A task of assessing full-reference visual quality of images is considered. Correlation between the obtained array of mean opinion scores (MOS) and the corresponding array of given metric values allows characterizing correspondence of a considered metric to HVS. For the largest openly available database TID2013 intended for metric verification, a Spearman correlation is about 0.85 for the best existing HVS-metrics. One simple way to improve an efficiency of assessing visual quality of images is to combine several metrics. Our work addresses a possibility of using neural networks for the aforementioned purpose. As leaning data, we have used metric sets for images of the database TID2013 that are employed as the network inputs. Randomly selected half of 3000 images of the database TID2013 has been used at the learning stage whilst other half have been exploited for assessing quality of neural network based HVS-metric. Six metrics “cover” well all types of distortions: FSIMc, PSNR-HMA, PSNR-HVS, SFF, SR-SIM, and VIF, have been selected. As the result of NN learning, the Spearman correlation between the NN output and the MOS for the verification set of database TID2013 reaches 0.93 for the best configuration of NN. This is considerably better than for any particular metric employed as an input (FSIMc is the best among them). Analysis of the designed metric efficiency is carried out, its advantages and drawbacks are demonstrated.
KEYWORDS: Image compression, Chromium, Hyperspectral imaging, 3D image processing, Data compression, Sensors, Signal to noise ratio, Interference (communication), Image processing, Data acquisition
A problem of lossy compression of hyperspectral images is considered. A specific aspect is that we assume a signal-dependent model of noise for data acquired by new generation sensors. Moreover, a signal-dependent component of the noise is assumed dominant compared to a signal-independent noise component. Sub-band (component-wise) lossy compression is studied first, and it is demonstrated that optimal operation point (OOP) can exist. For such OOP, the mean square error between compressed and noise-free images attains global or, at least, local minimum, i.e., a good effect of noise removal (filtering) is reached. In practice, we show how compression in the neighborhood of OOP can be carried out, when a noise-free image is not available. Two approaches for reaching this goal are studied. First, lossy compression directly applied to the original data is considered. According to another approach, lossy compression is applied to images after direct variance stabilizing transform (VST) with properly adjusted parameters. Inverse VST has to be performed only after data decompression. It is shown that the second approach has certain advantages. One of them is that the quantization step for a coder can be set the same for all sub-band images. This offers favorable prerequisites for applying three-dimensional (3-D) methods of lossy compression for sub-band images combined into groups after VST. Two approaches to 3-D compression, based on the discrete cosine transform, are proposed and studied. A first approach presumes obtaining the reference and “difference” images for each group. A second performs compression directly for sub-images in a group. We show that it is a good choice to have 16 sub-images in each group. The abovementioned approaches are tested for Hyperion hyperspectral data. It is demonstrated that the compression ratio of about 15–20 can be provided for hyperspectral image compression in the neighborhood of OOP for 3-D coders, which is sufficiently larger than for component-wise compression and lossless coding.
Modern visual quality metrics take into account different peculiarities of the Human Visual System (HVS). One of them is
described by the Weber-Fechner law and deals with the different sensitivity to distortions in image fragments with
different local mean values (intensity, brightness). We analyze how this property can be incorporated into a metric PSNRHVS-
M. It is shown that some improvement of its performance can be provided. Then, visual quality of color images
corrupted by three types of i.i.d. noise (pure additive, pure multiplicative, and signal dependent, Poisson) is analyzed.
Experiments with a group of observers are carried out for distorted color images created on the basis of TID2008 database.
Several modern HVS-metrics are considered. It is shown that even the best metrics are unable to assess visual quality of
distorted images adequately enough. The reasons for this deal with the observer’s attention to certain objects in the test
images, i.e., with semantic aspects of vision, which are worth taking into account in design of HVS-metrics.
