JPEG XT: A Compression Standard for HDR and WCG Images

H IGH BIT DEPTH data acquisition and manipulation have been largely studied at the academic level in the last 15 years and are rapidly attracting interest at the industrial level. An example of the high interest for High Dynamic Range (HDR) imaging is the use of 32-bit floating point data for video and image acquisition and manipulation that allows a variety of visual effects that closely mimic the real world visual experience of the end-user [1] (see Fig. 1 for an illustration). At industrial level, we are witnessing increasing traction towards supporting HDR and Wide Color Gamut (WCG). WCG leverages HDR for each color channel to display a wider range of colors. Consumer cameras are currently available with 14 or 16 bit A/D converter. Rendering devices are also appearing with the capability to display HDR images and video with a peak brightness of up to 4000 nits and to support wide color gamut (ITU-R Rec. BT.2020 [2]) rather than the historical ITU-R Rec. BT.709 [3]. This trend calls for a widely accepted standard for higher bit depth support that can be seamlessly integrated into existing products and applications. While standard formats such as JPEG 2000 [5] and JPEG XR [6] offer support for high bit depth image representations, their adoption requires a non-negligible investment that may not always be affordable in existing imaging ecosystems, and induces a difficult transition, as they are not backwardcompatible with the popular JPEG image format. Instead, most digital camera and mobile phone manufacturers either store images in proprietary RAW formats or, more commonly, offer an HDR mode, which produces a traditional low dynamic range image with improved details. The former solution creates a vendor lock-in problem for consumers, making it difficult to efficiently use images produced by such