A multi-modeling electro-optical transfer function for display and transmission of high dynamic range content

This paper proposes a multi-modeling Electro-Optical Transfer Function (EOTF) enabling efficient use of the code word to preserve the contrast details in the quantized High Dynamic Range (HDR) content. Different from the classic EOTF that employs one single model, the proposed EOTF considers four models to adjust the reproducible contrast according to the luminance level of the HDR content. Furthermore, the proposed EOTF and its inverse process functions can be integrated on HDR cameras and displays with a low computational cost. In order to evaluate the performance of the proposed EOTF, it has been applied into a HDR video transmission chain based on the High Efficiency Video Coding (HEVC) codec. The standardized Perceptual Quantizer (PQ) EOTF and Hybrid Log-Gamma (HLG) Opto-Electronic Transfer Function (OETF) are also introduced and compared with the proposed EOTF in terms of the reproducible contrast. The objective evaluation results show that the proposed EOTF brings a better quality of the decoded HDR video than that generated by the standard function. A subjective test was also conducted in a commercial HDR television and the results show that the proposed EOTF can present more visible details than PQ, particularly for the HDR content with dark scenes. Therefore, the proposed multi-modeling EOTF is useful for the transmission and display of the HDR content in the consumer electronics.

I. Introduction

The luminous intensity varies in a wide range in the natural world. The luminance of the moonlight can be as low as around 10⁻³ cd/m², while the sunshine in the sunny day can be over than 10⁵ cd/m² [1]. However, the conventional monitors have a Low Dynamic Range (LDR) for the display of the luminance. They need certain correction methods for the display of the High Dynamic Range (HDR) contents [2]. In order to bring a realistic visual experience, current commercial televisions have supported a high luminance range and have been able to display the HDR contents [3]. Besides the range of device, two signal transfer functions, the Opto-Electronic Transfer Function (OETF) and the Electro-Optical Transfer Function (EOTF), critically determine the quality of the HDR signals. OETF is used in the digital camera to convert the luminous intensity to the digital signal, while EOTF aims to convert the signal's carrier (analog voltage or digital code) to the luminous intensity in electric displays. Therefore, well designed systems with both HDR supported OETF and EOTF can provide realistic visual effect in multimedia applications. Conventional OETF and EOTF have been defined as standards in Rec.BT.709 [4] and Rec.BT.1886 [5], respectively. However, the Rec.BT.1886 was designed for the display of the LDR image/video [6]. It causes visible contouring artefacts for the HDR display [7] [8].