Recommendations on selecting a projector and a screen
1. What is multimedia projector?
A multimedia projector or a digital projector is a modern high-tech information display device that connects directly to either a computer signal source or to a video signal source (camera, DVD-player, satellite TV system, etc.) to project any size image (depending on the user’s choice and according to the technical capabilities of the projector).
Digital projectors require no special software, they work like PC monitors or TV sets. Any projector, just like a PC monitor or a TV set, has brightness and contrast adjustments, etc. Digital projectors need no complicated and frequent adjustments, they have only several control buttons and a convenient on-screen menu (in Russian as well).
The only replaceable part of the projector is the projection lamp. Multimedia projectors use special high brightness lamps with more even spectrum in comparison with the conventional incandescent lamps. Average lamp life is 2,000 – 3,000 hours in Standard operation mode. The projectors also have “Economy operation mode” function, which considerably increases the lamp life time.
Active development of projection technologies resulted in the launch of the new type of digital projectors – free of lamps. The conventional lamps in such devices were replaced by so-called LED, Hybrid (Laser/LED) or Laser light sources. Average life time of such a light source is not less than 20,000 hours in Standard Mode. Brightness of LED mobile projectors nowadays achieves up 1,000 and Hybrid/SSD mobile projectors – up to 3,000 - 4,000 ANSI-Lumens. On the market are already available Laser and Hybrid light source installation projector with up to 15,000 ANSI Lumens Brightness.
By weight the projectors can be divided into 2 main categories: a) mobile devices (weight up to 5 kg) and b) stationary (installation) projectors (weight more than 5 kg).
2. How does
multimedia projector operate?
The image in digital projectors is formatted by means of a powerful light source and a special converter of the input signal into an image based on LCD (TFT) matrixes (LCD technology) or DMD micro mirror chips (DLP technology).
In LCD projectors light is passing through LCD panel on which, like on ordinary film, a picture is created by digital electronic circuit. The light passing through the panels and the objective results in the image being projected onto the screen.
In DLP projectors light is reflected from a set of electronically managed micro mirrors with dimensions of 16x16 micron and projected onto the screen through the objective.
characteristics of the projector
Brightness and image resolution are the most important features of any display device (digital projectors, LCD or plasma displays, Video Cubes, etc.). By brightness of the projector we mean a light flow, or the amount of light emitted by the projector.
Light flow depends neither on the screen size nor on the throw distance and is measured in lumens (or ANSI-lumens – in this case, in accordance with the acting International Standard, the measurements are done in 9 points of the screen at specially adjusted brightness and contrast of the projector, and then are averaged).
Light flow (Brightness) depends on the construction of the projector, the quality of LCD panels or DLP chips, power and the type of the light source installed in that particular projector.
Average brightness of contemporary projectors goes beyond 2,500 – 3,000 ANSI-lumens (practical standard for office use), which is enough for conducting presentations at ordinary artificial or scattered daylight. At present, the maximum projector brightness achieved is 40,000 (!!!) ANSI-lumens (Christie Digital projectors).
Please note – when choosing a projector for presentations you should keep in mind that your device should provide at least 500 lumens per square meter brightness.
Quite the opposite situation is with Home Cinema projectors – you should take into account that the darkened or at least semi darkened rooms are the most convenient for film screenings. That’s the reason the brightness of Home Cinema projectors rarely exceeds 1,500 ANSI-lumens.
Resolution of digital projectors is measured in pixels (picture elements) and is defined as native (basic) and interpolated. Any projector has a function of digital interpolation. (compression or expansion) of the image and is able to operate with resolution at least 1-2 steps higher or lower than the native one.
Basic or native (physical) resolution is the density of the image displayed and is determined by the amount of physical pixels along one line and the number of these horizontal lines. This value allows to determine how many pixels are physically used to create the image.
Interpolated resolution is the ability of the device to display the information different from its native (physical) resolution. The interpolated image is generated by Video processor of the device using special mathematical algorithms. Please note - the quantity of physical pixels creating the interpolated image never changes and always corresponds to native (physical) resolution of the display.
| 1|| native SVGA *|| 800 x 600 pixels / total 480,000 pixels || Format 4:3 |
| 2|| native XGA ||1,024 õ 768 pixels / total 786,432 pixels || Format 4:3 |
| 3|| native WXGA ||1,280 õ 800 pixels / total 1,024,000 pixels || Format 16:10 |
| 4|| native SXGA ||1,280 õ 1,024 pixels / total 1,310,720 pixels || Format 16:9 |
| 5|| native SXGA+||1,400 õ 1,050 pixels / total 1,470,000 pixels || Format 4:3 |
| 6|| native UXGA ||1,600 õ 1,200 pixels / total 1,920,000 pixels || Format 4:3 |
| 7|| native Full HD ||1,920 õ 1,080 pixels / total 2,073,600 pixels || Format 16:9 |
| 8|| native WUXGA ||1,920 õ 1,200 pixels / total 2,304,000 pixels || Format 16:10 |
| 9|| native 2K ||2,048 õ 1,080 pixels / total 2,211,840 pixels || Format 1,85:1 |
| 10|| native 4K ||4,096 x 2,160 pixels / total 8,847,360 pixels || Format 1,85:1 |
| 11|| etc.||- || - |
* Projectors with native SVGA (800 x 600 pixels) resolution are mainly discontinued by the world’s leading manufacturers.
