So how can we compare high-resolution 2-D data without incurring high process times and power?
One solution is to design and build an expensive custom board, containing multiple high-end processors, filled with stacks of memory and logic devices.
The other solution is found hidden within the laws of diffractive optics. Optical processing is a truly parallel method of calculation, using the fastest medium there is – light. By exploiting the fact that the 2-D Fourier Transform of an image is analagous to its Far Field (Fraunhofer) Diffraction pattern, the two-dimensional Fourier transform of an image may be produced using a simple optical system:
But that is not all, because the process is parallel in nature, the process time does not scale with resolution. Every pixel of the image is compared with every other simultaneously, independent of resolution. This allows very large images to be Fourier transformed at the speed of light – orders of magnitude faster than the electronic equivalents.