Proceedings 1999 International Conference on Image Processing (Cat. 99CH36348)
In this paper we introduce a new image model calledMSEC (Multi-Scale Edge Compensation) and imple... more In this paper we introduce a new image model calledMSEC (Multi-Scale Edge Compensation) and implementan image compression system based on MSEC.MSEC consists of semantically meaningful componentsincluding edges of different types and scales, andthe background. The MSEC-based image coding techniquepermits some image analysis operations such asedge detection, enhancement, and content-based retrievalto be carried out directly in the compressiondomain.1 IntroductionMost existing image...
Multimedia and Expo, 2007 IEEE International Conference on, 2007
... grid. The low-resolution image Il can be then compressed by any existing image coding method.... more ... grid. The low-resolution image Il can be then compressed by any existing image coding method. If standard compatibility ... Specifically, a significant edge can be charac-terized by the following piecewise autoregressive (PAR) pro-cess: Xi,j = ∑ (m,n)∈Wi,j αm,nXi+m,j+n + υi,j (1) ...
2010 8th World Congress on Intelligent Control and Automation, 2010
An affordable and reliable indoor positioning is a highly needed service. Moreover, maps of the i... more An affordable and reliable indoor positioning is a highly needed service. Moreover, maps of the indoor environment are vital to many applications. In this paper, a method for joint localization and mapping using multipath delay estimates is developed. Required high-resolution estimates of multipath delays may be obtained using radio frequency or acoustic measurements among a set of nodes in a network. In this paper, the problem is modeled in two-dimensional space with arbitrary node configuration and assuming a convex polygonal room shape. Joint localization and mapping is formulated as an optimization problem. It is subdivided and relaxed into two convex subproblems, which can be solved in an alternating manner. A method for data association and a low-complexity mapping algorithm stemming from Hough transform are proposed. Both the estimation performance and identifiability of the indoor localization problem are improved. Moreover, a basic map of the propagation environment is produced.
2010 IEEE International Conference on Acoustics, Speech and Signal Processing, 2010
The first part of this thesis is concerned with efficient adaptive image interpolation techniques... more The first part of this thesis is concerned with efficient adaptive image interpolation techniques for real-time applications. A new image interpolation algorithm is developed that combines optimal data fusion and context modeling of images. Specifically, two estimates of missing pixels obtained by cubic interpolation in perpendicular directions are optimally fused under minimum mean square (MMSE) criterion. The fused result is further improved by a context-based error feedback mechanism to compensate for the error of cubic interpolation. The proposed image interpolation algorithm preserves edge structures well and achieves superior visual quality. This is accomplished at low computational complexity, making the new algorithm suitable for hardware implementation. The main part of this thesis is devoted to a more sophisticated image interpolation algorithm based on hidden Markov modeling (HMM). Most of existing interpolation algorithms rely on point by point decisions to estimate the missing pixels. In contrast, the HMM approach of image interpolation estimates a block of missing pixels via maximum a posterior (MAP) sequence estimation. The hidden Markov model can incorporate the statistics of high resolution images into the interpolation process and the MAP estimation technique can exploit high-order statistical dependency between pixels. The proposed HMM-based image interpolation algorithm is implemented and iv its performance is evaluated and compared with existing methods. The comparison study shows that the HMM-based image interpolation algorithm can reproduce cleaner and sharper image details than its predecessors, while suppressing common interpolation artifacts such as ringing, jaggies, and blurring. v I would like to give my special thanks to my supervisor Professor Xiaolin Wu, for his suggestions and support. I also want to appreciate his kind personality. He definitely has played a great role in my life. My deepest gratitude goes to my parents, my brother, Aydin, my sister, Ana, and my brother in law, Ali Rokoui.
2008 15th IEEE International Conference on Image Processing, 2008
We propose a new family of nonredundant 3-D directional transforms that are useful for video sign... more We propose a new family of nonredundant 3-D directional transforms that are useful for video signals. In our construction, taking into account the correlation amongst frames of video, we first decorrelate the temporal data using a stage of 1-D wavelet transform and then we employ the efficient 2-D Hybrid Wavelets and Directional filter banks (HWD) transform family to the resulting spatial data where we achieve 3-D HWD transform family. We construct translation-invariant version of the proposed family and show its efficiency in video denoising compared to other wavelet-based methods through several experiments.
