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Aliasing

An artifact produced by distorting or not using the high-frequency components of an image, signal, data stream, etc. due to some limitation such as undersampling or inadequate detection bandwidth. The result is unwanted appearance of low-frequency components (aliases), which produce a jagged edge, or stair-step effect. These must be filtered out and replaced with the missing high-frequency components. The process of removal/replacement of frequencies is called "anti-aliasing".

Analog

A form of data transmission using a continuously variable signal, in contrast to digital transmission, which breaks everything into numbers.

Analog to Digital Converter

A circuit that uses digital sampling to convert an analog signal into a digital representation of that signal This is done by taking samples of the analog signal at regular intervals. Each analog sample value is then quantized into a binary code.

Anti-aliasing

A filtering process to prevent aliasing or to reduce the aliasing that is already in the signal. For instance, smoothing out diagonal lines or curved surfaces in a digitally generated wipe pattern, or text from a character generator are particular cases of anti-aliasing. With reference to images it commonly means prevention of "jaggies". Removal of the same artifacts after sampling is usually more difficult and normally involves greater softening of the image.

Artifacts

A defect or distortion of the image, introduced along the sequence from origination and image capture to final display. A natural by-product of digital compression methods such as JPEG and MPEG, which permanently discard pixels. The greater the compression used, the more artifacts are likely, and fast motion sequences are a major contributor. As TV screens become larger, the distortions are more noticeable. When analog material is converted to digital, tiny discrepancies (quantization errors) may result.

Bandwidth

A range of frequencies used for transmitting information such as images and sound. In electronic communication, bandwidth is the width of the range (or band) of frequencies that an electronic signal uses on a given transmission medium. In this usage, bandwidth is expressed in terms of the difference between the highest-frequency signal component and the lowest-frequency signal component. Since the frequency of a signal is measured in hertz (the number of cycles of change per second), a given bandwidth is the difference in hertz between the highest frequency the signal uses and the lowest frequency it uses. For U.S. television broadcasters, the Federal Communications Commission (FCC) has allocated 6MHz for each channel. For DTV, the maximum bitrate possible within the bandwidth is 19.4 Mbps, which is used by one HDTV channel. SDTV has a lower bitrate, therefore the same bandwidth can accommodate more than one channel.

Bitrate

In telecommunications and computing, bitrate (or bit rate) is the number of bits that are conveyed or processed per unit of time. Bitrate is synonymous with data rate. The bitrate is quantified using the 'bits per second' (bit/s or bps) unit, often in conjunction with an SI prefix such as kilo- (kbit/s or kbps), mega- (Mbit/s or Mbps), giga- (Gbit/s or Gbps) or tera- (Tbit/s or Tbps). In digital communication systems, the gross bitrate, raw bitrate, data signaling rate or line rate is the total number of physically transferred bits per second over a communication link, including useful data as well as protocol overhead.

Block Artifacts

Video uses lossy compression, and the higher the compression rate, the more content is removed. Block artifacts are distortions that appears in compressed video material as abnormally large pixel blocks. At decompression, the output of certain decoded blocks makes surrounding pixels appear averaged together and look like larger blocks. This occurs when the encoder cannot keep up with the allocated bandwidth. As TVs get larger, blocking and other artifacts become more noticeable.

Color TV System

A method of encoding a color TV picture, according to agreed international specifications. The three major world systems are NTSC, PAL and SECAM.

Compression

A means of reducing the amount of data to be transmitted or stored. In communications, data compression is helpful because it enables devices to store or transmit the same amount of data in fewer bits, thus making the transmission of the data faster. Compression is possible since there always is some amount of data redundancy or there may be a predictable flow to the data. These characteristics of a set of data or a stream of data allow the use of a sort of mathematical algorithm to represent or describe the original data in fewer bits. Compression falls into two main categories: lossless compression and lossy

compression. With lossless compression, the original data can be restored to be an exact replica of the original, whereas with lossy compression, one accepts some quality losses in the compression/decompression steps. Lossy compression is used mainly for audio and video data, for which the loss in data quality is easily overlooked by the human user. A matching decompression process reverses the compression process and restores the data to its original form, or an approximation thereof. Compression serves to improve the efficiency of data transmission and storage, and is especially valuable if bandwidth and memory resources are limited.

