Fresnel transform over image
Within the context of optical image/signal processing, the Fresnel transform mathematically describes the manifestation of a physical phenomenon, known as diffraction, on the image formation process of a practical camera system using a finite aperture size.

Diffraction causes blurring on the image, and defines the physical limit of achievable image resolution, given an ideal lens system (which has no distortions of any kind on the image formation process). No better resolution is possible using that aperture size and optical imaging system.

Diffraction can be analysed through the Fourier transformation of the aperture function.