Showing papers on "Upsampling published in 2001"

A fast scheme for image size change in the compressed domain

Abstract: Given a video frame in terms of its 8/spl times/8 block-DCT coefficients, we wish to obtain a downsized or upsized version of this frame also in terms of 8/spl times/8 block-DCT coefficients. The DCT being a linear unitary transform is distributive over matrix multiplication. This fact has been used for downsampling video frames in the DCT domain. However, this involves matrix multiplication with the DCT of the downsampling matrix. This multiplication can be costly enough to trade off any gains obtained by operating directly in the compressed domain. We propose an algorithm for downsampling and also upsampling in the compressed domain which is computationally much faster, produces visually sharper images, and gives significant improvements in PSNR (typically 4-dB better compared to bilinear interpolation). Specifically the downsampling method requires 1.25 multiplications and 1.25 additions per pixel of original image compared to 4.00 multiplications and 4.75 additions required by the method of Chang et al. (1995). Moreover, the downsampling and upsampling schemes combined together preserve all the low-frequency DCT coefficients of the original image. This implies tremendous savings for coding the difference between the original frame (unsampled image) and its prediction (the upsampled image). This is desirable for many applications based on scalable encoding of video. The method presented can also be used with transforms other than DCT, such as Hadamard or Fourier.

Removing color aliasing artifacts from color digital images

Abstract: A method of minimizing color aliasing artifacts from a color digital image having color pixels is disclosed. The method includes providing luminance and chrominance signals from the color digital image; using the luminance and chrominance signals to compute neighborhoods of pixels which are to be processed and wherein such neighborhoods of pixels are substantially bounded by pixels defining edges; producing low frequency chrominance signals in response to the chrominance signals; using the low frequency chrominance signals and the computed neighborhood of pixels to produce noise-cleaned chrominance signals; upsampling the noise-cleaned chrominance signals to produce upsampled noise-cleaned chrominance signals; and using the luminance signals and the upsampled noise-cleaned chrominance signals to provide a color digital image having reduced color aliasing artifacts.

Discrete multitone modulation with reduced peak-to-average ratio using unloaded subchannels

Abstract: A transceiver (100) such as used in Discrete Multitone (DMT) modulation of digital signals for communication, such as in a DSL modem communications system, is described. The transceiver (100) includes a function (119) by way of which unloaded subchannels are encoded with a clip prevention signal. The clip prevention signal is derived to avoid clipping by an amplifier (18) after modulation into the time domain, upsampling, and filtering. The effects of the upsampling and filtering are considered in deriving the clip prevention signal, by considering the upsampling and filtering as a polyphase combination, and using the filter response for each phase. Frequency domain and time domain update alternatives are disclosed.

Generalized plenoptic sampling

Abstract: Image-based rendering (IBR) has become a very active research area in recent years. The optimal sampling problem for IBR has not been completely solved. In this paper, we show that theoretically, the optimal sampling efficiency can be achieved by employing the generalized periodic sampling theory with arbitrary geometry. When there is no occlusion in the scene and the scene is Lambertian, we show that the sampling density can be twice of that when we use rectangular sampling. We then propose a general framework for IBR sampling. Begin with an over-sampled dataset, we down-sample the data first in the discrete domain. To render an image from the down-sampled data, two approaches are proposed, i.e., to reconstruct the oversampled dataset first through up-sampling and then rendering, or to use a continuous interpolation filter to calculate the desired light rays directly. Eigenfilter method is employed to design filters during downsampling and up-sampling. We show that if the proposed approach adopts the same down-sampling density as the previous work, the reconstruction filter of the proposed approach is easier to design, and the reconstructed scene could have a higher quality. However, in practice rectangular sampling has several advantages over generalized sampling. We analyze the pros and cons for each sampling approach, and explain why in practice rectangular sampling is still more preferable.

Interpolating filter banks in arbitrary dimensions

Abstract: Interpolating filter banks are constructed for use with signals which may be represented as a lattice of arbitrary dimension d. The filter banks include M channels, where M is greater than or equal to two. A given filter bank is built by first computing a set of shifts τ i as D -1 t i , i=1,2, . . . M-1, where t i is a set of coset representatives taken from a unit cell of the input signal lattice, and D is a dilation matrix having a determinant equal to M. A polynomial interpolation algorithm is then applied to determine weights for a set of M-1 predict filters P i having the shifts τ i . A corresponding set of update filters U i are then selected as U i =P i */M, where P i * is the adjoint of the predict filter P i . The resulting predict and update filters are arranged in a lifting structure such that each of the predict and update filters are associated with a pair of the M channels of the filter bank. The input signal applied to the filter bank is downsampled in each of the M channels, and then interpolated using the M-1 predict filters and the M-1 update filters. The downsampled and interpolated signal may be reconstructed using complementary interpolation and upsampling operations.

