# A Display-Adaptive Pipeline for Dynamic Range Expansion of Standard Dynamic Range Video Content
## 4 Results and Evaluation
### HDR-to-xHDR Conversion  
Our LDR-to-HDR pipeline distinguishes itself from other methods through its innovative capability to achieve higher peak brightness levels. This forward-thinking feature ensures that our pipeline remains adaptable to future HDR displays that may surpass current brightness standards. Leveraging our pipeline presents an opportunity to increase the brightness and, consequently, the dynamic range of current HDR content, typically restricted to a peak luminance of around 1000 cd/m\({}^{2}\). This process, which effectively enhances standard HDR content to achieve significantly higher peak brightness, is what we refer to as \"HDR to xHDR conversion\" (xHDR: extended high dynamic range). This up-conversion process is a key technical novelty, enabling standard HDR content to reach substantially higher peak brightness levels, making it even more visually compelling and vibrant. Figure 15 presents our proposed pipeline for the conversion of HDR video sequences into xHDR. This \"modified\" pipeline, in contrast to its predecessor, reduces the conversion process to three steps: dynamic range expansion, highlight boosting, and saturation enhancement. Given that HDR content generally exhibits fewer noise and artifacts compared  
Figure 14: Results of our subjective experiment, comparing user preferences for HDR images generated through our proposed pipeline against the LDR input video sequences. The vertical bars indicate the frequency of participants’ preferences, showing whether they favored one type of video sequence over the other or found both sequences to be of equal quality. to LDR content, we have deemed the denoising/artifact suppression step unnecessary for our purposes. Similarly, in a pilot test, we found that false contours were not an issue during our conversion. Therefore, we consider removing the false contours step, which, like denoising, appeared to be non-essential in HDR-to-xHDR conversion. By eliminating these unnecessary stages, we can significantly accelerate the processing speed of our pipeline without reducing the visual quality of the up-converted HDR content. A key aspect of our pipeline is the dynamic range expansion operation based on mid-level mapping, initially developed for LDR input frames, that involves two key steps: (i) fixing the mid-level in value (\(m_{\text{i}}\)) and (ii) estimating the mid-level out value (\(m_{\text{o}}\)) using image features. In the pipeline's initial design, \(m_{\text{o}}\) was derived using image features extracted from the LDR input frame. However, as illustrated in Figure 15, our revised HDR-to-xHDR conversion method uses a different approach. We now use a tone-mapped version of the HDR input to compute these image features rather than computing them directly from the HDR input. This approach allows us to apply the same estimation formula outlined in Equation (4), developed through a multi-linear regression method, without requiring additional experimentation and training. On the other hand, when setting \(m_{\text{o}}\) for HDR-to-xHDR conversion, a seemingly obvious method might be to use the mid-level value typical for the HDR domain. Considering a maximum range of approximately 1000 cd/m\({}^{2}\), this value typically lies between 100 and 200 cd/m\({}^{2}\). However, applying a value between this range directly can lead to HDR images that look too bright. This problem occurs because our expansion operator, originally intended to increase brightness levels from approximately 250 cd/m\({}^{2}\) to 4000 cd/m\({}^{2}\), a significant increase, is now being used in a scenario where a much smaller increase in brightness is required. Consequently, using the same expansion ratio results in an overly intense increase in brightness. To effectively tackle the issue of excessive brightness during the HDR-to-xHDR conversion, we refined our method for calculating \(m_{\text{i}}\). Our goal was to establish an equivalence for \(m_{\text{i}}\) that is more aligned with the specific requirements of the HDR context.