Video projector

A video projector (including projector, digital projector, data video projector), colloquially usually Beamer [ bi ː mɐ ] (pseudo - English word coinage, derived from English beam, dt " beam " ) is a special projector, the images from a visual output device ( television receiver, computer, DVD player, VCR, etc. ) for an audience projected in enlarged form on a screen. The range of equipment ranging from small presentation projectors for mobile use up to stationary high-performance projectors.

• 3.1 luminosity
• 3.2 throw ratio (also Throw Ratio )
• 3.3 Positioning and keystone
• 3.4 Volume and noise

Display method

Video projectors can be fundamentally different in terms of the projection method used.

Eidophor system

The Eidophor system was the first system that could provide high-resolution images, the high-intensity and was common in the professional field until the late 1980s.

CRT projector

The first video projectors wider dissemination used special cathode ray tubes for the representation of the image. These tubes were trimmed to very high brightness to provide enough light for projection. For color projectors are three tubes - one for each primary color - used which have separate lenses. The brightness and the supported resolution generally increases with the tube size, there are now three main sizes for projection tubes namely 7, 8 and 9 inches. In terms of the highest possible sharpness of the electron beam, a distinction between ES ( electrostatic) and EM ( electromagnetic) focusing devices. EM devices can project an extremely sharp image at the correct setting. 9 -inch devices with EM focus found today in high-resolution flight simulators and high-end home theater use. 7-inch and 8- inch models have often been used in the past in rear projection televisions.

Advantages:

• Because of the picture tube, the projectors are very variable in the resolution. You can generally represent from NTSC to 1080p and 3D material ( Bluray 3D, 3D sequential ).
• The method has no pixels ( picture elements ). Thus, the images are somewhat blurred, but represented more natural.
• There is almost no lag time. This video is interlaced ( interlacing ) no problem.
• There is no lamp required, as the tubes themselves produce light and have typical lifetimes of at least 10,000 hours.
• The tubes produce very high contrast ( 10,000:1 to 30,000:1 ) and very good black levels.

Cons:

• Relatively low overall brightness. The room must be completely darkened on most models.
• The tubes are very susceptible to burn-in. Will Make the luminescent layer excited too strong or too long, they darken from there gradually.
• Since the three projection systems work separately with color projectors, they require a very elaborate setup procedure. The difficult mobile use.
• The projectors are through the tubes very hard.
• Apart from older used models are only built a few new devices ( Barco, VDC).
• Good used or new devices are still very expensive.

LCD Projector

Liquid crystal projectors (LCD) function in principle as slide projectors, instead of a slide are one or more transparent active-matrix liquid crystal display driven by thin film transistors are used. Nowadays, conventional devices use three separate LCD matrices ( 3LCD ) - one for each primary color - whose projection is assembled on a specially arranged projection system with dichroic mirrors to form an image. Thereby can be generated in each pixel, each color. Particularly high-quality devices use an optical unit with four separate LC matrices, a matrix is ​​used specially for the differentiated and high-intensity display of yellow. This allows you to connect high light output with good color balance, which conventional devices with three LC matrices quite difficult - their green display has a slight yellow tinge, a correction of the color cast is usually associated with a fairly high brightness loss. For devices with only a liquid crystal display are the three basic colors like LCD flat screens by three, arranged side by side, shown integrated matrices, which results due to the reduced resolution to a coarser image impression.