System and method for filtering frequency encoded imaging signals

Abstract: A method of filtering frequency encoded imaging signals includes receiving the frequency encoded imaging signals in the time domain and demodulating the frequency encoded imaging signals. The method further includes upsampling the frequency encoded imaging signals by an integer upsampling factor, reducing the bandwidth of the frequency encoded imaging signals, and downsampling the frequency encoded imaging signals by an integer downsampling factor. The frequency encoded imaging signals are resampled by a resampling factor substantially equal to the integer upsampling factor divided by the integer downsampling factor.

Assessment of image fusion algorithms based on noncritically-decimated pyramids and wavelets

Abstract: This work compares two general and formal solutions to the problem of fusion of multispectral images with high-resolution panchromatic observations. The former exploits the generalized Laplacian pyramid, which is an oversampled structure obtained by subtracting from an image its lowpass version. The latter relies on an undecimated wavelet decomposition, which is another bandpass representation achieved from a conventional octave wavelet transform by omitting all decimators and upsampling the filterbank. Both the methods selectively perform spatial-frequencies spectrum substitution from an image to another. The major novelty is that both the decompositions are not critically-sampled, thus avoiding possible impairments in the fused images, due to missing cancellation of aliasing terms. Quantitative results are presented and discussed on SPOT data (XS+P).

An H, Design Method for a Multi-Rate Servo Controller and Applications to a High Density Hard Disk Drive

Abstract: This paper proposes a method of designing a multi-rate servo controller for a hard disk drive that operates at a higher sampling frequency than the position error signal (PES). It is desirable to increase the servo performance without increasing the capacity overhead caused by the trding information on a disk. A zero-interpolator is introduced as an upsampling scheme to convert the plant to a higher sampling rate. Then a conventional H, method is applied to optimize the controller performance as well as to reduce the effects of aliasing noise caused by the upsampling scheme. This method is also applied to the design of a dual-stage actuator system of a hard disk drive. The performances are compared with single-rate controllers and improvements of 15 50% were obtained. Experiments using a 2.5” hard disk drive were carried out and the effectiveness was confirmed.

Minimizing power consumption in direct sequence spread spectrum correlators by resampling IF samples-Part I: performance analysis

Abstract: Most modern digital receivers sample the received RF signal at an intermediate frequency (IF), then downconvert to the baseband in the digital domain. The baseband samples are subsequently correlated with a time-limited square pulse, which is readily implemented as an integrator. Since correlation is performed at the sampling frequency, the receiver correlates at an unnecessarily high frequency. This high frequency results in significant power dissipation especially if parallel correlators are employed. By downsampling after appropriate filtering to slightly above the signal Nyquist rate, correlation is achieved at a fraction of the sampling frequency, resulting in corresponding reduction in power consumption. Furthermore, by resampling to an integer number of samples per chip, architectural changes in the correlators are possible, allowing even more reduction in power consumption. In this paper, a resampling correlator with minimal hardware overhead that outperforms the conventional correlator is presented.

Accurate and efficient modeling of beating and two-stage decay for string instrument synthesis

Abstract: In this paper a novel modeling method is presented for beating and two-stage decay. Here, one digital waveguide is used for each note and some resonators are run in parallel to simulate the beating and two-stage decay of those partials, where these phenomena are most prominent. The resonator bank is implemented by using the multi-rate approach, resulting in a decrease of computational cost by a factor of 10. By taking the advantage of the characteristics of the resonators, relatively simple upsampling and downsampling filters are used. Two different filtering approaches are presented and compared with respect to computational complexity. Examples are shown with the application to piano sound synthesis.

A computationally efficient cochlear filter bank for perceptual audio coding

Abstract: Many applications in auditory modeling require analysis filters that approximate the frequency selectivity given by psychophysical data, e.g., from masking experiments using narrow-band maskers. This frequency selectivity is largely determined by the spectral decomposition process inside the human cochlea. Currently used spectral decomposition schemes for masking modeling in audio coding generally do not achieve the non-uniform time and frequency resolution provided by the cochlea. These applications rather take advantage of the computational efficiency of uniform filter banks or transforms at the expense of coding gain. This paper presents a suitable analysis filter-bank structure employing cascaded low-order IIR filters and appropriate downsampling to increase efficiency. In an application example, the filter responses were optimized to model auditory masking effects. The results show that the time and frequency resolution of the filter bank matches or exceeds the masking properties. Thus, the filter bank enables improved masking modeling for audio coding at low computational costs.

