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