The stair-step or sawtooth effect seen on lines that are not horizontal or vertical or the edge of objects in digital displays. Also known as aliasing. Smoothing and ant aliasing techniques can reduce the effect of aliasing.
Abrupt variations in signal amplitude or timing that cause reproduction instability in audio, video and data. Usually caused by bandwidth limitations or impedance termination issues that can sometimes be caused by the cable and/or connections you are using. Power supplies can also be a source of this problem.
apparent stutter of on-screen movement. Motion judder in film is due to the fact that the 24 frame/second sampling rate is too slow to resolve camera panning motion. Judder is also caused by 3:2 pull down where movie frames are on screen for differing times due to frame rate translations. Also occurs on PAL to NTSC conversions.
A security device found on projectors and other electronic equipment that allows the equipment to be secured by key or combination to another object using a rubberized cable.
Keystoning occurs when the projector is not perpendicular to the screen, thereby creating an image that is not rectangular.
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 scaling to the image. Keystone correction can be one or two dimensional and manual or automatic depending on the projector and the manufacturer. Be aware that digital scaling will introduce some artifacts that are more evident when viewing small text and less evident in presentation type material or video.
The time between a device being requested to do something and the start of the device actually doing it. It’s a measurement usually used for LCDs where the shorter the latency the better. NSTC requires a latency of no more than 16ms in order to update the screen in time without leaving a ghost of the previous image.
Liquid Crystal Display. A display device for generating colour images using a matrix of LCD pixel elements. Each pixel element consists of 3 sub-pixels and an RGB colour filter of red (R), green (G), and blue (B). By controlling the voltage to each sub-pixel of an LCD, each cluster of RGB pixels can create a full spectrum of coloured light. LCDs are used in flatscreen displays, cameras and notebook computers to name a few.
Nearly every projector made with LCD technology uses 3 separate LCDs, one each for red, green and blue. Light from the projector lamp is separated into RGB with a set of dichroic mirrors. The three light beams (RGB) are passed through separate LCDs and recombined to project a colour image.
Light Emitting Diode. A light generating technology that uses a semiconductor diode that emits monochromatic (single colour) light when charged. LEDs are used in remote controls that are used to control electronic devices such as large displays. They are also used in pocket projectors as a light source, large outdoor electonic displays, and as indicators on electoronic devices such as power supplies and cameras.
A type of projector lamp that uses one or more LEDs as its light source. The benefit of LED lamps is their long life.
The purpose of "lens shift" is to eliminate keystone correction and provide greater flexibility in the placement of the projector relative to the screen or the alignment of stacked projectors. This is accomplished by allowing the optical lens to be physically shifted vertically and/or horizontally. These adjustments may be manual or motorized depending on the projector.
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.
A display’s ability to show an image’s geometric characteristics accurately. Also called geometric linearity.
Long Throw Lens
A long throw lens allows greater distance between the projector and the screen while being able to maintain the image size and brightness of a shorter throw lens for any given projector. Depending on the room, a long throw lens may be required due to mounting constraints nearer the projected image.
A filter that only passes frequencies under a specified Hertz.
A measurement unit of total illumination. Typically a 100-watt light bulb outputs 1700 lumens over a wide area. Projector light output is measured in ANSI lumens. A projector with a higher lumen number will produce a brighter image for a given image size.
The black and white part of a video signal. It is signified by the letter Y. Signals with a separated luminance and colour signal avoid interference. This interference can result in dot crawl among other image artifacts.
A standard for measuring light equal to the amount of visible light per square meter incident on a surface. 1 lux = 1 lumen/square meter or 0.093 foot-candles.
Sometimes used to refer to the distance from the screen that a projector can focus the image. Most of the time, it is the manufacturer's opinion of how far from a screen the projector can be to cast an image that is useable (bright enough) in a fully darkened room.
Maximum Image Size
The largest image a projector can reasonable throw in a darkened room.
Maximum Resolution refers to the highest resolution that a given display device can support. If the Maximum Resolution exceeds the Native Resolution, , the image is usually scaled to match or approximate the Native Resolution of the projector. Some display devices allow pan and scan where rather than scaling the image, the display devices allows you to use the native resolution of the display to view portions of the higher resolution image. Scaling reduces the image resolution and produces some artifacts in the image that are more apparent when viewing text than graphics or video.
