Faculty Publications
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Publications by NITK Faculty
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Item A Survey-Super Resolution Techniques for Multiple, Single, and Stereo Images(Institute of Electrical and Electronics Engineers Inc., 2014) Balure, C.S.; Ramesh Kini, M.R.This paper reviews some of the methods of super resolution (SR) (with multiple images and single image as input) with a focus on super resolution for stereo images with their advantages and disadvantages. This paper has attempted to fill the void of non availability of the survey of SR techniques for stereo image. © 2014 IEEE.Item Single depth image super-resolution via high-frequency subbands enhancement and bilateral filtering(Institute of Electrical and Electronics Engineers Inc., 2016) Balure, C.S.; Ramesh Kini, M.; Bhavsar, A.This paper addresses the problem of super-resolution (SR) from a single low-resolution (LR) depth image to a high-resolution (HR) depth image. A simple yet effective method has been proposed using Discrete Wavelet Transform (DWT), Stationary Wavelet Transform (SWT), and by utilizing the gradient information of the interpolated LR image. We propose an intermediate stage to enhance the high-frequency subbands to recover the HR image for both noiseless and noisy scenarios. The proposed method has been validated on Middlebury dataset for different upsampling factors (i.e. 2, 4, 8) and is shown to be superior when compared with some related DWT and SWT based SR methods. We also demonstrate encouraging performance of the approach on noisy depth images. © 2016 IEEE.Item Depth image super-resolution with local medians and bilateral filtering(Institute of Electrical and Electronics Engineers Inc., 2016) Balure, C.S.; Ramesh Kini, M.; Bhavsar, A.In this paper, we propose an approach for depth image super-resolution (SR). Given a noisy low resolution (LR) depth image and its corresponding registered high resolution (HR) colour image, our approach improves the resolution of the LR image while suppressing noise. We use the segmentation of HR colour images as a cue for depth image super-resolution. Our method begins with a highly over-segmented color image (using well-known segmentation approaches such as mean shift (MS) or simple linear iterative clustering (SLIC), and an interpolated LR depth image. We then use a combination of the local medians in the depth image (corresponding to the colour segments) and bicubic interpolation, followed by bilateral filtering to compute the SR depth image. We performed experiments for higher magnification factors 4, 8 using the Middlebury depth image dataset and evaluate the SR performance using the PSNR and SSIM metrics. The experimental results show that proposed method (including some variants), while being relatively simplistic, shows an average improvement of 1.2dB and 1.7dB on noiseless and noisy data respectively, over the popular method of guided image filtering (GIF) for upsampling factor 8. © 2016 IEEE.Item Depth image super-resolution: A review and wavelet perspective(Springer Verlag service@springer.de, 2017) Balure, C.S.; Ramesh Kini, M.We propose an algorithm which utilizes the Discrete Wavelet Transform (DWT) to super-resolve the low-resolution (LR) depth image to a high-resolution (HR) depth image. Commercially available depth cameras capture depth images at a very low-resolution as compared to that of the optical cameras. Having an highresolution depth camera is expensive because of the manufacturing cost of the depth sensor element. In many applications like robot navigation, human-machine interaction (HMI), surveillance, 3D viewing, etc. where depth images are used, the LR images from the depth cameras will restrict these applications, thus there is a need of a method to produce HR depth images from the available LR depth images. This paper addresses this issue using DWT method. This paper also contributes to the compilation of the existing methods for depth image super-resolution with their advantages and disadvantages, along with a proposed method to super-resolve depth image using DWT. Haar basis for DWT has been used as it has an intrinsic relationship with super-resolution (SR) for retaining the edges. The proposed method has been tested on Middlebury and Tsukuba dataset and compared with the conventional interpolation methods using peak signal-to-noise ratio (PSNR) and structural similarity (SSIM) performance metrics. © Springer Science+Business Media Singapore 2017.Item Local segment-based dense depth reconstruction from very sparsely sampled data(Institute of Electrical and Electronics Engineers Inc., 2017) Balure, C.S.; Bhavsar, A.; Ramesh Kini, M.R.In this paper, we propose two relatively