Conference proceedings : ... Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE Engineering in Medicine and Biology Society. Annual Conference, 2010
A context-based 3D interpolation technique is proposed to enhance the out-of plane resolution of ... more A context-based 3D interpolation technique is proposed to enhance the out-of plane resolution of 3D medical images. The proposed technique represents a new approach of aiding 3D interpolation and improving its performance by efficient use of domain knowledge about the anatomy, objects and imaging modalities. In the new approach a family of adaptive 3D interpolation filters are designed and conditioned on different spatial contexts (classes of feature vectors). Training is used to incorporate the domain knowledge into the design of these interpolators. Experimental results show significant improvement of the new approach over some existing 3D interpolation techniques.
2009 16th IEEE International Conference on Image Processing (ICIP), 2009
We propose a new image acquisition and recovery strategy of hybrid sensing (HS) that combines ran... more We propose a new image acquisition and recovery strategy of hybrid sensing (HS) that combines random sampling of compressive sensing (CS) and uniform down sampling. HS lets the two sampling schemes complement each other so that one can have the best of both worlds: signal-independent sparse sampling that is the hallmark of CS, and locally adaptive signal reconstruction that is afforded by uniform sampling. We suggest a few important applications of HS in image acquisition and communication, such as multispectral imaging, multiple description image coding, multiview video, and ultra-high throughput imaging (e.g., functional medical imaging).
2009 16th IEEE International Conference on Image Processing (ICIP), 2009
This paper presents a novel non-local iterative backprojection (NLIBP) algorithm for image enlarg... more This paper presents a novel non-local iterative backprojection (NLIBP) algorithm for image enlargement. The iterative back-projection (IBP) technique iteratively reconstructs a high resolution (HR) image from its blurred and downsampled low resolution (LR) counterpart. However, the conventional IBP methods often produce many "jaggy" and "ringing" artifacts because the reconstruction errors are back projected into the reconstructed image isotropically and locally. In natural images, usually there exist many non-local redundancies which can be exploited to improve the image reconstruction quality. Therefore, we propose to incorporate adaptively the non-local information into the IBP process so that the reconstruction errors can be reduced. Experimental results demonstrated that the proposed NLBP can reconstruct faithfully the HR images with sharp edges and texture structures. It outperforms the state-of-the-art methods in both PSNR and visual perception.
Demosaicking of the color CCD data is a key to the image quality of digital still and video camer... more Demosaicking of the color CCD data is a key to the image quality of digital still and video cameras. Limited by the Nyquist frequency of the color filter array (CFA), color artifacts often accompany high frequency contents in the reconstructed images. This paper presents a general approach of joint spatial-temporal color demosaicking that exploits all three forms of sample correlations: spatial, spectral, and temporal. By motion estimation and statistical data fusion between multiple estimates obtained from adjacent mosaic frames, the new approach can significantly outperform the existing spatial color demosaicking techniques both in objective measure and subjective visual quality.
Recently, many researchers started to question a long-standing paradox in the engineering practic... more Recently, many researchers started to question a long-standing paradox in the engineering practice of digital photography: oversampling followed by compression, and pursue more intelligent sparse sampling techniques. In this research we take a practical approach of uniform down sampling in image space, and the sampling is made adaptive by a spatially varying directional low-pass prefiltering. Since the down-sampled prefiltered image
Reported is a formal study on the visual quality of rasterized lines and the optimality of Bresen... more Reported is a formal study on the visual quality of rasterized lines and the optimality of Bresenham-type line generators. A straight line is rendered as a sequence of pixels on raster displays. Due to the finite resolution of raster devices quantization errors are inevitable in the rendering, often causing visually objectionable jagged digital lines. Different rasterization schemes will generate different digital lines. Thus a question of both theoretical and practical importance arises: is there an optimal line rasterization scheme different from the existing ones which can render visually most pleasing digital lines for the given device resolution? This paper will give an answer to this open question.
