Digital speckle reduction: a comparison between methods

Abstract

ABSTRACT Digital holography, as a ny other coherent imaging modalities, is subject to speckle noise . Speckles may degrade significantly the image quality, therefore many optical and digital techniques were developed to suppress the speckles . In this paper we present a comparison between si x digital speckle filtering techniques used for digital hologr aphy . Keywords: Digital Holography , Speckle denoising 1. INTRODUCTION Coherent imaging modalities such as digital holography are subject to speckle noise that may impose severe limitations on the image quality. Speckle noise causes to a signal depended distortion of the image which make s it difficult to identify small detail s in the image. Speckle occurs whenever coherent light passes through a randomly fluctuating medium, or is reflected from a rough surface , where the latter case i s of particular interest in digital holography. S peckle noise manifests as temporal or spatial fluctuations , depending on the speckle source . Speckle pattern dependence in time refers to as dynamic speckle If the speckle grains formation, destruc tion and movement are random, then, this speckle form is called boiling pattern. Spatial speckles, commonly formatted by surface roughness, are the more common in digital holography. Description of the speckle noise mechanism and their appropriate models can be found in Refs. 1, 2 . U nlike thermal and readout noise, speckle noise is object dependent, with a variance being proportional to the local field intensity. The lateral speckl e average size can be approximated as the reciprocal of the maximum spatial frequency, to have a value of