Advantages:

• Relatively inexpensive
• Easy to read text and graphic by the sharp demarcation of the pixels
• Small and light
• Compared to a single-chip DLP projectors the same light output class much better color intensity

Cons:

• The sharp initialed pixel structure ( "screen door " / screen door effect) can be perceived disruptive, HD projectors, however, no longer suffer as much from this problem as earlier XGA devices.
• Because of fixed display resolution in the device the best quality is given only at a specific resolution of the input signal. Otherwise, a quality-reducing scaling is necessary.
• In early devices: tightening of the image by the inertia of the LCDs.
• Liquid crystals have a relatively limited operating temperature range. Measures must be taken to ensure that the clearing point is not reached ( the transition from the liquid crystalline to the liquid phase ) ( infrared filter, high velocity fan ).
• LCD memory effect ( burn-in ): Will Make stimulated for too long with too bright images, so these places are slowly permanently dark. After a few 1000 hours of operation the electro- optical properties of a layer of organic liquid crystals due to the high light intensity (particularly the short-wavelength light component ) are permanently disrupted. With the use of polarizing films containing organic dyes and their optical properties can be reduced. Thus, the properties of the projector ( contrast, color spectrum) are impaired. Inorganic LCD panels, which are increasingly being used since 2008, this shortcoming have according to the manufacturer and no longer have a " much longer " as yet unspecified life.
• Noise from fans
• Sensitivity to dust and smoke, because both the lamp and the LCD of fresh air must be cooled. Encapsulation and sealing of the optical unit is not possible (unlike DLP projectors ). In very dusty or smoky environments, the image quality can therefore be claimed quickly.
• Faulty convergence in multi -panel projectors is possible.

DLP projector

As imager of a DLP projector (Digital Light Processing ) is a Digital Micromirror Device (DMD ) is used, an integrated circuit, on which there is a tiny, tiltable mirror by an electrical pulse for each pixel. The imaging is effected by selective actuation of the steering mirrors so that the light is directed or deflected towards the projection optics. Since this type of imaging only knows two states on and off, brightness levels must be achieved by a rapid pulsation. The DLP mirror switch up to 5000 times per second.

Most of the devices used for forming a color image of a rapidly rotating color wheel, wherein a DMD successively all three primary colors are projected. In DLP projectors newer design, the number of color segments was increased to six to seven to at color mixtures to achieve more accurate results. Noteworthy is the use of a transparent segment in the color wheel in all recent single-chip DLP projectors, which are not specifically designed for home theater use. This has the advantage of a higher light output in the display of white areas. However, the transparent segment of the color light at the expense of performance, which DLP projectors in the projection on major surfaces have a visible appearance and poorer color intensity. For projectors for professional use (eg cinema) three separate image device ( DMD) are used. LED projectors switch the colors around electronically.

The sole owner of the DMD technology is the production company Texas Instruments (Ti)

Advantages:

• Very high speed, therefore no afterglow or tightening of the image, thus very suitable for 3D projection
• No image retention (eg, computer games)
• Higher contrast ( through the blacker ) than the LCD projector
• Less pronounced than pixel structure of LCD projectors
• By sealed optics and durable DMD less sensitive to dust than LCD projectors.

Cons:

• Because of fixed display resolution in the device the best quality is given only at a specific resolution of the input signal. Otherwise, a quality-reducing scaling is necessary.
• Rainbow effects in some devices with color wheel when the wheel has no high rotation speed ( depending on the manufacturer ).
• In the representation of certain individual gray or color values ​​can cause a visible flicker.
• Color fidelity is sometimes given. In particular, DLP projectors have a problem to display rich green and all red and orange hues. This concerns mainly the consumer devices ( single-chip DLP), as these units Farbradtechnik is employed.
• Devices with white segment have a poorer color light output than LCD projectors the same brightness class.
• Noise from fans and color wheel

LED Projector

With LED projectors are LEDs ( Light Emitting Diodes) as the light source used. Imaging technique was initially a DLP element. Newer video projectors employ the LCD technology.

Since the light output of LEDs is not particularly high, especially in the countryside 540-610 nanometers wavelength, there are hybrid products where the green light is generated instead of a light-emitting diode by a laser diode.

Advantages:

• LEDs have over traditional projector lamps more energy efficient: the same lighting performance, less energy is converted into heat, causing the cooling demand decreases.
• The reduced cooling requirement allows smaller packages and lower fan noise (in the extreme case of passive cooling).
• The lower energy requirement allows operation with a battery.
• LEDs last more than 20,000 hours, whereas conventional projector lamps last around 4,000 hours.
• Since the colors are formed by sequential illumination of the RGB LEDs, also falls normally necessary for DLP projectors color wheel away.

