1,721,098 research outputs found
Decimated geometric filter for edge-preserving smoothing of non-white image noise
No full textA procedure of recursive decimation is proposed to improve the performance of geometric filtering, in the case of spatially correlated image noise. Edges and fine textures are preserved, and noisy backgrounds carefully smoothed in a smaller number of iterations. Both SNR and subjective comparisons demonstrate an enhanced effectiveness with respect to geometric filtering. Such application fields as SAR speckle filtering and digital video processing are discussed and shown to benefit from the proposed scheme
Dual-channel iterative even-median filter
No full textCombining two complementary iterative versions of medianfilter extended to an even (2 × 2) pixel set, results in efficient edge-preserving removal of impulsive image noise. Enhance spike suppression capability for heavy noise, MAE and visual comparisons show improvements over medianfilter
Content-matched geometric filtering of image subbands for edge-preserving noise reduction
No full textThe idea of the present scheme is to apply a directional version of geometric filter (complementary-hull) to the different sub-bands into which the noisy image is decomposed by the S-Transform, a dyadic Haar wavelet yielding integer valued coefficients. The hull algorithm is applied only on the direction(s) along which the signal is more structured. The number of iterations is adjusted to the SNR of the sub-bands, so as to preserve spatial details to the largest extent. Comparisons with the standard geometric filter are presented for images affected by synthetic multiplicative (speckle) noise. Results are pretty superior to those achieved without multiresolution context, both visually and in terms of SNR
Improved Coherent Processing of Synthetic Aperture Radar Data through Speckle Whitening of Single-Look Complex Images
No full textIn this study, we investigate the usefulness of the spectral whitening procedure, devised by one of the authors as a preprocessing stage of envelope-detected single-look synthetic aperture radar (SAR) images, in application contexts where phase information is relevant. In the first experiment, each of the raw datasets of an interferometric pair of COSMO-SkyMed images, representing industrial buildings amidst vegetated areas, was individually (1) synthesized by the SAR processor without Fourier-domain Hamming windowing; (2) synthesized with Hamming windowing, used to improve the focalization of targets, with the drawback of spatially correlating speckle; and (3) processed for the whitening of complex speckle, using the data obtained in (2). The interferograms were produced in the three cases, and interferometric coherence and phase maps were calculated through 3 × 3 boxcar filtering. In (1), coherence is low on vegetation; the presence of high sidelobes in the system’s point-spread function (PSF) causes the spread of areas featuring high backscattering. In (2), point targets and buildings are better defined, thanks to the sidelobe suppression achieved by the frequency windowing, but the background coherence is abnormally increased because of the spatial correlation introduced by the Hamming window. Case (3) is the most favorable because the whitening operation results in low coherence in vegetation and high coherence in buildings, where the effects of windowing are preserved. An analysis of the phase map reveals that (3) is likely to be facilitated also in terms of unwrapping. Results are presented on a TerraSAR-X/TanDEM-X (TSX-TDX) image pair by processing the interferograms of original and whitened data using a non-local filter. The main results are as follows: (1) with autocorrelated speckle, the estimation error of coherence may attain 16% and inversely depends on the heterogeneity of the scene; and (2) the cleanness and accuracy of the phase are increased by the preliminary whitening stage, as witnessed by the number of residues, reduced by 24%. Benefits are also expected not only for differential InSAR (DInSAR) but also for any coherent analysis and processing carried out performed on SLC data
A coarse-to-fine algorithm for fast median filtering of image data with a huge number of levels
No full textA two-step algorithm exploiting a reduced local grey-level histogram is proposed for efficient running-median calculation in digital monochrome images whose number of levels is considerably large, such as medical images, SAR images, or 2-D data maps. The first step borrows the concept of sliding window for fast update of the local histogram, as well as the strategy of percentile upgrade for fast median retrieval, and provides a coarse estimate of the actual median which is refined in the second stage, involving only a limited portion of the histogram. Comparisons in terms of theoretical number of operations evidence a computing time O(L2) instead of O(L), where L = L1.L2 is the number of levels, and L1 is the size of the reduced histogram. Also computer tests validate the ideal relationship and suggest a practical factorization criterion of the local histogram, when dealing with natural correlated images. Experimental results substantially prove the validity of the novel algorithm as a feasible alternative, for calculation of any rank-order value, to level-sorting techniques, whenever both classic histogram-based schemes and sorting algorithms are prohibitively time-consuming, as it happens in some practical image processing applications
Assessment of image fusion algorithms based on noncritically-decimated pyramids and wavelets
No full textThis 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)
Art-work image processing and transmission
No full textAfter a brief presentation of the scenario of Italian activities in national and EU projects, concerning processing and transmission of Art-Works images, some researches aimed at color correction carried out at the Uffizi Gallery Labs are described, and applications of remote processing for color certification are outlined. Interactions with the national project "Knowledge Through Images: an Application to Cultural Heritage" are highlighted as well
Intersensor statistical matching for pansharpening: Theoretical issues and practical solutions
No full textIn this paper, the authors investigate the statistical matching of the panchromatic (Pan) image to the multispectral (MS) bands, also known as the histogram matching, for the two main classes of pansharpening methods, i.e., those based on component substitution (CS) or spectral methods and those based on multiresolution analysis (MRA) or spatial methods. Also, hybrid methods combining CS with MRA, like the widespread additive wavelet luminance proportional (AWLP), are investigated. It is shown that all spectral, spatial, and hybrid methods must perform a dynamics matching of the enhancing Pan to the individual MS bands for MRA or a combination of them (the component that shall be substituted) for CS. For hybrid methods, the problem is more complex and both types of histogram matching may be suitable. Such an intersensor balance may be either explicit or implicitly performed by the detailinjection model, e.g., the popular projective and multiplicative injection models. An experimental setup exploiting IKONOS and WorldView-2 data sets demonstrates that a correct histogram matching is the key to attain extra performance from established methods. As a first result of this paper, the AWLP method has been revisited and its performance significantly improved by simply performing the histogram matching of Pan to the individual MS bands, rather than to the intensity component, thereby losing the original proportionality feature
Joint change analysis and speckle filtering of multitemporal ERS-1 imagery
No full textLocal-statistics speckle filtering has been extended to multi-temporal SAR data by exploiting the space-varying temporal correlation of speckle noise between two images of the same scene taken at different times. A recursive nonlinear transformation aimed at decorrelating the data across time while retaining the multiplicative noise model is defined from the pixel geometric mean and ratio of a couple of spatially overlapped observations. The average temporal correlation coefficient is estimated from the scatterplots of local standard deviation to local mean calculated on transformed couples of images, through an unsupervised clustering procedure. The images are filtered in the transformed domain and reversely transformed to yield despeckled observations in which seasonal changes are preserved, or even highlighted, and texture analysis is expedited. Tests on two SAR images from repeat-pass ERS-1 corroborate the theoretical assumptions and show the performances of the proposed approach
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