1080i is ATSC high definition 1920 x 1080 interlaced video format where a frame of video is delivered in two fields. The first field contains the odd lines of the image, while the second field contains the even lines. Each field is updated every 1/60th of a second resulting in 30 frames of video per second.
1080p is ATSC high definition 1920 x 1080 progressive scan video format where a complete frame of video is delivered at either 60 or 24 frames per second.
Aspect ratio of an HDTV signal which is 16 units by 9 units, whatever size those units may be. In the film trade aspect ratios are described in relation to one, which means this aspect ratio is described as 16/9 or 1.78:1.
Common 3 colour system for projecting images via LCD or liquid crystal display. Uses dichroic mirrors to separate the RGB components of white light coming from a projection lamp. Each colour is feed to separate LCD panels which control the about of coloured light that passes through. The light from each LCD is recombined using a dichroic prism before going out the lens and on to a screen.
480i is ATSC Standard Definition Television (SDTV) 720 x 480 or 640 x 480 interlaced video format where a frame of video is delivered in two fields. The first field contains the odd lines of the image and the second field contains the even lines. Each field is updated every 1/60th of a second resulting in 30 frames of video per second.
480p is ATSC Enhanced Definition Television (EDTV) 720 x 480 progressive scan video format where a complete frame of video is delivered at either 30 or 24 frames per second. 480p also refers to a display format comprised of 854 x 480 pixels, 16:9 widescreen.
720p is an ATSC high definition 1280 x 720 progressive scan video format where a complete frame of video is delivered at either 60, 30 or 24 frames per second.
Like the earlier 802.11b standard, it operates in the 2.4 GHz frequency range (2.4 GHz to 2.4835 GHz) but provides a throughput of up to 54 Mbps. Compatible with 802.11b devices at the 802.11b data speeds. Many other devices operate in the 2.4 GHz range where there is greater risk of interference. This can affect data throughput adversely.
Amplitude Modulation (AM) is a method of transmitting information using varying signal levels on a non-varying carrier signal. The waveform of the information being sent exists in the difference of signal level between the peak of the first carrier wave to the peak of the next carrier wave and so on.
American National Standards Institute. A private organization that coordinates and administers various voluntary consensus standards such as ANSI lumens. The first ANSI standard was for pipe threading in 1919 when it was called the American Engineering Standards Committee.
Contrast is the ratio between white and black. The larger the contrast ratio the greater the ability of a projector to show subtle colour 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.
ANSI lumens is a measurement of the overall brightness of a projector. Because the centre of a projected image is brighter than the corners, ANSI lumens are the most accurate representation of the image brightness. ANSI lumens are calculated by dividing a square meter image into 9 equal rectangles, measuring the lux (or brightness) reading at the centre of each rectangle, and averaging these nine points.
A device that controls amount of light admitted.
The ratio of image width to image height. Standard television is 4:3 or 1.33:1. Panavision or Cinemascope is 2.35:1 with 1.85:1 being quite common as well. Widescreen displays are 1.78:1 or 16:9.times the height. For example, if you want an image 40 inches high then you need a screen that is at least 40 * 1.78 inches wide or 71 inches. Other relatively common aspect ratios are 3:2, 4:3 and 5:4.
A system for detecting errors in colour balance in white and black areas of the picture and automatically adjusting the white and black levels of both the red and blue signals as needed for correction.
Audio/Video Interleave. The file format for Video for Windows (VfW). Used in conjunction with a codec to play back video. Format dictates how video and audio are stored in relation to each other but not the particular compression scheme used, which is handled by the codec.
Three conductor input with two signal conductors that are directly out of phase with each other. This cancels each other out when they pick up electromagnetic interference along the path but doesn’t affect the signal. The third conductor is ground.
The number of cycles per second (Hertz) expressed as the difference between the lower and upper limits of a frequency band; also, the width of a band of frequencies. Practically speaking, bandwidth is the amount of data that can pass through a given connection per unit of time.
Distortion where screen image expands outward towards edges of the screen. Instead of being square, edges are curved outward like the edge of a barrel. Opposite of pincushion.
Blackboard mode is a projector feature that allows the projector to detect the colour of the display surface such as a chalkboard of painted wall and automatically adjust its output to optimize accurate colour reproduction.
