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The Glossary is a reference guide for the basic technical terms used on this site to describe every kind of projector and projector accessories.
Aspect Ratio: Aspect ratio is the ratio of the width of an image to its height. For example, a projector with a 16:9 aspect ratio will produce an image that is 16 units wide for every 9 units high. This is also referred to as 1.78:1 meaning the width is 1.78 times the height. For example, if you want an image 40 inches high then you need a screen that is at least 40 x 1.78 inches wide or 71 inches. Other common aspect ratios are 3:2, 4:3 and 5:4. Native aspect ratio refers to the aspect ratio of the physical displays built into the projector. For example, a 1280 x 720 pixel display has a 16:9 native aspect ratio. A display that is 640 x 360 pixels is also a 16:9 aspect ratio, but with a fourth of the resolution of the other display. Nearly every projector today will support multiple aspect ratios; however each manufacturer must decide who their intended audience is and optimize the projector for that audience. This means each projector has a native aspect ratio that is optimized for specific viewing material. Images shown in native aspect ratio will utilize the entire resolution of the display and achieve maximum brightness. Images shown in other than native aspect ratio will always have less resolution and less brightness than images shown in native aspect ratio.
Bandwidth: The number of cycles per second (Hertz) expressing the difference between the lower and upper limiting frequencies of a frequency band; also, the width of a band of frequencies.
Brightness: The attribute of visual perception in accordance with which an area appears to emit more or less light.
Compressed Resolution: Most projectors automatically accept images that are of greater resolution than the native (true) resolution of the projector. The resulting image is scaled to fit the native resolution of the projector using a variety of scaling algorithms. Not all projectors use the same compression algorithms; therefore, the quality of compression can vary. The nature of compression in a digital device means that some image content is lost.
Contrast Ratio: The ratio between white and black. The larger the contrast ratio the greater the ability of a projector to show subtle color details and tolerate extraneous room light. There are two methods used by the projection industry: 1) Full On/Off contrast measures the ratio of the light output of an all white image (full on) and the light output of an all black (full off) image. 2) ANSI contrast is measured with a pattern of 16 alternating black and white rectangles. The average light output from the white rectangles is divided by the average light output of the black rectangles to determine the ANSI contrast ratio. When comparing the contrast ratio of projectors make sure you are comparing the same type of contrast. Full On/Off contrast will always be a larger number than ANSI contrast for the same projector.
Halogen Lamps: Used in most low and medium priced projectors, these lamps last about 40 hours, with consistant output throughout their life. Although halogens look very white compared to a normal incandescent lamp, they are not as white as metal halide units. Cost of operation: Under $0.50 per hour. Most projectors using halogen lamps carry a spare lamp inside.
Keystone: Keystoning occurs when the projector is not perpendicular to the screen, thereby creating an image that is not rectangular.
Keystone Correction: Keystone correction makes a projected image rectangular. This can be accomplished by positioning the projector to be perpendicular to the screen. Since this is not always possible, most projectors are equipped with keystone correction that allows the image to be keystone corrected (made rectangular) by adjusting optics, making mechanical adjustments, or applying digital correction to the image. Keystone correction can be one or two dimensional and manual or automatic depending on the projector and the manufacturer.
Lens Shift: The Lens Shift feature of a projector allows the optical lens to be physically shifted up and down (Vertical) or left and right (Horizontal). Most lens shift mechanisms are motorized with vertical lens shift being the most popular. With a projector that has lens shift you can optically correct for keystone distorted images. It is also used to help geometrically align images when stacking projectors.
Letterbox: A method of preserving the originally aspect ratio of a production when presented on a projector with a different aspect ratio. This is accomplished by showing the full image and black where no image exists. Often referred to as widescreen.
Metal Halide Lamp: The type of lamp used in many medium and all high end portable projectors. These lamps typically have a "half-life" of 1000-2000 hours. That means they slowly lose intensity (brightness) as they are used, and at the "half-life" point, they are half as bright as when new. These lamps output a very "hot" temperature light, similar to mercury vapor lamps used in street lights. Their whites are "extremely" white (with slight bluish cast.) and make Halogen lamp's whites look very yellowish by comparison.
Native Resolution: Native Resolution refers to the number of physical pixels in a display device. For example, an SVGA projector has 800 physical pixels of resolution horizontally and 600 pixels vertically or 480,000 total pixels. This is the native resolution of the projector. Projectors are capable of projecting greater or smaller resolution images into the same physical resolution through scaling. Scaling reduces the resolution of larger images and increases the resolution of smaller images to match the native resolution of the display device. This type of digital scaling always produces some artifacts in the image that are more apparent when viewing text than graphics or video.
