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This topic comprises 3 pages: 1 2 3
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Author
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Topic: 4K and 2K DCP have similar bitrates
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Edward Summerhays
Film Handler
Posts: 16
From: Sydney, NSW, Australia
Registered: Sep 2016
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posted 09-06-2016 01:08 AM
Hi,
First post! I am not in the industry, but love movies and have taken a real interest in the technical side of cinema in recent years.
My question is regarding the bitrate standards of DCP etc.
I noticed the other day that Sully, a film with a 4K Scope DCP, has a file size of only 88GB, for a 90min feature.
http://digitalcinema.bydeluxe.com/site/dlxportal/docs/Sully_US_RLS.pdf
I compared this to another Warner Bros title, War Dogs, which is a film with a 2K scope DCP, and it's file size is 142GB for a 124min feature.
http://digitalcinema.bydeluxe.com/site/dlxportal/docs/War_Dogs_US_RLS.pdf
Considering has Sully would have 4 times the amount of data per frame, why is it's bitrate 125mb/s, vs War Dog's 156mb/s?
I am surprised that the 4K DCP has a lower bitrate than the 2K DCP. I would have thought DCP standards would allocate a higher minimum bitrate for 4K content compared to 2K.
I have noticed the same for lots of other 4K DCPs. the file sizes are roughly the same as 2K DCPs of the same length. Why is this so? are 4K DCP's compressed more efficiently?
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Edward Summerhays
Film Handler
Posts: 16
From: Sydney, NSW, Australia
Registered: Sep 2016
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posted 09-06-2016 08:07 PM
Thanks for your replies. Some good info on the way DCPs are compiled.
It is interesting that the distributor wouldn't utilize the disc space, especially at 4K. The way I see it is a 4K film at 1.5 hours would have the same amount of video information stored as a 2K movie with a running length of 6 hours! Dividing Sully's bitrate by four, to compare to a 2K bitrate, brings it's bitrate to barely higher than blu-ray.
Of course, a higher pixel density would mean the viewer would have to half their viewing distance to see the same pixel density as a 2K feature, thus, compression less evident from their regular viewing distance.
As Bobby said, it there is a lot of temptation at the 'good enough' attitude with digital. I have noticed a lot recently films which have a 4K workflow, received a 2K DCP, because the viewer doesn't demand higher quality.
It baffles me more than some films have a 2K DCP created from a 4K master, as the additional resolution "isn't necessary" for cinema, but UHD blu-ray receives the true 4K master. The higher resolution would be far more beneficial at the cinema rather than on a 65" TV, and if the cinema has a 4K projector ready to go, then why not? I guess that's another topic all together though!
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Paul H. Rayton
Expert Film Handler
Posts: 210
From: Los Angeles, CA , USA
Registered: Aug 2003
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posted 09-06-2016 10:00 PM
Many members on here have actual mastering experience (creating DCPs), using DCP-O-Matic. That includes me. We have the option, in the program, for setting the master bitrate, from as low as we want to as high as 250mB/sec. for 2K DCPs. The same would apply to any studio mastering their commercial title. Why some of them choose to go at low bitrates bothers the crap out of me because, for crying out loud, you get the damn hard drive back when the shows are done, and you can erase it and use it for some other other show. So why "gyp" the audiences with low bitrates for a movie? I don't get it! You're saving a few electrons, but you get them back!
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Edward Summerhays
Film Handler
Posts: 16
From: Sydney, NSW, Australia
Registered: Sep 2016
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posted 09-06-2016 11:49 PM
quote:
quote Bobby Henderson
Actually the new Ultra HD Blu-ray format is dealing with a good amount of controversy due to what I call "Fake 4K" on many of the discs.
Yes, this is the main reason I am in no rush for 4K at home.
I will eventually come on board with 4K at home, but only once the price of 4K home projectors drop, and more true 4K titles are released.
I won't buy any UHD title that came from a 2K DI. And seeing as most of the titles released are modern titles sourced from a 2K, there is really no point!
Christopher Nolan's (ano other film makers) concerns on the limitations of digital are being validated now, with these fake 4K titles.
A movie from 50 years ago can be transferred to 4K, but a film from last year is stuck in 2K forever.
To find out if a film is truly 4K before going to the movies, I generally try to see the DCP title sheet so verify. I'll sit closer to the screen if it's a 4K DCP. This will come in handy for purchasing UHD blu-ray discs. If it's a 2K DI, might as well stick to standard blu-ray.
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