# A Fast and Reliable Luma Control Scheme for High-Quality HDR/WCG Video
## 5 Conclusions  
As a promising type of emerging immersive media, HDR/WCG is starting to replace the main stream of content production for providing far better quality ultra-high definition (UHD) media. The media format, known as HDR10 or HDR10+, has been adopted in various fields of media industry but has possible degradation on luminance perception. Luma control is a method to cope with such potential luminance perception problems and is perceived to be an essential preprocessing technology in HDR/WCG content production. In this paper, we proposed a fast and reliable luma control scheme that can significantly ameliorate the luminance perception error of HDR10/10+ format video and is highly suitable for hardware implementations.  
The proposed algorithm employs a linear approximation of EOTF using a straight line passing two points on the EOTF curve, where one is from the original signal and the other from a lower and an upper bound of the optimal luma value. This new linear approximation is the first contribution of this paper. Further, for a more accurate and robust approximation capability of the proposed straight line, we derived two new bounds on the true optimal value based on the solution using truncated Taylor series. This is the second contribution of this paper. Then, in order to demonstrate the feasibility of the proposed luma control scheme, we conducted an extensive comparison study among the previous representative luma control algorithms. Based on the contributions mentioned above, the proposed linear approximation has been identified to provide nearly the same quality of the optimal solution, i.e., only 0.04 dB less than the iterative luma control scheme, in tPSNR-Y on average. Moreover, nearly the same quality was obtained without iteration, resulting in a friendlier nature for hardware implementations. The proposed algorithm showed an impressive quality improvement over the previous fast luma control schemes, i.e., up to 7.4 dB in tPSNR-Y over the fast luma control scheme on the \"Fireplace\" sequence and up to 3.6 dB over the enhanced fast luma control algorithm on the  
Figure 6: Top 0.1% pixels having the biggest quality difference between the proposed and the fast luma control schemes. The green pixels attributed most to the tPSNR-Y difference between the two luma control schemes.  
\"Market\" sequence. Again, this quality improvement was obtained without any adaptive parameters, which were the required cost for the quality enhancement of the enhanced fast luma control scheme over the fast luma control algorithm.  
With these desirable features, the proposed scheme is expected to be highly useful for a practical production system of high-quality HDR/WCG video and to be more valuable due to tighter and more computation-efficient bounds on the optimal luma value.  
All authors are equally responsible for the concept of the paper, the software implementations, the results presented and the writing. The authors have read and approved the final published manuscript.  
This research was funded by Ministry of Culture, Sports and Tourism (MCST) and Korea Creative Content Agency (KOCCA) in the Culture Technology (CT) Research & Development Program 2018 under R2018020102_0000001. The APC was also funded by MCST and KOCCA.  
The authors would like to acknowledge the anonymous reviewers for their valuable and helpful comments, and Mr. [PERSON], who is an assistant editor of MDPI, for his prompt and faithful handling of the manuscript.  
The authors declare no conflict of interest.