NTSC: The United States standard for video and broadcasting and is also used in the western hemisphere, Japan, and other Asian countries. NTSC standards are 525 lines of resolution transmitted within a 6MHz channel at 30fps(frames per second.)
PAL: A European and international broadcast standard for video and broadcasting. Higher resolution than NTSC.
Poly-Si (silicon) LCD: A popular LCD technology for the top of the line LCD projectors. Monochrome Poly-Si LCDs are typically placed in each of the three color light paths inside a projector, one each for Red, Green, and Blue. This results in increased color saturation, with contrast ratios above 200:1. Poly-Si technology is also a bit faster than the Active Matrix TFT, for smooth video and multimedia.
Progressive Scan: A type of display in which all the horizontal lines of an image are displayed at one time in a single frame, unlike an interlaced scan in which a frame consists of two separate fields with the first field consisting of odd horizontal lines and the second field even horizontal lines. Progressive scan is used by projectors, computer monitors, DVD players and recorders, some TVs and HDTV systems, and some digital camcorders.
RGB: Red, Green, Blue; the normal type of monitor used with computers, examples of usage: RGB input or output often referred to as Computer input or output.
S-Video: A video transmission standard that uses a 4 pin mini-DIN connector to send video information on two signal wires called luminance(brightness, Y) and chrominance(color, C). S-Video is also refered to as Y/C. A composite signal, typically found coming out of an RCA jack on the back of most VCRs has the Y and C information combined into one signal. The advantage of having luminance and chrominance separated is that a comb filter is not needed inside the video projector to separate the composite signal into the luminance and chrominance signals. A comb-filter can reduce the sharpness of your video image.
SECAM: A French and international broadcast standard for video and broadcasting. Higher resolution than NTSC.
sRGB: sRGB stands for screen Red Green Blue and is a proposed standard for rendering color evenly across a variety of platforms. One objective is to replace the Web-safe palette of 216 colors with sRGB.
SVGA(800x600): SVGA is used to define a specific display resolution. Resolution is defined by the number of individual dots that a display uses to create an image. These dots are called pixels. An SVGA display has 800 horizontal pixels and 600 vertical pixels giving a total display resolution of 480,000 individual pixels that are used to compose the image delivered by a projector.
SXGA(1280x1024): SXGA is used to define a specific display resolution. Resolution is defined by the number of individual dots that a display uses to create an image. These dots are called pixels. An SXGA display has 1280 horizontal pixels and 1024 vertical pixels giving a total display resolution of 1,310,720 individual pixels that are used to compose the image delivered by a projector.
UXGA(1600x1200): UXGA is used to define a specific display resolution. Resolution is defined by the number of individual dots that a display uses to create an image. These dots are called pixels. A UXGA display has 1600 horizontal pixels and 1200 vertical pixels giving a total display resolution of 1,920,000 individual pixels that are used to compose the image delivered by a projector.
VGA(640x480): VGA is used to define a specific display resolution. Resolution is defined by the number of individual dots that a display uses to create an image. These dots are called pixels. A VGA display has 640 horizontal pixels and 480 vertical pixels giving a total display resolution of 307,200 individual pixels that are used to compose the image delivered by a projector.
WSXGA: WSXGA defines a class of SXGA displays with a width resolution sufficient to create an aspect ratio of 16:9. Resolution is defined by the number of individual dots that a display uses to create an image. These dots are called pixels. A WSXGA display has 1920 to 1600 horizontal pixels and 1080 to 900 vertical pixels respectively that are used to compose the image delivered by the projector.
WXGA: WXGA defines a class of XGA displays with a width resolution sufficient to create an aspect ratio of 16:9. Resolution is defined by the number of individual dots that a display uses to create an image. These dots are called pixels. A WXGA display has 1366 to 1280 horizontal pixels and 768 to 720 vertical pixels respectively that are used to compose the image delivered by the projector.
XGA(1020x768): XGA is used to define a specific display resolution. Resolution is defined by the number of individual dots that a display uses to create an image. These dots are called pixels. An XGA display has 1020 horizontal pixels and 768 vertical pixels giving a total display resolution of 783,360 individual pixels that are used to compose the image delivered by a projector.
Zoom Lens: A lens with a variable focal length providing the ability to adjust the size of the image on a screen by adjusting the zoom lens, instead of having to move the projector closer or further away.
Zoom Lens Ratio: Is the ratio between the smallest and largest image a lens can project from a fixed distance. For example, a 1.4:1 zoom lens ratio means that a 10 foot image without zoom would be a 14 foot image with full zoom. Conversely, a 10 foot diagonal image at 15 feet with no zoom would still be a 10 foot image at 21 feet at maximum zoom (15 x 1.4 = 21 feet). A zoom lens is "not as bright" as a fixed lens, and the higher the ratio, the less light output.
Used with permission from ProjectorCentral.com
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