Color images formed by modern digital cameras are often noisy, especially if they are captured in bad illumination
conditions. This makes desirable to remove the noise by image pre-filtering. A specific feature of the noise observed for
the considered application is that it can be spatially correlated. Filters to be applied have to effectively suppress noise
introducing only negligible distortions into processed images. Moreover, such filters have to be fast enough and tested
for a variety of natural images and noise properties. Another specific requirement is that a visual quality of processed
images has to be paid a specific attention. To carry out intensive testing of some denoising approaches, a recently
designed database TID2008 of distorted images provides a good opportunity since it contains 25 different images
corrupted by i.i.d. and spatially correlated noise with several levels of variances. Taking into account the known fact that
the color components are highly correlated, both modern 2D (component-wise) and 3D (vector) filtering techniques are
studied. It is demonstrated that the use of 3D filters that allow exploiting inter-channel correlation provides considerably
better results in terms of conventional and visual quality metrics. It is also shown how 3D filter based on discrete cosine
transform (DCT) can be adapted to a spatial correlation of noise. This adaptation produces sufficient increase of the
filter's efficiency. Examples of filter's performance are presented.
This paper presents a novel sharpness metric for color images. The proposed metric can be used for no-reference assessment
of image visual quality. The metric basically relies on local power of wavelet transform high-frequency coefficients. It also
takes into account possibility of presence of macrophotography and portrait photography effects in an image where the
image part (usually central one) in sharp whilst the remained part (background) is smeared. Such effects usually increase
subjective evaluation of image visual quality by humans. The effects are taken into consideration by joint analysis of
wavelet coefficients with largest and smallest squared absolute values. Besides, we propose a simple mechanism for
blocking artifact accounting (if an image is compressed by JPEG) and compensation of this factor contribution. Finally, the
proposed sharpness metric is calculated in color space YCbCr as a weighted sum of sharpness components. Weight
optimization has shown that a weight for intensity component Y is to be considerably smaller than weights for color
components Cb and Cr. Optimization of weights for all stages of sharpness metric calculation is carried out for specialized
database NRTID that contains 500 test images with previously determined MOS (Mean Opinion Score). Spearman rank
order correlation coefficient (SROCC) determined for the designed sharpness metric and MOS is used as optimization
criterion. After optimization, it reaches 0.71. This is larger than for other known available no-reference metrics considered
at verification stage.
Estimation of noise characteristics is used in various image processing tasks such as edge detection, filtering,
reconstruction, compression and segmentation, etc. It is very desirable to have as accurate as possible estimated noise
characteristics which influence the quality of further processing. This paper deals with evaluation of accuracy of earlier
proposed methods for blind estimation of speckle characteristics. Evaluation is done for TerraSAR-X single-look
amplitude images. It is shown that the obtained estimates depend upon image complexity. Besides, parameters of any
estimation method influence accuracy (bias) as well. Finally, spatial correlation of noise is yet another factor affecting
the obtained estimates. As it is demonstrated, blind estimation in aggregate allows to obtain the estimates of speckle
variance with relative error up to 20%, which is appropriate for practical needs. Besides, if speckle variance is
estimated, it becomes possible to get accurate estimates of noise spatial correlation in DCT domain. Such estimates can
be used in e.g. DCT-based filtering of SAR images.
Images formed by different systems are often noisy which makes filtering a typical operation of image pre-processing.
In many research papers, filter performance is analyzed for a limited number of standard test images and noise
variances. Here we use a recently created color image database TID2008 that allows assessing filter efficiency for 25
color images corrupted by noise with different values of variance, both i.i.d. and spatially correlated. Besides, this
image database serves the purpose of evaluating different quality metrics including those able to characterize visual
quality of original and processed images considerably better than conventional MSE and PSNR. The study is carried out
for filters based on discrete cosine transform (DCT) able to suppress both i.i.d. and spatially correlated noise depending
upon a way of threshold setting. It is shown that improvement of PSNR (IPSNR) due to filtering is very close for R, G,
and B components of color images and this improvement depends on image content. IPSNR reaches 9 dB for quite
simple images and it is only about 1 dB for highly textural images if initial PSNR=30 dB. Note that IPSNR is larger if
the original PSNR is smaller. The visual quality metric PSNR-HVS-M is studied as well. The metric PSNR-HVS-M
becomes larger due to filtering but in smaller degree than PSNR does. We demonstrate that it is possible to forecast
whether or not visual quality can be improved due to filtering or to detect in advance highly textural images for which
filtering can be not efficient enough. The provided output MSEs are also compared to potential limits calculated
according to the recently proposed methodology. It is demonstrated that for highly textural images the DCT filtering
with 8x8 full overlapping blocks and hard thresholding provides output MSE close to potential limits. The provided and
limit MSEs differ from each other by about 10%. For simpler images, the provided and limit MSEs can differ by
1.5...2.5 times. Analysis is also carried out for spatially correlated noise. It is shown that efficiency of filtering in this
case is lower.
