Hologram method boosts 3D image sharpness fivefold

by Robert Schreiber
Berlin, Germany (SPX) Feb 16, 2026

Researchers at the University of Tartu Institute of Physics have introduced a computational imaging method that sharpens three dimensional holographic images by increasing depth of focus fivefold after the recording step. The approach targets a key limitation of conventional microscopes and 3D imaging systems, where image properties are fixed once a hologram or frame has been captured.

Instead of recording a single hologram at one focal setting, the team led by junior research fellow Shivasubramanian Gopinath acquires a set of holograms at different focal distances during image capture. These multiple holograms are then combined into a single synthetic hologram that offers much greater depth of focus than standard methods and can be adjusted during post processing. This flexibility allows users to refocus digitally and optimize the appearance of three dimensional structures without repeating the experiment.

The work builds on Fresnel incoherent correlation holography, or FINCH, a digital holography technique that records three dimensional information under ordinary illumination and reconstructs it computationally. The researchers describe their new approach as post engineering of axial resolution in FINCH, or PEAR FINCH, to highlight that control of axial resolution is shifted into a post processing step. By reconfiguring the reconstruction pipeline, they show that axial resolution and depth of focus can be engineered from the recorded hologram ensemble.

PEAR FINCH is distinguished by several technical advances. The depth of focus can be tuned after recording rather than being fixed by the optics at acquisition time. A two step computational reconstruction procedure maintains high image quality and a strong signal to noise ratio across the extended depth range. Experiments demonstrate that the method achieves about a fivefold increase in depth of focus compared to conventional FINCH, while preserving image fidelity.

The technique also performs well under diffusive illumination, a condition that is common when imaging real biological samples that scatter and diffuse light. This robustness makes the method suitable for challenging microscopy conditions where optical access is limited or samples cannot be prepared for ideal illumination. According to Gopinath, this level of post recording flexibility has not previously been reported in holographic imaging and sets a new performance benchmark.

By making three dimensional holographic microscopy more adaptable and powerful, PEAR FINCH opens opportunities for studying complex biological structures that extend over significant depth. The method supports more intelligent and adaptive microscopes that can tailor reconstruction to the needs of a particular specimen or experiment. The researchers argue that the approach consistently outperforms both conventional direct imaging systems and standard FINCH configurations, pointing to a new paradigm for computational holographic imaging.

Research Report: Axial resolution post-processing engineering in Fresnel incoherent correlation holography