Showing papers on "Upsampling published in 1995"

Temporal and spatial error concealment techniques for hierarchical MPEG-2 video codec

Abstract: The MPEG-2 source coding algorithm is very sensitive to the channel disturbances. For instance a single bit error in the bitstream will cause a high degradation of picture quality due to error propagation. Hence, for picture replenishment error concealment techniques (ECTs) may be required at the receiver. The aim of the article is to study different ECTs for MPEG-2 hierarchical coded pictures applied for terrestrial broadcasting. For the base layer different temporal and spatial ECTs are investigated. Two temporal ECTs are considered: a simple temporal error concealment (EC) and a temporal EC with motion compensation. The latter method provides the best results in inter coded pictures (where motion vectors exist). For the intra coded pictures, where no motion information exists, two spatial interpolation techniques are considered. The main problem for spatial EC in MPEG-2 coded pictures is that only the top and the bottom macroblock can be used for interpolation, since one error in the bitstream causes one damaged horizontal stripe of macroblocks in the picture. Different ECTs for the upper layer of hierarchical coded pictures are also investigated. The possibility of upsampling the base layer for concealing the upper layer made by spatial scalability gives best results.

Modulator for a broadband communications system

Abstract: A multi-channel modulator for the transmission of telephony signals within a broadband communication system An interpolation module generates processed I and Q signal components by upsampling filtered I and Q signal components In turn, these processed I and Q signal components output by a filter are passed to a set of channel modulators Each channel modulator accepts a pair of processed I and Q signal components and, in response, modulates a selected carrier signal with one of the telephony signals to produce a complex modulated signal An adder module responds to the complex modulated signals by summing the real signal components to produce a real resultant signal, and to sum the imaginary components to produce an imaginary resultant signal A digital-to-analog converter (DAC) module coverts the real resultant signal and the imaginary resultant signal, which are represented by digital data streams, to analog signals A transmitter, responsive to the analog signals, transmits the modulated signals within a frequency band of the broadband communications network

Image resizing in the discrete cosine transform domain

Abstract: Image resizing is a task that must often be done when processing digital images. We present a novel approach to resize images by operating entirely in the discrete cosine transform (DCT) domain. We implement the lowpass filter for anti-aliasing or anti-imaging using the convolution-multiplication property of the DCT. We perform the equivalent of pixel-domain downsampling or upsampling by simple manipulation of the DCT coefficients. Our approach can be used as a standalone image resizing tool or it can be integrated into any image compression system based on a block DCT, such as JPEG, to provide an image resizing capability with relatively little additional complexity.

Preservation of subband symmetry in multirate signal coding

Abstract: The article derives necessary and sufficient conditions for a multirate linear phase FIR filter bank, acting on a symmetrically extended finite-length input signal, to produce either symmetric or antisymmetric downsampled subbands. Such techniques have gained popularity for image coding applications, and we provide the solution to a key technical problem in terms of the input and filter symmetries and the downsampling ratio.

Voice band enlarging device

Abstract: PURPOSE: To provide a clear voice with band feeling by enlarging a band limited voice band such as a telephone voice, etc., and synthesizing a wide band voice. CONSTITUTION: This device is composed of an LPC analysis part 12 extracting a spectrum envelope information and a residual waveform from an input signal, an envelope enlargement part 13 band enlarging the extracted spectrum envelope information, a drive voice source enlargement part 14 band enlarging an extracted residual signal, an LPC synthesis part 15 generating a synthetic voice by using the spectrum envelope information obtained from the envelope enlargement part and the residual signal obtained from the drive voice source enlargement part 14, a waveform smoothing part 16 smoothing the synthetic voice on a time base, a filter part 17 filtering a frequency band to be added to the input signal from the smoothed signal, an upsampling part 11 converting the input signal to a high sampling frequency and an addition part 18 adding an output signal from the filter part 17 to the output signal from the upsampling part 11. COPYRIGHT: (C)1996,JPO

Apparatus and method for upsampling chroma pixels

Abstract: A computer-implemented method and apparatus for upsampling subsampled chroma pixels of a picture. According to a preferred embodiment, there is provided a plurality of subsampled chroma pixels as well as a plurality of luma pixels. The subsampled chroma pixels are upsampled as a function of luma pixels of the plurality of luma pixels to provide at least one upsampled chroma pixel.

