A few of the most common questions we are asked at ExpressDCP.
Here is a quick Digital Cinema Mastering glossary…
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Digital Cinema Mastering |
The process of converting a film into a Digital Cinema Package. |
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DCP |
Digital Cinema Package. A DCP can be thought of as just another film format like DVD or Blu-ray. It is the format used by digital cinemas all over the world. A DCP consists of a bundle of files containing the various elements that make up a film - picture, sound, subtitles and metadata. This bundle is fed into a digital cinema server from a hard drive so that the film can be projected. |
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DCDM |
Digital Cinema Distribution Master. This is what is fed into our system and converted into a DCP. The DCDM is a master version of the film that has been prepared for digital cinema encoding. It conforms to the correct aspect ratio, colour space and sound format to be converted. ExpressDCP generates its own DCDMs so you don't have to. |
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Colour Space |
The available colours used to create a digital image. Read more about colour space here… http://en.wikipedia.org/wiki/Color_space |
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LOG |
The colour space preferred by the film industry because it mimics the natural light response of film emulsions. Also, log images are optimized for the perceptual range of the human eye. This means they make more efficient use of the available data that makes up an image. |
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XYZ |
The colour space used for Digital Cinema because it is more future proof than other colour spaces and integrates efficiently with the gamut used by Xenon digital projectors. Here is a fantastic film that explains more about XYZ colour... |
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REC709 |
A commonly used video colour space. |
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EXT2/3 |
EXT2 or EXT3 is the Linux formatting used to create DCI-compliant hard drives. |
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Server |
The "brains" of a digital cinema projection system. The server passes the decoded image data onto the projector. |
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LUT |
Look up table. A file that describes to a computer how to convert the colours in an image. A LUT is useful in digital cinema mastering to convert between colour spaces such as LOG to XYZ. |
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3D LUT |
A type of LUT used by DI facilities to show how a film will look when it is projected. We like to use 3D LUTS so that we can ensure that the film is displayed from the DCP exactly as it was in the grade. |
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DCI |
The digital cinema initiatives. A rulebook for everybody working in the D-Cinema industry. You can see it here… http://www.dcimovies.com/ |
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SMPTE |
Society of Motion Picture and Television Engineers who also set standards followed throughout the D-Cinema industry. http://www.smpte.org/home/ |
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Aspect Ratio |
Describes the shape of the projected picture. D-Cinema normally accommodates for 1.85:1 (known as "Flat") and 2.35:1 (known as scope). Confusingly, 2.35:1 is actually 2.39:1. But it has somehow become traditional to refer to it as 2.35. So, in a 1.85 picture, the width of the image is 1.85 times greater than its height. And in a 2.39 picture (or 2.35 depending on what you want to call it!) the width of the image is 2.39 times greater than the height. Scope gives a much wider "epic" feel. |
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24P |
The frame rate required for digital cinema. 24 "Progressive" frames per second. This means that, unlike television, a D-cinema frame should not contain any fields. Fields are two images that make up a single frame of a television picture. Ideally, a cinema film should never be shot using fields. But there are ways a television picture can be "de-interlaced" to use for cinema projection. This is a service we can provide. |
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DPX |
An uncompressed image file format similar to Cineon (see below) |
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CIN |
Cineon. An uncompressed image format Invented by Kodak to be used as a digital equivalent to a frame of film. |
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TGA |
Another uncompressed format. There are many others, TIFF, PIC, SGI, EXR and many more. They all do roughly the same thing and we can use any of them. |
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Gig |
A Gigabyte. 1000 Megabytes. A film in DPX form usually takes up around a Terabyte (1000 Gigs). A feature length DCP usually takes up around 70 Gigs. |
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KDM |
Key Delivery Message. A message we send to cinemas that contains a code used by the projectionist to "unlock" an encrypted film. |
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Encryption |
A security measure used to stop digital films being stolen. We are able to encrypt DCPs so only certain cinemas can play them at certain times. The film is unlocked with a KDM (Key Delivery Message). |
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DI |
Digital intermediate. A term that refers to the a celluloid film when it is in the stage between being scanned and printed. The DI stage is when all the grading and digital effects are applied. Grading facilities are referred to as DI facilities. Confusingly, with digital workflows that originate and end in a digital form, we still use the term DI, even though the film is digital throughout every step of the process. |
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JPEG2000 |
A codec used by Digital Cinema to compress the film images. Jpeg 2000 is a little more advanced than standard JPEG because its compression artifacts are softer and less blocky. Jpeg stands for the Joint Photographic Experts Group… http://www.jpeg.org/ |
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2K |
An image that is 2000 pixels wide. Although it isn't ever exactly 2000 pixels. A Scope image is actually 2048 pixels wide. A Flat image is 1998 pixels wide. |
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4K |
Same as 2K, just double all the numbers. 4K is a super high res form of Digital Cinema. Not all cinemas accommodate it yet. 2K remains the most common form for now. Although 4K is likely to become more popular in the future. Most servers can downscale 4K DCPs to 2K. |
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Codec |
A system used to compress and decode (CO-DEC) digital images. Popular Codecs include MPEG2 , H264 and, in the case of digital cinema, we use JPEG2000. |
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Scope |
2.35:1 aspect ratio. It gives films a wider more epic look. |
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Flat |
1.85:1 aspect ratio. Used more for trailers, adverts and lower budget films. |
How come the DCP file sizes are so small compared to my original master?
It's not surprising that this question pops up a lot. Clients see the DPX files on their master hard drive take up over a Terabyte. Yet their finished DCP is just a measly 70 Gigs. What's going on? Well, a file such as a DPX is designed as a digital intermediate. It's the digital equivalent of a frame of celluloid. That means it contains a massive amount of uncompressed information so that colourists can squeeze out every last drop of detail in dark and bright areas . VFX artists have all the data they need for tracking, keying and colour correcting. However, once the film is finished, a lot of this data becomes unnecessary. When the film is converted into a DCP, each frame is turned into a JPEG2000 or an MPEG2 image. This means it is highly compressed. Whilst a JPEG or an MPEG image would be unsuitable for grading or VFX work, it works just fine as an exhibition format. Both JPEG2000 and MPEG are great forms of compression. When used correctly, they do very little perceivable damage to the image.
I'm confused by colour space. What is it?
That's a big question. Here is the long answer… http://en.wikipedia.org/wiki/Color_space
A short answer might be this. Colour space describes the paint palette used to produce a digital image. So different colour spaces represent different palettes.
How do you verify your DCPs work on any server?
All our DCPs are tested on industry standard Dolby servers and carefully checked for data integrity. When master drives are copied, each clone is verified sector for sector. We have never known one of our DCPs fail and we have sent them all over the world. We have thoroughly tested our encoding process and we know our DCPs are fully DCI-compliant.
What equipment do you use to generate DCPs?
Every project is different and we use various software packages to manage LUTS, DCDM creation and KDM management. DCDMs are mainly created using a Final Cur Pro workstation with support for dual SDI and 4444. Faster than realtime DCP packaging is performed using OpenCube.
How long does the process take?
For a feature film delivered as DPX, about two days to create a DCDM and a DCP. If delivering on a tape format such as HDCAM SR and no DCDM is required, encoding takes just a few hours.
Can I see a demo of your work?
Yes. If you are in London, pop into Soho Screening Rooms any time and we'll do our best to accommodate. If you are abroad and you have access to a D-Cinema projector, we'd be happy to send you an example DCP.
Do you have any questions? Email us and we'll do our best to answer.