The paper deals with JPEG adaptive lossy compression of color images formed by digital cameras. Adaptation to noise
characteristics and blur estimated for each given image is carried out. The dominant factor degrading image quality is
determined in a blind manner. Characteristics of this dominant factor are then estimated. Finally, a scaling factor that
determines quantization steps for default JPEG table is adaptively set (selected). Within this general framework, two
possible strategies are considered. A first one presumes blind estimation for an image after all operations in digital
image processing chain just before compressing a given raster image. A second strategy is based on prediction of noise
and blur parameters from analysis of RAW image under quite general assumptions concerning characteristics
parameters of transformations an image will be subject to at further processing stages. The advantages of both strategies
are discussed. The first strategy provides more accurate estimation and larger benefit in image compression ratio (CR)
compared to super-high quality (SHQ) mode. However, it is more complicated and requires more resources. The second
strategy is simpler but less beneficial. The proposed approaches are tested for quite many real life color images acquired
by digital cameras and shown to provide more than two time increase of average CR compared to SHQ mode without
introducing visible distortions with respect to SHQ compressed images.
In many modern applications, methods and algorithms used for image processing require a priori knowledge or estimates of noise type and its characteristics. Noise type and basic parameters can be sometimes known in advance or determined in an interactive manner. However, it occurs more and more often that they should be estimated in a blind manner. The results of noise-type blind determination can be false, and the estimates of noise parameters are characterized by certain accuracy. Such false decisions and estimation errors have an impact on performance of image-processing techniques that is based on the obtained information. We address some issues of such a negative influence. Possible structures of automatic procedures are presented and discussed for several typical applications of image processing as remote sensing data preprocessing and compression.
A typical tendency in modern remote sensing (RS) is to apply multichannel systems. Images formed by them are in
more or less degree noisy. Thus, their pre-filtering can be used for different purposes, in particular, to improve
classification. In this paper, we consider methods of multichannel image denoising based on discrete cosine transform
(DCT) and analyze how parameters of these methods affect classification. Both component-wise and 3D denoising is
studied for three-channel Landsat test image. It is shown that for better determination of different classes, DCT based
filters, both component-wise and 3D variants are efficient, but with a different tuning of involved parameters. The
parameters can be optimized with respect to either standard MSE or metrics that characterize image visual quality. Best
results are obtained with 3D denoising. Although the main conclusions basically coincide for both considered
classifiers, Radial Basis Function Neural Network (RBF NN) and Support Vector Machine (SVM), the classification
results appear slightly better with RBF NN for the experiment carried out in this paper.
In many image-processing applications, observed images are contaminated by a nonstationary noise and no a priori information on noise dependence on local mean or about local properties of noise statistics is available. In order to remove such a noise, a locally adaptive filter has to be applied. We study a locally adaptive filter based on evaluation of image local activity in a "blind" manner and on discrete cosine transform computed in overlapping blocks. Two mechanisms of local adaptation are proposed and applied. The first mechanism takes into account local estimates of noise standard deviation while the second one exploits discrimination of homogeneous and heterogeneous image regions by adaptive threshold setting. The designed filter performance is tested for simulated data as well as for real-life remote-sensing and maritime radar images. Recommendations concerning filter parameter setting are provided. An area of applicability of the proposed filter is defined.
In design of many image processing methods and algorithms, it is assumed that noise is i.i.d. However, noise in real life
images is often spatially correlated and ignoring this fact can lead to certain problems such as reduction of filter
efficiency, misdetection of edges, etc. Thus, noise characteristics, namely, variance and spatial spectrum are to be
estimated. This should be often done in a blind manner, i.e., for an image at hand and in non-interactive manner. This
task is especially complicated if an image is textural. Thus, the goal of this paper is to design a practical approach to
blind estimation of noise characteristics and to analyze its performance. The proposed method is based on analysis of
data in blocks of fixed size in discrete cosine transform (DCT) domain. This allows further use of the obtained DCT
spectrum for denoising and other purposes. This can be especially helpful for multichannel remote sensing (RS) data
where interactive processing is problematic and sometimes even impossible.