The higher is the basic (native) resolution the more detailed image this device is capable to display. The higher is the native resolution, the more information is displayed. For example, WXGA LCD panel or DMD Chip has only 1,024,000 pixels while WUXGA has 2,304,000. Regardless of the image creation technology, each visible pixel is an active element of the matrix. The more pixels there are in the matrix – the sharper and the more detailed is the image. Naturally, the higher is the native resolution the more expensive is the display device.
Of course not all of the above listed resolution values are widely used in the industry. Prevailing on the market are: a) projectors for presentations with native XGA, WXGA, Full HD and WUXGA resolutions and b) projectors for Home and Professional Cinema with native Full HD, 2K and 4K resolutions.
When choosing a projector the following question often arises: “What resolution is required in case the projector is to be mostly used for video demonstrations?” Having taken into account the fact that Full HD (1,900 x1, 080 pixels) resolution has become the de facto standard for Home Cinema the recommended minimal native resolution should not be less than native WXGA (1,280 x 800 pixels). The progressive price fall of native Full HD projectors makes such a purchase not only affordable, but also economically justified (Return of Investment - RoI).
While choosing the video signal source it is necessary to keep in mind that Blue-ray player has Full HD (1,080 TV lines) output resolution while the now almost-forgotten VHS video recorders had the maximum resolution of only 240 TV lines (TVL), S-VHS video recorders and analog video cameras - 400 TVL.
Contrast ratio is an important indicator for assessing the image quality of the display device. Its value determines the shades transmission depth - image distinguishability details in the darkest and brightest areas. Used in projectors DLP technology generally provides a higher contrast than LCD-technology.
There are also such definitions as Static and Dynamic contrast. The latter has more higher value and is achieved by means of specially designed automatic diaphragms (IRIS) mainly used in Cinema projectors.
It should be noted that Contrast Ratio of regular office projectors higher than 3,000:1 claimed by some manufacturers is nothing more than a so-called "Marketing ploy" and is completely untrue. See for yourself, DLP-chips are still produced by >only one company in the world (Texas Instruments) and the same chip used by different manufacturers can not provide drastically different contrast ratios in different projector models. Please also note - according to the authoritative study by HP the human eye is not able to distinguish the contrast (the ratio of white to black) higher than 1,000:1.
Functional abilities of multimedia projector
Every digital projector has several inputs: one or two inputs for computer signal (RGB or/and DVI) and some inputs for video signal (composite, S-video, Component or/and HDMI). The majority of the office projectors have special output for connecting the PC-monitor (function “Monitor out”) very convenient for the presentations conducted from a stationary PC.
Many stationary (installation) projectors also have a Picture-in-Picture (PIP) function, which gives the possibility to simultaneously display images from 2 different sources in additional window inside the main large image . This function is realized in multimedia projectors, LCD/plasma displays and equipped with 2 TV tuners TV sets.
All the mobile projectors are equipped with sound amplifiers and loudspeakers, volume of which is generally ample for average sized rooms. The majority of projectors have also the audio output for connecting with the outside audio equipment.
All the projectors on the market are multi-system and work with all the acting video standards (PAL/SECAM/NTSC). This means that you can project any TV program, video camera signal or DVD disc.
Practically all multimedia projectors have lenses with variable focal distance (so called vario objectives). These kind of lenses give the possibility to change the image size without moving the projector itself. In the majority of projectors the focal distance is changed manually. Installation models are equipped with motorized objectives permitting image scaling via a remote control unit.
Manual control is quicker and more precise, but the motorized objectives are more convenient for remote control, e.g., when the projector is fixed high under the ceiling.
Short-Throw projectors are usually equipped with lenses with a fixed focal length (Fixed Zoom). Short-Throw projectors are mainly used with interactive whiteboards or for Rear projection in cases of very limited distance to the screen (video cubes, special projects).
Practically all the stationary (installation) projectors are equipped with interchangeable lenses: additional telephoto lenses allow the use of these projectors in big halls while wide-angle lenses allow the use in the conditions of limited space, for instance, behind the Rear Projection screens.
Many projectors can be controlled via a PC. For this purpose the projector should be connected to PC by RS-232 or USB interface and all the commands can then be directly sent from the computer. It is possible to control presentations directly from the projector connected to the computer via a COM or a USB port.
Active development of network technologies affected the multimedia projector market as well. Some of the latest projectors have the built-in network concentrators, which allow to connect several PCs in a single network within one room, as well as to connect this network to a LAN or Internet.
It should be taken into account that for the overwhelming majority of the models connecting the projector to PC via wired Ethernet interface (RJ-45) will only allow control of the projector from the PC, but not data transmission. Meanwhile some Mitsubishi projectors equipped with LAN Display function are capable of projecting data received via LAN.
It is important to especially mention the projectors equipped with wireless network adapters (built-in or optional). The possibility of data transmission between a computer and a projector via radio channel substantially facilitates the presentation as it allows to get rid of numerous cables.
