Zonal brightness coherency for video tone mapping

Tone Mapping Operators (TMOs) compress High Dynamic Range (HDR) contents to address Low Dynamic Range (LDR) displays. While many solutions have been designed over the last decade, only few of them can cope with video sequences. Indeed, these TMOs tone map each frame of a video sequence separately, which results in temporal incoherency. Two main types of temporal incoherency are usually considered: flickering artifacts and temporal brightness incoherency. While the reduction of flickering artifacts has been well studied, less work has been performed on brightness incoherency. In this article, we propose a method that aims at preserving spatio-temporal brightness coherency when tone mapping video sequences. Our technique computes HDR video zones which are constant throughout a sequence, based on the luminance of each pixel. Our method aims at preserving the brightness coherency between the brightest zone of the video and each other zone. This technique adapts to any TMO and results show that it preserves well spatiotemporal brightness coherency. We validate our method using a subjective evaluation. In addition, unlike local TMOs, our method, when applied to still images, is capable of ensuring spatial brightness coherency. Finally, it also preserves video fade effects commonly used in post-production.