# A Display-Adaptive Pipeline for Dynamic Range Expansion of Standard Dynamic Range Video Content
## 4 Results and Evaluation
### HDR-to-xHDR Conversion: Subjective Evaluation  
We conducted a subjective experiment to evaluate the effectiveness of our proposed HDR-to-xHDR pipeline. For this, we created a test dataset comprising 65 HDR videos. Each video has a resolution of 1920 \(\times\) 1080 pixels and a duration of approximately 10 s, featuring several frame rates ranging from 24 to 120 fps and peak luminance values used  
Figure 16: HDR-to-xHDR conversion: Frames obtained from our test HDR video sequences and the expansion maps computed (on the right). The HDR images were tone-mapped for presentation. in mastering, spanning 1000 to 1400 cd/m\({}^{2}\). Figure 17 provides previews of some of these short test video sequences utilized in our subjective evaluation. We extracted the frames from test video sequences and converted them into linear values within the Rec709 color space. This step ensured compatibility with the color space specifications of the SIM2 HDR display used in our experiments. Subsequently, we processed the HDR frames using our HDR-to-xHDR conversion pipeline. In the dynamic range expansion step, the \(m_{\text{o}}\) value was determined using Equation (4). The values of \(L_{\text{h}}\), \(C\), and \(P_{\text{ov}}\) (image statistics) were computed using a tone-mapped version of the input HDR frame. For this, we employed the tone-mapping technique outlined in [60], specifically the photographic tone reproduction method for digital images. The \(m_{\text{i}}\) value was set using Equation (7). We derived the max_hdr_lum value from the metadata in the HDR video sequence, noting that this value can vary across different HDR files. Regarding max_ldr_lum, typically, 100 cd/m\({}^{2}\) is the maximum luminance value used in  
Figure 17: Preview of some HDR video sequences employed in our HDR-to-xHDR conversion evaluation experiment, sourced from publicly available HDR video content. All video sequences were down-scaled to 1920 \(\times\) 1080 to fit the resolution of the HDR display used in our experiments. (The original producers of the video sequences retain all rights pertaining to the frames shown in this figure). LDR video sequences. However, our expansion operator was trained on a dataset graded in LDR using a Grade 1 display designed specifically for the broadcast and cinema industries. These types of displays usually operate within a luminance range of 300 to 500 cd/m\({}^{2}\), matching the specific requirements of the production environment and industry standards. Our experiments led us to the conclusion that setting the max_ldr_lum (maximum LDR luminance) values within this range in Equation (7) yielded the best results. Specifically, for our subjective experiment, we set the max_ldr_lum to 300 cd/m\({}^{2}\). Table 4 outlines the parameters we used for processing the video sequences in our subjective experiment. We replicated the setup and methodology employed in Section 4.3. The HDR and xHDR video sequences were cropped to 960 \(\times\) 1080 pixels, keeping the main objects in the center, and presented side by side on the SIM2 HDR47 ES6 MB display. To ensure unbiased assessment, the placement of the video sequences was randomized for each trial. Each video was alternately positioned on the left half or right half of the screen. This strategy was employed to eliminate any bias that might arise from consistently positioning either the HDR or xHDR version in the same location. Additionally, a 30-pixel wide gray line was introduced between the two videos to provide a clear visual separation, aiding in the comparative analysis of the sequences. Participants, seated 1.5 m from the screen, were asked to assess the quality of the video sequences. They were instructed to determine which one of the two, left or right, exhibited superior quality or to indicate if they appeared to be of equal quality. The criteria for superior quality were consistent with our previous subjective experiment presented in Section 4.3: a video was considered superior if it more closely resembled a natural scene and exhibited fewer artifacts.