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Components of Digital Cinema

This article gives a small introduction to some of the individual components that make a Digital Cinema – The Digital Camera, Processing Tools, Content Distribution, Server/Theatre Management and Digital Projectors. As the name suggests, Digital Cinema aims to make all the processes completely digital using the above individual components.

In this near to digital world ruled by the 1’s and 0’s, the cinema industry has long been ruled by the Analog Film based acquisition, distribution and projection techniques. The purists have been, and still favour films to make and show their cinemas. But all that is changing fast with the introduction of Digital Cinema.

Digital Cinema is not only about digital acquisition, digital mastering, digital distribution and digital projection. Though, that’s what we will talk about in this article, Digital Cinema is more about a paradigm shift in the way in which cinema is conceived, shot, processed and shown. The concept that what ever happens in front of the camera being recorded and shown as a cinema is changing. The recorded material becomes just a small portion of what is actually shown in the screen – for example, the background setting/colour can be completely changed or even created in the PC and characters can be introduced in this new setting. Animation and special effects create an alternate reality that may not exist, but still catch the fantasies of the movie audience. Digital cinema can bring even extinct creatures before the screen and give us a perception of them being real.

The digital processing has also been happening with analog films – the video shot by the analog cameras with the films were converted in to digital data for editing, mixing, adding special effects/animations etc and then converted back to analog films for displaying them in the theatres. But now, the entire process is slowly being converted digital end to end. Let us look at the major components that make a Digital Cinema:

Digital Cameras:

Digital cameras can shoot with a resolution of 2k, 3k, 4k and some even higher! Depending on the resolution, the frame rates vary from 20 to 120 fps. Of course, the higher the resolution, lower the possible frame rates. The depth of field is usually equivalent to 35 mm cine lenses. These cameras generally contain more than 10 Mega Pixels and 4k resolution means 4520 x 2540 pixels.

There is also a video preview to enable directors to see the video shot immediately and decide if a change is required in the lighting conditions or a re-shoot is required. There is also an option for direct audio recording with attached external microphones. Digital media connectivity for direct recording is provided with the cameras via USB, HDD, Compact Flash Module, Solid State RAM etc.

The video data is sometimes compressed before transferring it to the attached external media as the storage required is as high as 20GB/min for higher resolutions. RAW data can also be recorded, if required. One striking advantage of certain digital cameras is the ability to upgrade them indefinitely by replacing the electronics/sensor units, without having to change the peripherals/accessories.

Digital Processing:

Of course, this is the heart of the digital cinema. Once the digital data is shot with the digital cameras, it is much easier to do editing, picture enhancement, colour correction, composting, visual effects, multi-format delivery etc, using digital processes. You can also mix and match formats, frame rates and resolutions much easier with digital cinemas.

Animation and special effects, no need to say, have become the mainstay of many super hit digital cinemas. Interestingly, even the digital re-mastering of classic movies shot with analog films are done using digital processes.

Digital Distribution:

Once the cinema is processed and edited, it is ready to be distributed to the various movie halls. But now, instead of the individual heavy tapes being shipped across the world, the digital data is sent electronically over the Internet, leased lines, satellites and even inexpensive hard-disks and DVD’s. This saves time, money and effort. The data is encrypted while sending them across public networks like Internet.

Digital Cinema Servers:

The encrypted data is received and decrypted by the digital cinema servers which are located at the individual cinema halls. It then re-encrypts it and outputs the image data to the digital cinema projector and audio data to the sound processor. The theatre projectors of today support 128 bit AES encryption/decryption for media.

The digital cinema servers generally support the most common JPEG 2000 media playback format for compatibility as required by the DCI multi-vendor Compliance and may optionally support additional formats like MPEG-2 etc. The media block in the server which does the bulk of the work is reprogrammable to accommodate for future developments in image and sound formats. Generally, the industry standard audio/video formats are supported for the output.

The hard disks are generally in the form of an array and they support RAID to ensure redundancy of stored data. All the hard-disks, power supplies, cooling fans etc. are hot swappable. Some of them have a direct fiber termination option for connecting to the network.

The digital cinema projectors can be monitored and upgraded over the network. Some of them even provide a sort of an external remote to control basic functions like Play, Pause, Stop etc. There is an optional theatre management software to enable easy set-up, scheduling and management of multi-screen shows (usually in a multiplex with multiple screens) over the central network so that subsequent manual intervention may not be required.

Digital Cinema Projectors:

These projectors directly accept and play digital format images in high quality. Majority of the digital cinema projectors use DLP – Digital Light Processing technology to project images while some of them might use LCD or some kind of modified LCD crystals for projection. Some projectors come with media block as well which can store/decrypt the digital data.

Common projectors support 2k, 4k resolutions and have a brightness level in excess of 15,000 Lumens. They employ 1.5-7.5W Xenon Lamps (some times two lamps together) as a source of illumination (LED lamps are also getting popular) and the contrast ratio is around 2000:1 which is sufficient to show the minute variations of shades for colours.

The digital cinema projectors support input/output formats according to the DCI standards so that interoperability is not a issue. There are optional lenses to change the throw distances (as they are normally fixed for a particular distance) to adjust according to the theatre conditions. There are even 3D Lens adaptors which enable playing of 3D digital content, whose effect can be felt along with 3D polarizing glasses.

These projectors implement normal projector functions like keystone correction (to make the image appear like a perfect rectangle), electronic focus and zoom (with memory, so that the picture size doesn’t change on the screen when the display format is changed). Some projectors also help maintain the luminance levels automatically.

The digital cinema projectors must confirm to the SPB-2 and other anti-tampering requirements of the DCI – Digital Cinema Intitiatives which might want the projectors to require physical keys to open the body (instead of screws), automatically start recording logs when the projectors are opened and a host of other security measures.

Related Reading:
Advantages and Disadvantages of Digital Cinema

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