simplistic and efficient methods for depth reconstruction from very sparsely sampled random depth data. Both the proposed approaches exploit the segmentation cue from a registered colour image of the same scene. The first approach which we term as plane fitting depth reconstruction (PFitDR), involves cost computations on plane-fitted depth values over local segments. The second approach, which we call median filled depth reconstruction (MFillDR) is an even simpler method, wherein the reconstruction is carried out using computation of median of depth values over local segments. We demonstrate dense reconstruction from very less number of available depth points (e.g. as low as 1%). Our methods favorably compare with a recent related state-of-the-art method, both qualitatively as well as quantitatively in terms of peak signal-to-noise ratio (PSNR) and structural similarity (SSIM) indices. © 2017 IEEE.Item GMM based single depth image super-resolution(Springer Verlag service@springer.de, 2018) Balure, C.S.; Ramesh Kini, M.R.; Bhavsar, A.Super-resolution (SR) is a technique to improve the resolution of an image from a sequence of input images or from a single image. As SR is an ill-posed inverse problem, it leads to many suboptimal solutions. Since modern depth cameras suffer from low-spatial resolution and are noisy, we present a Gaussian mixture model (GMM) based method for depth image super-resolution (SR). We train GMM from a set of high-resolution and low-resolution (HR-LR) synthetic training depth images to learn the relation between the HR and the LR patches in the form of covariance matrices. We use expectation-maximization (EM) algorithm to converge to an optimal solution. We show the promising results qualitatively and quantitatively in comparison to other depth image SR methods. © Springer Nature Singapore Pte Ltd. 2018.Item Guided depth image reconstruction from very sparse measurements(SPIE spie@spie.org, 2018) Balure, C.S.; Bhavsar, A.; Ramesh Kini, M.Depth images captured from modern depth cameras generally suffer from low spatial resolution, noise, and missing regions. These kinds of images cannot be used directly in applications related to depth images, e.g., robot navigation, 3DTV, and augmented reality, which basically need high-resolution input images with no noise o missing regions to function properly. To address the problem of low spatial resolution, noise degradation, and missing regions in depth images, we propose methods based on a guidance color image for depth reconstruction (DR) from sparse depth inputs and depth image super-resolution (SR). We also suggest a scenario wherein these problems can be integrated and addressed simultaneously. Further, we also demonstrate applications of the proposed approach for depth image denoising and depth image inpainting. In our approach, the guidance color image is used for obtaining the segment cues by applying mean-shift (MS) or simple linear iterative clustering (SLIC) segmentation on it. These strong segment cues help in aiding the DR and SR problems by considering the corresponding segments in the input depth image, and estimate the unknown pixels by either plane fitting or median filling approaches. Furthermore, we explore both direct and pyramidal (hierarchical) approaches for SR and DR-SR for higher upsampling factor. As such, our approaches are relatively simpler than some of the contemporary methods, yet the experimental results of the proposed methods show superior performance as compared with some other state-of-the-art DR and SR methods. © 2018 SPIE and IS&T.Item Guidance-based improved depth upsampling with better initial estimate(Inderscience Publishers, 2021) Balure, C.S.; Ramesh Kini, M.Like optical images, depth images are also gaining popularity because of its use in many applications like robot navigation, augmented reality, 3DTV and more. The commercially available depth cameras generate depth images which suffer from low spatial resolution, corrupted with noise, and missing regions. Such images need to be super-resolved, denoised and inpainted before using them to have better accuracy. Super-resolution (SR) techniques can be used to produce a high-resolution output. Since SR is an ill-posed inverse problem, a good initial estimate is always a good regulariser to find the optimal solution. We propose an initial estimate as part of our SR pipeline, esp. ×8, which will helps in quick convergence and accurate output. We propose a cascade approach by combining residual interpolation (RI) method with anisotropic total generalised variation (ATGV) method, both uses HR guidance image. The improvements are shown qualitative and quantitative with different levels of noise. © 2021 Inderscience Publishers. All rights reserved.