Strategies for reducing speckle noise in digital holography

Digital holography (DH) has emerged as one of the most effective coherent imaging technologies. The technological developments of digital sensors and optical elements have made DH the primary approach in several research fields, from quantitative phase imaging to optical metrology and 3D display technologies, to name a few. Like many other digital imaging techniques, DH must cope with the issue of speckle artifacts, due to the coherent nature of the required light sources. Despite the complexity of the recently proposed de-speckling methods, many have not yet attained the required level of effectiveness. That is, a universal denoising strategy for completely suppressing holographic noise has not yet been established. Thus the removal of speckle noise from holographic images represents a bottleneck for the entire optics and photonics scientific community. This review article provides a broad discussion about the noise issue in DH, with the aim of covering the best-performing noise reduction approaches that have been proposed so far. Quantitative comparisons among these approaches will be presented.Digital holography: Tackling speckleDigital holography has become an important and popular imaging technology with applications in biomedicine, metrology and 3D displays. However, its coherent nature means that it suffers from speckle, an undesirable source of noise that degrades the quality of holographic images. In a Review of the topic, Vittorio Bianco and coworkers now discuss the details of the problem and the various optical and numerical solutions that have been developed to combat the issue. Optical approaches discussed include the use of optical sources with either reduced or no coherence such as white light and random lasers or alternatively employing rotating or moving diffusers. In addition, a wide variety of denoising algorithms and digital spatial filtering methods have also been successfully developed to reduce the appearance of speckle.