Visual Information Processing and Communication, 2010
In most applications, video deinterlacing has to be performed in real time. Numerous algorithms h... more In most applications, video deinterlacing has to be performed in real time. Numerous algorithms have been developed to strike a good balance between throughput and quality. The motion adaptive deinterlacing algorithm switches between two modes: direct merging of two fields in areas of no motion, or intrafield adaptive interpolation when motions are detected. In this paper, we propose a fast GPU-aided implementation of a motion adaptive deinterlacing algorithm using NVIDIA CUDA (Compute Unified Device Architecture) technology. We discuss the techniques of adapting the computations in motion detection and adaptive directional interpolation to the GPU architecture for maximum video throughput possible. The objective is to fully utilize the processing power of GPU without compromising the visual quality of the deinterlaced video. Experimental results are reported and discussed to demonstrate the performance of the proposed GPU-aided motion adaptive video deinterlacer in both speed and visual quality.
W e examine color quantization of images using trellis-coded quantization (TCQ) in both the RGB d... more W e examine color quantization of images using trellis-coded quantization (TCQ) in both the RGB domain and YUV domain. Together with a simple dithering scheme, an eightbit trellis-coded color quantizer reproduces images that are visually indistinguishable from the 24-bit originals. It can be viewed as a predictive trellis-coded color quantization scheme. We also study trellis-coded vector quantization (TCVQ) for color quantization. Our proposed TCQ-based color quantization schemes are universal in the sense that no training or look-up table is needed. The complexity of TCQ is linear with respect to image size, making trellis-coded color quantization suitable for color printing, real-time interactive graphics and window-based display environment.
... Since FPGAs have a flexible architecture that can be reconfigured according to user-specified... more ... Since FPGAs have a flexible architecture that can be reconfigured according to user-specified ... with the computing blocks are described in Section 3. Partitioned DBWT-based HDTV compression approach is described in Section 4. FPGA implementations with ...
Single sensor digital color cameras capture only one of the three primary colors at each pixel an... more Single sensor digital color cameras capture only one of the three primary colors at each pixel and a process called color demosaicking (CDM) is used to reconstruct the full color images. Most CDM algorithms assume the existence of high local spectral redundancy in estimating the missing color samples. However, for images with sharp color transitions and high color saturation, such an assumption may be invalid and visually unpleasant CDM errors will occur. In this paper we exploit the image non-local redundancy to improve the local color reproduction result. First, multiple local directional estimates of a missing color sample are computed and fused according to local gradients. Then nonlocal pixels similar to the estimated pixel are searched to enhance the local estimate. An adaptive thresholding method rather than the commonly used nonlocal means filtering is proposed to improve the local estimate. This allows the final reconstruction to be performed at the structural level as opposed to the pixel level. Experimental results demonstrate that the proposed local directional interpolation and nonlocal adaptive thresholding (LDI-NAT) method outperforms many state-of-the-art CDM methods in reconstructing the edges and reducing color interpolation artifacts, leading to higher visual quality of reproduced color images.
Progressive image coding is a useful feature for image databases, image communications, and muIti... more Progressive image coding is a useful feature for image databases, image communications, and muItimedia information systems. Centrat to progressive image coding is a multiresolution image pyramid. Quadtree-based recursive regular tessellation is a popular form of image pyramid. But regular tessellation is often too rigid to capture the scene structure of an image; consequently, it may not generate a compact image representation. This paper proposes a scheme of hierarchical piecewise linear approximation as an adaptive image pyramid. A progressive segmentation-bred image coder comes naturally from the proposed image pyramid. The new image pyramid is semantically more powerful than regular tessellation while syntactically simpler than free segmentation. Thi,s good compromise between the adaptability and complexity of image segmentation contributes to high compression ratios achieved by our progressive image coder. In addition to its advantages in data compression and progressive transmission, our image coder also facilitates many other image manipulations.
