Showing papers on "Upsampling published in 1991"

The commutativity of up/downsampling in two dimensions

Abstract: The authors state and prove a theorem solving the problem of commutativity in two dimensions. It is shown under which conditions upsampling and downsampling can be interchanged in two dimensions. This is the generalization to arbitrary two-dimensional lattices of the result that one-dimensional upsampling and downsampling commute if and only if their sampling rates are coprime. Some illustrative examples are given. The result holds for arbitrary sampling lattices. >

Subband decomposition procedure for quincunx sampling grids

Abstract: Filters with diamond shaped passbands and stopbands are used in image and video processing for several different tasks, one of which is the subband decomposition of signals. This subband decomposition can be carried out in a tree-structured manner by using diamond prefilters followed by downsampling on quincunx grids at each stage. In order to use such a decomposition in hierarchical coding it is desirable to choose the lowpass filter to be a halfband filter so as to limit the amount of aliasing in the low frequency component of the signal at each stage. This paper addresses the design and implementation of a two-channel filter bank for such an application. A special class of one-dimensional (1-D) prototype filters is used to derive the filter banks. The procedure is based on obtaining a halfband filter using a pair of lower order halfband filters. The resulting solutions preserve the exact reconstruction property even when the filter coefficients are quantized, a property which is useful in implementation. Examples of such filter banks are presented.

Spread spectrum receiver

Abstract: PURPOSE:To reduce the synchronization acquisition time by utilizing positively a synonym phenomenon caused when an inverse spread signal obtained resulting from applying inverse spread processing to a spread spectrum signal is digitized by a down-sampling method. CONSTITUTION:When an inverse spread signal is digitized by a downsampling method in a spread spectrum receiver, a high frequency component is looped back and restores to a frequency within a frequency band less than a half of the sampling frequency. This is referred to as a synonym phenomenon. Thus, a noise signal is eliminated by a synchronizing signal detection filter 12 from the digitized signal in this way. The processing for synchronization establishment is implemented and when the synchronization is not established, the frequency search is tried for a frequency range below a half the sampling frequency and the synchronization is established. When the band width of the filter 12 is variable, the band width is made wide before the synchronization establishment to allow the synchronization to be easily established and the band width is made narrow after the synchronization establishment to a degree that an inverse spread signal is able to be passed. As the band width of the filter 12 gets narrower, the S/N of the inverse spread signal is improved.

Multiplier-free FIR filters with periodically time-varying ternary coefficients

Abstract: A multiplier-free realization for FIR (finite impulse response) filters is proposed. The realization uses a periodically time-varying (PTV) system, preceded and followed by an upsampler and a downsampler, respectively, to achieve time-invariant operation. The PTV system uses only ternary coefficients. With an upsampling ratio of 3 to 5, one can achieve coefficient precision of 9 to 25 bits, which is sufficient for most applications. The implementation requires only add/subtract operations with a few shift-and-add operations at the input and output of the PTV system. >

A General Theory Of Time-sequential Sampling

Abstract: In this paper, we consider the problem of optimum sampling of spatiotemporal signals. Recently, there has been increasing interest in this topic partly due to the advent of next generation television systems, and partly due to the growing need for sophisticated real time vision modules used in a variety of motion estimation and tracking tasks. Time-sequential sampling is a sampling paradigm in which samples are taken from the signal, one at a time, according to a prescribed ordering which is repeated after one complete frame of data is acquired. This paper extends previous work on time-sequential sampling [l] to include sampling on lattices with arbitrary geometries as well as sampling patterns which are replicated with arbitrary periodicities on these lattices. As a result, a unifying theory is developed which includes such classical field-instantaneous patterns as field-quincunx (body-centered orthorhombic lattice) and line-quincunx (hexagonal lattice with four field periodicity), proposed for downsampling of high-definition television signals, as specific examples. In this context, downsampling, e.g. from 2:l line-interlaced to one of the above patterns, can be analyzed in a straightforward manner. Such a treatment of downsampling also provides a systematic way for studying the aliasing effects of the ordering in which a signal is downsampled. The design and analysis of time-sequential sampling patterns is facilitated by introducing a powerful technique from the geometry of numbers which permits these tasks to be carried out in a coordinate system where the time-sequential patterns are rectangularly periodic. The resulting anti-aliasing patterns have a congruential structure. By further extending the theory to include time-sequential sampling on selected cosets of a lattice, we can analyze those sampling strategies for which the spectral replications are not confined to a geometrical lattice. This is the case with the bit-reversed sampling pattern.