Point spread function estimation from projected speckle illumination

The resolution of an imaging apparatus is ideally limited by the diffraction properties of the light passing through the system aperture, but in many practical cases, inhomogeneities in the light propagating medium or imperfections in the optics degrade the image resolution. Here we introduce a powerful and practical new approach for estimating the point spread function (PSF) of an imaging system on the basis of PSF Estimation from Projected Speckle Illumination (PEPSI). PEPSI uses the fact that the speckles’ phase randomness cancels the effects of the aberrations in the illumination path, thereby providing an objective pattern for measuring the deformation of the imaging path. Using this approach, both wide-field-of-view and local-PSF estimation can be obtained by calibration-free, single-speckle-pattern projection. Finally, we demonstrate the feasibility of using PEPSI estimates for resolution improvement in iterative maximum likelihood deconvolution. A simple, calibration-free scheme for estimating and mitigating imaging systems’ aberrations should benefit wide-field microscopy. Researchers at the Technion – the Israel Institute of Technology – describe a new method for estimating the point spread function (PSF) of an imaging system by projecting a speckle pattern onto the imaged object, thereby providing a critical measure of the imaging performance and of the presence of aberrations. The approach, named PSF Estimation by Projected Speckle Illumination (PEPSI), relies on the fact that the phase randomness of speckles cancels the troublesome effects of aberrations in the illumination path. As PEPSI is simple to implement, requiring only a diffuser to be switched into the illumination path, the researchers anticipate that it can be readily integrated into any fluorescence microscope, and may benefit other types of imaging systems as well.