Color demosaicking is critical to the image quality of digital still and video cameras that use a... more Color demosaicking is critical to the image quality of digital still and video cameras that use a single-sensor array. Limited by the mosaic sampling pattern of the color filter array (CFA), color artifacts may occur in a demosaicked image in areas of high-frequency and/or sharp color transition structures. However, a color digital video camera captures a sequence of mosaic images and the temporal dimension of the color signals provides a rich source of information about the scene via camera and object motions. This paper proposes an inter-frame demosaicking approach to take advantage of all three forms of pixel correlations: spatial, spectral, and temporal. By motion estimation and statistical data fusion between adjacent mosaic frames, the new approach can remove much of the color artifacts that survive intra-frame demosaicking and also improve tone reproduction accuracy. Empirical results show that the proposed inter-frame demosaicking approach consistently outperforms its intra-frame counterparts both in peak signal-to-noise measure and subjective visual quality. Index Terms-Bayer color filter array, data fusion, digital video, subpixel motion estimation, temporal color demosaicking. I. INTRODUCTION M OST digital cameras capture a color image with a single sensor array that sub-samples color bands in a particular mosaic pattern, such as the Bayer color filter array (CFA) [3] shown in Fig. 1. At each pixel, only one of the three primary colors (red, green, and blue) is sampled. The full color image is reconstructed by interpolating the missing color samples. This process is called color demosaicking, which is critical to the quality of reconstructed color images. The problem of color demosaicking has been extensively studied in spatial and frequency domains for still digital cameras [1], [2], [4], [6], [7], [9], [11], [13]-[17], [22], [23], [26]. Early demosaicking techniques mostly work in the spatial domain, such as nearest neighbor replication, bilinear interpolation, and cubic B-spline interpolation [13]. They are easy to implement but susceptible to many artifacts such as blocking, blurring and zipper effect at edges. The problem can be mitigated by an appropriate use Manuscript received July 15, 2004; revised February 3, 2006. This work was supported in part by the Natural Sciences and Engineering Research Council of Canada through an industrial research chair in digital cinema. The associate editor coordinating the review of this manuscript and approving it for publication was Dr.
Proceedings 1999 International Conference on Image Processing (Cat. 99CH36348)
In this paper we introduce a new image model calledMSEC (Multi-Scale Edge Compensation) and imple... more In this paper we introduce a new image model calledMSEC (Multi-Scale Edge Compensation) and implementan image compression system based on MSEC.MSEC consists of semantically meaningful componentsincluding edges of different types and scales, andthe background. The MSEC-based image coding techniquepermits some image analysis operations such asedge detection, enhancement, and content-based retrievalto be carried out directly in the compressiondomain.1 IntroductionMost existing image...
Multimedia and Expo, 2007 IEEE International Conference on, 2007
... grid. The low-resolution image Il can be then compressed by any existing image coding method.... more ... grid. The low-resolution image Il can be then compressed by any existing image coding method. If standard compatibility ... Specifically, a significant edge can be charac-terized by the following piecewise autoregressive (PAR) pro-cess: Xi,j = ∑ (m,n)∈Wi,j αm,nXi+m,j+n + υi,j (1) ...
2010 8th World Congress on Intelligent Control and Automation, 2010
An affordable and reliable indoor positioning is a highly needed service. Moreover, maps of the i... more An affordable and reliable indoor positioning is a highly needed service. Moreover, maps of the indoor environment are vital to many applications. In this paper, a method for joint localization and mapping using multipath delay estimates is developed. Required high-resolution estimates of multipath delays may be obtained using radio frequency or acoustic measurements among a set of nodes in a network. In this paper, the problem is modeled in two-dimensional space with arbitrary node configuration and assuming a convex polygonal room shape. Joint localization and mapping is formulated as an optimization problem. It is subdivided and relaxed into two convex subproblems, which can be solved in an alternating manner. A method for data association and a low-complexity mapping algorithm stemming from Hough transform are proposed. Both the estimation performance and identifiability of the indoor localization problem are improved. Moreover, a basic map of the propagation environment is produced.
