**5. Conclusions**

Defining objective quality metrics for immersive media is a very challenging task.

It needs a good understanding of both acquisition and rendering devices and subjective perception.

It depends on several parameters, which are difficult to be identified. The knowledge acquired in these decades from the use of images and videos has led to the definition of objective metrics, methodologies, and sufficiently defined test materials.

In the case of new media, the direct transfer of this knowledge is not possible. It is necessary to understand the possibilities of the application of new media and their limitations. The definition of use cases and the identification of significant parameters is needed. In addition, there is a need for databases annotated with subjective data, such as Mean Opinion Score, eye-tracking information, content definition. Open research questions are related to the understanding of the impact of the content on the quality of experience, to the definition of specific assessment protocols, and the definition of effective quality metrics. It is worthful to underline that what is needed in the evaluation of the Quality of the Experience, rather than the 'simple' quality of the media. Therefore, the human factor must be included in all the phases of the design of the immersive system.
