Projector Help

Choosing a video projector can be abit of a mine field as there are many different technologies and phrases used, This is a small guide to give you a helping hand.

Resolution

Resolution refers to the number of lines of picture image displayed on screen. The greater the resolution, the greater the picture quality. For example, a standard TV signal displayed on a standard TV set consists of 480 lines of resolution. HDTV (high-definition) signals, on the other hand, contain more than 700 lines -- hence their superior quality.

Portable home-theater LCD and DLP projectors both come in different "fixed" resolutions. That is, not every projector has the same resolution as every other. And a projector's fixed resolution rarely matches the exact resolution of the incoming signal. Therefore, the projector must first resize the signal's image internally, through shrinking or stretching, to map it onto its own fixed-resolution LCD or DLP panel.

Common Projector Resolutions:

4:3 Format: VGA - 640x480, SVGA - 800x600, XGA - 1024x768, SXGA - 1280x1024, SXGA+ - 1400x1050, UXGA - 1600x1200, QXGA - 2048x1536, QSXGA - 2560x2048

16:9 Format: WVGA - 852x480, WXGA - 1366x768, WXGA+ - 1440x900, WSXGA+ - 1680x1050, WUXGA - 1920x1200, WQSXGA - 3200x2048, WQUXGA - 3840x2400

Video 16:9 Format: 720p - 1280x720, 1080p 1920x1080

ANSI Lumens:

An ANSI lumen in a particular unit of measurement for the light output of a projector. A lumen (lm) is a unit for measuring luminous flux, or the perceived output of a light source. ANSI is an acronym for the American National Standards Institute. As such, an ANSI lumen is a lumen measured in the specific method defined by the American National Standards Institute.

The ANSI method for measuring lumens is very accurate and is therefore used in the marketing of projectors. Manufacturers almost always list the ANSI lumen output of their projectors as a point of comparison.

Constrast Ratio:

If you're concerned about picture quality, don't just look at brightness. Contrast is just as important. In short, it's a measure of how well the projector can block out light from the lamp, ie. how black is the black? This is especially important for home cinema applications.

An average contrast ratio is about 700:1 for LCD projectors, whilst DLP projectors have contrast ratio of 4000:1.

Weight: 

If you are on the move, you'll appreciate having a projector that's as portable as you can afford. Thankfully, today's projectors are smaller than ever, with the lightest at around 1.1kgs and easy to carry over the shoulder. However, the desktop models still have more features and represent better value if the projector is going to stay in one place.

Data & Video Inputs:

Every projector on the market is fitted with a varying number of “slots” or inputs which enable you to plug in a number of input devices such as laptops and computers. Nearly all projectors have a standard composite jack since composite video is the most common way to transmit video data. However, as technology advances more and more ways in which video signals can be transmitted have become available, these have, over time, been incorporated into the connection electronics of projectors. Potentially, projectors may offer more than eight different possible input connections. While our dedicated cables section will explain in depth the various cables and their associated inputs, this is a brief description of the possible video inputs.

Composite video projector cabling
The composite video cable is the most common and most rudimentary form of video input since it was the cable first used at the advent of colour television. Consequently it is not fully optimised to work with new LCD or DLP projectors, and it cannot transmit High Definition digital images. Even the standard definition pictures that composite video can broadcast are not rendered very sharply.

Composite video is formed from three coloured cables. The yellow cable is used to transmit the video signals and a combination of red and white cables is used to send the left and right channel audio data.

S-Video projector cabling
First invented in the 1980s, as the name suggests s-video (separated video) cabling differs from composite cabling in that it isolates the two types of video signals which would be combined on a composite cable. By separating the colour signals from the brightness signals (chrominance from luminosity), the colours are more clearly separated and the image will appear sharper. However, since s-video is still only an analog video signal it can only carry standard definition resolutions signals and is incapable of broadcasting HD TV. Furthermore, the white and red connectors still need to be used to carry audio signals, just like in composite video.

Component video projector cabling
Component cables offer a substantial increase in picture quality from composite because three separate red, blue, and green cables are used that are dedicated to transmitting the video signal. If these three cables are labelled Y, Pb, and Pr then the component cable can accept High Definition video, where as if the inputs are tagged Y, Cb, and Cr they will only output videos in standard definition. Regardless of whether the picture is transmitted in high definition or in standard definition, the image that will be displayed is of a much higher quality and colour saturation than component or s-video pictures. However, as with component and s-video, both red and white audio channel connectors are needed to transmit left and right audio channel signals.

DVI projector cabling
Digital Video Interface (DVI) cables were originally designed as a way to connect an LCD monitor to a computer. However, it has now become a common way to hook up audiovisual devices such as projectors, especially because DVI is capable of transmitting High Definition signals. DVI consists of a single video cable that is screwed into the back of the device in the same way that a VGA cable is. While this sounds simple, it is important to be aware that DVI cables only carry video signals, so you therefore need separate red and white audio cables to receive sound.

VGA projector cabling
This type of connection (Video Graphics Array) is most commonly used to connect computer monitors to computers. Due to the fact that nearly every laptop comes with a VGA output connection and that it is a simple one cable connection, VGA cables are often also used to connect laptops to projectors and HD TVs. However, like DVI, composite and s-video connections, VGA cables only carry video signals so a separate audio connection is necessary if sound is required.

HDMI projector cabling
High Definition Multimedia Interface is a type of digital cable recently developed specifically for the High Definition era consumer electronics products. If you wish to receive the best looking images on your display device then HDMI should be your first choice. It is the highest quality cable on the market since it incorporates both High Definition video signals and multi-channel Dolby digital audio. Furthermore, it is the simplest type of cable to set up since it is just a small, single cable and is readily available in lengths over 30 metres. HDMI is also the preferred choice of cable for Hollywood film studios since it includes High bandwidth Digital Content Protection (HDCP), which is used to prevent the pirating of high definition signals.

USB projector cabling
USB – or Universal Serial Bus is a type of computer cable system that was designed to allow many different types of devices to connect to computers. Nowadays USB devices such as portable hard drives and memory “sticks” can connect up to projectors as an easy means of transferring data without needing to use a laptop. USB was designed to replace serial and parallel ports and is frequently used for computer peripherals.

RGBHV projector cabling
RGBHV (which stands for Red, Green, Blue, Horizontal and Vertical) transmits separate red, blue and green colour signals and horizontal and vertical video sync signals to HD displays. RGBHV is sometimes found on higher end projector models but more commonly when connecting computers and monitors.

Keystone Correction:

'Keystoning' is the name given to the effect on the projected image when the projector sits below or above the centre of the screen. Keystone correction counteracts this effect by digitally compressing the image at the bottom or top, resulting in a squarer, more professional image.

Lens Shift Function:

Lens shift is generally a feature of high-end projectors or specialist home cinema models. Lens shift has a simular effect effect to 'Keystone correction' except that the effect is achieved by physically adjusting the angle of the projectors lens to square up the image. This is a better method of producing a square image, rather than using keystone correction as the correction with lens shift is acheived optically (rather than digitally) resulting in no loss of quality

Lens shift can also be useful for fine-tuning the position of the projected image on your screen.

 

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