2010 IEEE International Conference on Acoustics, Speech and Signal Processing, 2010
The first part of this thesis is concerned with efficient adaptive image interpolation techniques... more The first part of this thesis is concerned with efficient adaptive image interpolation techniques for real-time applications. A new image interpolation algorithm is developed that combines optimal data fusion and context modeling of images. Specifically, two estimates of missing pixels obtained by cubic interpolation in perpendicular directions are optimally fused under minimum mean square (MMSE) criterion. The fused result is further improved by a context-based error feedback mechanism to compensate for the error of cubic interpolation. The proposed image interpolation algorithm preserves edge structures well and achieves superior visual quality. This is accomplished at low computational complexity, making the new algorithm suitable for hardware implementation. The main part of this thesis is devoted to a more sophisticated image interpolation algorithm based on hidden Markov modeling (HMM). Most of existing interpolation algorithms rely on point by point decisions to estimate the missing pixels. In contrast, the HMM approach of image interpolation estimates a block of missing pixels via maximum a posterior (MAP) sequence estimation. The hidden Markov model can incorporate the statistics of high resolution images into the interpolation process and the MAP estimation technique can exploit high-order statistical dependency between pixels. The proposed HMM-based image interpolation algorithm is implemented and iv its performance is evaluated and compared with existing methods. The comparison study shows that the HMM-based image interpolation algorithm can reproduce cleaner and sharper image details than its predecessors, while suppressing common interpolation artifacts such as ringing, jaggies, and blurring. v I would like to give my special thanks to my supervisor Professor Xiaolin Wu, for his suggestions and support. I also want to appreciate his kind personality. He definitely has played a great role in my life. My deepest gratitude goes to my parents, my brother, Aydin, my sister, Ana, and my brother in law, Ali Rokoui.
2008 15th IEEE International Conference on Image Processing, 2008
We propose a new family of nonredundant 3-D directional transforms that are useful for video sign... more We propose a new family of nonredundant 3-D directional transforms that are useful for video signals. In our construction, taking into account the correlation amongst frames of video, we first decorrelate the temporal data using a stage of 1-D wavelet transform and then we employ the efficient 2-D Hybrid Wavelets and Directional filter banks (HWD) transform family to the resulting spatial data where we achieve 3-D HWD transform family. We construct translation-invariant version of the proposed family and show its efficiency in video denoising compared to other wavelet-based methods through several experiments.
Conference proceedings : ... Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE Engineering in Medicine and Biology Society. Annual Conference, 2010
A context-based 3D interpolation technique is proposed to enhance the out-of plane resolution of ... more A context-based 3D interpolation technique is proposed to enhance the out-of plane resolution of 3D medical images. The proposed technique represents a new approach of aiding 3D interpolation and improving its performance by efficient use of domain knowledge about the anatomy, objects and imaging modalities. In the new approach a family of adaptive 3D interpolation filters are designed and conditioned on different spatial contexts (classes of feature vectors). Training is used to incorporate the domain knowledge into the design of these interpolators. Experimental results show significant improvement of the new approach over some existing 3D interpolation techniques.
2009 16th IEEE International Conference on Image Processing (ICIP), 2009
We propose a new image acquisition and recovery strategy of hybrid sensing (HS) that combines ran... more We propose a new image acquisition and recovery strategy of hybrid sensing (HS) that combines random sampling of compressive sensing (CS) and uniform down sampling. HS lets the two sampling schemes complement each other so that one can have the best of both worlds: signal-independent sparse sampling that is the hallmark of CS, and locally adaptive signal reconstruction that is afforded by uniform sampling. We suggest a few important applications of HS in image acquisition and communication, such as multispectral imaging, multiple description image coding, multiview video, and ultra-high throughput imaging (e.g., functional medical imaging).
