Correcting artifacts from finite image size in Differential Dynamic Microscopy

TL;DR

This paper introduces a windowing technique in Differential Dynamic Microscopy to reduce edge artifacts caused by objects moving out of view, thereby improving analysis accuracy and extending the range of measurable wave vectors.

Contribution

The study demonstrates that applying a spatial windowing filter before DDM analysis significantly reduces artifacts and enhances the method's capabilities, including revealing size polydispersity.

Findings

Windowing reduces artifacts from objects crossing image edges.

Extends the range of wave vectors accessible in DDM.

Reveals size polydispersity in colloidal suspensions.

Abstract

Differential Dynamic Microscopy (DDM) analyzes traditional real-space microscope images to extract information on sample dynamics in a way akin to light scattering, by decomposing each image in a sequence into Fourier modes, and evaluating their time correlation properties. DDM has been applied in a number of soft-matter and colloidal systems. However, objects observed to move out of the microscope's captured field of view, intersecting the edges of the acquired images, can introduce spurious but significant errors in the subsequent analysis. Here we show that application of a spatial windowing filter to images in a sequence before they enter the standard DDM analysis can reduce these artifacts substantially. Moreover, windowing can increase significantly the accessible range of wave vectors probed by DDM, and may further yield unexpected information, such as the size polydispersity of a colloidal suspension.