Visible band lens-free imaging using coded aperture techniques

Traditionally, coded aperture techniques have been applied to short-wavelength imaging: X-rays and γ-rays. For these wavelengths, it is valid to neglect diffraction and describe the operation of the imager in purely geometric-optics terms. We have investigated coded aperture imaging in the visible band. The much longer wavelengths in this region of the spectrum mean that diffraction effects cannot be neglected. We describe the effects of diffraction and the implications for image resolution. We present experimental results from a lens-free coded-aperture imager operating in the visible band and describe the techniques used to obtain good quality images of complex greyscale scenes.