How Movies are Prepared for the Cinema and the Home
Movies are normally shot on film or digital cameras. In either case, the usable resolution is between 4K and 10K depending on the medium. However, even movies shot on optical need to be converted to something called the Digital Intermediate (DI) to do digital effects, colour grading and other digital manipulation to the image before released to cinemas including being printed back onto optical print for older cinemas as well as release onto home video. Therefore the Digital Intermediate limits the final resolution and picture quality attainable from the source.
Unfortunately, most of the movies even now are finished using a 2K DI. Did you know that 2K has a resolution of 2048×1080? Compare that to Full HD (1080p) with a resolution of 1920×1080 and you are only getting an increase of 128 vertical lines which amounts to 6% of a resolution boost over 1080p. It is in fact so small that you are unlikely to notice it.
Enter UHD Blu Ray
For any movie finished with a 2K DI, what the movie studios do is upscale the 2K DI to a 4K image, which is almost 4x the resolution of the original creating extra pixels in the process. They cannot add any more detail, they simply use algorithms to guess the extra information. This can work to some degree just like the upscaling of your TV can work well with 1080p material. But then why not save the money, buy the Blu Ray and let your TV upscale – or something super-capable like Panasonic’s UHD players.
To add insult to injury, they then put it on a disk that’s almost the same size as your standard Blu Ray: 66GB versus 50GB disks as the 100GB disks are not really used, only for longer movies. They then compress using an algorithm that actually produces a slightly softer picture if not given enough bandwidth so really you arrive at a picture that’s not really better than 1080p for a price much higher than the standard Blu Ray. This is why reviewers are sometimes hard pressed to find much difference in detail between the Blu Ray and UHD versions. This is atrocious in my opinion.
Now granted, there are UHD disks that have been produced from a higher quality DI such as 3.2K, 4K and very rarely 8K. Those are the disks worthy of your attention. Always check before buying. 4K is not always 4K. Unfortunately, the format isn’t going to shine until they start using the 100GB disks as standard to give the bitrate room to breathe and start using 6K and 8K DIs. Then we will see what the format is really capable of. The current state of the format is sub-standard compared to what it could be.
To understand if a movie is real 4K or fake 4K, check out https://4kmedia.org/real-or-fake-4k/, which keeps tabs on whether the release was fake 4K or real 4K.
Now of course, there is more to UHD than just resolution, there is (the messy world of) HDR and also Wide Color Gamut (WCG). But that’s for another article.