# A Display-Adaptive Pipeline for Dynamic Range Expansion of Standard Dynamic Range Video Content
Luminance, a measure of emitted light intensity, is quantified in candelas per square meter (cd/m\({}^{2}\)), often referred to as \"nits\". One nit equals a luminance value of 1 cd/m\({}^{2}\). In the real world, scenes can vary widely in brightness, ranging from extremely bright, such as sunlight that exceeds 10,000 cd/m\({}^{2}\), to very dark shadows with near-zero luminance. The contrast ratio, a key aspect of display performance, is the ratio of the brightest and darkest luminances a display can reach. Contrast ratio, also known as \"dynamic range\", is measured in exposure value (ev) differences, also known as \"stops\", which is the logarithm base-2 of the contrast ratio. Therefore, one unit increase in one ev, or one-stop, means that the screen's brightness has doubled [1]. While conventional display technology typically achieves brightness levels ranging from 1 cd/m\({}^{2}\) to 300 cd/m\({}^{2}\) and encompasses a limited dynamic range of up to eight stops, it pales in comparison to the luminance variations encountered in real-world scenes. This stark contrast becomes even more pronounced when considering that the human eye discerns a dynamic range of up to 14 stops within a single visual field. Evidently, conventional display technology falls short in faithfully reproducing the nuanced luminance realism inherent to our visual experiences. Recent advancements in display technology have ushered in a new era of HDR displays, offering a remarkable boost in dynamic range and brightness. HDR prototype displays utilizing arrays of independent high-power light emission diodes (LEDs) as backlight units have achieved extraordinary milestones, boasting a peak brightness of 10,000 cd/m\({}^{2}\) and an impressive 17 stops of dynamic range [2; 3]. Similarly, organic light-emitting diode (OLED) technology has started taking a significant market share in the production of HDR consumer televisions. Figure 1 illustrates the fundamental differences between LED and OLED display technologies. As illustrated, LED displays utilize high-power LED backlights to illuminate liquid crystal pixels. In contrast, the LEDs in OLED technology independently emit light without the need for a backlight, thereby dramatically improving contrast ratio and energy efficiency [4]. Recently, at the Consumer Electronics Show (CES) in 2023, the company LG presented its new OLED META technology. This technology incorporates two major components into LG's current OLED platform: a MLA (micro lens array), which significantly enhances the light emission efficiency of OLED displays, and a META booster, which is an advanced algorithm that dynamically analyzes and adjusts scene brightness in real-time. This innovation allows for improved brightness, contrast, and energy efficiency of OLED displays, allowing them to achieve a peak brightness of 2100 cd/m\({}^{2}\). Emerging technologies such as mini-LEDs (mLEDs) and micro-LEDs (\(\mu\)LEDs) are also making significant contributions to enhancing the dynamic range in modern displays [5; 6]. It is expected that, in the coming years, HDR displays for the consumer market will reach higher peak brightness than today's standards, enhancing their ability to mimic the luminance of real-world scenes more accurately. HDR content, associated with cutting-edge HDR display technologies, features media with dynamic ranges surpassing 14 stops [7]. This capability allows HDR content to showcase a much wider spectrum of luminance and colors compared to traditional low dynamic range (LDR) content, also known as standard dynamic range (SDR). While LDR is a  
Figure 1: Comparison between LED and OLED display technology. general term for media with limited dynamic range, SDR specifically refers to conventional broadcast standards. The terms LDR and SDR are often used interchangeably, which can lead to confusion. However, for the purposes of this article, they are synonymous and refer to content characterized by a lower dynamic range.