1-D signal - A signal that its value depends only on one independent variables. Such a signal is an audio signal (its value depends on the time).
2-D signal - A signal that its value depends on two independent variables. Such a signal is an image (its value depends on the width and the height).
Analog signal - A signal that takes analog values e.g. electric voltage or electric current intensity.
AR modelling - A power spectrum estimation algorithm driven by a white noise process.
Autocorrelation - A function that estimates the product of a signal by its complex conjugate.
Blackman-Tukey estimator - A power spectrum estimator that produces smooth estimation by using a suitable window.
Circular convolution - A convolution were the delay variables are calculated circularly, by using modΝ, where Ν is the length of the signal.
Cosal prediction - The prediction of a pixel luminance value based on the pixels luminance values that have been already calculated.
Digitization - The process that converts a signal (audio, image etc.) from analog to digital.
Distinct signal - A signal that takes values only for distinct values of its variables. It is usually a result of an analog signal sampling.
Edge detector mask - A matrix that contains weight vectors that are used to detect edges towards certain directions.
Edge detection operators - Arithmetic operators that when they are applied on an image or a part of an image they detect its edges.
Edge following - The process that is applied on an edge image in order to detect connected edges.
Edge thresholding - The process that follows an edge detector algorithm and decides whether an edge is present or not. The thresholding can be based on local or global information.
Entropy coding - A coding algorithm based on the coding of the luminance of an image.
FFT Butterfly - The elementary calculation in FFT.
Filter - A 2-D discrete system that transforms a signal (input) to another signal (output).
Histogram - A function that shows the luminance values distribution of an image.
Hough Transform-An algorithm that detects small geometrical shapes in edge images.
Huffman coding - A coding algorithm that uses codewords to replace the most probable bit sequences with codewords of small length.
Huffman tree - A tree structure that is used to construct the Huffman code.
Image edge -The border between two homogeneous regions of an image, which have different luminance values.
Impulse response - The output of a system when its input is an impulse.
Impulsive noise - Noise that appears as white or black pixels.
Image entropy - A measure of the information contained in an image.
Image compression - Techniques that are used to reduce the memory needed for the storage of digital images.
Lowpass signal - A signal that its spectrum has a lot of energy around the origin (low frequencies).
LZW algorithm - A lossless compression algorithm based on the formation of a matrix that contains codewords. Each codeword corresponds to a bit sequence. The more probable a bit sequence is, the shorter the codeword should be.
Laplace operator - It is defined based on the second order partial dirivants of an image function. It is used as an edge detector.
Luminance local variance - A measure for the homogeneity of an image region. When the local variance is small the region is considered homogeneous.
Modified READ coding - Coding that takes into account vertical correlations among run transitions in consecutive image lines.
Modified Huffman code - Modification of the Huffman code based on statistics observed when typical documents were transmitted using FAX.
Multidimensional signal - The signal that its value depends on more than two independent variables.
Neighboring pixel - A pixel that is spatially next to another pixel.
Prediction coding - A coding algorithm that takes into account the spatial correlation of pixel values in order to predict neighboring pixel values.
Predictive differential pulse code modulation - Coding using prediction coefficients and coded prediction error.
Optical detector - The mechanism for digital image formation. There are two types; the photochemical (film) and the photoelectric (camera).
Photoelectric detector - It is a digital image formation mechanism that is used in cameras. Types of photoelectric detectors are Vidicon, Charge Injection Denices (CID), Charge Coupled Devices (CCD) cameras.
PCM modulation - A coding scheme that uses a uniform quantizer.
Prediction window - A small part of a signal (neighbor) that is used for prediction.
Periodogram - The Fourier transform of the autocorrelation function.
Predictability - The ability to predict the luminance of a pixel based on the luminance values of its neighborhood.
Prediction coefficients - The coefficients of the prediction window that can be selected to optimise the prediction of the signal.
Quantization - The process that substitutes the values of a signal with approximations which are contained in a set of values.
Row column FFT - An algorithm that calculates DFT by using 1D DFTs over rows and columns.
Run length coding - A coding algorithm that uses the number of sequential pixels with equal luminance.
Spectrum distortion - Any change in the spectrum of a signal (e.g. if certain frequencies are removed)
Sample - The value of a signal at a certain moment (e.g. for an audio signal) or at a certain point (e.g. for an image).
Sampling interval - The time interval between succesive samples during the sampling process.
Separable signal - A 2-D signal that can be expressed as a product of two 1-D signals.
Sampling frequency - The frequency that is used to sample an analog signal and produce a digital signal.
Spectrum - The Fourier transformation of an image or a signal in a frequency domain.
Support region - The orthogonal region where a discrete signal takes non zero values.
Transform image coding - Any coding that uses coefficients of an image transformation, in order to compress an image.
Transition pixel - A pixel in the reference line or the coding line that indicates a luminance change (used in modified READ coding).
Uniform sampling - The sampling process with equal sampling intervals (e.g. one sample every one second).
Vector Radix FFT - An algorithm that calculates DFT by using smaller 2-D DFTs.
White noise - The noise that spreads equally in all frequencies.