Showing papers on "Upsampling published in 1997"

Fast algorithms for DCT-domain image downsampling and for inverse motion compensation

Abstract: Straightforward techniques for spatial domain processing of compressed video via decompression and recompression are computationally expensive. We describe an alternative approach wherein the compressed stream is processed in the compressed, discrete cosine transform (DCT) domain without explicit decompression and spatial domain processing, so that the output compressed stream, corresponding to the output image, conforms to the standard syntax of 8/spl times/8 blocks. We propose computation schemes for downsampling and for inverse motion compensation that are applicable to any DCT-based compression method. Worst case estimates of computation savings vary between 37% and 50% depending on the task. For typically sparse DCT blocks, the reduction in computations is more dramatic. A by-product of the proposed approach is improvement in arithmetic precision.

Video coding apparatus and decoding apparatus

Abstract: Video coding apparatus and decoding apparatus capable of reproducing decoded pictures without introducing unwanted noises, even if any considerable difference in pixel values or discontinuity exists at a certain block boundary. In a video coding apparatus employing predictive techniques, a dequantizer and an inverse DCT processor reproduce a prediction error signal from quantized transform coefficients. Here, a first resolution conversion unit (or downsampling unit) might have subsampled the original prediction error signal to reduce its picture resolution. If this is the case, a second resolution conversion unit (or upsampling unit) attempts to restore the original resolution of the prediction error signal by applying an upsampling process to the reproduced prediction error signal having the reduced resolution. In this upsampling process, each new pixel value in a certain block are calculated with reference to some surrounding pixels. The upsampling process, however, will not refer to the pixels belonging to any adjacent blocks that are subject to another coding scheme which is different from the coding scheme of the present block of interest. As an alternate arrangement, the upsampling process will entirely neglect the pixels in any other blocks but will refer only to the present block.

Space-variant filtering for correction of wavefront curvature effects in spotlight-mode SAR imagery formed via polar formatting

Abstract: Wavefront curvature defocus effects can occur in spotlight-mode SAR imagery when reconstructed via the well-known polar formatting algorithm (PFA) under certain scenarios that include imaging at close range, use of very low center frequency, and/or imaging of very large scenes. The range migration algorithm (RMA), also known as seismic migration, was developed to accommodate these wavefront curvature effects. However, the along-track upsampling of the phase history data required of the original version of range migration can in certain instances represent a major computational burden. A more recent version of migration processing, the Frequency Domain Replication and Downsampling (FReD) algorithm, obviates the need to upsample, and is accordingly more efficient. In this paper the authors demonstrate that the combination of traditional polar formatting with appropriate space-variant post-filtering for refocus can be as efficient or even more efficient than FReD under some imaging conditions, as demonstrated by the computer-simulated results in this paper. The post-filter can be pre-calculated from a theoretical derivation of the curvature effect. The conclusion is that the new polar formatting with post filtering algorithm (PF2) should be considered as a viable candidate for a spotlight-mode image formation processor when curvature effects are present.

Variable-raster multiresolution video processing with motion compensation techniques

Abstract: The standard format for video acquisition, transmission and presentation uses an interlaced scanning technique. On the other hand for digital video services, the progressive format is more desirable in many situations, and different resolutions of the signal are required. The interlaced scan is based on a tight concatenation of vertical and temporal sampling effects. This paper introduces the technique of motion-compensated vertical filters within pairs of fields to solve the problem of sampling rate conversion between interlaced and progressive raster. It is shown that the motion-compensated vertical filter is a polyphase realization of a factor-2 up- or downsampling filterbank, with polyphase shift controlled by motion parameters. Possible applications are down- and up-conversion between progressive and interlaced formats, and multiresolution representation of video data within a spatio-temporal subband or wavelet framework.