Discrete Cosine Transform (DCT)

A technique used in signal and image processing and particularly in lossy compression techniques. DCT separates an image into discrete blocks of pixels of differing importance with respect to the overall image. DCT expresses a function or signal in terms of a sum of sinusoidal waveforms that vary in amplitude and frequency, essentially transforming the image from the spatial domain into the frequency domain. In the process, the average luminance of each block is evaluated using the DC coefficient. Transform compression is based on the premise that the low-frequency components of a signal are more important than the high-frequency components. Therefore, a substantial reduction in the number of bits used to represent a high-frequency component will degrade the quality of the image only slightly.

Decoder

A device performing a 'decoding' function (i.e. a digital-to-analog converter).

De-interlacing

De-interlacing is the complex process that converts a traditional interlaced video source like common analog television signals, into the progressive scan format required by modern high definition displays. However, not all de-interlacing processors are equal, and some other de-interlacers on the market will leave you looking at noisy artifacts and motion blurs.

Digital

Expressed or represented by a series of numbers. For example, a digital signal is expressed by the numerical value of the signal size at regular points in time. Sounds and pictures can be recorded, stored, and played back digitally with no distinguishable difference from the original if the time interval between samples is sufficiently small.

Digital to Analog Converter

A device (usually, a micro-chip) which transforms a signal from digital form to analog form. This is done by conversion of binary codes into analog signal values and holding these signal values during sampling intervals.

Encoder

A device performing an 'encoding' function (i.e. an analog-to-digital converter).

Field

Half of an interlaced video frame containing either all the odd or even horizontal lines. The frame is the entire image consisting of two fields. An interlaced image such as the NTSC analog television standard draws all the odd lines of an image followed by all the even lines of an image (first drawing lines 1, 3, 5, 7, and so on then coming back to draw lines 2, 4, 6, 8, and so on). A field consists of all the odd or even lines that combine to create a complete image.

Format Conversion

Any transformation from one video format to another (i.e.from serial digital component video to serial digital composite video). This term is often used informally to imply that an encoding/decoding process is taking place.

FPGA

Field Programmable Gate Array is an integrated circuit programmable in the field after manufacture.

Frame

One complete screen in a video image. A single frame is related to a single picture. By combining multiple frames in rapid succession, the illusion of motion is created. In the movies, 24 frames pass by every second. On television, there are 30 frames displayed each second.

Frames Per Second (FPS)

A measure of the number of pictures (or frames) that are displayed per second to create a moving image. For TV, this is typically between 50 and 60 FPS.

Frame Rate Conversion

Conversion of video signals from one frame rate to another, usually preserving the number of lines per frame.

Frame Synchronizer

A device which retimes an incoming video signal to a set reference such as genlock, bi-level or tri-level sync signals

Interlaced Scan

For television display, interlaced scanning refers to the process of transmitting and re-assembling a single picture frame from two passes of the image. First the odd lines (i.e. 1,3,5,...) are transmitted together, and displayed on screen. Next, the even lines (i.e. 2,4,6,...) for the same frame are transmitted and displayed. The entire frame is displayed in two passes, or scans, each taking 1/60th of a second. The human eye sees it as a single picture. Interlaced video was originally invented to reduce flicker given that video technology of the time could not draw video frames fast enough to keep the top of the picture from fading before the bottom of the picture was completed.

Jaggies

Professional jargon for spatial aliasing (i.e. Stair-like lines) that appear in an image where there should be smooth horizontal straight lines or curves. They can occur for a variety of reasons, including a lack of pre-filtering or if the output device does not have enough resolution to portray a smooth line

Jitter

Small,unwanted, periodic, rapid variations in timing and/or displacement upon transmission or arrival of digital signal due most often to mechanical disturbances.

Judder

A temporal artifact associated with moving images when the image is sampled at one frame rate and converted to a different frame rate for display. As a result, motion vectors in the display may appear to represent discontinuously varying velocities.

Mosquito Noise

Mosquito noise is a type of distortion sometimes seen around the edges of moving objects in MPEG and other video frames that are compressed with the discrete cosine transform (DCT). It is characterized by moving artifacts around edges and/or by blotchy patterns superimposed over the objects, resembling a mosquito flying around a person's head and shoulders. Mosquito noise usually occurs during decompression when the decoding engine has to approximate the discarded data by inverting the transform model. The mosquito noise appears as random aliasing in these areas and requires sophisticated detection circuits to eliminate it. As TVs get larger, mosquito noise and other artifacts become more noticeable.

