A New Paradigm for Imaging Systems

Today’s imaging systems today frequently have digital components, and some image processing is done in the camera. The potential for dramatically increased perfor­ mance is not realized, however, until the complete imaging system, including the optics and signal processing, is designed as a coherent whole. In such a system, the optics produces an intermediate image, and the final image is produced by signal processing. By designing an integrated optical/digital imaging system, one can use completely different aberration balancing to achieve performance that otherwise would be impossible. Modification of the optics makes it possible to compensate for all focus-related aberrations with signal processing. This frees the optics to compensate optimally for the other aberrations. The result can be high-performance, single-element lenses, or even two-element zoom lenses. Alternatively, if the optics alone corrects for all aberrations adequately, then the depth of field of the imaging system can be dramatically extended. An example is a 10X increase in the depth of field of a microscope. Hybrid Optical/Digital Imaging The new design paradigm requires a modification of the optics to “code” the wave in the aperture stop or an image of the aperture stop. The coding produces an “intermediate” image formed by the optical portion of the system that gathers the image. Signal processing is then required to “decode” the intermediate image to produce a final image. The coding can be designed to make the imaging system invariant to focus-related aberrations. For example, these new focus-invariant imaging systems can have more than an order of magnitude increase in the depth of field. This new paradigm for design of imaging systems has been termed Wavefront Coding. Wavefront Coded optical systems are arrived at by designing the coding optics and the signal processing as an integrated imaging system. Coding of signals to optimally convey particular information is not new. In radar, the pulses are coded to optimally provide information concerning a target’s range, for example. Brenner, Lohmann, and Ojeda-Castañeda showed that a tool that is useful in the design of radar signals, Wood­ ward’s ambiguity function, is also useful in examining the 1 Optical Transfer Function (OTF) of an imaging system. Using this technique, it was shown that certain phase plates extend the depth of focus of a hybrid imaging system. A phase plate with the shape