# A Novel Consistent Quality Driven for JEM Based Distributed Video Coding
## 4 Performance Evaluation
### Consistent Video Quality Evaluation  
Several experiments have been performed with different values of QPs and QMs to show the effectiveness of our proposed consistent quality driven (CQD) method.  
Figure 8 shows the results of the decoded key frame at the 14 th position in the _Foreman_ sequence that was obtained by DISCOVER DVC and the proposed JEM-DVC in terms of subjective quality evaluations.  
Figure 8: Evaluation of visual quality consistency for the 14\({}^{th}\) decoded key frame of _Foreman_ sequence obtained by (**a**) Original, (**b**) DISCOVER DVC, (**c**) H.265-DVC, and (**d**) proposed JEM-DVC. The bottom row shows the distortion images between the decoded key frames and the original frame, obtained by (**e**) DISCOVER DVC, (**f**) H.265-DVC, and (**g**) proposed JEM-DVC.  
Figure 7: Key frame coding evaluation with different codecs: H.265-DVC, DISCOVER DVC, and the proposed JEM-DVC performed on different test sequences: (**a**) _Foreman_, (**b**) _Soccer_, (**c**) _Coalsguard_, and (**d**) _Hall Monitor_.  
The error or distortion images in Figure 8e-g show the differences between the original key frame and the decoded frames. As shown in Figure 8, both the DISCOVER DVC, H.265, and JEM-DVC codecs can provide a good image quality with a small distortion for the decoded key frame as compared to the original frame. However, for the decoded WZ frame, the performance of DISCOVER DVC codec is critically degraded due to annoying artefacts that were seen around the face of the _Foreman_, as shown in Figure 9b. Correspondingly, the WZ coding scheme of the DISCOVER DVC generally introduces much higher distortion areas in the decoded WZ frames as compared to the key frame coding scheme. This leads to the fluctuation in the video quality playing over the decoded key and WZ frames.  
In contrast to the DISCOVER DVC, for the proposed JEM-DVC, as can be seen in Figure 9d, the artifacts seen around the face of the _Foreman_ have been effectively reduced, and then the distortion errors yielded in the decoded WZ frame are very small and it is quite similar to that yielded in the decoded key frame. This allows for a smooth and consistent video quality playing for both key and WZ frames for the proposed JEM-DVC codec.  
Figure 10 shows more details on the fluctuation in the PSNR performance between the key and WZ frames. In Figure 10, the PSNR fluctuation is evaluated by measuring the different PSNR, \(\Delta PSNR=\left|PSNR_{K}-PSNR_{WZ}\right|\), where \(PSNR_{K}\) and \(PSNR_{WZ}\) are the average PSNR obtained for the decoded key and WZ frames, respectively, at the different values of QPs and QMs setup for the DISCOVER DVC and JEM-DVC codecs. In Figure 10, \(\Delta PSNR\) is measured based on four pairs  
Figure 9: Evaluation of visual quality consistency for the 14\({}^{th}\) decoded WZ frame of _Foreman_ sequence obtained by **(a)** Original, **(b)** DISCOVER DVC, **(c)** H.265-DVC, and **(d)** proposed JEM-DVC. The bottom row shows the distortion images between the decoded WZ frames and the original frame, obtained by **(e)** DISCOVER DVC, **(f)** H.265-DVC, and **(g)** proposed JEM-DVC.  
of different QPs and QMs, {((\(Q\)P\({}_{i}\), \(QM\)\({}_{i}\)), \(i\) = 1, 2, 3, 4], which are configured for the key and WZ coding schemes of the DISCOVER DVC and JEM-DVC codecs. As expected, for all of the test video sequences, the proposed JEM-DVC can solve the problem of quality fluctuation more effectively than the DISCOVER DVC. For example, in the case of the _Soccer_ sequence (Figure 10b), the fluctuation in the PSNR performance is reduced up to 2.1 dB for the proposed JEM-DVC as compared to the prior DISCOVER DVC. This feature is very important for the proposed JEM-DVC codec, since it is confirmed that the JEM-DVC codec can provide an effective solution to improve the user's QoEs.