Cons:

• Because of fixed display resolution in the device the best quality is given only at a specific resolution of the input signal. Otherwise, a quality-reducing scaling is necessary.
• The light output of LEDs is sometimes considerably lower than in conventional projector lamps. Especially convenient devices have sometimes only 1/100 of the light output of conventional projectors. In summer 2011 there was the first LED projector with 1,000 ANSI lumens.
• A permanent reduction in luminous flux of the LEDs makes the image appear to be steadily darker. An LED is possible to change some not readily available. A partially used adaptive increase the LED current can compensate for this loss of brightness again.
• Even without color wheel it comes with the DLP - based models to the rainbow effect, as the basic colors are projected one after another.

LCoS Projector

In the LCoS technology (Liquid Crystal on Silicon), which also liquid crystal displays are used, the LCDs in the reflexive mode can be used. Unlike the DLP technology, this LCD technology is represented at the different manufacturers by different brand names such as SXRD (Sony ) or D -ILA or DLA ( Sanyo). The projection optical system is similar to that of a DLP projector, as the liquid crystal displays are mounted on a reflector with underlying control electronics. The main advantage of the LCoS chips is that the signal lines for controlling the individual pixels behind the mirror surface, so that the distances between the pixels compared to a conventional LCDs will slow down, causing the well-known "screen door " effect is reduced significantly and higher contrast and in particular, deeper blacks are to be realized

Advantages:

• Compact design
• Sharp images
• Low light loss when using high-resolution LCDs

Cons:

• Because of fixed display resolution in the device the best quality is given only at a specific resolution of the input signal. Otherwise, a quality-reducing scaling is necessary.
• Light drag on the image
• LCD memory effect
• Decreasing image quality with increasing operating time ( reducing color saturation, contrast, and homogeneity )

Laser Projector

The previously developed for the professional market techniques rely on a screen layout with the help of a modulated laser beam deflected and quickly. Two different techniques are known: the laser display technology (see below) and the GLV technology ( Grating Light Valve ). Strictly speaking it is not a projection - Lenses are solely for the beam expansion, not the illustration.

When developed in Gera and Jena Laser Display Technology (LDT ), the image is written line by line on the screen. Deflection is performed by a special scanner with a facet mirror ( line structure ) and a tilting mirror (line feed ). The laser beam is modulated previously, which the brightness and color of each pixel are defined. In contrast to the GLV technology speckle effect of the laser with the LDT is almost completely suppressed. For this purpose, the laser beam is pulsed in the picosecond range. Risks caused by the laser beam can be excluded by the combination of different security techniques. Projection systems, laser display technology are in use for flight simulators. Here is an entire hemisphere is illuminated with four projectors (360 ° horizontal × 90 ° vertical).

Advantages:

• Almost arbitrarily shaped projection
• No focusing necessary
• Large gamut by the mixture of pure primary colors ( RGB ), ie monochromatic light

Cons:

• Limited light intensity
• The laser projectors are classified as laser class 3R (GLV ) or 4 (LDT ), the operation is therefore permitted only by properly trained personnel.
• Potential hazard to the eye through directly into the eye -guided radiation

Alternatively, there are also approaches in which fanned the laser beam and with a conventional imager combined (eg LCoS ).

Field of application

Depending on the application, some of the above projection techniques are more suitable than others.

For the projection of films, it is sensible to use projectors with widescreen ( eg 16:9, 16:10 or 21:9 ), since it black bars at the top and bottom of the screen can be reduced. Home theater projectors of this type are based on a well- darkened screening room and are not designed for excessive brightness, but rather a natural color representation. They often have large fans which rotate slower for the same air mass movement and cause less noise.

