Temporal coherency for video tone mapping

Abstract

International audienceTone Mapping Operators (TMOs) aim at converting real world high dynamic range (HDR) images captured withHDR cameras, into low dynamic range (LDR) images that can be displayed on LDR displays. Several TMOshave been proposed over the last decade, from the simple global mapping to the more complex one simulating thehuman vision system. While these solutions work generally well for still pictures, they are usually less efficient forvideo sequences as they are source of visual artifacts. Only few of them can be adapted to cope with a sequenceof images. In this paper we present a major problem that a static TMO usually encounters while dealing withvideo sequences, namely the temporal coherency. Indeed, as each tone mapper deals with each frame separately,no temporal coherency is taken into account and hence the results can be quite disturbing for high varyingdynamics in a video. We propose a temporal coherency algorithm that is designed to analyze a video as a whole,and from its characteristics adapts each tone mapped frame of a sequence in order to preserve the temporalcoherency. This temporal coherency algorithm has been tested on a set of real as well as Computer GraphicsImage (CGI) content and put in competition with several algorithms that are designed to be time-dependent.Results show that temporal coherency preserves the overall contrast in a sequence of images. Furthermore, thistechnique is applicable to any TMO as it is a post-processing that only depends on the used TMO

Evaluation of HDR video tone mapping for mobile devices

“…In addition TMOs for HDR video need to also take into account temporal coherency [3], [6] , [8]. This because significant luminance changes may occur in a sequence of frames and, if the frames are processed individually, this may cause some noticeable flickering as the individual processing of a single frame has not taken into consideration the luminance levels of the adjacent frames or of the overall video.…”

“…Boitard: This paper [8] investigated temporal coherency for video tone mapping that preserves the overall contrast of the video. To achieve this, the authors considered perception consistency of an object throughout the video and strived to preserve the temporal overall contrast consistency.…”

“…In this paper we present the results of the evaluation of six HDR video TMOs that focus on different properties. The TMOs evaluated were: Spatio-Temporal based on a Retina model [3], the model of visual adaptation [4], the method proposed by [5] that encodes HDR video using a model of human cones, the display adaptive technique [6], a time-dependent visual adaptation approach [7], and the TMO proposed by Boitard et al [8] that takes account temporal coherency. This evaluation intends to determine:…”

Screen reflections impact on HDR video tone mapping for mobile devices: an evaluation study

“…HDR video tone mapping is a growing field and a number of successful video TMOs have been proposed and successful in previous evaluations using mobile devices ( [8,15]) such as the time-dependent visual adaptation TMO [6], the display adaptive TMO [7], the visual adaptation for realistic images TMO [19], or the temporal coherence tone mapping method [20]. Other examples of well-known TMOs that were designed to address HDR video are the encoding of HDR with a model of human cones [21], the temporally coherent local tone-mapping of HDR Video [22], or the real-time noise-aware tone mapping [23].…”

“…The method proposed by [20] follows a different approach as it post-processes the HDR content as it is not capable of doing real-time processing. This is because initially, the method analyzes the whole video sequence in order to preserve the temporal stability of the video sequence.…”