A study of focus metrics and their application to automated focusing of inline transmission holograms

Abstract

In this article, we will explore the use of several spatial-domain focus metrics frequently applied in non-coherent (classical) imaging systems, and evaluate their suitability for the automated numerical focusing of marine holograms such as those collected with eHoloCam, the underwater digital holographic camera developed at Aberdeen University. Metrics will be applied to a set of particle holograms chosen to represent a range of features within the three categories: opacity, edge roughness and distance from image sensor.

Keywords:

• hologram
• Tenengrad
• entropy
• variance
• Brenner
• Sobel