Quasi noise-free digital holography
One of the main drawbacks of Digital Holography (DH) is the coherent nature of the light source, which severely corrupts the quality of holographic reconstructions. Although numerous techniques to reduce noise in DH have provided good results, holographic noise suppression remains a challenging task. We propose a novel framework that combines the concepts of encoding multiple uncorrelated digital holograms, block grouping and collaborative filtering to achieve quasi noise-free DH reconstructions. The optimized joint action of these different image-denoising methods permits the removal of up to 98% of the noise while preserving the image contrast. The resulting quality of the hologram reconstructions is comparable to the quality achievable with non-coherent techniques and far beyond the current state of art in DH. Experimental validation is provided for both single-wavelength and multi-wavelength DH, and a comparison with the most used holographic denoising methods is performed. By combining smart recording with numerical processing methods, a research team has realized digital holography that is virtually noise free. Noise originating from the coherent nature of laser light is the scourge of digital holography, always causing holographic images to be of lower quality than conventional photographs. Now, Pasquale Memmolo of the Institute of Applied Sciences and Intelligent Systems in Italy and co-workers have devised a way to practically eliminate this noise. They achieved this by using a two-stage algorithm: one stage is based on the encoding of multiple holograms, providing the enhanced grouping and the next one performs sparsity enhancement filtering. The output obtained exhibited both qualitative and quantitative improvement over recently developed de-noising techniques. In particular, the algorithm reduced noise in background regions by 98% and in signal regions by 92%.