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Thematic glossary
THEMATIC GLOSSARY
- What is the difference between a large video screen and a video projector?
- How to choose the dimension of the screen for an event?
- What is a “pixel”?
- How to prepare the programme to broadcast on a large video screen?
- How much power is needed for a screen and how to provide this power supply?
- How does Supervision get involved in the installation and operation of a large video screen at an event?
- What are the items to be considered when integrating the installation of a large video screen in a project?
1. What is the difference between a large video screen and a video projector?
A full daylight large video screen and a video projector are both technologies for the reproduction of a video image. However, the difference liesin the way the image is produced with a totally incomparable result in terms of brightness.
A video projector is very similar to a cinema projector: it sends a light ray through the video image (via a special device) and the video image is reproduced on a screen or any other white surface. This technology requires very low light conditions in order to have a better reproduction of the video image.
A large video screen “emits” light through millions of tiny colour dots which compose its final surface. These full colour dots are very powerful and bright even under the strongest sun, this brightness being reinforced by the presence of “shaders” comparable to real “sunhats” under each horizontal row of dots.
These millions of colour dots (the minimum required being 50.000 to have an acceptable definition) are responsible for reproducing the final video image for the spectator's eyes.
2. How to choose the dimension of the screen for an event?
According to the maximum distance of the audience
As a guide, please consult the following chart for screens in 4/3 format:
|
Maximum distance of the audience |
50 m |
75 m |
100 m |
150 m |
200 m |
250 m |
300 m |
|
Recommended minimum surface in m² |
5 to 8 |
11 to 15 |
20 to 25 |
35 to 45 |
50 to 60 |
70 to 80 |
90 to 100 |
According to the setting
The location and the environment will certainly determine the dimension of the screen either in a positive or a negative way depending on how important the venue is.
The above parameter, together with the audience distance from the screen, is necessary to choose the dimension of the equipment.
For example, spectators in a soccer stadium, placed in front of an 8 m² screen, will certainly have the impression of a small screen even if the distance is correct.
If the same screen is installed in a small square or a yard, spectators will have the impression of being in front of a bigger screen.
A 5 m² screen in the stage of a podium car (stage of approx. 3 m height x 10m width) will always impose; whilst the same screen installed in an open space without setting will seem much smaller.
This element is variable. We may always give you some recommendations provided you know in advance the configuration of the installation site and the nature of the event.
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3. What is a “pixel”?
The image surface of a large video screen is composed of a thread of “pixels”. The pixel dimension of a screen will determine the resolution, and the fineness of image on the screen.
In a full colour video screen, a “Pixel” is the smallest full colour dot able to combine the three basic colours of light (Red, Green and Blue) and to produce a resulting colour. More than 50.000 pixels are necessary to produce a sufficiently distinct image (192 pixels height x 256 pixels width).
There are two types of “pixel”:
Fixed Pixel
All three colours are processed by the image-processing system of the screen in order to produce a final colour per pixel. The dimension of the pixel corresponds exactly to the dimension of the smallest group of Led or Crt combining the three colours and processed simultaneously.
Dynamic Pixel
Each colour dot is processed separately by the image-processing system of the screen and the spectator's eye composes the final colour. The dimension of the pixel is variable according to a fixed or motion image broadcasting.
An effective method for comparing fixed pixel definition with dynamic pixel definition is to consider that the dynamic pixel dimension measures 1.5 times the dimension of each line of colour dots of the dynamic pixels. (This “rule” is almost always valid).
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4. How to prepare the programme to broadcast on a large video screen?
Since a large video screen is a real giant television, it is possible to broadcast any type of video image, on any format, including images produced with a computer.
The image sources may be the live television broadcast, the image recording on site, video cassettes, CD Rom…
Our screens integrate special conversion devices allowing the processing of almost any type of signal. Others require the inclusion of these conversion devices.
In fact, the screen itself presents no broadcasting limitations, and the only restrictions encountered apply to the resolution required for certain images (i.e. web pages with many details) and the necessary dimension of the images depending on the reading distance.
Supervision is also able to provide specific video equipment for the preparation of a special programme: character generator…
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5. How much power is needed for a screen and how to provide this power supply?
Full daylight large video screens require approx. one Kva per m².
Nevertheless, we double the required power supply in order to be able to respond to any strong power requirements since changing from black to white increases the demand (changes that may occur in 1/60th of a second), and to avoid any risk of voltage failure on the image processing system, which would certainly create a conflict and thusrequire to the re-initialisation of the whole system…
In the technical data of each screen we provide the required power supply according to its dimension.
Power supply may be provided by means of:
- direct connection to the city power supply, with a P17 plug 3 phases + neutral + earth, with a different amperage depending on the type of screen (see technical data)
- power generator with electronic regulation
6. Supervision involvement in the installation and operation of a large video screen at an event:
- Transportation of the large video screen to and from the site
- Installation and dismounting
- Video and electrical cabling
- Specialised technicians for the operation of the screen
- Provision of a broadcasting control room
- Possibility of taking care of the provision of the scaffolding structure, power generator, crane, and even the image recording on site
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7. What are the items to be considered when integrating the installation of a large video screen in a project?
Convenient access
Without a site visit beforehand by Supervision, it is recommended that the client verifies the equipment access possibilities and the feasibility of its installation.
Particular care should be taken withthe heavy weight truck access and on the manoeuvring possibilities when positioning the truck mounted large video screen once on site, as well as on the ground weight resistance of the concerned areas.
Programme to broadcast
The client is responsible for the content of the programme to be broadcasted on the large video screen. However, at the client's request, Supervision may be responsible for the recording of images, edition, television and satellite signal reception…
Power supply
The client is in principle responsible for the power supply of the screen, but at the client's request, Supervision may also provide a power generator as part of the service.
Authorisations
The client is responsible for obtaining all the necessary authorisations for the accomplishment ofits event and for the installation of the required basic technical structures and equipment, including the large video screen.
The clientis also responsible for the broadcasting authorisations, if necessary.
Regarding the support structures of the screen to be certified by a Security Commission, Supervision (or the local supplier) provides the Calculation Report approving the installed structures.
The Security Commission may require an independent third party in which case the client will be in charge of asking for a counter-valuation by a duly authorised consultancy firm (Socotec, Bureau Veritas, CEP…).
Sound
Supervision is in a position to provide a simple sound system for events not requiring extraordinary means.
Do not hesitate to ask if the sound system of the large video screen and/or the event requires our involvement. We will guide you in the selection of the appropriate sound company.
Insurance
It is the client's responsibility to insure the organisation of the event (full coverage insurance including civil responsibility etc….
Supervision large video screens are covered by an “All Risk Policy” withinthe Risks of Physical Loss and/or Damage Insurance. Nevertheless, the client's responsibility may be involved in the event of “Serious Fault” or proved negligence by the client.
It is highly recommended to the client to thoroughly verify security at the large video screen installation site (access routes and installation site weight resistance), and to install security barriers around the screen, both for the audience and the equipments' protection.
Installation structures
In agreement with Supervision, and particularly when dealing with installations far from Supervision's warehouse, it is normal procedure that the client is in charge of the scaffolding structures construction, the crane and/or forklift rental, the supply of local manpower…