Video distortion where colour “bleeds” from an object onto other parts of the image which are not supposed to be that colour.
Overall light output from an image. While a brightness control can make an image brighter, it is best used to better define the black level of the image.
Brilliant Colour - a technology developed by Texas Instruments for its DLP projectors that produces six channels of colour including red, green, blue, cyan, magenta, and yellow; thereby, allowing an increase in the colour gamut.
Image distortion where phosphors are discoloured at a differing rates in a display device such as a plasma, CRT or SED TV. Usually caused by displaying a static image for extended periods. Screensavers are used to prevent burn-in on CRTs and plasma displays use a periodic dynamic single pixel shift of the image to avoid burn-in.
Centre designated signal of a 5.1 audio system. Typically for home theater, the corresponding speaker should be as close as possible to the video image associated with the sound.
An audio or video cable with a single internal wire with an outer shield that is ground. In audio, a speaker type where one speaker is positioned within another larger speaker’s cone.
Calibration pattern used to adjust the brightness, saturation and hue of video displays.
Image anomaly which looks like a rainbow at the edge of bright objects on screen. Also called rainbow effect where sequential colour systems, such as single chip DLP projectors or some LCoS RPTVs, update colour information at different locations on the screen because of quick movement of screen objects or a viewer’s gaze. For instance, the red component of a white object will show at a different location on the screen than blue when an object moves quickly across because colour is being displayed sequentially. This also occurs with quick relative movement such as moving your gaze from point to point across the screen. Most noticeable in bright objects.
Circuit in a display device that separates the colour part of the signal from the luminance. Can effect picture quality if set by manufacturer to compensate for higher colour temperature of overdriven displays or other colour variations.
The whitest whites, reddest reds, bluest blues and greenest greens. High colour dynamics are a result of dynamic range/contrast ratios. Having excellent colour dynamics implies rich colours, excellent definition, high contrast.
Measure of colour purity. Highly saturated colours emit a very narrow band of wavelengths of light instead of the broader spectrum of frequencies emitted from mixed colours. A display with good saturation capability will look vibrant.
Colour balance of white light which goes from red to blue as the temperature rises. Measured in degrees Kelvin, which starts at absolute 0 or –273 degrees Celsius, colour temperature matches the reference standard of the light being emitted from a carbon block heated to the stated degrees. For instance, the early morning sun is around 2500K, which is the same warm light that a carbon block heated to 2227° Celsius would emit. Heating the block further to ~10000° Celsius would emit the same bluish light of a blue-sky mid-day sun. Common colour temperatures are 5500 Kelvin (black and white movies) and 6500 Kelvin (standard colour films).
Rotating wheel with 3 or more translucent colour filters used to display sequential colour on single imager light valve based projection devices. The imager reflects or transmits the colour component of a given image when the wheel’s corresponding colour filter is affecting the light passing through to the lens. A 1X wheel cycles through all colours in 1/60th of a second.
Component Video is a method of delivering quality video (RGB) in a format that contains all the components of the original image. These components are referred to as luma and chroma and are defined as Y'Pb'Pr' for analog component and Y'Cb'Cr' for digital component. . It is comprised of luminance (Y) and two chrominance channels of blue minus luminance and red minus luminance.
Composite Video Signal
Single signal version of video where both chroma and luma are carried with chroma on a 3.58MHz sideband of the luminance signal, usually through a 75 Ohm cable. Poorest quality signal type.
Most projectors and displays automatically accept images that are of greater resolution than the native (true) resolution of the video device. The resulting image is scaled to fit the native resolution of the video device using a variety of scaling algorithms. Not all video devices 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 increases as the white point increases. Increasing the white point creates a greater difference between white and black.
The ratio between white and black. The larger the contrast ratio the greater the ability of a video device to show subtle colour details and tolerate ambient room light. There are two industry methods used: 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 video devices 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 video device.
An issue for CRT displays, projectors, and RPTVs. Convergence is the alignment of the component colours of a display where the respective electron beams or pixels must sit at the precisely correct position for the proper colour to be rendered.
