# A Framework for Symmetric-Quality S3D Video Streaming Services
## 2 Related Work
### Conditional Replenishment Algorithm  
In the hybrid 3 DTV system, the resolution of the decoded right-view video is generally lower than that of the decoded left-view video. Specifically, it is assumed that the resolution of the right-view video is less than or equal to 1/4 of the resolution of the left-view video. Therefore, to form a high-quality stereoscopic image in 3D video services, an upscaling process is necessary before combining the left and right videos. However, simply upscaling the resolution of the video can lead to quality degradation compared with the original video, which may result in asymmetric picture quality between the left and right views in the combined 3D video. In the past, there have been questions about whether the difference in image quality between the left and right views in S3D videos causes discomfort during viewing. However, it has generally been observed that the discomfort experienced by users is less severe than expected. This is due to the binocular suppression effect (BSE) [10]. The binocular suppression effect refers to the characteristic of the human visual system where, when there is a difference in image quality between the left and right fields of view, the subjective image quality is determined based on the higher-resolution image. This effect has been shown to reduce the perceived impact of quality degradation in one of the images in the combined 3D video, making the reduction in resolution less noticeable [19]. However, recent studies have shown that when the quality difference between the left and right images becomes too large, the binocular suppression effect does not function effectively. This result was confirmed using the DSIS (Dual Stimulus Impairment Scale) method, which is one of the subjective video quality assessment methods [20]. The DSIS method involves showing the evaluator the original video first, followed by a second video that contains some degradation. The evaluator is then asked to rate the second video based on the quality of the first one. This method is similar to the DCR (Degradation Category Rating) method described in ITU-T P.910, and it uses the same 5-point scale to measure the impairment between the two videos. The DCR method evaluates the quality  
Figure 4: Improved Cross-View SHVC. difference between the original and test videos by playing them sequentially and asking the evaluator to rate the difference across five categories. While DCR only shows the original and test videos once, DSIS repeats the sequence one or two times according to a specific time pattern. Through these experiments, it was found that when the _PSNR_ (Peak Signal-to-Noise Ratio) difference between the left- and right-view videos exceeds an average of 1.9 dB, viewers quickly notice a degradation in the quality of the S3D video [20]. This result supports the technical necessity of maintaining symmetry in the image quality of S3D videos. Therefore, to ensure symmetry between the left and right images, we identified the need for a technology that minimizes the _PSNR_ difference between the two videos. To address this, we developed the conditional replenishment algorithm [15]. This algorithm takes advantage of the fact that although there are differences between the left- and right-view images due to disparity, they still share a very high correlation. By comparing the images at a block level, the algorithm uses left-view image blocks to supplement and enhance the quality of the right-view image. Figure 5 is a schematic diagram of the conditional replenishment algorithm. Block searching is performed using the high-resolution left-view video to improve the decoded low-resolution right-view video. During this process, replacement blocks are found in the higher-resolution left-view video, and the corresponding position is indicated by calculating the Inter-View Vector (IVV). This calculation is performed on blocks of various sizes based on a quad-tree structure. The quad-tree structure efficiently partitions and searches the blocks to find the optimal replacement blocks.