All-optical image denoising using a diffractive visual processor

TL;DR

This paper presents an all-optical, non-iterative image denoising method using a diffractive visual processor that operates at the speed of light, offering high efficiency and minimal computational overhead for removing noise from images.

Contribution

The authors introduce a novel analog diffractive image denoiser that physically scatters noise features using deep learning-optimized passive layers, enabling real-time optical noise removal without digital computation.

Findings

Effectively removes salt-and-pepper noise and spatial artifacts

Achieves 30-40% power efficiency

Demonstrated with a terahertz spectrum diffractive processor

Abstract

Image denoising, one of the essential inverse problems, targets to remove noise/artifacts from input images. In general, digital image denoising algorithms, executed on computers, present latency due to several iterations implemented in, e.g., graphics processing units (GPUs). While deep learning-enabled methods can operate non-iteratively, they also introduce latency and impose a significant computational burden, leading to increased power consumption. Here, we introduce an analog diffractive image denoiser to all-optically and non-iteratively clean various forms of noise and artifacts from input images - implemented at the speed of light propagation within a thin diffractive visual processor. This all-optical image denoiser comprises passive transmissive layers optimized using deep learning to physically scatter the optical modes that represent various noise features, causing them to miss the output image Field-of-View (FoV) while retaining the object features of interest. Our results show that these diffractive denoisers can efficiently remove salt and pepper noise and image rendering-related spatial artifacts from input phase or intensity images while achieving an output power efficiency of ~30-40%. We experimentally demonstrated the effectiveness of this analog denoiser architecture using a 3D-printed diffractive visual processor operating at the terahertz spectrum. Owing to their speed, power-efficiency, and minimal computational overhead, all-optical diffractive denoisers can be transformative for various image display and projection systems, including, e.g., holographic displays.