# A Display-Adaptive Pipeline for Dynamic Range Expansion of Standard Dynamic Range Video Content
## 4 Results and Evaluation
### Ldr-to-Hdr Conversion: Subjective Evaluation  
As described in Section 2, many of the existing techniques in the literature for LDR-to-HDR conversion of video sequences do not reach the peak luminance reached by our pipeline. Moreover, as observed in our objective evaluation, these techniques often introduce temporal artifacts that affect the quality of their results, which is not accurately reflected in the objective quality score estimated by HDRVQM. Therefore, we determined that an objective comparison of our proposed LDR-to-HDR pipeline against other inverse tone mapping techniques for video sequences would not yield accurate results. In addition, given that most other techniques do not produce HDR video sequences with the same peak brightness as ours, a side-by-side subjective evaluation may be biased and provide inconclusive results. Considering the subjectivity of brightness preferences, it is expected that an average observer would favor an artifact-free and high-contrast HDR video in a pairwise comparison experiment [53]. This assumption was supported by a preliminary experiment we conducted using the HDR images produced by SR-ITM and FMNet. Therefore, we decided to conduct a subjective evaluation study aimed at discerning whether our inverse tone mapping pipeline can enhance HDR video sequences beyond the quality of their LDR inputs. In our previous work, as detailed in [54], we explored the benefits of employing inverse tone mapping versus a straightforward linear expansion of the dynamic range of LDR content when displayed on an HDR display. In this present study, we shift our focus to comparing the perceived quality of HDR video sequences generated from our proposed LDR-to-HDR pipeline to original LDR video sequences, which are also used as input to the LDR-to-HDR pipeline. Our primary objective was to evaluate whether there exists a clear improvement in quality when expanding the dynamic range of LDR content into  
Figure 11: Sample frames illustrating artifacts in highly saturated regions, with visible distortions generated by the SR-ITM and FMNet methods. These artifacts become more noticeable when the video sequences are displayed on the SIM2 HDR screen. Images have been tone-mapped for presentation. HDR using our proposed LDR-to-HDR pipeline. To assess this, we employed a pairwise comparison method (PWC) in a subjective experiment to discern user preferences. In this evaluation approach, we simultaneously presented the original LDR video sequence alongside the HDR version produced by our pipeline, enabling observers to directly compare and select the one that most closely resembled a natural scene while exhibiting the least distortions, thereby indicating superior quality. This direct comparison methodology minimizes subjective variances among participants by simplifying the evaluation process. The evaluation task is simple and intuitive, making it more suitable for participants unfamiliar with image quality assessment tasks (non-expert observers) [55; 56]. The experiment setup is shown in Figure 12. The experiment was conducted in a dimly lit room, maintaining ambient lighting of around 40 lux and viewing conditions according to the ITU-R BT.500-14 recommendation [57]. Both the LDR video sequence and its inverse tone-mapped HDR version were simultaneously presented side by side on the SIM2 HDR47E56 MB display. This 47-inch 1920 \(\times\) 1080 resolution display supports a peak luminance of up to 6000 cd/m\({}^{2}\) and 17.5 stops of dynamic range. Due to the display's resolution constraints, videos were cropped to fit half of the display, i.e., 960 \(\times\) 1080 pixels, ensuring that salient objects remained centrally positioned. Furthermore, for enhanced visual separation of the two videos, a 30-pixel wide gray line was inserted between them. The LDR video sequences were linearized and adjusted to emulate how they would appear on an LDR screen with peak brightness restricted to 250 cd/m\({}^{2}\).