Colours of a colour component display such as a CRT or projector do not line up correctly to create a proper image and create colour halos or incorrect colour.
dB or decibel is a measure of relative loudness. 0 dB is the threshold of hearing. 60 dB is equivalent to normal conversation. 120 to 140 dB is the threshold of pain such as a jackhammer or gun shot. 10 db of change will double the loudness.
Method to get rid of magnetic fields that build up in CRT monitors and distort the video signal causing discolouration.
The diagonal of a screen or flat panel can be computed by using the Pythagorean theorem: squaring the width, squaring the height, adding them together and taking the square root. A 100" diagonal 16:9 screen measures 49" high by 87" wide; a 100" diagonal 4:3 screen measures 60" high by 80" wide.
A usually undesirable variation from an intended output caused by the characteristics of a particular device.
Method of displaying intermediate colours that don’t exist in a limited palette by using a pattern of small dots out of that palette.
Video format based on the MPEG 4 standard. Commonly used for downloadable video files.
DLP (Digital Light Processing) is a commercial name for a display technology from Texas Instruments (TI). The technology inside is often referred to as DMD (Digital Micro-Mirrors). It consists of an array of mirrors where each mirror represents a pixel element. For example, a high-definition DLP projector or rear projector with 1920 x 1080 pixel resolution would have over 2 million tiny mirrors. Each mirror is attached to an electronically driven hinge that controls the amount of coloured light that is reflected from the mirror into the projection lens and onto a screen. Projection systems using DLP technology use 1 to 3 DMD devices.
A document camera can be attached to any projector; however, there are projectors that integrate these features either as a camera on an arm that is attached to the projector or a document scanner that is built into the body of the projector.
The distance between side-by-side phosphor colour groups (RGB) on a direct view display that uses phosphors. The smaller the better.
A Dual Lamp projector has two lamps where one lamp either serves as an automatic backup to the other lamp or is pre-programmed to switch at specific intervals. The benefit of this type of lamp system is it significantly reduces the probability of lamp failure during use.
DVD Player Projector
A projector with an integrated DVD player.
Digital Visual Interface. DVI is a standard that defines the digital interface between digital devices such as projectors, flatscreens and personal computers. For devices that support DVI, a digital-to-digital connection can be made that eliminates the conversion to analog and thereby delivers an unblemished image.
It can also carry an analog signal and comes as DVI-I (integrated - analog and digital), DVI-D (digital only) and DVI-A (analog only). Dual link DVI connections add additional resolution capabilities. Digital cable lengths should not exceed 15 feet.
A technique used to increase apparent resolution by increasing contrast around object edges. Usually counterproductive with already high-resolution sources and can become a source of image distortion.
Feedback occurs when the output of a device returns as the input of the same device. A microphone recording the sound from a speaker which is playing back the same microphone as a source is an instance where this can occur. Signals get replicated multiple times and if they are amplified, the amplification gets repeated as well. This is how room noise turns into a loud screech if microphones aren’t placed properly; however, this can occur to any electrical signal.
The distance from the surface of a lens to its focal point.
Frames Per Second.
A frame is one complete video image. When all lines of the video image are delivered sequentially, it is called progressive video. When the odd lines and even lines are delivered as separate fields, it is called interlace video.
A system where the projector sits in front of the screen with the image getting reflected back to the audience.
Front Room Projector
A projector that sits close to the screen and is capable of throwing a large image.
Full On/Off Contrast
Contrast is the ratio between white and black. The larger the contrast ratio the greater the ability of a projector or flat panel to show subtle colour details and tolerate extraneous room light. There are two methods used: 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 contrast ratio, make sure you are comparing the same type of contrast. Full On/Off contrast will always be a larger number than ANSI contrast for a given product.
Adjustment to gamma or how gray levels between black and white are displayed as the eye is sensitive to these in a logarithmic manner. For example, good gamma correction allows subtle shadow detail in a dark image to be easily perceived.
Characteristic of a display to accurately show an image without distorting it. When a display’s geometry is good, it represents square objects as a square, etc. See pincushioning and barrel distortion.
A faint duplicate image, usually offset from primary image. Can be caused by multipath, which is a delayed, attenuated duplicate signal bounced off an object to an antenna or other interference.
