Fig. 1: Schematic of a size-selective imaging processor acting as a rectangular band-pass filter operator.
From: Nonlocal flat optics for size-selective image processing and denoising
A conceptual illustration of a nonlocal flat optics-based filter, designed to execute the rectangular band-pass OTF (H(kr)), capable of modulating and filtering specific spatial frequencies associated with targets of different sizes. This modulation is achieved by configuring the band-pass numerical aperture (NA) range (NA1–NA2). Such customization facilitates differentiated image processing, including size-selective edge detection (red, yellow, and green parts), specifically, high NA edge detection (green part), and denoising (blue part) tailored to different targets. For example, the red part can detect the edge of the larger image ‘C’ but allows images with other sizes to pass through unchanged; similarly, the yellow part applies to image ‘B’, and the green part applies to the smaller image ‘A’. Meanwhile, the blue part effectively reduces noise without altering the images ‘A’, ‘B’, and ‘C’.
