7.4  Relationship between the depth and texture bit rate

A recurring question in literature on multi-view depth and texture coding is how the bit rate is distributed over texture and depth [43]. A common approach is to employ fixed ad-hoc quantization settings that enable a sufficient rendering quality for most multi-view sequences. Practically, it means that the depth bit rate is restricted to an arbitrarily selected percentage/ratio of the total bit rate, e.g., 10 - 20% of the total bit rate. However, this approach of employing a-priori fixed ad-hoc quantizer settings is not appropriate because of the two factors that influence the bit-rate ratio between the depth and texture. The first factor is the individual complexity of the depth and texture images, and thus, the corresponding bit rate required for encoding. More specifically, there exists no fixed relationship that couples the complexity of the texture and the depth signal. Our aim is to show that fixed quantizer settings are not optimal for joint encoding of the multi-view depth and texture video and that a joint optimization of the independent quantizers is preferred. The second factor that influences the rendering quality, and thus, the depth and texture bit-rate ratio, is the number of reference views employed for rendering. For example, it can be readily understood that employing a large number of reference views yields a high rendering quality. Therefore, an optimization of the quantization parameters should be performed not only for a specific multi-view sequence, but also for the selected number of reference views. Therefore, Section 7.6 presents experimental results obtained from using two different multi-view sequences while also employing one and two reference views.