Motoharu SONOGASHIRA†a) , Nonmember, Masaaki IIYAMA †b) , Member, and Michihiko MINOH †c) , Fellow SUMMARY Blind deconvolution (BD) is the problem of restoring sharp images from blurry images when convolution kernels are unknown. While it has a wide range of applications and has been extensively studied, traditional shift-invariant (SI) BD focuses on uniform blur caused by kernels that do not spatially vary. However, real blur caused by factors such as motion and defocus is often nonuniform and thus beyond the ability of SI BD. Although specialized methods exist for nonuniform blur, they can only handle specific blur types. Consequently, the applicability of BD for general blur remains limited. This paper proposes a shift-variant (SV) BD method that models nonuniform blur using a field of kernels that assigns a local kernel to each pixel, thereby allowing pixelwise variation. This concept is realized as a Bayesian model that involves SV convolution with the field of kernels and smoothing of the field for regularization. A variationalBayesian inference algorithm is derived to jointly estimate a sharp latent image and a field of kernels from a blurry observed image. Owing to the flexibility of the field-of-kernels model, the proposed method can deal with a wider range of blur than previous approaches. Experiments using images with nonuniform blur demonstrate the effectiveness of the proposed SV BD method in comparison with previous SI and SV approaches. key words: blind deconvolution, deblurring, shift-variant, variational Bayes
IntroductionBlind deconvolution (BD) for deblurring is one of the most extensively studied topics in image processing [1], [2]. Essentially, blurring of images is modeled as convolution of images and kernels. Deconvolution is the inverse of this process, which effectively restores sharp images from blurry ones. The objective of BD is to perform deconvolution when kernels are unknown, which is often the case in practice [1]. Since undesirable blur is quite common in the real world, BD has a wide range of applications, e.g., mobile photography [3], computational photography [4], computer vision [5], astronomical imaging [6], and biomedical imaging [7].Traditional shift-invariant (SI) BD assumes uniform blur produced by kernels that do not vary spatially across images, such as the example in Fig. 1 (b). However, in reality blur kernels often spatially vary, producing nonuni- . For example, independently moving objects produce different effects of motion blur, and objects distant from a camera are more subject to defocus blur than close objects. Blur is often more complex since both motion and defocus blur can simultaneously occur, as shown in Fig. 1 (c). In such cases, SI BD methods fail in kernel estimation and also in deconvolution [1]. Although specialized BD methods for nonuniform blur have been recently developed, they can only handle certain types of blur, e.g., motion, defocus, or locally uniform blur [2]. Consequently, the applicability of BD to general blurry images remains limited.I...