Multiresolution maximum intensity volume rendering by morphological pyramids

Abstract: We propose a multiresolution representation for maximum intensity projection (MIP) volume rendering, based on morphological pyramids which allow progressive refinement and have the property of perfect reconstruction. The pyramidal analysis and synthesis operators are composed of morphological erosion and dilation, combined with dyadic downsampling for analysis and dyadic upsampling for synthesis. The structure of the multiresolution MIP representation is very similar to wavelet splatting, the main differences being that (i) linear summation of voxel values is replaced by maximum computation, and (ii) linear wavelet filters are replaced by (nonlinear) morphological filters.

Extraction of pitch information in noisy speech using wavelet transform with aliasing compensation

Abstract: Although many wavelet-based pitch detection methods have been proposed in the literature, there still remains a need to investigate new wavelet-based methods for more accurate and more robust pitch determination. In this paper, an improved wavelet-based method is developed for extraction of pitch information in noisy speech. At each decomposition in the wavelet transform, an aliasing compensation algorithm is applied to approximate and detail signals, in which the distortion of aliasing due to downsampling and upsampling operations of the wavelet transform is eliminated. In addition, this paper utilizes the concept of spatial correlation function used in signal denoising to improve the performance of pitch detection in a noisy environment. It is shown in various experimental results that this new type of method has a considerable performance improvement compared with other conventional methods and wavelet-based methods.

Data compression of stereoscopic image pairs

Abstract: An emerging feature of multimedia and telepresence systems is stereo imagery. Stereo images provide an enhanced sense of presence, and have been found to be operationally useful in tasks requiring remote manipulation or judgment of spatial relationships. A conventional stereo system with a single left-right pair needs twice the raw data as a monoscopic imaging system. As a result there has been increasing attention given to image compression methods specialized to stereo pairs. In this paper, the mixed-resolution coding, is a psychophysically justified technique that exploits known facts about human stereovision to code stereopairs in a subjectively acceptable manner, is used to the stereo image compression. By combining both the mixed-resolution coding and SPT(subspace projection technique)-based disparity-compensation techniques, the left image can be compressed by a wavelet-transform-based scheme independent of the right image. By performing low-resolution SPT-based disparity-compensation technique, the disparity is able to predict the low-resolution right image from the left image at a lower resolution using the disparity relation. The low-resolution images are obtained using the wavelet decomposition. At the decoder, the low-resolution right subimage is estimated using the disparity from the low-resolution left subimage. A full-sized resolution is obtained by upsampling with a factor of 4 and resonstructing with the synthesis low pass filter. We provide experimental results, that show that our proposed scheme achieves a PSNR gain of about 0.98 dB as compared to a block-based disparity compensation coding scheme, encoded at the same bit rate.© (2001) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Video-signal decoder and method for removing interferences in a video image

Abstract: The invention relates to a video-signal decoder for generating a video image that consists of cumulative image data blocks, of a differential image comprising differential image data blocks and motion vectors, and of a down-sampling device (28) which down-samples the cumulative image data blocks for producing reduced reference image data blocks. The video-signal decoder further comprises a reference image data memory (30) for the intermediate storage of the reduced reference data blocks, an upsampling device that upsamples the reduced reference image data blocks that are read out from the reference image data memory and that are motion-compensated by means of the motion vectors, thereby producing reference image data blocks. A reconstruction filter (36) filters the reference image data blocks produced by upsampling and produces predecessor image data blocks, said reference image data blocks being filtered by interpolation within the data block limits. A summation circuit (12) produces a sum of the produced predecessor image data blocks and the differential image data blocks to produce the cumulative image data blocks.

