Search results for: Thrasyvoulos N. Pappas
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IEEE Transactions on Multimedia > 2016 > 18 > 12 > 2432 - 2445
We propose a dynamic interactive system for conveying visual information via hearing and touch to blind and visually impaired people. The system is implemented with a touch screen that allows the user to actively explore a two-dimensional layout consisting of one or more objects with the finger while listening to auditory feedback. Sound is used as the primary source of information for object localization,...
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We propose a hybrid Markov random field (MRF) model and a two stage cutset-MRF approach for reconstructing bilevel images from cutsets. We show that the proposed approach leads to substantial improvements over previous cutset-MRF approaches in terms of both reconstruction error and visual quality (continuity of reconstructed segments and preservation of image structure). The proposed approach approaches...
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We propose a family of cutset sampling schemes and a generalized k-level image reconstruction approach formulated under a minimum mean squared error (MMSE) framework. The k-level reconstruction approach is a direct generalization of the recently proposed pattern-based approach, and can be applied to periodic samples either on a cutset or on a grid. Our experimental results indicate that the generalization...
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We propose a pattern-based approach for reconstructing k-level images from cutsets. We construct a database of k-level cutset block patterns and use it for reconstruction based on fuzzy pattern retrieval and Markov random field (MRF) energy minimization. The proposed approach outperforms previously proposed cutset-MRF approaches as well as inpainting approaches. When integrated into a lossy bilevel...
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Matched-texture coding (MTC) exploits the redundancy of textured regions in natural images in order to achieve low-encoding-rate structurally lossless compression. A key element of MTC identifying large image blocks that can be replaced with previously encoded blocks that have similar structure. The side matching (SM) approach attempts to do this by matching the upper and left boundary (side) of a...
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Traditional point-by-point image similarity metrics, such as the ℓ2-norm, are not always consistent with human perception, especially in textured regions. We consider the problem of identifying textures that are perceptually identical to a query texture; this is important for image retrieval, compression, and restoration applications. Recently proposed structural texture similarity (STSIM) metrics...
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In order to provide ground truth for subjectively comparing compression methods for scenic bilevel images, as well as for judging objective similarity metrics, this paper describes the subjective similarity rating of a collection of distorted scenic bilevel images. Unlike text, line drawings, and silhouettes, scenic bilevel images contain natural scenes, e.g., landscapes and portraits. Seven scenic...
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Matched-Texture Coding is a novel image coder that utilizes the self-similarity of natural images that include textures, in order to achieve structurally lossless compression. The key to a high compression ratio is replacing large image blocks with previously encoded blocks with similar structure. Adjusting the lighting of the replaced block is critical for eliminating illumination artifacts and increasing...
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IEEE Transactions on Image Processing > 2014 > 23 > 4 > 1652 - 1665
An effective, low complexity method for lossy compression of scenic bilevel images, called lossy cutset coding, is proposed based on a Markov random field model. It operates by losslessly encoding pixels in a square grid of lines, which is a cutset with respect to a Markov random field model, and preserves key structural information, such as borders between black and white regions. Relying on the...
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We develop a new type of statistical texture image feature, called a Local Radius Index (LRI), which can be used to quantify texture similarity based on human perception. Image similarity metrics based on LRI can be applied to image compression, identical texture retrieval and other related applications. LRI extracts texture features by using simple pixel value comparisons in space domain. Better...
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Proceedings of the IEEE > 2013 > 101 > 9 > 2044 - 2057
Texture is an important visual attribute both for human perception and image analysis systems. We review recently proposed texture similarity metrics and applications that critically depend on such metrics, with emphasis on image and video compression and content-based retrieval. Our focus is on natural textures and structural texture similarity metrics (STSIMs). We examine the relation of STSIMs...
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IEEE Transactions on Image Processing > 2013 > 22 > 7 > 2545 - 2558
We develop new metrics for texture similarity that accounts for human visual perception and the stochastic nature of textures. The metrics rely entirely on local image statistics and allow substantial point-by-point deviations between textures that according to human judgment are essentially identical. The proposed metrics extend the ideas of structural similarity and are guided by research in texture...
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We propose a new texture-based compression approach that relies on new texture similarity metrics and is able to exploit texture redundancies for significant compression gains without loss of visual quality, even though there may visible differences with the original image (structurally lossless). Existing techniques rely on point-by-point metrics that cannot account for the stochastic and repetitive...
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We propose a hierarchical lossy bilevel image compression method that relies on adaptive cutset sampling (along lines of a rectangular grid with variable block size) and Markov Random Field based reconstruction. It is an efficient encoding scheme that preserves image structure by using a coarser grid in smooth areas of the image and a finer grid in areas with more detail. Experimental results demonstrate...
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This paper builds upon previous work for image reconstruction problems in which samples are taken on evenly spaced rows and columns, i.e., a Manhattan grid. A new reconstruction method is proposed that uses three steps to interpolate the interior of each block under the model that an image can be decomposed into piecewise planar regions plus noise. First, the K-planes algorithm is developed in order...
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We focus on the evaluation of texture similarity metrics for structurally lossless or nearly structurally lossless image compression. By structurally lossless we mean that the original and compressed images, while they may have visible differences in a side-by-side comparison, they have similar quality so that one cannot tell which is the original. This is particularly important for textured regions,...
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We present a Z-SIFT based 3D surface registration algorithm that utilizes the depth information enhanced SIFT features to make initial alignment and the 2D feature weighted Iterative Closest Point (ICP) algorithm to realize accurate registration. The combination of SIFT features and depth information extracts faithful corresponding points between the 2D images and provides good coarse alignment for...
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This paper presents a new approach to sampling images in which samples are taken on a cutset with respect to a graphical image model. The cutsets considered are Manhattan grids, for example every Nth row and column of the image. Cutset sampling is motivated mainly by applications with physical constraints, e.g. a ship taking water samples along its path, but also by the fact that dense sampling along...
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We present a high-accuracy shape acquisition approach that uses a combined Gray code and phase-shifting structured light projection. The Gray code pattern coarsely divides the projected plane into local regions, whereas phase-shifting precisely determines the pixel-accurate index for each point on the plane. The combination of the two codifications greatly decreases the number of patterns as compared...
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The design of benchmark imagery for validation of image annotation algorithms is considered. Emphasis is placed on imagery that contains industrial facilities, such as chemical refineries. An application-level facility ontology is used as a means to define salient objects in the benchmark imagery. In-strinsic and extrinsic scene factors important for comprehensive validation are listed, and variability...
