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This topic comprises 3 pages: 1 2 3
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Author
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Topic: 'UNBROKEN' 4K file size...
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Antonio Casado
Film Handler
Posts: 36
From: Madrid, Madrid, Spain
Registered: Apr 2013
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posted 01-18-2015 04:14 AM
I can answer about that, because I professionally make DCPs and I have done a lot of test regarding this...
Well, first of all, the tool you use can be more or less efficient. For example, at the same bitrate, OpenJPEG is more heavy in size, but EasyDCP (kadaku encoder) is less weight.
You can think that less size is less quality. Not in JPEG2000, that have a very optimized algorithm.
I use a tool that use other Jpeg2000 encoder and the results are really amazing.
Second, the bandwidth. The maximum Mbit/sec for DCP is 250 Mbit/sec (including audio tracks). Really, no one make DCPs to that Mbit/sec because is not needed.
In fact, more that 150Mbit/sec is considered garbage and there is NOT difference visually with a 250Mb/sec DCP. When you low to 100 mbit/sec is when you can loss some high frequency textures, so not recommended at all. 25Mbit/sec cause severe degradation in the image, and the image look like plains colors, really funny :-D
Third, the use of VBR Encoding. When you use it, is when you make the "magic". Prior to the use of VBR, you mark a target Mbit/sec and ALL Jpeg2000 files will be compressed at this Mbit/sec. So a black image will size like a full detailed pic. This is a nonsense.
The VBR encoding can lower A LOT the final size, as a black image can be as low as 2Kb, and that is very good.
Also, if the original image is NOT HD (DVD Scaled to HD, for example, or something similar), the size will be much lower, by using VBR encoding (equal pixels surronding will be compressed and the final image will be lower in size, but retaining the original Quality).
I have done a lot of projections of very high frequency images (with a lot of detail), and when you compare a 150Mbit/sec DCP with a 250Mbit/sec DCP, there is NO difference. Itīs the same.
Of course, a final cause is the duplication time. Itīs not the same copy a 200GB DCP that a 100GB DCP. You can lower the time, and make more copies in the same time. And the quality is the same. So, why to spent useless bytes?.
About H265, I donīt think that H265 will be used in DCP. H265 is a very good codec, I have done test at 4K and using the same bitrate of Bluray at 1080P the quality blow away. Imagine a 1080P H265 Feature weighting only the half of the size but the same quality. Really cool!. This is intended to use for streaming and Digital Download, not Cinema.
But who knows how can be the Digital Projection in 10 or 15 years from now...
I only know that Jpeg2000 is one of the best codecs to use in delivery, much better that anyone other...
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Antonio Casado
Film Handler
Posts: 36
From: Madrid, Madrid, Spain
Registered: Apr 2013
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posted 01-19-2015 02:04 AM
Thanks Steve!
About Bluray and DVD, as these media is compressed in origin, a 140 Mbit Bitrate will be fine.
The SAME movie in DVD will compress A LOT (because the image need to be scaled and the pixels repeats, so a lot of optimization will occur).
I do not recommend to transfer to DCP from a DVD, itīs really crappy, but I understand that sometimes is the only source, unfortunately.
I receive A LOT of compressed, interlaced, resized, pulldown material, the clients doesnīt know anything about DCinema and thinks that "all is good" to project in DCinema. What a mess!
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Antonio Casado
Film Handler
Posts: 36
From: Madrid, Madrid, Spain
Registered: Apr 2013
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posted 01-19-2015 12:38 PM
Marco:
I have projected in a 300 meters square screen, so trust me, 150/160Mbits is fine and the quality is very good (but at these levels of screen we need 4K)
92Mbit/sec is really a low low bitrate!. The Scope format also helps to lower the bitrate (as the pixel count is lower that Flat/Full), but that is not the point. I NEVER lower from 125mbit/sec. I use 125mbit/sec for ads, because they are "temporal", but for Features and other things, I set mainly 150/160mbit/sec.
Of course, the final size varies in function of the type of images, I have a rule of 1 min = 1GB, so 90 minutes will size 90GB or more (suggested more, of course)
Lyle:
About 4K, as the maximum bitrate is 250mbits for both format I suggest to up to 170/180 mbits, not more. And even 160Mbits will be fine too, as the "degradation" in a 4K image is less noticeable, and ONLY the very near seats can "see" the true 4K resolution (and you need a reasonably big screen too).