Enhancements of NP-3 UHF image quality using digital spotlighting technique

Abstract: This paper is concerned with signal processing issues that are associated with foliage penetrating (FOPEN) USA Navy NP-3 ultra-wideband (UWB) synthetic aperture radar. The digital signal processors that were developed for the NP-3 data commonly used a radar beamwidth angle that was limited to 35 degrees. Provided that the NP-3 radar beamwidth angle was 35 degrees, the NP-3 SAR system would approximately yield alias-free data in the slow-time Doppler domain. We show that the NP-3 data possess a 50-degree beamwidth angle within the entire 215-730 MHz band of the NP-3 radar that is imposed by the radar (radial) range swath gate. The 50-degree beamwidth of the NP-3 system results in slow-time Doppler aliasing within the frequency band of 444-730 MHz. We outline a slow-time processing of the NP-3 data, that we refer to as digital spotlighting and PRF upsampling, to minimize the Doppler aliasing. The digital spotlighting is also used for in-scene target calibration.

Audio information processor

Abstract: PROBLEM TO BE SOLVED: To obtain an audio information having high sound quality without increasing the number of D/A converters and without complcating the construction of an audio information processor. SOLUTION: An audio decoder 7 supplies audio data having a fundamental sampling frequency fs to twofold upsampling circuits 8, 9, 10, 11. Respective twofold upsampling circuits 8, 9, 10, 11 convert the sampling frequency of the audio data into twofold frequencies to supply pertinent audio data whose frequencies are already converted to respective D/A converters 12, 13, 14 via terminals (b), (d), (f), (h).

Artifact reduction in sinc interpolation using adaptive filtering

Abstract: We propose a new method for artifact reduction of upsampled multidimensional signals. These artifacts are evident near edges and they are due to the spectral narrowing associated with upsampling. The method is based on first upsampling the signal with conventional optimal sinc interpolation and then applying a local filter that reduces the high frequencies associated with the ringing artifacts along the edges while leaving unchanged the directions orthogonal to them. The method is specially suitable when dealing with medical images that contain small structures, such as thin bones in CT.

Wave-carried signal generator for complex modulator

Abstract: A method for generating digital carrier signals for application as the carrier to a digital modulator includes providing a first repeating sequence of complex values occurring at a given sample rate and upsampling these values to a higher sample rate. A second repeating sequence of complex values is provided, wherein respective complex values in the second repeating sequence occur at the higher sample rate. The second sequence of complex values is employed to modulate the upsampled first sequence of complex values and thereby provide the complex carrier signal.

Multiresolution Maximum Intensity Volume Rendering by Morphological Adjunction Pyramids

Abstract: We describe a multiresolution extension to maximum intensity projection (MIP) volume rendering, allowing progressive refinement and perfect reconstruction. The method makes use of morphological adjunction pyramids. The pyramidal analysis and synthesis operators are composed of morphological 3-D erosion and dilation, combined with dyadic downsampling for analysis and dyadic upsampling for synthesis. In this case the MIP operator can be interchanged with the synthesis operator. This fact is the key to an efficient multiresolution MIP algorithm, because it allows the computation of the maxima along the line of sight on a coarse level, before applying a two-dimensional synthesis operator to perform reconstruction of the projection image to a finer level. For interpolation and resampling of volume data, which is required to deal with arbitrary view directions, morphological sampling is used, an interpolation method well adapted to the nonlinear character of MIP. The structure of the resulting multiresolution algorithm is very similar to wavelet splatting, the main differences being that (i) linear summation of voxel values is replaced by maximum computation, and (ii) linear wavelet filters are replaced by (nonlinear) morphological filters.

Conformance test of MPEG-4 shape decoding

Abstract: Most of the current video coding standards, such as H.261 and MPEG-1, are frame based while MPEG-1 can encode objects. Shape coding is a process of coding a visual object. This paper proposes conformance test methods for BAB (binary alpha block) decoder, CAE (context based arithmetic encoding) decoder for intra and inter VOPs (video object planes), upsampling and downsampling. Our test generates all possible cases of binary shape encoding.

Method for removing color aliasing artifacts from color digital images

Abstract: of EP1202220A method of minimizing color aliasing artifacts from a color digital image having color pixels is disclosed. The method includes providing luminance and chrominance signals from the color digital image; using the luminance and chrominance signals to compute neighborhoods of pixels which are to be processed and wherein such neighborhoods of pixels are substantially bounded by pixels defining edges; producing low frequency chrominance signals in response to the chrominance signals; using the low frequency chrominance signals and the computed neighborhood of pixels to produce noise-cleaned chrominance signals; upsampling the noise-cleaned chrominance signals to produce upsampled noise-cleaned chrominance signals; and using the luminance signals and the upsampled noise-cleaned chrominance signals to provide a color digital image having reduced color aliasing artifacts.