Most modern methods of image processing exploit a priori knowledge or estimates of noise type and its characteristics
obtained in blind or interactive manner. However, the results of noise type blind determination can be false with some
hopefully rather small probability. Similarly, the obtained estimates of noise parameters are characterized by certain
accuracy. Clearly, false decisions and errors of estimates influence performance of image processing techniques that
exploit the information on noise properties obtained in a blind manner. In this paper, we consider some aspects of such
influence for several typical applications.
In various practical situations of remote sensing image processing it is assumed that noise is nonstationary and no a
priory information on noise dependence on local mean or about local properties of noise statistics is available. It is
shown that in such situations it is difficult to find a proper filter for effective image processing, i.e., for noise removal
with simultaneous edge/detail preservation. To deal with such images, a local adaptive filter based on discrete cosine
transform in overlapping blocks is proposed. A threshold is set locally based on a noise standard deviation estimate
obtained for each block. Several other operations to improve performance of the locally adaptive filter are proposed and
studied. The designed filter effectiveness is demonstrated for simulated data as well as for real life radar remote sensing
and marine polarimetric radar images.
A common assumption concerning noise in radar images is that it is of multiplicative nature and spatially uncorrelated.
Meanwhile, recent studies have shown that additive noise component cannot be neglected, especially for images formed
by side look aperture radars (SLARs). Moreover, majority of radar image filtering techniques are designed under assumption
that noise is i.i.d., i.e. spatially uncorrelated. However, in many practical situations the latter assumption is not
true. Besides, spatial correlation properties of noise can be different and they are often a priori unknown. In this paper
we demonstrate that complex statistical and spatial correlation characteristics of noise in radar images can and should be
taken into consideration at image filtering stage. We design a modification of the denoising algorithm based on discrete
cosine transform (DCT) that is able to easily incorporate a priori information or obtained estimates of noise statistical
and spatial correlation characteristics. This can be done in automatic (blind) manner due to utilizing a sequence of blind
estimation operations. We present simulation results that show appropriate accuracy and robustness of these operations.
Finally, real life image filtering examples are given that confirm the effectiveness of the designed techniques.
Remote sensing images are commonly formed on-board an observation platform, then transferred via a communication
downlink, and finally processed on-land. There are many ways of compressing and then classifying remote sensing
images. In this paper we focus on considering two lossy compression techniques under the assumption that the original
images are noisy. No pre- or postprocessing is applied. Two classifiers are examined, namely, those based on trained
radial basis function neural networks and support vector machines. We study how the parameter that controls the compression
ratio of two coders based on the discrete cosine transform influences classification accuracy of these classifiers
for a real life three-channel optical image. It is shown that attaining the optimal operation point for both coders is practically
equivalent to providing the maximal probability of correct classification of multichannel data. At the same time,
the efficiency of image compression characterized in terms of compression ratio, peak signal-to-noise ratio, and probability
of correct classification considerably depends upon the coder used. Finally, it is shown that compressing multichannel
remote sensing data in the neighborhood of the optimal operation point and near the maximum of the probability
of correct classification can be performed in automatic manner.
Majority of image filtering techniques are designed under assumption that noise is of special, a priori known type and it
is i.i.d., i.e. spatially uncorrelated. However, in many practical situations the latter assumption is not true due to several
reasons. Moreover, spatial correlation properties of noise might be rather different and a priori unknown. Then the assumption
that noise is i.i.d. under real conditions of spatially correlated noise commonly leads to considerable decrease
of a used filter effectiveness in comparison to a case if this spatial correlation is taken into account. Our paper deals with
two basic aspects. The first one is how to modify a denoising algorithm, in particular, a discrete cosine transform (DCT)
based filter in order to incorporate a priori or preliminarily obtained knowledge of spatial correlation characteristics of
noise. The second aspect is how to estimate spatial correlation characteristics of noise for a given image with appropriate
accuracy and robustness under condition that there is some a priori information about, at least, noise type and statistics
like variance (for additive noise case) or relative variance (for multiplicative noise). We also present simulation
results showing the effectiveness (the benefit) of taking into consideration noise correlation properties.