Synthetic aperture radar interferometry using one bit coded raw and reference signals

Abstract: This paper is concerned about the generation of interferometric phase patterns using synthetic aperture radar (SAR) images obtained by processing the raw data and reference function both quantized at one bit (Signum Coded). Such processing technique involves one-bit coded (i.e., binary) sequences, and can be efficiently implemented in real time using very simple and low cost hardware. It is shown that the proposed SC processing technique preserves, besides the image intensities, also interferometric phase patterns, before and after phase unwrapping. To test the performance of the proposed technique, experiments have been carried out on real data relative to the ERS-1 mission. Quantitative comparison between the results of conventional and SC processing clearly show that the presented method can be used for quick-look DEMs generation. Moreover, in accordance with the SC-SAR theory, an upsampling has also been performed on the signals to be processed to obtain higher quality patterns. This produce a noticeable improvement of the obtained results, so that the SC techniques can be considered a valid alternative to the conventional ones, still preserving the advantages in terms of real time.

Frequency-domain scalable coding without upsampling filters

Abstract: In a method of coding discrete time signals (X1) sampled with a first sampling rate, second time signals (x2) are generated using the first time signals having a bandwidth corresponding to a second sampling rate, with the second sampling rate being lower than the first sampling rate. The second time signals are coded in accordance with a first coding algorithm. The coded second signals (X2c) are decoded again in order to obtain coded/decoded second time signals (X2cd) having a bandwidth corresponding to the second sampling frequency. The first time signals, by frequency domain transformation, become first spectral values (X1). Second spectral values (X2cd) are generated from the coded/decoded second time signals, the second spectral values being a representation of the coded/decoded time signals in the frequency domain. To obtain weighted spectral values, the first spectral values are weighted by means of the second spectral values, with the first and second spectral values having the same frequency and time resolution. The weighted spectral values (Xb) are coded in accordance with a second coding algorithm in consideration of a psychoacoustic model and written into a bit stream. Weighting the first spectral values and the second spectral values comprises the subtraction of the second spectral values from the first spectral values in to obtain differential spectral values.

Downsampling and upsampling of binary images

Abstract: This provides for processing information by receiving downsampled pixel values, via, for instance, error diffusion, and upsampling each of the downsampled pixel values to construct a block of upsampled pixel values using statistics based on template pattern values of a predetermined number of downsampled pixel values or using replication.

MMSE design of interpolation and downsampling FIR filters in the context of periodic nonuniform sampling

Abstract: The generalized sampling theorem states that any analog signal whose spectrum is limited to 1/T can be exactly recovered from N sequences of samples taken at a rate 2/NT and all having a different sampling phase. When N=2, the exact interpolation formula can be derived quite easily. The ideal interpolation filters have infinite impulse responses (IIRs). This paper addresses first the question of recovering from the two initial sequences any other sequence taken at the same rate 1/T and with a different sampling phase. The design problem is dealt with for finite length filters, and the criterion is the minimization of the mean squared interpolation error. Next, the problem of computing from the two initial sequences a third one at a lower rate is addressed. FIR decimation filters are also designed for an MMSE criterion. These problems are illustrated for two typical covariance functions.

Use of radix-r recoding schemes for the realization of multiplier-free FIR filter with periodically time-varying coefficients

Abstract: The paper introduces a high-precision multiplication-free realization for FIR filters. The realization is based on the use of a linear periodically time-varying (PTV) system together with upsampling and downsampling to achieve time-invariant, multiplication-free FIR. Radix-r recoding schemes are used for obtaining the filter coefficients, which are periodically time-varying. The impulse response samples of the target filter are used to calculate the PTV coefficients. In the radix-r recoding scheme, the values of the PTV coefficients take any value from the set {/spl plusmn/2/sup p/, /spl plusmn/(2/sup p/-1), ..., /spl plusmn/2, /spl plusmn/1, 0}, where p=log r-1. These values are either power-of-two or sum of two power-of-two, accordingly, the realizations need only addition/subtraction and shift operations. The use of recoding schemes results in more accurate characteristics and higher precision than the case of using radix-r encoding.