A feature on some projectors that allows photos, documents and/or presentation material to be projected using a memory card and thereby eliminating the need of a computer.
The closest position that a projector can focus an image onto a screen.
An artifact of MPEG compression which looks like a mosquito buzzing around. Usually found around sharp edges and most easily seen on solid colour areas. It is a time dependent video compression impairment in which the high frequency spatial detail in video images having crisp edges is aliased intermittently.
Moving Picture Experts Group. A working group of ISO/IEC in charge of developing codecs and standards for moving pictures with synchronized audio.
Some projectors use multiple lamps that can be controlled by the user to increase or decrease the brightness of the image. This lamp redundancy significantly minimizes the risk of total lamp failure during use.
Another type of multi-lamp system is a Dual Lamp. With a dual lamp projector one lamp can serve as a backup to the other lamp in the event of failure or the lamps can be programmed to switch at specific intervals.
A display device capable of operating at multiple scan rates, usually starting at 30KHz up.
Native Aspect Ratio
Nearly every projector or display 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 device 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.
Native Resolution is the number of physical pixels in a display device. For example, an XGA display has a native resolution of 1024 physical pixels of resolution horizontally and 768 pixels vertically or 786,432 total pixels. See Maximum Resolution.
Negative Gain Screen
A screen with a gain rating of under 1 which actually reduces the amount of light reflected back from a projected image. Usually gray, they are used to increase apparent contrast by lowering the black level.
An unwanted random signal.
Also known as progressive scan. Describes how video frames are drawn which, in this case, is completely from to bottom at every screen update.
Organic Light Emitting Diode. A self-illuminating, energy-efficient, direct-view imaging system. Uses an organic film sandwiched between 2 transparent electrodes.
Typically the less expensive projectors come with a built-in lens that is designed to serve a specific type of setting or application. A projector that supports optional lenses can address a wide variety of installation needs. This gives a projector great flexibility at an incremental cost.
A device consisting of a light source, a transmissive or reflective platform, and a focusable lens assembly. An OHP is designed to project images from tranparencies or LCD projection panels onto a screen.
Multiplies outgoing signal samples in order to more easily filter out aliased sounds but doesn’t create fidelity that isn’t there to begin with.
Given as a percentage or pixel count, the amount that a particular display device crops the edges of an incoming video signal. This is done to ensure the image area contains only picture information.
Phase Alternating Line. Broadcast standard developed in Germany in 1963 and adopted in 1967. It’s used in many countries throughout Europe including the UK and transmits 576 viewable lines at 25 frames per second interlaced.
A method to fit source material of a different resolution or aspect ratio onto another. Sometimes used with computer input when the input resolution exceeds the resolution of the display device. Used extensively for broadcast and DVDs, it simply crops the sides of widescreen material and the transfer operator chooses the best part of the frame to show. Often an electronic camera pan is used to change the area being shown. This is used when characters are talking to each other but one is off screen due to cropping and they become the focus of the shot.
A marketing term to describe a small hand held projector that can fit in your pocket. A pico projector can be a stand-alone device that connects to a computer or other video device or a projection module that is integrated with a phone, portable computer, MP3 player or other small device.
Poly-Si (silicon) LCD
One of several projector display technologies. Monochrome Poly-Si LCDs are typically placed in each of the three colour (red, green, blue) light paths inside a projector to produce a colour image from a common light source. Poly-Si technology is a bit faster than the Active Matrix TFT providing slightly smoother video.
A motor driven lens that adjusts focus using a button on the projector's control panel and/or a remote control.
With audio amplifiers, the amount of power sent to drive the speakers. Peak output is quite often specified, which is somewhat misleading compared to the average amount of power an amplifier can continously produce (RMS rating).
A zoom lens that is driven by a motor and controlled from the projector's control panel and/or remote control.
A display mode 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, HDTV systems, and some digital camcorders. Progressive Scan requires a faster horizontal scan frequency than interlaced images of the same resolution
A projector is a device that integrates a light source, an optics system, electronics and display(s) for the purpose of projecting an image from a computer or video device onto a wall or screen for large image viewing. These devices attach to a computer or video device as you would connect a monitor or television.