Due to a very good black level many DLP projectors have a very large contrast ratio of up to 4000:1 compared to other projection technologies. For optimized home theater LCD projectors achieve peak dynamic contrast ratio of 10000:1, primarily through use of a mechanical iris diaphragm, which reduces the light output for dark images. The In -image contrast of LCD projectors located behind the DLP projectors, as LCD technology lets through even when black pixels detected residual light. This degrades the black level and reduces the possible contrast.

For presentations you still used historically to date often the 4:3 format. More and more, the 16:9 sets - or 16:10 aspect ratio by in the office environment, because both laptops as well as the display of desktops are delivered in this format. The availability of office video projectors with this ratio therefore rises continuously. Video projectors of this type are often designed for large projection brightness in order to also not particularly darkened offices produce a visible image can. It often suffers from the color fidelity ( accuracy of color representation).

Technical aspects

Luminosity

An essential criterion for the usability of video projectors with a larger projection distance or large projection screen is the brightness.

Commercial video projectors have luminosities 1000-4500 lumens, large models for conference rooms or Lichtspieltheater also to 30,000 lumens. The actual usable light output depends on the settings of the projector in terms of contrast and color gradient from. With a balanced, natural color mixing, he is sometimes significantly lower than nominally specified. The brightness information from the manufacturers contain comparatively large tolerances. Usually the difference is 10-20 %. In principle, the lamp aging leads to a loss of brightness. After her life specified by the manufacturer is reached, the brightness will still be 50 %.

Since the bulbs usually used to convert a substantial portion of the supplied electrical energy into heat, they have to be cooled, usually by fan. Very compact and very powerful video projectors therefore fall on acoustic.

Home theater models have in addition usually larger fans partly through a so-called Eco mode, in which the brightness and the fan speed is reduced, causing less noise. In addition to this noise reduction, the lamp life can be lengthened and reduces the burn-in LCD.

Throw Ratio (also Throw Ratio )

With the throw ratio can be at a given distance, the picture size (or size range ) or directions to a desired image size of the required projection distance.

The throw ratio is the ratio of projection distance from the screen width and is dependent on the used lens. Since the devices are usually equipped with a zoom lens, an area is specified for the mapping relationship. At a projection distance of 6 meters, so a zoom lens with the projection ratios from 1.8:1 to 2.3:1 results in an image which has a minimum width of 2.61 meters and a maximum width of 3.33 meters.

The image width is calculated as follows, the image height can be determined from the aspect ratio, that is, for projectors with a classic 4:3 aspect ratio or for devices with widescreen 16:9 format.

Commercial models have depending on the lens, a projection ratio between 0.6:1 and 3.0:1. Most conventional devices have potential projection ratios between 1.5:1 and 2.2:1, although there are significant differences in the flexibility of the zoom or the projection ratio. Many cheap video projectors do not have a zoom; is available to them image resizing only the displacement of the projector to the screen to or away available. Professional video Projectors some have the ability to change lenses.

Positioning and keystone

Projects the device not hitting the screen, but horizontally or vertically offset so that the projection axis is no longer perpendicular to the projection plane, the result is a keystone of the image. The further away from the projector the screen is then increased while the projector is the reduced nearest resulting image. The distortion can be determined analogously by lens adjustment ( engl. lens shift ) or be compensated by digital keystone correction.

Lens adjustment possibilities can be found usually only in higher-value models for professional use or home cinema models. It is carried out mechanically and leaves the resolution of the projector without prejudice. Models with this option are not tipped to undistorted display the image off the projection axis

Devices without lens shift options are usually tilted when they are placed away from the central image normal, but still aimed at the same projection area. Many units look to correct the keystone distortion occurring before the keystone correction, the digitally distorted the image before it is projected. Optimally, this deliberate distortion compensates for the distortion caused by the oblique projection, so that the expected parallel edges and lines form on the screen. A disadvantage of this approach are the reduced resolution caused by the interpolation blurs and staircase artifacts in the image, the reduced effective light output and the visible in darkened rooms, good black areas outside the actual image. The latter effect occurs mainly in LCD projectors.