Motion Adaptive

A processing technology whose optimizing formula varies, depending on whether the subject matter depicted is stationary/steady or moving/changing. The best devices may vary their processing dozens of times within a single scan line. The device must digitize several video fields, save them on a rolling basis, and compare the content in small groups of pixels to determine whether subject matter was moving or not, for the purpose of avoiding or reducing some motion related artifacts.

MPEG2

High-quality audio/video compression format developed by the Motion Picture Experts Group using perceptual coding and predictive technologies similar to MPEG1 but including a higher bit-rate and more control over the compression and technology. MPEG2 features a bitrate of 3.5 to 10 megabits per second as opposed to MPEG1’s 1.5 megabits per second. The MPEG2 format can be used to provide very high-quality images and is used with DVD, DBS (direct broadcast satellite) and HDTV (in a modified high-resolution format).

MPEG4

MPEG-4 was defined by the Moving Picture Experts Group (MPEG) and is designed to deliver DVD (MPEG2) quality video at lower data rates and smaller file sizes. Like MPEG1 and MPEG2 previously did for CD-ROMs and DVDs, MPEG4 promises to create interoperability for video delivered over the Internet and other distribution channels. MPEG4 will play back on many different devices, from satellite television to wireless devices.

Noise

Any unwanted distortions or artifacts in analog and digital video images that are caused by a variety of circumstances. Various types of noise have been defined including mosquito noise, granular noise, Gaussian noise, impulse noise, quantization noise, etc...

NTSC

An abbreviation for the National Television Standards Committee. An analog video format with 525 lines per frame at 60 fields/second, used as the broadcast standard for United States, Canada, Japan and several other countries.

PAL

An abbreviation for Phase Alteration Line. An analog video format with 625 lines per frame, at 50 fields/second, used as the standard for most Western European broadcasters, and other parts of the world (outside North America and Japan) including South America, Asia, and Oceania

Progressive Scan

Most computer monitors, and some high-definition TV sets use progressive scan, as opposed to the NTSC standard of interlaced. In progressive scanning, all the horizontal scan lines for a single frame are painted on the screen from top to bottom in a single pass. Progressive or non-interlaced video produces a higher quality image.

Pulldown (3:2 Pulldown)

One method of committing a 24 frame per second movie on film to 60 field per second or 60 frame per second video. Every other film frame is scanned three times and the intervening frames scanned twice to obtain video fields or frames.

Refresh Rate

The vertical scan rate of a video display, or the number of times per second that a video display can paint an entire screen with a video signal. The standard refresh rate in the U.S. for video (television, DVD, VHS, laserdisc) is 60 Hz.

Scaling

The reformatting of video or digital pictures to occupy a different number of scan lines or a different horizontal or vertical pixel count. Also referred to as "re-sampling". This is done to zoom an image on the screen without spreading out the existing scan lines, or to change the video from one format to another, for example HDTV to NTSC or NTSC to SECAM.

Scanning Standards

A set of parameters defining the scanning, blanking and synchronization processes. Usually represented in short-form as three numbers separated with a slash: Number of Lines/Field (Frame) Rate/Interlace Ratio (i.e.1250/50/2:1).

SECAM

An abbreviation for Sequential Couleur avec Memoire. A television broadcast standard in France, the Middle East, and most of Eastern Europe, SECAM uses a similar timing and resolution to PAL, and is one of three main television standards throughout the world.

Serial Digital Interface (SDI)

A SMPTE standard for digital video transmission over coaxial cable. The SDI signal can also contain up to four independent digital audio signals along with the video signal. Two variations of SDI standard exist, based on the data rate: standard-definition (SD)-SDI and high-definition (HD)-SDI. The SDI standard is widely used in broadcasting and the video production industry because of the ability to transmit video signals over long distances with no loss of information.

SMPTE

An abbreviation for the Society of Motion Picture and Television Engineers. SMPTE is a professional organization that recommends standards for the film and television industries.

Standards Conversion

The conversion of video signals between different scanning standards (i.e. NTSC to PAL, or 1250/50/2:1 to 625/50/2:1).

Telecine

A device that transfers motion picture film to video. This sometimes involves changing the frame rate by inserting a 3:2 pulldown.

Transcoding

The conversion of video signals with different color TV systems but with the same scanning standard (i.e. PAL to SECAM, NTSC to PAL, etc...). Often used in North America (particularly Quebec) to mean standards conversion.

Upconversion

The conversion of video with a lower picture resolution to one with a higher definition. Typically, it refers to taking programming in standard definition (480i) and making it into high definition (720p, 1080i, or 1080p). This is done though interpolation, which gives a false precision as to what the extra pixels should be.