It is a quite common that acquired images are noisy and image filtering is a necessary step to enhance them. Usually
image filtering effectiveness is characterized in terms of MSE or PSNR although nowadays it is well understood that
these criteria do not always correspond adequately to visual perception of processed images. Recently several new
measures of image quality have been proposed. In particular, two metrics, called PSNR-HVS and PSNR-HVS-M, were
designed and successfully tested. Both take into account different sensitivity of a human eye to spatial frequencies,
the latter one also accounts for the masking effects. Using these two metrics as well as a traditional PSNR and used by
NASA metric DCTune, we have analyzed performance of five different filters (standard mean and median, sigma, Lee
and DCT based filters) for a set of test images corrupted by an additive Gaussian noise with a wide set of variance values.
It has been shown that there are many situations when PSNR after filtering improves while one or all other metrics
manifest image quality decreasing. Most often this happens if noise variance is small and/or an image contains texture.
Comparisons show that DCT based filter commonly outperforms other considered filters in the sense of denoised image
visual quality. At the same time, the standard mean filter produces worse visual quality of processed images even its
scanning window size is 3x3.
Bayer Pattern Color Filter Arrays (CFAs) are widely used in digital photo and video cameras. Generally these images are
corrupted by a signal and exposure dependent quantum noise. An automatic image processing carrying out within
camera usually implies a gamma and color corrections and an interpolation. And at the same time the noise in the image
becomes non-quantum and spatially correlated. This results in a drastic decrease of posterior noise reduction.
Considerably better quality of output images can be provided if non-processed Bayer Pattern CFAs (in RAW format) are
extracted from a camera and processed on PC. For this case, more effective noise reduction can be achieved as well as
better quality image reconstruction algorithms can accessed. The only drawback of storing images in a camera in RAW
format is their rather large size. Existing lossless image compression methods provide image compression ratios (CRs)
for such images of only about 1.5...2 times. At the same time, a posterior filtering in addition to noise reduction results
in appearing losses in the image. Therefore, the use of lossy image compression methods is defensible in this case while
final decreasing of effectiveness of noise reduction is inessential. The paper describes a method of adaptive selection of
quantization step for each block of a Bayer Pattern CFAs for DCT based image compression. This method allows
restricting the decreasing of the posterior noise reduction by only 0.25...0.3 dB. Achieved CRs for the proposed scheme
are by 2.5...5 times higher than for strictly lossless image compression methods.
A practical impossibility of prediction of signs of DCT coefficients is generally accepted. Therefore each coded sign of
DCT coefficients occupies usually 1 bit of memory in compressed data. At the same time data of all coded signs of DCT
coefficients occupy about 20-25% of a compressed image. In this work we propose an effective approach to predict signs
of DCT coefficients in block based image compression. For that, values of pixels of already coded/decoded neighbor
blocks of the image are used. The approach consist two stages. At first, values of pixels of a row and a column which
both are the nearest to already coded neighbor blocks are predicted by a context-based adaptive predictor. At second
stage, these row and column are used for prediction of the signs of the DCT coefficients. Depending on complexity of an
image proposed method allows to compress signs of DCT coefficients to 60-85% from their original size. It corresponds
to increase of compression ratio of the entire image by 3-9% (or up to 0.5 dB improvement in PSNR).
In different applications, it is often desirable to retrieve useful information from multichannel (color, multispectral, dual
or full-polarization) images. On one hand, multichannel images are potentially able to provide a lot of useful information
about sensed objects (terrains). On the other hand, the task of its reliable extraction is very complicated. And there are
many reasons behind this like inherent noise, lack of a priori information about object features, complexity of scenes,
etc. Therefore, numerous different approaches based on various functional principles and mathematical background have
been already put forward. In majority of them, image classification and segmentation are common operations that precede
estimation of object parameters. However, practically all methods are far away from completeness and/or perfection
since they suffer from different drawbacks and application restrictions. Recently we have proposed methods based
on learning with local parameter clustering that were rather successfully applied to image locally adaptive filtering and
detection of objects with certain properties. This paper is an attempt to extend this approach to image classification,
segmentation and object parameter estimation. A particular application of substance quantitative analysis from color
images is considered. The proposed approach is shown to solve the aforementioned task quite well and to have a rather
high potential for other applications.