A table of shading devoid of colour, progressing from black to white. The number of discernible gray levels defines the colour resolution of the display device and is used to evaluate colour acuity and contrast.
HDMI (High Definition Multimedia Interface) is an uncompressed, all-digital audio/video interface that supports audio/video sources such as a set- box, DVD player, A/V receiver, and video monitors such as a digital projector or digital television (DTV). HDMI is backward compatiable with DVI 1.0 specification and supports HDCP.
HDMI supports standard, enhanced, or high-definition video, plus multi-channel digital audio, and interactive controls on a single cable. It transmits all ATSC (Advanced Television Systems Committe) HDTV standards and supports 8-channel digital audio. First product releases using HDMI occurred in 2003.
High Gain Screen
A screen that uses one of many methods to collect light and reflect it back to the audience, which dramatically increases the brightness of the image over a white wall or semi-matte screen. Technologies used include curved screens, special metal foil screens (some polarized), and certain glass bead screens. High gain screens achieve higher brightness by directing more of the reflected light towards the centre of the screen.
Horizontal 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.
Horizontal lens shift typically allows the projector to be placed anywhere between right and left edge of the projection screen and may also be used to geometrically align images when stacking projectors. Vertical lens shift is also available on some projectors.
Amount of pixels across an image, from left to right. A 1920 x 1080 HDTV has a horizontal resolution of 1920 pixels.
Horizontal Scan Rate
Period of time it takes to refresh an image on a screen, usually measured in Hertz (cycles per second). Computer monitors typically have scan rates starting at 60Hz going to 85Hz.
Hue or tint is the parameter of colour that allows us to distinguish between colours.
Also called FireWire or iLink. A serial bus which can address up to 63 devices, communicating at up to 400Mbps but is limited to a cable length of 4.5 meters. Its content copy protection scheme is called DTCP or 5C. Most DV camcorders have a IEEE 1394 port as well as D-VHS VCRs and some set- boxes for cable and satellite.
In audio, a particular system’s ability to reproduce sound so that it seems to be coming from a particular location.
An infra-red (IR) remote control transmits in the spectrum of infra-red light, such as a television remote. Unlike RF remotes, IR remotes must point at the receiver (line of sight) or reflect the IR from the screen to the receiver. Typical range is limited to 30 feet including the distance to and from reflected surfaces.
For example, if you are controlling a projector and you point the remote at the screen which is 12 feet from you and the projector is 10 feet from the screen, then the total distance is 22 feet. Unlike RF remotes, IR remotes must have a clear path or a clear reflected path to the IR receiver to operate.
Most projectors have an IR sensor in both the front and rear of the projector, whereas, flatpanels generally have a single IR sensor in the front of the unit. When working at or near the maximum distance, pointing right at the receiver will give better results.
Interactive projectors became popular in 2010 and come in many variations. As the name implies, the presenter is allowed to interact with either the projected image and/or the projector or, in some cases, another device using either an electronic pen or a mechanical pen or even a finger.
These Interactive Projectors essentially create an electronic whiteboard on any surface where the image is projected. As the presenter "writes" on the projected surface the motion of the electronic or mechanical pen is captured and overlaid on the video image.
This ability to capture motion of the pen or object can also be used to control a device such as a computer slide show. On some system the annotation and/or control can be captured and replayed, printed, copied or distributed. There are even homemade solutions. For example, using a Nintendo Wiimote and infrared LED light pens.
A process where a video image is delivered in two fields each containing half the video image rather than a single frame that contains the entire image. The first field contains all the odd lines and the second field contains all the even lines. For example, each 480i frame is made up of two fields of 263 and 262 lines of resolution and updated at 60Hz. 480 denotes the active picture area; however, the total frame size is actually 525 lines. 480i and 1080i are interlaced signals whereas 720p is a progressive signal where each video image is delivered in a single frame. Interlaced video was introduced with the first televisions because of bandwidth limitations.
Invert image flips the image from to bottom, to compensate for ceiling mounting a projector upside down. Projectors typically ceiling-mount upside down, because most have a built-in offset that allows you to mount the screen at a comfortable height, yet still project an image without tilting the projector and causing keystone distortion.
Part 2 to follow .........