MIL-HDBK-1300A
bw. Data interface - Refers to the communications interface required for a terminal device to operate properly over a communications channel.
bx. Data link layer - Layer two in the ISO OSI Reference Model. The role of the data
link layer is to group the bits of the physical layer into frames, and to deal with transmission errors to allow the sending of frames between adjacent nodes in the network.
by. Data Terminal Equipment (DTE) - 1. Digital end instrument that convert the user information into data signals for transmission, or reconvert the received data signals into user information. 2. The functional unit of a data station that serves as a data source or a data sink and provides for the data communication control function to be performed in accordance with link protocol. Note: The DTE may consist of a single piece of equipment that provides all the required functions necessary to permit the user to intercommunicate, or it may be an interconnected subsystem of multiple pieces of equipment, to perform all the required functions.
bz. Data transfer rate - The average number of bits, characters, or blocks per unit time passing between corresponding equipment in a data transfer system.
ca. Data unit - A block in DCT-based processes; a sample in lossless processes. cb. DC coefficient - The DC coefficient for which the frequency is zero in both
dimensions. Note: The DC coefficient (in the context of JPEG compression) is a measure of the
average value of the 64 image samples within an 8x8 block. Because of the usually strong correlation between the DC coefficients of adjacent blocks, the DC coefficients can be very efficiently encoded, and are treated separately from the encoding of the AC coefficients.
cc. DC prediction - The procedure used by DCT-based encoders whereby the quantized DC coefficient from the previously encoded 8x8 block of the same component is subtracted from the current quantized DC coefficient.
cd. DCT coefficient - The amplitude of a specific cosine basis function. Note: The
Discrete Cosine Transform changes the representation of an image from a set of numbers
representing the brightness of each pixel to another set of numbers that can be used to reconstruct the image mathematically. The process is similar to synthesizing music electronically from separate tones. In this case the "tones" are cosine basis functions, each of which have the properties of amplitude and frequency; but instead of referring to amplitude and frequency as a function of time, these properties relate to each of the two principal directions across the image. For this reason, the term spatial frequency is often used to emphasize that the process involves direction rather than time. The coefficients in the DCT matrix are the amplitudes of these basis functions. There is always one basis function with a zero frequency in both directions. In simple terms, "zero frequency" implies a constant, and the coefficient of this wave is labeled DC. All other coefficients have at least one non- zero directional component, and are labeled AC. The terms DC and AC are analogous to the zero- frequency (DC) and non-zero frequency (AC) components in electrical circuits.
ce. Decoder - An embodiment of a decoding process.
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