KEYWORDS: Image compression, Chromium, Remote sensing, Radar, JPEG2000, Lab on a chip, Image filtering, Data compression, Denoising, Data communications
It is often necessary to compress remote sensing (RS) data such as optical or radar images. This is needed for transmitting them via communication channels from satellites and/or for storing in databases for later analysis of, for instance, scene temporal changes. Such images are generally corrupted by noise and this factor should be taken into account while selecting a data compression method and its characteristics, in the particular, compression ratio (CR). In opposite to the case of data transmission via communication channel when the channel capacity can be the crucial factor in selecting the CR, in the case of archiving original remote sensing images the CR can be selected using different criteria. The basic requirement could be to provide such a quality of the compressed images that will be appropriate for further use (interpreting) the images after decompression. In this paper we propose a blind approach to quasi-optimal compression of noisy optical and side look aperture radar images. It presumes that noise variance is either known a priori or pre-estimated using the corresponding automatic tools. Then, it is shown that it is possible (in an automatic manner) to set such a CR that produces an efficient noise reduction in the original images same time introducing minimal distortions to remote sensing data at compression stage. For radar images, it is desirable to apply a homomorphic transform before compression and the corresponding inverse transform after decompression. Real life examples confirming the efficiency of the proposed approach are presented.
Image filtering or denoising is a problem widely addressed in optical, infrared and radar remote sensing data processing. Although a large number of methods for image denoising exist, the choice of a proper, efficient filter is still a difficult problem and requires wide a priori knowledge. Locally adaptive filtering of images is an approach that has been widely investigated and exploited during recent 15 years. It has demonstrated a great potential. However, there are still some problems in design of locally adaptive filters that is generally too heuristic. This paper puts forward a new approach to get around this shortcoming. It deals with using learning with clustering in order to make the procedure of locally adaptive filter design more automatic and less subjective. The performance of this approach to learning and locally adaptive filtering has been tested for mixed Gaussian multiplicative+impulse noise environment. Its advantages in comparison to another learning methods and the efficiency of the considered component filters is demonstrated by both numerical simulation data and real-life radar image processing examples.
A robust version of Lee local statistic filter able to effectively suppress the mixed multiplicative and impulse noise in images is proposed. The performance of the proposed modification is studied for a set of test images, several values of multiplicative noise variance, Gaussian and Rayleigh probability density functions of speckle, and different characteris-tics of impulse noise. The advantages of the designed filter in comparison to the conventional Lee local statistic filter and some other filters able to cope with mixed multiplicative+impulse noise are demonstrated.
Among the most important types of information contained in radar and optical images are the textural features. In real life images these features are partially masked by noise that is always present in registered data, basically multiplicative in radar images and additive in optical ones. Thus, one of the basic steps in processing remote sensing data is the filtering of the observed image. However, despite the fact that a lot of filters have been already designed, relatively little attention has been paid to texture preservation properties of noise attenuation methods. Thus, there are the following actual tasks: 1) to analyze the texture preservation properties of different filters; 2) to design image processing methods that are able to preserve texture features simultaneously with effective noise suppression. In this paper, the texture feature preserving characteristics of different filters are examined using a set of texture samples, different noise levels and a set of parame-ters including spatial correlation and higher order statistics. The traditional locally adaptive two-state hard switching filters are modified to the three-state ones where texture is considered as a particular class. For “detection” of texture regions, special, rather simple, classifiers that are based on joint analysis and processing of the two local activity indicators are proposed. The recommendations concerning the parameter setting of the classifiers are given. All this provides an appropriate trade-off of the designed filter properties. It improves the PSNR for entire image in comparison to the component filters used within the three-state local adaptation framework. Local PSNRs for the considered types of image fragments are practically the same or even better than for the filter type recommended for the processing of the corresponding classes. Real life image examples are presented to demonstrate the efficiency of the proposed filter.