However, the special attention should be paid to the fact that it is still practically impossible to transmit live video even using currently the fastest data transmission protocol 802.11n.
All the projectors are equipped with Remote Control units (RC) that allow to distantly adjust projector brightness, sound volume, resolution, focus and zoom (the last 2 functions are only for the projectors equipped with the motorized lenses), to change inputs (computer/video), etc. In some models RC is combined with a remote mouse (for a remote control of the PC) and has a built-in laser pointer.
There is no such thing as “the best” or “the most universal” projector. Listing of technical characteristics and functional capabilities finally pursues the only one goal - to assist you in choosing the best corresponding to your needs model. The selection of the projector depends primarily on such factors, as where and how it is planned to be used, at what lighting conditions; will it be a stationary (installation) model or the projector will often be moved from one place to another, etc.
5. How to choose the most suitable for your requirements projector?
When planning a projecting system first of all it is necessary to take into consideration the interrelation between the projector brightness (ANSI lumens) and the size of the projection screen. The higher is the brightness of your projector the larger image size can be obtained at given lighting conditions and screen’s material quality.
For rooms with high ambient light you should have 500 – 600 lumens of light output for a square meter of the screen.
When you have less than 250-300 lm/m2 the room should be partially or completely darkened. This is because when the size of your projection screen is, for instance, 3.0 x 2,5m and the brightness of your projector is about 2,000 lumens you have only 296 lumens per m2, which means the image will be visible in a partially dimmed out room. There is only one solution – either to increase the brightness of the projector or to decrease the size of the screen.
Outdoor projection using standard quality screens is possible only in the late evening and nighttime. In the daytime, such demonstration is possible only in the absence of direct sunlight, usage of the most powerful projectors and very specific and rather expensive projection screens.
When selecting equipment for Home Cinema it is recommended to choose the high-contrast DLP models or the high-contrast LCD projectors specifically designed for film screening with special hardware processing algorithms for color space. As of today, the ideal choice would be the native Full HD projectors certified to HQV (Hollywood Quality Video) standard.
For professional movie-screenings are used only the projectors that fully correspond to DCI (Digital Cinema Initiative) standard. Nowadays only three manufacturers in the world (Christie, Barco, NEC) have models certified to this standard.
6. How to choose a projection screen most suitable for your requirements?
There are several very simple rules that will help you choose the right projection screen.
1. Sizing a projection screen to the room :
Choosing the correct projection screen is of great importance. The purpose of the projection screen is twofold: to display the visual information without loss of image quality and to direct the projected light towards the audience. Both requirements must be satisfied in order to ensure optimum perception of the projected image. If you want everyone in the room to see what is on the screen, make sure you use the right size projection screen.
The use of high resolution projectors in most applications creates quality images with great detail. This higher resolution also implies smaller font text and images which has its effect on the correct choice of projection screen size.
The InfoComm International standard therefore recommends the following rules to determine the correct size of the projection screen:
- 16:9 HDTV and 16:10 WIDE aspect ratios
You can calculate the diagonal of the projection screen by dividing the room depth by two.
- 2.35:1 CINEMASCOPE aspect ratio
To calculate the correct dimension for a 2.35:1 aspect ratio, you can use the following rule. The height of a screen should be 1/4 of the distance from the screen to the last row of viewers.
- 4:3 VIDEO aspect ratio
To calculate the correct dimension for a 4:3 aspect ratio, you can use the following rule. The height of a screen should be 1/6 of the distance from the screen to the last row of viewers.
You should also consider:
2. Optimal positioning of the projector and the signal source:
It is always necessary to take into consideration the distance between the signal source and the projector: Please note -at distances exceeding 10m data (analogue VGA or DVI) and digital video (HDMI) signals should be amplified, and the special signal amplifiers should be placed at every 10m. It is also possible to use high quality and rather expensive cables by some manufacturers (Extron, TLS, etc.) that don’t require amplification for a distance of up to 20m.
- Ceiling height - take it into account in your calculation as this is often a limiting factor.
- Comfortable viewing height:
- For professional and educational applications the distance between the floor and the viewing area of a projection screen should be not less than 135 - 150 cm to make sure those sitting in the rear of the audience can see the projection.
- For home entertainment applications this distance should be between 60 and 90 cm.
- Comfortable viewing distance to top..
- For professional and educational applications the first row of seats should be approximately 1.5 screen heights away.
- For home entertainment applications the first row of seats should be approximately 2 screen heights away.
As to analogue video signals (composite, S-video or component), they will not substantially deteriorate up to 25 – 30m of the cable’s length.
3. The choice of the projection type:
It is necessary to determine the type of projection: front or rear projection, ceiling installation or placement on the table.
It is also necessary to determine the distance between the projector and the screen. Depending on the distance there might either be a need to substitute the standard lens of the projector (if such an option is available for your projector) with a special one (short- or long- throw) or the standard lens will be quite enough.
Also, it should be mentioned that the black frame, well known by everyone from cinema screens, increases the contrast of the projected image and reduces the need to adjust the image.