Glossary of Selected Video Terms

 

3:2 Pulldown

3:2 Pulldown – Movies are filmed at twenty-four frames per second (fps). Televisions display a picture at thirty frames per second. If we simply show the movie at 30fps it will appear to go too fast—the “Keystone Cop” effect. The 3:2 pulldown method repeats selected movie frames a second time to display the 24fps movie on the 30fps television at the right speed. Note that in interlaced presentation (420i, 1080i) as shown schematically at right, two of five TV frames show a mix of two frames. The effect of this is noticable to some. Since progressive presentation shows an entire TV frame in 1/60 second, this mixing of film frames never occurs, but successive film frames are shown for either 1/30 or 1/20 second, again, noticeable to some.

480i, 480p, 540p, 720p, 1080i, 1080p – All are descriptions of television scan rates, designating the number of lines from top to bottom of the screen and whether the lines are displayed as interlaced (i) or progressive (p).

Black Level, Blackness – The Brightness control on a television actually sets the black level of your picture. That is, it sets the darkest color you can see. On a television, black is not truly black, it is the darkest shade of grey that can be displayed on the screen. Compare with White level.

Brightness – see Black level.

Color, Color Control – This controls the intensity or saturation level of color in the picture. At its lowest intensity, the picture appears to be black and white. At its highest intensity, all colors are very bright and appear to glow.

Component Video CableComponent Video, Component Video Cable – the most common method of displaying High Definition and Progressive scan video signals. Although the signal itself is usually digital, Component Video is actually a high-resolution analog display method. The three wires in the cable are color coded green, blue, and red and are often labeled Y/Pb/Pr. Compare with DVI (Digital Video Input) and HDMI.

Composite Video Cable

Composite Video, Composite Video Cable – the combined color signal provided via broadcast over the airwaves or via cable. It was originally developed so that old black and white sets could receive the same broadcast as color TV's.

Contrast – See White level.

Contrast Ratio – The brightness ratio (in lumens) between the brightest color your television can display (white level—see White level) and the darkest color (black level—see Black level.) your television can display. On better display formats this is over 2000:1.  Note that this figure is only meaningful on a properly calibrated TV.  In color, the Human eye can only see a contrast ratio of about 800:1.  When you see a contrast ration of 200,000:1, for example, the measurement was taken under circumstances you will never encounter while viewing (usually full contrast up/brightness up vs TV off (literally).  These numbers are, at best, a reference for comparing TVs, they are rarely if ever meaningful measurements.

Digital Streaming – see Streaming

Digital Television, Digital TV, Digital Video – Since it's invention in the 1940's television has all been analog. Broadcasting a single analog channel uses a lot of bandwidth. The number of channels available using the old NTSC system is very limited. In addition, all the pictures are 4x3 (1.66) format. The picture is only one third wider than it is high. In 1998 the FCC approved a new digital broadcast standard that allowed a lot more channels and eighteen different broadcast formats (e.g. 480i, 480p, 1080i see scan). Of these eighteen formats, eight are considered High Definition or HD. The rest are considered standard definition, SD, for which the picture is not as good. All HD formats are wide-screen, which means a 16x9 (1.78) width to height ratio. Some of the new SD formats are also in the “wide” 16x9 format; the rest are still 4x3.  Note that this 1.78 ratio is a broadcast video standard not a movie standard.  Only movies made for TV at shot at 1.78.  Most movies today are filmed at 2.39 (called 2.4) which is much wider.

DLP

DisplayPort - A very robust standard for a Digital Video Interface/Encoding from VESA.  Developed as a successor to DVI, DisplayPort supports many more formats than other standards including HDMI.  DisplayPort output, usually on a computer can usually be converted to any other kind (e.g. HDMI) with inexpensive adaptors.

 

DLP (Digital Light Projection) – A type of Projection TV that uses light reflected by an optical semiconductor (called a Digital Micromirror Device chip, or DMD) to create a picture. Systems may use one light source with a color wheel, or three light sources. Although the optics with three lights is easier to control and gets rid of the "rainbow artifact" completely, the color wheel method is still more common. Invented in 1987 by Texas Instruments, the DMD uses millions of microscopic mirrors to redirect light. The mirrors are spaced less than 1 micron apart—much closer than the pixels in an LCD panel.

