Frame Rate (FR)

The effect of this parameter on the quality is not as significant as in the BR or LR (see below) cases. This is clearly shown in Figs. 7.4, 7.8, 7.9 and 7.10. For (BR=0.8, LR=0 %, CLP=2, and RA=0.1), an improvement from 6.6 up to 7.6 is achieved when the FR varies from 6 to 30 fps. Similarly, there is an absolute change of 0.8 for BR=0.15, as depicted in Figure 7.4. We can also note that the enhancement of the quality for FR greater than 16 is negligible, as already observed in previous works [119]. As the BR decreases, the effect of FR becomes smaller, see Figure 7.14. The improvement of the quality when the LR changes from zero to 10 % (MOS value varies from 6.5 up to 7.5 for FR=30 fps) decreases until it becomes negligible as shown in Figure 7.8. From Figure 7.10, we can see that we can get constant relative improvements of the quality whatever the value of RA (from 6.0 to 7.0 for RA=0.05 and from 6.4 to 7.3 for RA=0.5 - this is for BR=0.6, CLP=2 and LR=0 %). These results may seem surprising, but they have been observed in different previous studies. For example, experimental results showed that for FR larger than 16 fps, the viewer is not so sensitive to changes in FR values [119]. The work done in [53] clearly shows that the enhancement of the quality for a wide range variation from 6 to 25 fps is really small. Both studies were based on subjective quality tests.

Figure 7.6: The impact of BR and CLP on video quality.

  

Figure 7.7: The impact of BR and RA on video quality.