This apply too to 3D and HFR, where the FPS will be doubled and the size of the files are lower too.
Thatīs because HFR 3D need 500Mbit/sec, to make the really good quality needed, as 250Mbit/sec will be insuficient (but possible!)
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Carsten Kurz
Film God
Posts: 4340
From: Cologne, NRW, Germany
Registered: Aug 2009
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posted 01-19-2015 01:13 PM
As I mentioned before, there are some differences between common J2K encoders. The Dolby encoder e,g, manages lower bitrates very well, while OPENJPEG does not.
I talked so someone dealing with DCP mastering and disc & satellite distribution professionally. He did confirm that, though rarely, sometimes the rights owner/distributor do in fact instruct the mastering companies to lower the bitrate in favour of certain distribution channels and cost. Some distribution companies actually charge per GB, so they actually do save with smaller files.
I hope they will not overdo this in the future as more and more satellite and broadband distribution taking over.
J2K/Wavelets deal very well with higher resolution content. That's one of the reasons DCI chose this codec. You can add a lot more detail without having to increase the datarate significantly.
When recompressing DVD or BluRay, J2k as intraframe also does not pile up more motion artifacts as with most other interframe codecs. These would show up badly on the big screen. So, it is relatively easy to conserve at least the original BluRay quality using J2K. BluRay also has only 8Bit 4:2:0. These 'flatter' files will compress a lot higher than DCPs 12Bit 4:4:4 as they contain a lot more redundancy.
Proper color/gamma conversion is more important than bitrate settings when doing DCP conversions - even for DVD.
- Carsten
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Carsten Kurz
Film God
Posts: 4340
From: Cologne, NRW, Germany
Registered: Aug 2009
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posted 01-19-2015 02:07 PM
Steve,
actually I have set my DCP datarate at 150 and hardly ever touch it. I usually do not care if one of these conversions has a couple of GB more or less. Yes, DVD could probably be set well below 100MBit/s, but I really do not care. You do know that different discs can have very different resolution/quality, so, while you could take an edge with one disc, it may not work with a different one. So I just play safe with 150MBit/s. That would still be sufficient with high quality 4:4:4 10/12Bit source footage.
REC709 is right for both DVD and Bluray. The problem is that there is a strange gamma uncertainty, discussed at various places, claiming that there is not a single gamma setting that fits all media.
http://dcinemaforum.com/forum/index.php?topic=451.0
I have actually seen strange lifted blacks on some BluRay conversions, but not others. I have a hard time to understand why these differences do not show up as drastically in their original intended playback environment - home cinema, etc. I can only advise to keep a close look at the blacks/colored shadows and keep the issue in mind. All DCP converters with support for REC709 should do gamma correction from 2.4 to 2.6 (2.2 to 2.6 for sRGB sources) while converting to xyz color. But sometimes this simple scheme fails. When I did my first full lenght Bluray-DCP conversion two years ago, I only noticed too late that in some scenes there were torn up blocky blacks and strange clipped saturated dark colors. At the time I did not have the time for a new conversion, let alone thorough testing. So I had to adjust the projector settings to fix it. Best of course would be to have an A/B comparion between disc and DCP on the DCI machine. But who has the time to do that for every conversion?
- Carsten
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Marcel Birgelen
Film God
Posts: 3357
From: Maastricht, Limburg, Netherlands
Registered: Feb 2012
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posted 01-20-2015 04:36 AM
quote: Owen Morgan
I doubt that they are using any 'open' JP2K encoders..
The open JPEG2000 encoders are OK, but not extremely great. I think there is just limited interest in improving those open tools and libraries for JPEG2000, compared to open libraries for formats like H.264 or H.265.
A more refined encoder can definitely make a whole lot of difference and get better quality out of the same bitrate.
Also, keep in mind if you're coming from Blu-Ray and going to JPEG2000, you're going from one lossy format to the other. You should always take a safe margin here, or else you're layering lossy compression artifacts of one format on top of the other.
quote: Carsten Kurz
I have actually seen strange lifted blacks on some BluRay conversions, but not others. I have a hard time to understand why these differences do not show up as drastically in their original intended playback environment - home cinema, etc.