DVI (Digital Video Input) – An alternative to component video for true digital input to a television for display of HD video. A significant difference between HDMI and DVI is that HDMI supports audio as well as video.  This interface is obsolete in the video world and rapidly disappearing in the computer world in favor of HDMI or VESA DisplayPort.

Frame, Frame Rate – Televisions display pictures as a series of still pictures called frames. If we show consecutive frames fast enough, objects in the series of pictures appear to be in motion. The frame rate is how fast the frames are displayed. Televisions use a frame rate of 30 frames per second. This is too slow to appear to the eye as smooth motion; that is, the picture will flicker. See Scan for an explanation of how this is handled.

 

HDMI (High-Definition Multimedia Interface) – An alternative to component video for true digital input to a television for display of HD video. A significant difference between HDMI and DVI is that HDMI supports audio as well as video.

HDTV (High Definition Television) – eight of the eighteen digital TV formats approved by the FCC. All HD formats are wide-screen (16x9). The image information is denser, resulting in a clearer picture with more detail. See Digital Television.

IP (Internet Protocol) – Internet Protocol specifies the format (the layout) and the addressing scheme (how the system knows where it goes) in a network like the internet. It's used in other places besides the internet, and one of them can be a network that passes commands from remote control units to a media server or an automation control device.

IR (Infrared) – A method of transmitting remote control signals to electronic devices using infrared light, which is invisble to the human eye. Most consumer remote controls use IR. This method is strictly line-of-sight and cannot be used to control devices through walls or furniture. As a result, it is often used for home theater but rarely for home automation applicatons like controlling the lights or air conditioning. See RF for a common alternative.

Interlaced, Interlaced Scan – A scan method in which the scan lines are shown in two series: first the odd numbered lines are displayed, then the even numbered lines. Compare to Progressive Scan.

LCD, LCD TV, Liquid Crystal Display – a solid-state display technology used in televisions. Light passes through a panel of “liquid crystals” and produces an image directly on a flat panel television (this technology was alos used in rear projection television). LCD televisions tend to be very light weight and provide very good picture quality. Their primary drawback is they tend not to be as bright as some other technologies such as plasma.

Media Server, Multimedia, Multimedia Server – a computer-based device that provides audio or audio/video data (including “still” photos and text) to an IP distribution network, available to multiple locations. Dynamic content is delivered via streaming technology.

OLED (Organic Light Emitting Diode) – a light-emitting diode (LED) that generates light in a film of organic compounds. A significant benefit of OLED displays over traditional liquid crystal displays (LCD's) is that OLED's do not require a backlight to function. Because there is no need to distribute backlighting, an OLED display can be much thinner than an LCD panel. OLED-based display devices also can be more effectively manufactured than LCD's and plasma displays. But degradation of OLED materials has limited the use of these materials. OLED TV's are not expected to be available until at least 2010.

Plasma, Plasma TV – Plasma is a television display technology that provides very high quality pictures on extremely thin flat panel displays that can be wall mounted. Plasma televisions are similar to conventional televisions in that they use a coating (a “phosphor”) on the front of the screen to create the picture. However, instead of a heavy picture tube, plasma televisions use a very hot gas (a “plasma”) to light up the phosphor. Plasma screens show excellent pictures (in some cases the best pictures) and can be viewed from very wide angles, but tend to be expensive. Plasma televisions can fade over time just like picture tube televisions, but have very few technological or picture-quality drawbacks. However, it is important to note that a number of “low-priced” plasma televisions are available at the bottom of the price range. Even though these will accept a high-definition signal, most do not display it as a high definition picture. They “down-convert” the picture to a lower resolution picture (usually 480p) so it does not look nearly as good as it should. HD plasmas only cost a few hundred dollars more and produce a much better display.

Progressive, Progressive Scan – A scan method in which the scan lines are shown in a single series from the top of the frame to the bottom. The system displays the entire frame twice in a row. Compare to Interlaced Scan.

Projection TV – Any television where the displayed picture is not created on the viewing screen itself, but is projected onto a separate screen, similar to a movie screen.

Pulldown – See 3:2 Pulldown.

RF (Radio Frequency) – A method of transmitting remote control signals to electronic devices using radio waves. Unlike Infrared, RF is not line-of-sight and can operate through walls. RF is often used for home automation applications like controlling the lighting since the receiver/server may be in a different room from the lights. However, RF is not commonly used for Home Theater since Viewers are usually sitting right in front of the television they are watching and IR is more immune to interference. See IR for a common alternative.