The problem of blind evaluation of noise variance in images is considered. Typical approaches commonly presume getting a set of variance estimations in small size blocks and further analysis of the obtained estimations set distribution with finding its maximum. However, such methods suffer from the common drawback that their accuracy becomes drastically worse if an image contains a lot of texture. To alleviate this drawback we propose an approach based on the fact that the statistical properties of DCT coefficients corresponding to high spatial frequencies in small size blocks greatly depend upon noise variance. As shown, these coefficients can be processed in nonlinear manner in order to eliminate the influence of informative component of the image itself. The dependence of the method accuracy on the used nonlinear operation and its parameters is carried out. It is shown that the proposed method produces appropriately good accuracy of blind evaluation of noise variance for a set of considered test images. The comparison analysis of the proposed method and some known analogs is performed.
In some practical situations it is often necessary to process radar images for which a priori information about noise characteristics is limited. Evaluating these characteristics, in particular, estimating speckle noise variance, is quite a complicated and time consuming task. In order to carry out both tasks efficiently enough for typical practical situations an automated robust procedure for SAR image filtering and preliminary analysis is proposed. It consists of several stages: a) blind evaluation of speckle relative variance for the original image, b) pre-processing using the local statistic Lee filter, c) blind evaluation of the residual noise relative variance for the pre-processed image, d) post-filtering. It is shown that the proposed procedure provides rather accurate estimations of noise characteristics. The effectiveness of the filtering scheme is confirmed for both simulated and real scene SAR images.
KEYWORDS: Reconstruction algorithms, Image processing, Remote sensing, Digital filtering, Data communications, Linear filtering, Nonlinear filtering, Analytical research, Telecommunications, Signal attenuation
The tasks of digital elevation map reconstruction from isogram maps and the arising problems are considered. An iterative algorithm based on discrete cosine transform and histogram filtering with taking into account several nonlinear constraints is proposed. The algorithm efficiency and accuracy analysis for test and real data is carried out. The advantages of the proposed technique and the perspectives of further investigations are shown.
The peculiarities of radar images and the problems of their filtering are considered. A two-stage procedure of radar image despeckling based on successive application of the local statistic Lee and sigma filters is proposed. The recommendations concerning filter parameter selection are presented. The performance characteristics of the proposed procedure are evaluated for a set of test artificial images. It is shown that the two-stage despeckling can be successfully applied to both images formed by side look aperture radar (SLAR) or synthetic aperture radar (SAR). An available trade-off of filter basic properties is provided. The examples for real data demonstrating the proposed procedure efficiency and benefits are also given.
Methodology and stages of data processing in multichannel airborne radar imaging systems are considered. It is shown that data fusion in such systems requires special techniques, algorithms, and software for image processing and information retrieval. Some approaches and methods are proposed. The results are demonstrated for simulated and real images.
The sigma and mean filters with adaptive window size are proposed. The sigma filter with adaptive window size is intended for processing radar images with multiplicative noise and the main goal in its design is to improve the noise suppression effectiveness for homogeneous regions of images. The mean filter with adaptive window size can be applied for relief recovery when one initially has the isogram map and its primary approximation by constant level regions. The performance of the proposed filters is tested for simulated images and then analyzed for real data.
A method for isogram extraction from topographic maps is proposed and analyzed. Main part of the extraction is done using automatic software based on nonlinear algorithms. Possibly needed final corrections are done in an interactive mode. Iterative procedures are used both to provide reliability and to minimize the number of operations performed by the user in the interactive mode. Illustrations are presented to clarify the operations, goals and obtained results. Also, techniques for relief recovery are proposed and their accuracy is studied.
The expedience of use of expert system and fuzzy logic based decisions to image recognition and filtering is discussed. One possible approach including the calculation of several local parameters for every image pixel scanning window position combined with expert system preliminary training and decision undertaking for image recognition and adaptive filtering is proposed. The efficiency and the peculiarities of considered procedure are analyzed and demonstrated for simulated data.
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