I've dealt with the same issues, but I'm not entirely sure it's really a REC.709 to XYZ conversion error, but rather a production error that somehow doesn't get noticed or production companies don't really care about it.
I've seen the same "blocky" MPEG artifacts when playing back the non-transcoded Blu-Ray rip on a computer screen. Obviously this computer screen was in no way calibrated and probably too bright. But it shows that it doesn't need much of a "miscalibration" to get those obviously shoddy encoding artifacts into visual levels.
Another explanation could be some rendering defect in the H.264 decompression library off course.
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Bobby Henderson
"Ask me about Trajan."
Posts: 10973
From: Lawton, OK, USA
Registered: Apr 2001
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posted 01-20-2015 09:03 AM
Adobe Photoshop has a built in JPEG 2000 image encoder. I don't know if Adobe has updated it lately. I wasn't very impressed with it the last time I messed with it. I didn't see much difference over the standard Photoshop JPEG filter. Fireworks, a program Adobe acquired from Macromedia, can compress JPEG images more efficiently. But Adobe is not developing that program any further.
quote: Antonio Casado
Third, the use of VBR Encoding. When you use it, is when you make the "magic". Prior to the use of VBR, you mark a target Mbit/sec and ALL Jpeg2000 files will be compressed at this Mbit/sec. So a black image will size like a full detailed pic. This is a nonsense.
The VBR encoding can lower A LOT the final size, as a black image can be as low as 2Kb, and that is very good.
It sounds like your encoder is using techniques similar to those used in GIF and PNG images, where large fields of solid color can be compressed very efficiently and even lossless compressed in some cases.
quote: Antonio Casado
About 4K, as the maximum bitrate is 250mbits for both format I suggest to up to 170/180 mbits, not more. And even 160Mbits will be fine too, as the "degradation" in a 4K image is less noticeable, and ONLY the very near seats can "see" the true 4K resolution (and you need a reasonably big screen too).
What viewers can and cannot see in 4K really depends on a number of factors. 4K done right should be noticeable on a big screen to more than just the first few rows of people.
Some imagery, such as low depth of field imagery and imagery deliberately shot a little out of focus (to hide pancake makeup, wrinkles on faces, etc.), isn't going to look much different in 2K or 4K. Imagery that is heavily processed in post production may have a lot of its native detail killed through over zealous filter tweaks.
Then you have all the movie theaters that, for various reasons, dial their projectors slightly out of focus. They don't want viewers seeing that electronic pixel grid. Or they have a moiré issue between the perforations of their movie screen and the projector's pixel grid. Or maybe their projector's lens just isn't very good.
Graphics items with hard edges, such as lettering and logos, can reveal the pixel grid in a very obvious way. Likewise, if the projector is slightly out of focus those items are going to look soft.
I have seen tack sharp imagery many times in film presentations of the past, especially with 70mm film. I have never seen tack sharp imagery with any digital show. It's all been various levels of softness. The sad thing is I've seen razor sharp image quality on 4K UHDTV sets showing 4K demo material. So I guess as 4K TV sets grow more popular and 4K content starts becoming more common we can look forward to a whole new round of home viewers talking about how much better the home viewing experience is than the theater.
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Antonio Casado
Film Handler
Posts: 36
From: Madrid, Madrid, Spain
Registered: Apr 2013
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posted 01-20-2015 09:19 AM
The Jpeg2000 encoder of Adobe Photoshop is NOT DCinema compliant. There is some branches into the Jpeg2000 encoding, lossy and lossless, and DCinema is one of them, with his own particularities...
Jpeg2000 is NOT Jpeg, they cannot compare as both have very big differences. In fact, the Wavelet encoding used in Jpeg2000 is the same used un Cineform and others high-end codecs.
"My" encoder use the same algorithms of the high end encoders, such as Dolby, EasyDCP and so on. The use of VBR is very common right now and itīs the best option to make a DCP with high quality but weighting less. Think that type of compression like ZIP or RAR does over a image with large areas of solid colors. Itīs the same approach.
About 4K...well..is long to talk. Better in another thread, really...
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