S-Video & SVHS (Super VHS) – is a type of VCR recording that provides a higher quality picture than standard VHS but not as good as DVD. SVHS is the original source of the S-Video display method. S-Video was useful for long runs when the television was far from the source of the picture, but has been superceded by newer technology, such as HDMI over Cat-5e or CAT-6. It's usefulness will continue to fade.

Scan – Televisions and movie projector create “moving pictures” by showing a series of still pictures one after another, very rapidly. In both movies and tv, each still picture is called a frame.

That's where the similarity ends. In a movie, each frame is a complete picture, which you can see by looking at a section of movie film with a magnifying glass. On a television, each frame is a set of straight lines drawn across the screen, starting at the top and sequencing toward the bottom. Television technology draws thirty new frames every second. This causes a problem: if frames are displayed at a rate much slower than sixty frames per second, the human eye can detect the individual frames and the “moving picture” flickers.

To overcome the flicker problem, television technology draws the frames at a rate of sixty times a second. Since there are only thirty frames, this raises the question, “where do the extra frames come from?”

There are two ways to accomplish this. In the way regular television has always worked, the systems draws each frame twice, but only half of the lines each time. The first time, it draws the odd numbered lines (1, 3, 5…) in half of one thirtieth of a second (i.e., one sixtieth of a second). In the next sixtieth of a second, the system goes back to the top of the screen and draws the even numbered lines (2, 4, 6…). In this way, it takes one thirtieth of a second to show a frame, but the screen is redrawn twice in that amount of time. This method of displaying the screen is called interlaced because of the alternating lines.

A newer way of displaying the television frames is called progressive. In this method, the lines are displayed in their real order (1, 2, 3, 4, 5…). To avoid flicker, the frame is displayed in one sixtieth of a second, and then displayed a second time in the next sixtieth of a second. This uses up the entire thirtieth of a second allotted to each frame.

Another factor in the definition of the scan format is the number of lines from the top to the pottom of the screen. In the original way of displaying the picture, the technology used 480 lines. Using the suffix “i” for interlaced and ”p” for progressive completes the modern method of labelling the scan format for television display. 480i indicates 480 lines, displayed using the interlaced method—this is original way all television was broadcast. 480p indicates the same sized picture, but shown using the progressive method. Two of the new high definition formats are 720p (720 lines displayed progressively) and 1080i (1080 lines displayed with interlacing).

Sharpness – in the world of digital television, this term describes edge enhancement in the television picture. The higher the sharpness, the more the edges of objects on the screen tend to show. Unfortunately, this is not really an adjustment of the focus, as it would be with a camera or a CRT television. It is an electronic process that makes edges bigger. This effect usually results in the fat edges covering up picture detail, thus distorting the picture. A good guideline is to turn sharpness all the way down. If you then take some time to get used to the increased detail, the picture will be much better. If the picture is just too soft-looking, a test pattern should be used to properly adjust the sharpness.

Streaming, Digital Streaming, Streaming Technology – transferring data so that it can be processed as a continuous stream. Streaming originated as an internet technology, developed because most users don't have fast enough access to download large audio or video files in reasonable time. The data is converted from analog form to digital form (digitized data), which conveys much more information in the same bandwidth. The receiving device starts displaying the data before the entire file has been transmitted by collecting the data, which may arrive sporadically, and saving it in a buffer. It then passes the data along at a uniform rate. If the client receives the data more quickly than is needed, the buffer holds the excess. If the data arrives too slowly, its presentation will be sporadic unless a significant amount of it is received and buffered before playback begins.

THX – An audio and video standard for movie reproduction. Originally put forward by George Lucas, this tells how a DVD player should produce a picture and how the surround sound channels should work. There are many flavors of THX including Select, Ultra, and Ultra 2. Many people contend that good THX reproduction is often not good music reproduction. Ultra 2 addressed some of this critcism.

Tint, Hue – The control on a television that adjusts the hue of color you see on the screen. Typically this control adds red or blue to the overall appearance of the picture. Green is generally unaffected.

White Level, Whiteness – The Contrast control on a television actually sets the white level of your picture—the brightest color you can display. Compare with Black Level.

Wireless – A system of controlling a device with a “remote.” The Remote Control can signal the device using either Infrared (IR), or Radio Frequency (RF).