Temporal coherency for video tone mapping
Résumé
Tone Mapping Operators (TMOs) aim at converting real world high dynamic range (HDR) images captured with
HDR cameras, into low dynamic range (LDR) images that can be displayed on LDR displays. Several TMOs
have been proposed over the last decade, from the simple global mapping to the more complex one simulating the
human vision system. While these solutions work generally well for still pictures, they are usually less efficient for
video sequences as they are source of visual artifacts. Only few of them can be adapted to cope with a sequence
of images. In this paper we present a major problem that a static TMO usually encounters while dealing with
video 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 varying
dynamics 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 temporal
coherency. This temporal coherency algorithm has been tested on a set of real as well as Computer Graphics
Image (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, this
technique is applicable to any TMO as it is a post-processing that only depends on the used TMO.