to have private viewing conditions and sometimes use shared viewing like co-view during lunch or just to share funny stories or clips [15, 21]. These differences would also reflect the difference in requirement of merging 3DTV and mobile TV into mobile 3DTV.

Mobile TV fundamentally offers the entertainment for users to kill time or to get informed or to watch TV while being on the move. Mobile 3DTV adds a higher interest to mobile TV in the content through raised realism, atmosphere, and emotional identification using the stereoscopic 3D technologies. The 3D representation of the content also increases the realism and naturalness of the content and contributes to a raised feeling of being inside the content or being present at it, according to user experience research [19]. A few guidelines from consideration of users, systems, and contexts are given for designing mobile 3DTV systems and services [23]:

1. User
   • Mobile 3DTV must offer a program to satisfy users with different motivations in different contexts.
   • Mobile 3DTV needs to fulfill the needs for entertainment and information so that viewers can relax, spend time, and learn through mobile 3D services.
   • Mobile 3DTV should provide increased realism and naturalness of content and the feeling of being there when compared to 2D systems.
   • Mobile 3DTV needs to minimize simulator sickness and increase the excitement and fun of 3D for high viewing comfort.
2. System and Service
   • Mobile 3DTV should provide 3D video contents which can satisfy the need for information and entertainment to reflect the added values of 3D.
   • Mobile 3DTV should offer interactive content such as 3D games to fully exploit the potential of 3D stereoscopic technologies.
   • Mobile 3DTV must have a display device with a size of 4–5 inches or at least over 3 inches.
   • Mobile 3DTV should offer both monomodal (audio or visual only) and multimodal (audiovisual) presentation modes as well as fluent shifts between these modes and 2D/3D visual presentation.
   • Mobile 3DTV must offer an easy manipulation interface for service navigation and 3D content handling.
   • Mobile 3DTV should provide functions to save, send, receive, and capture 3D content.
   • Mobile 3DTV should provide the same requirements as for 2D mobile services, such as long battery life, high storage capacity, spontaneous access to all preferred or needed services or multiple network connection interfaces.
   • Mobile 3DTV should have simple and clear payment models to finance the service.
3. Context
   • Mobile 3DTV contents can be watched in public and private locations as well as outdoors and indoors. These locations probably include public transport, parks, cars, cafes, waiting rooms, as well as the home.
   • Mobile 3DTV contents are primarily designed for private viewing, but shared viewing may be needed.
   • Duration of viewing 3D content generally depends on the usage context. The duration can vary from a short period of time in waiting situations to a long period of time during journeys.

The contextual situations affect the usage of mobile 3DTV. Video services for mobile phones are basically used for entertainment for a short period of free time and thus short entertainment and information programs should be popular and attractive for mobile 3DTV services.