Contrast Ratio - The contrast ratio is a metric of a video display, defined as the ratio of the light intensity of the brightest possible color to the darkest possible color a display is capable of displaying simultaneously. The higher the contrast ratio, the better the display is.
Examples are 800:1, 700:1, and 500:1 from higher to lower capability. Infinite contrast ratios can be achieved by devices capable of emitting no light at all as their darkest color. Contrast ratio is most commonly considered in connection with transmissive displays, such as LCD, in which all pixels share the same light emitter, and manipulate the brightness of transmitted light individually. Technological challenges make it hard to design a mechanism to shut off 100% of transmitted light in these displays. Additionally, any optics in front of the matrix of light modulators that can potentially mix the light from different pixels, such as the lens of a DLP/LCD projector, will also degrade the contrast ratio.
Emissive display technologies - where all pixels emit light individually, such as OLED, plasma, FED and SED - are capable of achieving a very good contrast ratio. This is also true with the case of CRT. Poor contrast ratio manifests itself in the lack of true black, and in noticeably de-saturated colors (the darker is the supposed color - the stronger is the de-saturation).
A notable recent development in the LCD technology is the so called "dynamic contrast". When there is a need to display a dark image, the display would underpower the backlight lamp (or decrease the aperture of the projector's lens using a shutter), but will proportionately amplify the transmission through the LCD panel. This gives the benefit of realizing the potential static contrast ratio of the LCD panel in dark scenes, when the image is watched in a dark room. The drawback is that if a dark scene does contain small areas of super-bright light, they may be sacrificed and blown out. This may not sound too bad though, as the static contrast ratio of a human eye is just around 100 and so the details in those highlights might not be resolvable anyway. The trick for the display is to determine how much of the highlights may be unnoticeably blown out in a given image under the given ambient lighting conditions.
Composite – Composite Video is a single signal which carries both the chrominance (color) and luminance (brightness) components of a video signal, along with sync information, on a single wire. Unlike an RF signal, a composite video signal does not need to be demodulated to be understood by a video display. Like other baseband video formats, a composite video signal does not carry any audio content, which must be handled separately. Component - The various RGB (red, green, blue) analog component video standards (e.g., RGBS, RGBHV, RG&SB) use no compression and impose no real limit on color depth or resolution, but require large bandwidth to carry the signal and contain much redundant data since each channel typically includes the same black and white image. Most modern computers offer this signal via the VGA port
Converting video into luma and chroma allows for chroma subsampling, a method used by JPEG images and DVD players to reduce the storage requirements for images and video. The YPbPr scheme is usually what is meant when people talk of component video today. Many consumer DVD players, high-definition displays, video projectors and the like, use this form of color coding.
HDMI - The High-Definition Multi-media Interface (HDMI) is an industry-supported, uncompressed, all-digital audio/video interface. HDMI provides an interface between any compatible digital audio/video source, such as a set-top box, DVD player, and A/V receiver and a compatible digital audio and/or video monitor, such as a digital television (DTV).
HDMI supports standard, enhanced, or high-definition video, plus multi-channel digital audio on a single cable. It is independent of the various DTV standards such as ATSC, DVB(-T,-S,-C), as these are encapsulations of the MPEG data streams, which are passed off to a decoder, and output as uncompressed video data, which can be high-definition. This video data is then encoded into TMDS for transmission digitally over HDMI. HDMI also includes support for 8-channel uncompressed digital audio.
Lumens - The cost of a device is not only determined by its resolution, but also by its brightness. While most modern projectors will provide sufficient brightness at night or under controlled lighting such as in a basement with no windows, a projector with a higher lumens rating is required for a room with a higher amount of ambient light. A rating of 1000 to 1500 ANSI lumens or lower is suitable for smaller rooms with controlled lighting or low ambient light. Between 1500 to 3000 ANSI is suitable for medium sized rooms with some ambient light or dimmed light. Over 3000 ANSI is appropriate for very large screens in a large room with no lighting control (for example, a conference room). Projected image size is also important, as the total amount of light does not change, as size increases, brightness decreases. An increase in a widescreen image from 80 inches diagonal to 100 inches diagonal reduces the image brightness by 35 percent.
Resolution - The display resolution of a digital television or computer display is the number of pixels (or maximal image resolution) that can be displayed on the screen, usually given as a product of the number of columns (horizontal, "X"), which is always stated first and the number or rows (vertical, "Y") to make up the aspect ratio. There are two types of resolution, the number of discrete pixels or scan lines and the number of resolvable lines, the latter determined by the number of alternating black and white stripes that can be displayed across the picture without them merging together. The relationship between the two is known as Kell factor. Computer Standard Resolution Ratio Pixels
SVGA 800×600 4:3 480,000
XGA 1024×768 4:3 786,432
WXGA 1366×768 16:9 1,049,088
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Example of pixel layouts
LCD - To display images, LCD (liquid crystal display) projectors typically send light from a Metal halide lamp through a prism that separates light to three poly silicone panels -- one each for the red, green, and blue components of the video signal. As polarized light passes through the panels (combination of polarizer, LCD panel and analyzer), individual pixels can be opened to allow light to pass or closed to block the light. The combination of open and closed pixels can produce a wide range of colors and shades in the projected image.
DLP - In DLP projectors, the image is created by microscopically small mirrors laid out in a matrix on a semiconductor chip, known as a Digital Micromirror Device (DMD). Each mirror represents one or more pixels in the projected image. The number of mirrors corresponds to the resolution of the projected image (often half as many mirrors as the advertised resolution due to wobulation). 800x600, 1024x768, 1280x720, and 1920x1080 (HDTV) matrices are some common DMD sizes. These mirrors can be repositioned rapidly to reflect light either through the lens or on to a heatsink (called a light dump in Barco terminology).
LCoS - Liquid crystal on silicon (LCOS or LCoS) is a "micro-projection" or "micro-display" technology typically applied in projection televisions. It is a reflective technology similar to DLP projectors; however, it uses liquid crystals instead of individual mirrors. By way of comparison, LCD projectors use transmissive LCD chips, allowing light to pass through the liquid crystal. In LCoS, liquid crystals are applied directly to the surface of a silicon chip coated with an aluminized layer, with some type of passivation layer, which is highly reflective.
This technology can produce much higher resolution images than liquid crystal display and plasma display technologies, which makes it less expensive to implement in such devices as televisions.