QXGA is a display resolution of 2048 horizontal pixels by 1536 vertical pixels giving a total display resolution of 3,145,728 pixels. A QXGA display has 4 times the resolution of an XGA display.
An image anomaly that can be seen by a small percentage of people when viewing a single chip DLPTM front or rear projection system. The anomaly appears as a colour breakup at the edge of objects when the eye transitions rapidly between light and dark areas of the image. The problem is characteristic of sequential colour systems with low refresh rates.
The speed at which a display updates its picture given in Hz.
A measure of the ability of a display or sound system to render detail.
The frequency at which any physical object naturally oscillates. All objects have this property including rooms, which will favor certain frequencies over others and may 'colour' sound.
All sound reflections within an enclosed space that continue to bounce around after the source has sped. Also an audio effect, which mimics various room sizes.
Red, Green and Blue. A component signal representing each colour separately. Sync signals can be sent on green or sent separately as a composite signal or dual H/V signals (Horizontal sync/Vertical sync). Very common signal for analogue computer displays.
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(colour, C). S-Video is also referred to as Y/C. Considered a higher quality video source than composite video.
Sony/Philips Digital Interface. A transport protocol related to AES/EBU for sending PCM digital audio signals between devices. Uses either 75-Ohm coaxial cable or fiber-optic cable.
The speed at which data representations of an analog signal are duplicated. The higher the number, the better the quality. Another quality aspect is the granularity of the scale used for representation where 16 bits allows 65536 discrete levels and 24 bits allows about 17 million.
Saturation is a measure of colour intensity. In the absence of saturation the colour hue is a shade of grey. A highly saturated hue has a vivid, intense colour, while a less saturated hue appears more muted and grey.
The line drawing speed of a display, usually given in kHz. A standard definition TV has a scan rate of 15.75 kHz which when you divide by 525 scan lines, gives a horizontal refresh rate of 30 fps or Hz.
As it applies to projectors, gain is the measurement of a projection screen’s light reflectance with unity gain being one. A high gain screen will reflect more light along a narrower path than lower gain screen. Screen gains under one use a gray screen to absorb ambient light to help maintain contrast ratios.
A 12V connection from a projector to an electric screen which tells the screen to deploy when the projector is turned on and roll up when the projector is turned off.
A feature of speakers and cables where a metal layer is added to contain and protect a signal from creating or receiving electromagnetic interference.
Short Throw Lens
A lens designed to project a large image from a short distance.
Short Throw Wall Mount Projector
A projector that mounts on a wall adjacent to the projection screen. The throw distance is generally just a few inches and allows people to move freely through the room without concern of intercepting the light path.
The ratio of noise to signal measured in dB. The higher the number, the better.
A signal distortion where one part of a signal arrives at a different time than another and causes colour fringes to the sides of an object.
Sony/Philips Digital Interface. SPDIF is a unidirectional digital audio interface for connecting audio equipment.
sRGB stands for standard Red, Green, and Blue, and is a standard for rendering colour evenly across a variety of platforms.
A visual artifact of trailing colours behind an on-screen object or across a screen.
SVGA is a display resolution measuring 800 pixels horizontally by 600 pixels verically giving a total display resolution of 480,000 individual pixels. SVGA has a 4:3 aspect ratio.
SXGA is a display resolution measuring 1280 pixels horizontally by 1024 pixels vertically giving a total display resolution of 1,310,720 individual pixels. SXGA has a 5:4 aspect ratio.
TCO Certified Projectors
A TCO-labelled projector is certified to reproduce excellent images to a maximum projected image size, the TCO Image Size. In addition, the projector complies with stringent environmental requirements such as low energy consumption and minimal levels of environmentally hazardous substances. There is also an eco mode requirement so the projector can be set to lower luminosities, thus reducing noise, energy consumption and increasing the life of the bulb. The label also requires manufacturers to prove they are working proactively on environmental improvements to the production process and social responsibility issues.
Throw distance is the measurement from the projector's lens to the screen. A projector with a zoom lens will have a range of throw distances for any given image size, while a projector without a zoom lens will only be able to project one image size at a given distance from the screen. In Projector Central's articles, throw distance is normally quoted for a 100" diagonal screen.