2009 16th IEEE International Conference on Image Processing (ICIP), 2009
This paper presents a novel non-local iterative backprojection (NLIBP) algorithm for image enlarg... more This paper presents a novel non-local iterative backprojection (NLIBP) algorithm for image enlargement. The iterative back-projection (IBP) technique iteratively reconstructs a high resolution (HR) image from its blurred and downsampled low resolution (LR) counterpart. However, the conventional IBP methods often produce many "jaggy" and "ringing" artifacts because the reconstruction errors are back projected into the reconstructed image isotropically and locally. In natural images, usually there exist many non-local redundancies which can be exploited to improve the image reconstruction quality. Therefore, we propose to incorporate adaptively the non-local information into the IBP process so that the reconstruction errors can be reduced. Experimental results demonstrated that the proposed NLBP can reconstruct faithfully the HR images with sharp edges and texture structures. It outperforms the state-of-the-art methods in both PSNR and visual perception.
Demosaicking of the color CCD data is a key to the image quality of digital still and video camer... more Demosaicking of the color CCD data is a key to the image quality of digital still and video cameras. Limited by the Nyquist frequency of the color filter array (CFA), color artifacts often accompany high frequency contents in the reconstructed images. This paper presents a general approach of joint spatial-temporal color demosaicking that exploits all three forms of sample correlations: spatial, spectral, and temporal. By motion estimation and statistical data fusion between multiple estimates obtained from adjacent mosaic frames, the new approach can significantly outperform the existing spatial color demosaicking techniques both in objective measure and subjective visual quality.
Recently, many researchers started to question a long-standing paradox in the engineering practic... more Recently, many researchers started to question a long-standing paradox in the engineering practice of digital photography: oversampling followed by compression, and pursue more intelligent sparse sampling techniques. In this research we take a practical approach of uniform down sampling in image space, and the sampling is made adaptive by a spatially varying directional low-pass prefiltering. Since the down-sampled prefiltered image
Reported is a formal study on the visual quality of rasterized lines and the optimality of Bresen... more Reported is a formal study on the visual quality of rasterized lines and the optimality of Bresenham-type line generators. A straight line is rendered as a sequence of pixels on raster displays. Due to the finite resolution of raster devices quantization errors are inevitable in the rendering, often causing visually objectionable jagged digital lines. Different rasterization schemes will generate different digital lines. Thus a question of both theoretical and practical importance arises: is there an optimal line rasterization scheme different from the existing ones which can render visually most pleasing digital lines for the given device resolution? This paper will give an answer to this open question.
Visual Information Processing and Communication, 2010
In most applications, video deinterlacing has to be performed in real time. Numerous algorithms h... more In most applications, video deinterlacing has to be performed in real time. Numerous algorithms have been developed to strike a good balance between throughput and quality. The motion adaptive deinterlacing algorithm switches between two modes: direct merging of two fields in areas of no motion, or intrafield adaptive interpolation when motions are detected. In this paper, we propose a fast GPU-aided implementation of a motion adaptive deinterlacing algorithm using NVIDIA CUDA (Compute Unified Device Architecture) technology. We discuss the techniques of adapting the computations in motion detection and adaptive directional interpolation to the GPU architecture for maximum video throughput possible. The objective is to fully utilize the processing power of GPU without compromising the visual quality of the deinterlaced video. Experimental results are reported and discussed to demonstrate the performance of the proposed GPU-aided motion adaptive video deinterlacer in both speed and visual quality.
W e examine color quantization of images using trellis-coded quantization (TCQ) in both the RGB d... more W e examine color quantization of images using trellis-coded quantization (TCQ) in both the RGB domain and YUV domain. Together with a simple dithering scheme, an eightbit trellis-coded color quantizer reproduces images that are visually indistinguishable from the 24-bit originals. It can be viewed as a predictive trellis-coded color quantization scheme. We also study trellis-coded vector quantization (TCVQ) for color quantization. Our proposed TCQ-based color quantization schemes are universal in the sense that no training or look-up table is needed. The complexity of TCQ is linear with respect to image size, making trellis-coded color quantization suitable for color printing, real-time interactive graphics and window-based display environment.
... Since FPGAs have a flexible architecture that can be reconfigured according to user-specified... more ... Since FPGAs have a flexible architecture that can be reconfigured according to user-specified ... with the computing blocks are described in Section 3. Partitioned DBWT-based HDTV compression approach is described in Section 4. FPGA implementations with ...
