Bidirectional Translation Between UHD-HDR and HD-SDR Videos

With the popularization of ultra high definition (UHD) high dynamic range (HDR) displays, recent works focus on
upgrading
high definition (HD) standard dynamic range (SDR) videos to UHD-HDR versions, aiming to provides richer details and higher contrasts on advanced modern displays. However, joint considering the
upgrading
&
downgrading
translations between two types of videos, which is practical in real applications, is generally neglected. On the one hand,
downgrading
translation is the key to showing UHD-HDR videos on HD-SDR displays. On the other hand, considering both translations enables joint optimization and results in high quality translation. To this end, we propose the bidirectional translation network (BiT-Net), which jointly considers two translations in one network for the first time. In brief, BiT-Net is elaborately designed in an
invertible
fashion that can be efficiently inferred along forward and backward directions for
downgrading
and
upgrading
tasks, respectively. Based on this framework, we divide each direction into three sub-tasks, i.e., decomposition, structure-guided translation, and synthesis, to effectively translate the dynamic range and the high-frequency details. Benefiting from the dedicated architecture, our BiT-Net can work on 1) downgrading UHD-HDR videos, 2) upgrading existing HD-SDR videos, and 3) synthesizing UHD-HDR versions from the downgraded HD-SDR videos. Experiments show that the proposed method achieves state-of-the-art performances on all these three tasks.