The dcineco glossary contains explanations of some of the terms used on our
site and reflects their common use in the world of
digital cinema. We
understand these terms are not unique to digital cinema
and may have different meanings in other applications.
anamorphic image is one that has been horizontally scaled so it can be
accommodated in a frame with a smaller
aspect ratio. As
an example, widescreen television images have an aspect ratio of 1.78:1 and
they are horizontally squeezed to fit the standard television frame of
1.33:1. Correct reproduction requires the image to be horizontally expanded
to the original aspect ratio.
alternative to anamorphic processing, the image can be stored in its
original aspect ratio but utilising less than the full height of the frame.
This format is usually known as letter-box.
Manipulation of the image aspect ratio can be performed by resizing
equipment and format converters. Digital cinema projectors usually
incorporate image resizing capability that will perform any necessary
conversion provided they are adjusted to suit the format of the
ratio of an image is the ratio of its width to its height. It is usually
expressed as a ratio to unity by dividing the width by the height. So a
standard TV image may be shown as 4:3 or 1.33:1.
different aspect ratios have been used in the past. Film, in particular,
has utilised a variety of aspect ratios to create new experiences. Digital
cinema systems are most likely to need to accommodate the following ratios:
1.33:1 Academy Silent (full-gate) ratio for film, traditional TV images
1.38:1 Academy Sound ratio for film - exact ratio is 1.375:1
1.66:1 Early European Widescreen ratio for film
1.75:1 UK Widescreen standard film ratio during 1960’s and 70’s
1.78:1 Widescreen TV and High Definition standard (16:9)
1.85:1 US Widescreen film standard - now effectively World
2.39:1 Panavision Anamorphic film format - often called "Scope"
- it was changed from 2.35 in 1995
many forms and degrees of automation in cinemas. Simple automation systems
may just need a connection to the lighting system to bring up the lights
when the show finishes. Full automation may have the entire performance
scheduled and controlled by a computer. Digital cinema systems can be fully
integrated into existing automation schemes through good system design.
Digital cinema servers
generally have their own event-driven automation which may connect directly
to an existing film-based system. During the design process, it is
important to identify any incompatibilities between systems and specify any
additional equipment required to achieve translation of the signals.
Colour-space refers to the form in which the colour information of images is
encoded for electronic storage and transmission. Different colour-spaces
are used for different applications. Incorrect management of colour-space
can result in subtle or gross errors in colours so it is frequently
necessary to perform a colour-space conversion to correctly reproduce an
image. Digital cinema
projectors usually contain colour-space converters which will perform
the task provided they are correctly adjusted for the
content and the effect
of other system components.
for standard-definition television
BT.709 for high-definition television
P7 for digital cinema
cinema projection systems contain powerful colour processors that, when
correctly adjusted, ensure the projected images look exactly as the
intended. Subtle errors in the reproduction of colours will spoil carefully
crafted content and lessen the audience’s experience. The process of
adjustment requires accurate measurement of the whole projection system with
specialist instruments. Once calibrated, the system should not require
further adjustment unless there is some change to the
provided with appropriate colour mapping data, digital cinema projectors can
emulate the performance of other types of projector and even the whole chain
of film printing, processing and projection. This is a really valuable
feature when working with digital intermediates. The ability to get instant
visual confirmation of the affect of changes in colour-correction and
dynamic range dramatically improves the accuracy and speed of this part of
uncompressed digital data for a typical full-length feature film consumes
Terabytes (millions of megabytes) of storage space. Data of this size is
difficult to transport and store so methods of reducing the size have been
developed. Compression processes reduce the size of the data without
noticeably impairing the appearance or sound of the
content. The processes
frequently exploit our understanding of human sensory systems by reducing or
removing portions that convey little or no value.
requirements of digital cinema necessitate very high performance compression
schemes. While some existing methods have been extended to cope with the
requirements, the best results have been demonstrated by schemes that were
designed to specifically meet the needs of high-quality, large-screen
“content” is widely used to refer to a specific piece of material consisting
of visual and/or sound images or to a collection of such pieces. Content
generally refers to the images rather than the form in which they are
embodied so it is important that the physical format is also specified.
may be a particular feature film, a rock concert or a TV programme. This
could be delivered on film, videotape, disk, or by network transmission. In
each case there is more than one possible format so this must also be
specified. Other information may also be required to ensure the content can
be accurately reproduced.
feature film may be available on HD-D5 tape with 1920 x 1080 format frames
anamorphic 2.35:1 aspect ratio images for replay at 24
frames/second. We would also need to know the
colour-space for which the
content was mastered and the number, format and encoding of the soundtracks.
cinema is the electronic projection of
content with a level of quality that
meets or exceeds that of 35mm film. The content used for digital cinema may
have originated on film or have been electronically captured. Reproduction
of the content should preserve the full range of the original image
resolution, colours, contrast and sound tracks.
of quality can only be achieved by equipment and systems designed to
stringent performance objectives. Film supports a huge range of colours and
a wide dynamic range. Normal electronic reproduction and projection systems
cannot reproduce these subtle variations so special equipment is required.
cinema system typically includes a
projector, a sound processor
world of digital cinema, distribution refers to the way in which
a digital form is delivered to the point at which it is to be presented to
an audience. There is no ideal method for all circumstances and the best
solution for a particular application is one that meets the economic,
security and time goals.
distribution is often best achieved through the use of physical media – such
as high-capacity data tapes. At the receiving end, the content is loaded
from the tapes onto a
server for eventual playback. The tapes can be
encrypted to reduce the risk of unauthorised use and are small enough to be
carried by normal or secure postal services. The cost of a tape is very
small compared with that of a film print.
