Introducing our new 2 for 4K offering.
Simple DCP is proud to offer complementary 2K packaging for 4K DCPs! When you purchase a 4K DCP conversion, we will create a 2K copy of the DCP free of charge giving you ideal flexibility and control over your film’s exhibition.
But wait, why?
One of the more common questions we get at the lab is whether it is worth it to create a 2K or 4K version of a DCP when starting from a 4K source master. The answer is . . . it depends. There’s nothing quite like First, we need to understand a bit about the technology.
2K vs. 4K
Image Encoding
The specifications for digital cinema packaging were developed long before powerful Graphic Processing Units became available let alone affordable. Many of the functions that GPUs handle effortlessly today were, and still are, monumental tasks for floating point processors. To eliminate bottlenecks in the decoding process, engineers chose JPEG2000 to form the backbone of the DCI spec. Apart from being an extremely high fidelity, open source codec, JPEG2000 was purpose-built for maximum flexibility in decoding. This is in part because JPEG2000 uses a technique called progressive decoding to reorder the information in the codestream to allow for optimal decompression both at the pixel accuracy level and resolution level.
Simply put, your JPEG2000 application can stop reading and decoding a file once it has enough information to effectively render that content per your input specifications. Let’s assume you’re watching a DCP which encodes colors at 12-bit color accuracy, on a monitor with 10-bit color accuracy. Rather than render out a lot of color information you don’t need, your player can bypass that data and free up resources for smoother playback. The same holds true for image resolution. If you start with a 4K image and play back that image 2K, the player simply discards that extra data and renders a 2K image with zero additional overhead!
These innovations allow 2K and 4K digital cinema to be completely interoperable. 2K DCPs can play back on 4K projectors and 4K DCPs can play back on 2K projectors.
Data Rate
The trade off comes when taking bitrate into consideration. DCPs, whether 4K or 2K, must be encoded at a maximum bitrate of 250Mbps for DCI compliance. As anyone uploading videos to YouTube will confirm, larger images require higher bitrates to maintain the same quality. To play back a 4K DCP on a 2K projector requires discarding a layer of resolution. This is akin to removing that data entirely from the rendered image and effectively reduces the maximum possible bitrate from your final 2K projected image. Strictly speaking, you’d be better off encoding the file natively at 2K.
The good news is that the average viewer (and many professionals) really cannot tell the difference. JPEG2000 is a wavelet codec, which means that you won’t see a lot of the standard compression artifacts you get with codecs like H.264. At most you’ll see blurring around edges and a general loss of detail. That may not be great news if you shot on 35mm and were REALLY aiming for that high contrast, fine grainy detail, but the effects are otherwise indeterminable.
File Size
If there’s anything that a 4K DCP does better than a 2K DCP, it’s take up space on a hard drive. The maximum bitrate for a DCP allows for data rates to reach up to 2GB/min of run time. It’s not uncommon for feature length 4K DCPs to exceed 200GB in size. This presents major logistical concerns for yourself and your exhibitor alike. The larger your file is, the larger the likelihood that something may go wrong in transit. Even if it gets to the theater on time and in one piece, ingest time and storage space will be the prescient consideration for your projectionist. The show must go on, even if it means co-opting the experience by playing off of a Blu-Ray.
Be Prepared
Rest assured, your film will look fabulous in 2K and 4K. When in doubt, come prepared. At the end of the day, your audience will remember the story you tell and not the number of pixels.