Stereoscopic

Stereoscopic (also called stereoscopy or 3D imaging) display refers to a technique for creating the illusion of depth in an image by presenting two offset images separately to the left and right eye of the viewer. Both of these 2D offset images are then combined in the brain to give the perception of 3D depth. Stereoscopic 3D display includes head mount system, anaglyph system, polarized filter system, field sequential system and so on [29].

Namely, three strategies have been used to accomplish the following: 1) have the viewer wear eyeglasses to combine separate images from two offset sources, 2) have the viewer wear eyeglasses to filter offset images from a single source separated to each eye, and have the light source split the images directionally into the viewer's eyes (no glasses required).

In our work, we use the have viewer wear glassed to combine separate images from two offset sources.

Kim and Sohn found that in stereoscopic images is visual fatigue, but they used a depth-based view synthesis algorithm to handle the whole regions in rendering process.

And then they performed depth-based view synthesis to the contents which were predicted

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to cause visual fatigue [30]. A subjective evaluation showed that the proposed depth adjustment method generated comfortable stereoscopic images.

Ramos-Diaz et al. allow the minimization of artifacts like ghosting and overlapping areas, and they reduce dynamic range of depth map value [31]. Okuyama et al. mention that informed consent for patients becomes important in clinics where the doctor explains diseases and treatments [32]. But patients have difficulty understanding Medical Images, i.e. X-rays, CT or MRI because the patient is not an expert in reading these medical images.

They tried to reconstruct the stereoscopic image of CT and MRI and display these using a simple and low cost auto-stereoscopic viewer. Su et al. apply augmented reality overlay of reconstructed 3D-computed tomography images onto real-time stereo video footage which is able to use iterative closest point and image-based surface tracking technology that does not use external navigation tracking systems or preplaced surface markers [33]. Kersten et al. present empirical studies that consider the effects of stereopsis and simulate aerial perspective on depth perception in translucent volumes [34]. They consider a purely absorptive lighting model, in which light is not scattered or reflected, but is simply absorbed as it passes through the volume. A purely absorptive lighting model is used, for example, when rendering digitally reconstructed radiographs (DRRs), which are synthetic X–ray images reconstructed from CT volumes. Surgeons make use of DRRs in planning and performing operations, so an improvement of depth perception in DRRs may help diagnosis and surgical planning.

Bouguila and Yoshida have undertaken experiments to prove that the observer’s perceived depth is not the same with the theoretical depth completely [35, 36]. Bouguila proposed integrating haptic sensation with stereopsis cues to improve the task of localizing objects [35]. Yoshida presented the possible factors that affect perceived depth, such as measuring errors of the eye separation, the distance between the viewpoint and screen [36].

Then an effective method was performed by modification of both the viewing position and the screen. Lin et al. supposed there is deviation between perceived depth and theoretical depth of virtual object in stereoscopic virtual environment [37]. They analyzed its possible causes with optical geometry. In addition, a correcting method performed by setting synthetic viewpoint dynamically is proposed to show that this method can reduce the depth deviation to less than 10 millimeter, and meets the requirements for locating and direct

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manipulation in virtual environment. Yamagishi et al. discuss stereoscopic viewing yielded an exact 3-D observation of the abdominal vascular structure. Real time rendering of the stereoscopic images could be performed by VOXEL-MAN [14]. Using the data of clinical cases gave an impact on medical students.

Liao et al. proposed a high-resolution stereoscopic surgical display using the integral videography (IV) and multiple projectors [38]. IV projects a computer generated graphical object by multiple rays through “fly’s eye lens,” which can display geometrically accurate auto-stereoscopic images and reproduce motion parallax in 3-D space. The technique requires neither special glasses nor sensing device to track viewer’s eyes. Thus it is suitable for pre-operative diagnosis and intra-operative use and for reporting the use of multiple reduction projection display system and a parallel-calculation to achieve high-resolution IV image. They evaluate the feasibility of this display by developing a 3-D CT stereoscopic image and applying it to surgical planning and intra-operative guidance. The main contribution of it is application and modulation of medical stereoscopic technique originally developed in high-resolution multi-projector stereoscopic display system. Liao et al. also developed the auto-stereoscopic display and analysis system to aid the development of 3-D cardiac imaging for use during minimally invasive cardiac surgery [39].

Also they integrated the high-quality auto-stereoscopic display system into image guided cardiac surgery. The human heart was scanned in a sequence of volumetric images which is based on dynamic information of heart from CT scanning. It represented the motion of the human heart throughout the cardiac cycle. Time sequence 3-D image analysis can be particularly useful in cardiac applications. This approach will allow them to acquire the optimum method to produce 3-D cardiac image for planning and guidance of minimally invasive cardiac surgery.

2.5.1. Anaglyph

Beyond those methods we mentioned, the most accessible is the anaglyph stereo [40], which is based on the principle of spectral separation and uses the properties of filters.

It filters the rays of one color and delays the rays of other colors. Anaglyph images are much easier to view than either parallel, diverging or crossed-view pairs stereograms.

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Each pixel of the computer image is composed of three color components: red, green and blue. On the screen simultaneously displaying two images forms the stereo pair. At the same time in each pixel of the total image red component corresponds to the red in the left image, and the green components or blue components in the right. However, these side-by-side types offer bright and accurate color rendering, which anaglyphs can hardly achieve.

Figure 2-1 is Paper anaglyph filters producing an acceptable image at low cost and suitable for inclusion in magazines.

Figure 2-1 Paper anaglyph filter glasses. Retrieved from Wikipedia, the free encyclopedia, http://en.wikipedia.org/wiki/File:Anaglyph_glasses.png

2.5.2. Polarization Systems (Passive)

To present stereoscopic pictures, two images are projected superimposed onto the same screen through polarizing filters or presented on a display with polarized filters. For projection, a silver screen is used so that polarization is preserved. The viewer wears low-cost eyeglasses which also contain a pair of opposite polarizing filters. As each filter only passes light which is similarly polarized and blocks the opposite polarized light, each eye only sees one of the images, and the effect is achieved.

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Figure 2-2 RealD circular polarized glasses. Retrieved from Wikipedia, the free encyclopedia, http://en.wikipedia.org/wiki/File:REALD.JPG

2.5.3. Shutter Systems (Active)

With the shutter method using the concept of alternate-frame sequencing, a shutter blocks light from each appropriate eye when the converse eye's image is projected on the screen or displayed on the computer display,. This was the basis of the Teleview system which was used briefly in 1922. There have been many examples of shutter glasses over the past few decades, such as SegaScope 3-D glasses for the Sega Master System and the Atari/Tektronix Stereotek 3D system, but the NVIDIA 3D Vision gaming kit introduced this technology to mainstream consumers and PC gamers. Also see Time-division multiplexing. Fig. 2-3 is a pair of LCD shutter glasses used to view XpanD 3D films. The thick frames conceal the electronics and batteries.

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Figure 2-3 A pair of LCD shutter glasses. Retrieved from Wikipedia, the free encyclopedia, http://en.wikipedia.org/wiki/File:Xpand_LCD_shutter_glasses.jpg

2.5.4. Holographic

Similar to stereoscopic display, a holographic display is a kind of 3D display. The viewer can move around the image in any direction because it incorporates a true parallax element and the image maintains its integrity. Holographic displays are of great interest because users can view 3D images without wearing glasses. Creating a virtual image in space can be viewed from any direction as if it were a real physical object. However, unless the stored images can be updated, holographic technology will remain unsuitable for a wide variety of 3D display applications [41].