Single sensor digital color cameras capture only one of the three primary colors at each pixel an... more Single sensor digital color cameras capture only one of the three primary colors at each pixel and a process called color demosaicking (CDM) is used to reconstruct the full color images. Most CDM algorithms assume the existence of high local spectral redundancy in estimating the missing color samples. However, for images with sharp color transitions and high color saturation, such an assumption may be invalid and visually unpleasant CDM errors will occur. In this paper we exploit the image non-local redundancy to improve the local color reproduction result. First, multiple local directional estimates of a missing color sample are computed and fused according to local gradients. Then nonlocal pixels similar to the estimated pixel are searched to enhance the local estimate. An adaptive thresholding method rather than the commonly used nonlocal means filtering is proposed to improve the local estimate. This allows the final reconstruction to be performed at the structural level as opposed to the pixel level. Experimental results demonstrate that the proposed local directional interpolation and nonlocal adaptive thresholding (LDI-NAT) method outperforms many state-of-the-art CDM methods in reconstructing the edges and reducing color interpolation artifacts, leading to higher visual quality of reproduced color images.
Progressive image coding is a useful feature for image databases, image communications, and muIti... more Progressive image coding is a useful feature for image databases, image communications, and muItimedia information systems. Centrat to progressive image coding is a multiresolution image pyramid. Quadtree-based recursive regular tessellation is a popular form of image pyramid. But regular tessellation is often too rigid to capture the scene structure of an image; consequently, it may not generate a compact image representation. This paper proposes a scheme of hierarchical piecewise linear approximation as an adaptive image pyramid. A progressive segmentation-bred image coder comes naturally from the proposed image pyramid. The new image pyramid is semantically more powerful than regular tessellation while syntactically simpler than free segmentation. Thi,s good compromise between the adaptability and complexity of image segmentation contributes to high compression ratios achieved by our progressive image coder. In addition to its advantages in data compression and progressive transmission, our image coder also facilitates many other image manipulations.
Color demosaicking is critical to the image quality of digital still and video cameras that use a... more Color demosaicking is critical to the image quality of digital still and video cameras that use a single-sensor array. Limited by the mosaic sampling pattern of the color filter array (CFA), color artifacts may occur in a demosaicked image in areas of high-frequency and/or sharp color transition structures. However, a color digital video camera captures a sequence of mosaic images and the temporal dimension of the color signals provides a rich source of information about the scene via camera and object motions. This paper proposes an inter-frame demosaicking approach to take advantage of all three forms of pixel correlations: spatial, spectral, and temporal. By motion estimation and statistical data fusion between adjacent mosaic frames, the new approach can remove much of the color artifacts that survive intra-frame demosaicking and also improve tone reproduction accuracy. Empirical results show that the proposed inter-frame demosaicking approach consistently outperforms its intra-frame counterparts both in peak signal-to-noise measure and subjective visual quality. Index Terms-Bayer color filter array, data fusion, digital video, subpixel motion estimation, temporal color demosaicking. I. INTRODUCTION M OST digital cameras capture a color image with a single sensor array that sub-samples color bands in a particular mosaic pattern, such as the Bayer color filter array (CFA) [3] shown in Fig. 1. At each pixel, only one of the three primary colors (red, green, and blue) is sampled. The full color image is reconstructed by interpolating the missing color samples. This process is called color demosaicking, which is critical to the quality of reconstructed color images. The problem of color demosaicking has been extensively studied in spatial and frequency domains for still digital cameras [1], [2], [4], [6], [7], [9], [11], [13]-[17], [22], [23], [26]. Early demosaicking techniques mostly work in the spatial domain, such as nearest neighbor replication, bilinear interpolation, and cubic B-spline interpolation [13]. They are easy to implement but susceptible to many artifacts such as blocking, blurring and zipper effect at edges. The problem can be mitigated by an appropriate use Manuscript received July 15, 2004; revised February 3, 2006. This work was supported in part by the Natural Sciences and Engineering Research Council of Canada through an industrial research chair in digital cinema. The associate editor coordinating the review of this manuscript and approving it for publication was Dr.
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Papers by Xiaolin Wu