If, like me, you're wondering what 'mastered in 4K' means, here's Sony's explanation:
"Sony Pictures Home Entertainment has released Blu-ray Disc movies Mastered in 4K and Optimized for 4K Ultra High Definition Televisions. These Blu-ray Disc movies will include the following technologies to yield the greatest possible high definition picture quality and will upscale to create a satisfying 4K experience.
* Utilization of 4K movie masters created either from a film source scanned digitally with more than 4K resolution, or shot with 4K digital cameras that provides a more precise and detailed picture.
* The utilization of x.v.YCC color gamut to the 4K movie master delivers an expanded range of rich color contained in the original source when viewed on a high definition television compatible with x.v. * YCC specification.
* Sony worked together with Sony Pictures to optimize the algorithms of down-converting 4K movie masters to upscale it with the Sony 4K-Reality Pro Engine when viewed on a Sony 4K LED TV."https://us.en.kb.sony.com/app/answers/detail/a_id/43225/~/what-does-it-mean-when-a-blu-ray-disc-movie-is-mastered-in-4k