are many sites that need access to the content, distribution by satellite
broadcast may be the best option. A high level of encryption would be
employed to ensure that the content was only of use to the intended
recipients. The content could be presented, live, as it is being received
or stored on a server for later showing. The cost of the satellite
bandwidth necessary to transmit Gigabytes of data may be high but when
shared over a large number of receiving sites, it makes economic sense.
major cities may be able to employ fibre-optic links for fast – even
real-time – transfer of digital content. Networks of “dark-fibres” have
been laid between many cities and a connection point at or near a site may
already exist. This type of link is point-to-point so unauthorised
reception is less likely but some level of encryption would still be
advisable. The cost of this approach varies according to the bandwidth of
the link and the amount of time it is required. It is most suited for
probable that a practical distribution strategy will employ a combination of
techniques and will evolve to accommodate the number of recipients whilst
exploiting advances in digital connectivity.
is delivered in many, increasingly, different forms – in terms of the both
the physical medium and the way in which the images and sound are encoded.
The form in which it is available may not always be ideal for the intended
use and a conversion step may be necessary.
up or down conversion
apparent brightness of a projected image is referred to as its luminance.
There are recognised standards for luminance in cinemas and
produced on the assumption that it will be projected to those standards. If
the projection system does not conform to the standards then the content
will not be reproduced correctly and the audience will not enjoy the
experience as the director intended.
is dependent on the whole projection path from the lamp to the screen. Each
component in the path has an effect on the light which must be considered
for accurate calculation of screen luminance and required lamp power.
luminance of a 35mm film projector is usually measured by running it with no
film in the gate and measuring the light reflected from the screen with a
spot light-meter. The commonly accepted standard for this “open-gate”
reading is 16 foot-Lamberts (55 candelas per square metre). The actual
luminance of a projected image would never be this high as even clear film
would reduce it by about 25%.
projectors have no equivalent to an open-gate reading so luminance
measurements are made during projection of a full-frame, peak-white test
pattern. As this corresponds to the mechanical projection of clear film,
the luminance standard for digital cinema is 75% of the open-gate figure (12
foot-Lamberts) for comparable brightness with actual images.
projectors use electronic masking so that the image can be adjusted
to exactly fit the screen dimensions. Recent models allow independent
adjustment of the position, angle and curvature of each edge of the
projected image. This is equivalent to an electronic version of a film
projector aperture plate but is a lot more accurate and can be changed in an
instant. Correct adjustment of the electronic masking can dramatically
improve the appearance of the image and improve the audience’s experience of
content. Adjustment of the projector masking must take into account all
aspect ratios that may be required as well as the physical properties of
the screen, its fixed or variable masking and compatibility with film
suitable for digital cinema, projectors must meet stringent objectives for
image quality. The electronic reproduction of images to, and beyond, the
performance of 35mm film projection requires special capabilities. In
particular, a digital cinema projector should meet or exceed the
characteristics of film projection in the following areas:
gamut – the range of colours that can be individually perceived
ratio – the dynamic range of brightness between extremes of
the visibility of fine details in the projected image
portrayal – depiction of movement within the image
output – to achieve optimum image brightness at required image size
cinema systems also offer noticeable advantages over film projection in the
stability of the image (absence of film-weave and focus-flutter),
repeatability (no wearing or scratching of the film) and lack of visible
standards are still under development but hundreds of cinemas are already
benefiting from the technology. These sites all have systems based on
Cinema technology from Texas Instruments. This technology was the first to
be approved by the major Hollywood studios for projection of feature films
and has been deployed in real cinemas across the world for five years. DLP
Cinema projectors – incorporating the technology – are available from three
manufacturers and their worldwide representatives:
Barco Digital Cinema
Christie Digital Systems
Digital Projection Cinema
for digital cinema is stored and distributed in very high quality digital
form. The owners of the content, quiet reasonably, want to ensure that
their product is protected from unauthorised reproduction or modification.
This requires appropriate levels of security for each situation where the
content is stored or transported.
content is present on
servers or storage media, physical access should be
limited to authorised personnel. Server access should be controlled through
the use of individual user identification and passwords – which should be
subject to periodic, mandatory change.
be encrypted so it can only be loaded and played on servers when a security
key is present. The key – either physical or in the form of software – can
be set to be valid for limited periods of time. The encryption may also
encompass the link between server and
projector to prevent electronic
copying of the content during playback.
where content is vulnerable – just as much with film as with digital cinema
– is with copying through the use of camcorders in the auditorium. There
are some promising developments in image processing that could, in future,
prevent this form of piracy for digitally projected content. Until then, it
is common for content to be unobtrusively marked (watermarked) by the owners
so that illegal copies can be analysed and the source identified. This
technique can be enhanced, with digital cinema projection, by including in
the watermark details of the date and time of the screening in addition to
the location of the cinema.
cinema server provides the means to store and play digital
generally employ arrays of hard disks to store the content. High-quality
content requires a lot of disk space – even when
compressed – so server
storage capacities will be several hundreds of Gigabytes (thousands of
megabytes) or a number of Terabytes (millions of megabytes).
usually provide a number of ways in which content can be loaded into
storage. Digital tape cartridges are frequently used to transport content
but optical disks (DVD-R) and removable hard drives are also often
supported. In addition it is common for servers to have Ethernet ports to
allow content to be transported by various types of network.
cinema content is generally compressed to avoid the need for impractical
sizes of storage media. Servers incorporate hardware and software to
decompress the content during playback. Servers
usually offer high levels of
security to prevent unauthorized copying or
playback of restricted content. In some cases the content will only play on
a server if a time-sensitive, site-specific key value is provided.
Server suppliers include:
EVS Digital Cinema
Technicolor Digital Cinema
QuVIS Digital Cinema