The development of remote sensing sensor techniques allows us to now readily capture many types of indoor and outdoor scene images, which often include many weak texture regions with notable geometric distortions. Obtaining qualified matches from these difficult stereo images using existing methods is challenging. The recent achievements of deep-learning models have shown that the convolutional neural network (CNN) is adept at the image matching task. However, in practical applications, the following challenges remain: first, it is difficult to detect features in the weak texture regions of an image, and existing CNNs fail to extract discriminative image information from the quantized features of weak texture; second, as a result of the complex distortion across wide-baseline stereo images, it is difficult to match feature primitives detected in the image pair. To solve these problems, we propose the perspective invariant local feature transformer (PILFT) algorithm. Our method includes four main steps. (1) The affine scale-invariant feature transform is proposed to automatically extract the corresponding features from images, and then the perspective of the matched image is corrected to eliminate as much geometric deformation as possible. (2) The residual network is used to extract potential features from stereo images to obtain coarse and fine feature maps at different scales. (3) Using an attention mechanism, location and context information are added to the coarse level features, which are predicted by a dual-softmax function layer. (4) The features are precisely predicted on the fine feature map using the coarse reference, and the final matching results are determined by calculating the matching probability. A large number of experiments on wide-baseline weak texture images demonstrate that the proposed method has advantages over the existing algorithms in the number of matches, correct match rate, and matching accuracy. The pseudocodes of PILFT are available at https://github.com/KiltAB/PILFT.
Large oblique stereo images are of great interest because they have a large coverage and a high reconstruction precision. However, severe distortions are more likely to occur in this type of image. This can make conventional algorithms inaccurate, computationally expensive, and invalid. We present a new robust quasidense image matching algorithm for large oblique images. Our algorithm can be divided into two steps. First, we find a sufficient number of highly accurate seed matches that are uniformly distributed by integrating complementary affine invariant feature matching with least-squares matching. Second, we consider quasidense matches covering overlapping areas of images. We use match propagation beginning with the best seed, iteratively applying the local perspective invariant neighborhood transform (PINT) with the normalized cross-correlation metric. The local PINT is dynamically updated using the current new match set, and the erroneous matches are eliminated according to their geometric consistency. We conducted experiments on simulated and real large oblique images to demonstrate that the proposed algorithm is effective and can robustly find quasidense matches. Comparisons with the existing methods demonstrated that it is superior in terms of accuracy and efficiency.
In order to mosaic neighboring and partly overlapping orthophotos of a scene into one large image, the paper proposes a
large block orthophoto mosaicking method. In our method, seam lines firstly are delineated through overlap areas among
orthophotos according to an optimal geometrical criterion. Then a network of mosaicking is built based on these
delineated seam lines, and related topology information may be easily abstracted from the mosaicking network. In the
second stage of our method, each seam line is optimized again by a modified snake algorithm. The algorithm makes
every seam line meet the requirements of maximum color similarity of the images and maximum texture similarity. In
order to searching an optimal seam line in a large overlap area as fast as possible, a hierarchical strategy is adapted. In
that way, an optimized path through the overlap area is found, where the color and texture of the two images are similar.
The still remaining jumps in hue and the differences in intensity and saturation have to be leveled by smooth
interpolation in the vicinity of the seam line. After having processed all overlapping areas, a large block of orthophotos
are automatically merged to a final large image.
The development of Digital Photogrammetric System is forward to distributed and parallel processing. There are many
researches on distributed and parallel Digital Photogrammetry System and a lot of researches are carried out on High
Performance Computing systems (i.e. Blade). But there are few distributed and parallel research performed in the context
of PC clusters. According to the principles of distributed systems, a middleware-based distributed system of
orthorectification for high resolution satellite imagery is proposed in the context of PC clusters. The paper emphasizes
the descriptions of the components in the system and discusses the corresponding strategies of task scheduling and
performance in the module. The feasibility of the system is proved in the practice.
Based on the FFT-enhanced IHS transform method a modified fusion method for SPOT5 images is proposed. Because of
demanding computation in image fusion a combination of pipeline parallelism and data parallelism is applied in practice.
Experimental results indicate that the spectral effect of fused images is good and distributed parallel processing solves
the problem of demanding computation in fused images.
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