Tunable downsampling using fractional delay filters with applications to digital TV transmission

Abstract: An efficient technique for sampling rate conversion for arbitrary (incommensurate) ratios is proposed The technique is based on fractional delay filters that are efficient to implement and that can be controlled with a small number of arithmetic operations per output sample The authors consider an application in digital television (DTV) transmission where, according to present standard proposals, conversions between several incommensurate sampling rates must be possible Rather than trying to design separate rate fixed filters for each possible conversion, the authors outline a system which may be tuned for any possible downsampling ratio A sampling rate conversion system based on the straightforward and simple Lagrange interpolation technique is illustrated with a level and highly efficient implementation structure Various error sources involved are analyzed and a mean-square-error (MSE) type cost function is defined to aid in the system design

A class of high-precision multiplier-free FIR filter realizations with periodically time-varying coefficients

Abstract: Proposes a class of high-precision, multiplier-free realizations for FIR filters. These realizations use upsampling and downsampling in conjunction with a periodically time-varying system to achieve time-invariant, multiplier-free FIR filter operation. Nonbinary encoding schemes are used for obtaining the filter coefficients, which are periodically time-varying (PTV), i.e., they vary in a periodic fashion. Each target filter coefficient is directly mapped into a set of PTV coefficients so that the realizations are easy to obtain. The values of the PTV coefficients are restricted to either the ternary set. >

Spatial scalable HDTV coding

Abstract: In this paper, we discuss the coding strategy when a two-layer digital HDTV service is considered. We propose to use-three different strategies in performing compression to yield the best quality based on the respective requirements on bandwidth, picture quality and efficiency. These three modes are as follows. Strategy A: if the bandwidth for the enhancement layer is not sufficient to achieve high quality, the base layer encoder should perform the compression at a reduced spatial resolution using the combined bandwidth. The top layer video signal will be obtained from upsampling the base layer. Strategy B: if the bandwidth is sufficient to support quality requirements at both layers, the typical two-layer spatial scalable coding scheme is used. Strategy C: if the quality requirement at the top layer is critical, a single layer compression at a full spatial resolution is used. To receive the low resolution signal, certain bit stream scaling can be used to get a usable quality signal. A theoretical qualitative analysis gives an insight of our experimental results. Such a strategy is useful in designing future HDTV services for television sets with different capabilities, resolutions and complexities. The results are also applicable to the problem of HDTV/standard TV compatibility.

Making the Best of JPEG at Very High Compression Ratios: Rectangular Pixel Averaging for Mars PathFinder

Abstract: As more and more NASA missions are turning to image compression to maximize their data return at constrained bit rates, and very often adopting JPEG as the centerpiece of their image compression system, they are noticing one limitation of JPEG: its poor performance at very high compression ratios (typically 32 and above). This is the case for engineering uses of image data on Mars Pathfinder such as assessment of lander condition and deployed airbags, and rover navigation. Unlike science scenes, images for engineering at low resolution are often sufficient. Unfortunately, at very high compression ratios, JPEG produces unacceptable artifacts, due to the limitation of the size of the Discrete Cosine Transform to 8, for which no clever quantization or entropy coding can compensate. Still, JPEG can successfully be used as part of a compression scheme if the encoding is preceeded by low-pass filtering and downsampling, while the decoding is followed by interpolation and upsampling, to restore the image to its original size. The choice for the horizontal and vertical downsampling/upsampling factors is made based on the known distance to the objective and its size, as well as on the fact that resolution in azimuth degrades more gradually than in elevation, leading to a larger downsampling factor in azimuth. Assuming unweighted pixel averaging is used as the low-pass filter before decimation, optimal interpolation filters which minimize the mean squared reconstruction error (MSRE) in the absence of JPEG are derived. In the presence of large JPEG-induced quantization noise however, bilinear interpolation filters are shown to outperform the optimal interpolation filters derived above. Engineering assessment of images compressed with this scheme at ratios up to 126-to-1 using bilinear interpolation confirm its performance and its success in extending the operational compression ratio range of JPEG.

Study of statistical properties of random signals in multirate filter banks

Abstract: Previous works on subband-related signal processing were mainly dedicated to the applications of subband systems and to the formulation of multirate filter banks. Only very limited results can be found that treat statistical properties of random signals inside a multirate filter bank. In this paper, such a theoretical study is performed from the statistical viewpoint. Our main interest lies in how a multirate structure interacts with a random signal. The key statistical properties examined are stationarity, autocorrelation, cross-correlation, power spectral density, and spectral flatness measure. Exact explicit expressions are obtained. These results have their counterparts in a fullband system; however, inside a multirate structure or a subband system, the aliasing effect caused by decimation should be taken into account. In a multirate system, stationarity is not preserved when an upsampling (or expanding) operation is encountered. Furthermore the equivalent filtering operation is nonlinear. A test example of an AR-1 process is included for demonstration. From this example, an interesting phenomenon is observed. When the correlation coefficient of the AR-1 process is close to 1, the lowpassed signal is not, in any sense, a rough replica of the source. This example justifies the significance and necessity of a theoretical analysis of subband systems from a statistical viewpoint. We believe that stochastic signal processing applications of a subband structure such as estimation, detection, recognition, etc. will benefit from study of this nature.© (1995) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.