Volume and noise

The light source in a video projector produces waste heat that is removed usually by one or more fans. Depending on the location and purpose, the resulting size of the projector and the light-generating technology come with different sized fan of this size -dependent speeds are used. Fan -based cooling concepts cause audible noise. To mitigate this, a video projector supplier mainly provide the home cinema to a so-called Eco mode, in which the luminance is reduced. This makes it possible to reduce the fan speed.

Home theater projectors are usually built voluminous, so that large fans can be installed, which realize a specified air flow rate at a lower speed than smaller fans. This allows quiet operation in seat nearby.

Office projectors are designed for brightness, in order to project a easily readable image even in daylight. This leads to a stronger heating of the lamp, which in turn requires a larger cooling requirements. Consequently, the fan must be large and / or fast rotation. The larger compared with home theater projectors noise is tolerated by virtue of an already fair office environment.

Professional projectors, such as in digital cinema projection or conference projectors for large halls are due to the high volume of the fan sometimes quite loud. They project usually from a greater distance to the audience or, in cinemas, in separate rooms.

The volume can be specified in dB. Quiet video projectors produce less than 25 dB, loud more than 30 dB. Very quiet projectors generate noise in the range of 19 decibel, very loud even reach close to 50 decibels.

Connectivity

Video projectors process analog and at least since about 2005 ( price-dependent ) digital image signals ( eg from a DVD player, a PC, VCR, DV camcorder, TV tuner, etc.). One finds similar connections as YPbPr component video inputs ( three RCA connectors), SCART, S- Video, composite video, RGBHV or VGA. Since most current video projectors internal digital work (LCD, DLP, etc. ), analog input signals are first digitized, which can lead to loss of quality.

Digital inputs (usually HDMI, DVI rare ) on the video projector are mostly able to process encrypted signals (HDCP ).

In the professional field offices also have the Serial Digital Interface (SDI ) or HD -SDI with high image resolution.

There are occasionally other special connections. With home theater projectors can be found, for example, so-called triggers that can trigger the unrolling or rolling up a motorized screen. Hard -to-mount projectors are sometimes equipped with a serial interface through which you can remotely control the menu. There are also devices with connectors for a cable connection with a remote control.

Accessories

The handling and the quality of video projection in addition to the performance features of the projector itself influenced by important accessories: projector mounts and screens. For mobile or temporary reproduction for example Beamer Beamer stands or carts are available, while ceiling or wall mounts are designed for fixed installation. Similar criteria are obtained for the projection. Where permanently a projection surface is desired, provide specially coated surfaces or fixed frame screens a good choice dar. For mobile projection Stretched Screens are available. For example, where in the home theater area for reasons of space no fixed projection screen is available, roll screens have proven with or without motor drive.

DIY projects

2004 became the publication of computer hardware website Tom 's Hardware Guide greater prominence in the building instructions were given, as obtained from a (used) flat screen TV and an overhead projector creates an XGA Own Projector. The guide was assumed that the necessary hardware is bought on eBay, which led to designated material cost of 250 euros.

Need for alternatives to conventional video projectors was partly due to the then high new prices for video projectors with resolutions up to 800 × 600 pixels and the expensive replacement light sources. Overhead projectors are operated partly with standard incandescent bulbs, which spoke in the very price comparison for DIY projector.

Speak different arguments against this type of video projectors. The Ausleuchtungseinstellmöglichkeiten an overhead projector are minimal. The flat panel is not designed for the luminance and illumination of a projector, so the image quality from professional equipment can not be achieved. Color distortions are a typical feature. Furthermore, use overhead projectors relatively much energy.

Even with a smart phone can make a simple projector. In a self-made " darkroom " is projected on the wall through a magnifying glass of the mobile screen. Unfortunately, the illumination of the projector is not optimal, so that the sharpness of a professional device can not be reached.