**6.2 3D quality systems**

3D stereoscopic dimension carries all the 2-D quality assessment, but in addition some other specific factors must be analyzed to assure the QoE of the final consumer. In this chapter some general aspects to understand 3D video are described in order to justify the alternatives used in quality assessment and their differences with 2-D video.

The term 3D denotes stereoscopy, i.e. two-view system used for visualization. Due to the difficulty of creating this type of contents by the use of dual cameras, still a high percentage of stereoscopic video is obtained by the conversion of video from 2D to 3D based on the extraction of depth information from monoscopic images.

The quality is improving with this method, but it is necessary to evaluate the results in depth calculation and the experience of the final user. This aim is of vital importance in 3D quality assessment, at least until the production of all the contests are in real 3D.

## **Formats and Encoding 3D**

Another feature to consider is the different ways of encoding the views, left and right. As both views are correlated, and present similar content with small differences between them, the techniques for compression take advantage of this feature to reduce the amount of data generated, because it is much higher the amount of data required for broadcasting, and new systems of encoding are necessary to develop its features. It is also important the synchronism, i. e. the methods used in compression are recommendable to assure that both views are seen at the same time with each eye. For this purpose, a series of systems appeared in two groups:

Video Quality Assessment 149

sensation of discomfort often associated with the viewing of stereoscopic images. Sources of visual discomfort may include excessive binocular disparities, conflicts between accommodation and vergence (the simultaneous movement of both eyes in opposite directions), appearance of

A large number of studies have been developed in order to predict the response of the user to this parameter, analyzing the maximum exposure time to avoid the fatigue and the main reasons of visual discomfort, in order to avoid it in the future and obtain better quality of

The parallax is the corresponding distance on the plane of the image to the inter-ocular distance when visualizing a determined object. The effect over the objects differs in the capture of the images modifying the distance between the pair of cameras used to take the

Hyper-stereoscopy is a very characteristic effect in 3D images in which the observer appreciates the volume of the objects much closer to them. This effect is a consequence of modifying the parallax on the image. When separating the pair of cameras a distance higher than the average of the distances between human eyes. So, it could be a reality that the hyper-stereoscopy increases the quality of experience in users who are viewing this kind of images, but it is necessary to define a limit in which this effect stops being satisfying to the

The quality of experience increases but it is necessary to develop new studies to determine the limits of parallax in order to develop recommendations for contents creators and

Crosstalk, also known as ghosting, is the artifact defined as the leakage of one eye's image

specific artifacts such as crosstalk or boundaries and imperfections in 3D rendering.

experience. M. Lambooij reviews the principle conclusions in this field.

**6.5 Parallax and depth adjustment** 

Fig. 15. Scheme of parallax distance

**6.6 Artifacts related to stereoscopic systems** 

into the image of the other eye, i.e. imperfect image separation.

users.

broadcasters.

**Crosstalk (Ghosting)** 

stereoscopic images.


Also, depending on the type of 3D display, the method of assessment is different, according to the settings of each technique used. The groups of technologies according to its displaying technique are:

	- Passive glasses (normally with circular or linear polarization). In FSC, both views are content in every frame. The glasses help the eyes to separate the views and redirect them to the corresponding eye.
	- Active glasses. The image is presented to each eye alternating from one view to other every frame. The system must assure the synchronism between display and glasses.