Tom Holman's experiment. A certification for audio equipment and installation done to a standard set by THX Ltd., a company owned by George Lucas. Usually geared towards audio playback for video and cinema.
THX video certification signifies that a product has been designed and tested to meet the rigorous performance standards defined by THX.
Replicated versions of an object that slowly fade as the object moves across the screen.
The analog measurement of image fidelity, it is the number of resolvable vertical lines divided by the aspect ratio. A VHS tape is typically rated at 240 lines where the live feed of a broadcast camera can be as high as 800 lines. It is not the same as pixel resolution.
A measurement of the evenness of the brightness of white or a particular colour across a display indicated as a percentage. A measurement of 80% means the brightness of an image is 20% less at its dimmest point compared to its brightest.
A projection screen with a gain rating of one that reflects light with a wide viewing angle back to the viewer.
UXGA is a display resolution measuring 1600 pixels horizontally and 1200 pixels vertically giving a total display resolution of 1,920,000 individual pixels. UXGA has an aspect ratio of 4:3.
Vertical Lens Shift
The purpose of Lens Shift is to eliminate keystoning and provide greater flexibility in the placement of the projector relative to the screen. Lens shift may be a manual adjustment or motorized depending on the projector.
Vertical lens shift will typically allow the projector to be placed anywhere between 1.5 screen heights above or below the centre of the projection screen and may also be used to geometrically align images when stacking projectors. Horizontal lens shift is also available on some projectors.
VGA is a display resolution measuring 640 horizontal pixels and 480 vertical pixels giving a total display resolution of 307,200 individual pixels. VGA has a 4:3 aspect ratio.
Vertical Helical Scan. Also known as Video Home System and is the most common consumer videotape format. It is a ½” magnetic tape format introduced in 1976 by JVC. Offers about 240 vertical lines of resolution.
An output connector on the projector that allows a monitor or another projector to share the same video source.
The signal level that corresponds to the maximum picture brightness. The white level is set by the contrast control.
Wi-Fi is Wireless Fidelity, and is a type of wireless network used to connect digital devices without the need for cables. It is mostly used for wireless broadband access and inexpensive consumer wireless antennas are available at electronics stores. There are four specifications currently in the family: 802.11, 802.11a, 802.11b, and 802.11g.
International standard for wireless networking that operates in the 2.4 GHz frequency range (2.4 GHz to 2.4835 GHz) and provides a throughput of up to 11 Mbps. This is a very commonly used frequency. Microwave ovens, cordless phones, medical and scientific equipment, as well as Bluetooth devices, all work within the 2.4 GHz frequency band.
Any aspect ratio that is wider than 4:3. Widescreen televisions are 16 units wide and 9 units tall. Common widescreen film aspect ratios are 1.66:1, 1.85:1 and 2:35:1.
WSXGA defines a class of SXGA displays with a width resolution sufficient to create an aspect ratio of 16:9. A WSXGA display has 1920 to 1600 pixels horizontally and 1080 to 900 pixels vertically.
WXGA defines a class of XGA displays with a width resolution sufficient to create an aspect ratio of 16:9. A WXGA display has 1366 to 1280 pixels horizontally and 768 to 720 pixels vertically.
XGA is a display resolution measuring 1024 pixels horizontally and 768 pixels vertically giving a total display resolution of 786,432 individual pixels. XGA has a 4:3 aspect ratio.
A free and open source MPEG-4 video codec that was created by a group of volunteer programmers trying to overcome the closed source and platform limitations of DivX (XviD spelled backwards).
Digital component video. Y stands for the luma signal itself and Cb is the blue signal subtracted from luma and finally, Cr equals the red signal subtracted from the luma signal.
Analog component video. Y stands for the luma signal itself and Pb is the blue signal subtracted from luma and finally, Pr equals the red signal subtracted from the luma signal.
A lens with a variable focal length providing the ability to adjust the size of a projected image without moving the projector or provide a range of projector placements that can produce the same size image. See Zoom Ratio.
Zoom ratio is the ratio between the smallest and largest image a lens can projector 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 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.