Image processing without a computer
Channel: simonjelley
Date: 2018-11-03

This is a demonstration of an all-optics approach to performing image processing without a computer. 

Instructions on how to make this can be found in my instructable:
https://www.instructables.com/id/Image-Processing-Without-the-Computer/

The arrangement is called a 4f correlator, and it uses diffractive optical effects to transform an image into its fourier transform, and then transforms it back to the image again, allowing filtering in the fourier domain to be applied to the image. 

What is the fourier domain? Information is stored based on the different frequency components of the image, with the centre of the fourier image being the DC (zero frequency) content, the left and right edges being high horizontal frequencies (narrow vertical stripes or sharp vertical edges), and the top and bottom corresponding to high frequencies in the vertical direction (narrow horizontal stripes or sharp horizontal edges). This is actually how JPEGs are stored and it is comparable to the way MP3s are stored as the different frequencies (notes) present.

Fourier domain filtering enables most image processing done on computers. It can create many filters from simple blurs (including directional blurs) to edge detection and enhancement, right through to image identification (or correlation). Here I demonstrate enhancing edges.

I show a demonstration using cheap, off the shelf components, with dining room table implementation: 
Telescope (mine isn't that cheap but a £30 beginner's scope would work)
Cree 3W LED
2x lens from Smart phone projector
I used a bundle of retort stands though you could make stands from scrap wood, etc.
35mm projector slides
Tin foil, pins and cocktail sticks for filters

To 'read' the filtered image, I focus the image onto my camera with the front lens removed, although projecting onto a sheet of paper would also work.