The use of feedback for enhancing the capabilities of optical image processing systems as well as introducing new operational characteristics is the subject of much recent interest. This paper presents a review of the various processing schemes utilizing feedback developed in the past two years. Such schemes are categorized into optical analog and digital optical techniques. Analog processors with feedback can achieve greater effective dynamic range and a wider variety of transfer functions. Incorporation of gain into the feedback loop helps enhance these aspects, and further adds the possibility of constructing an optical operational amplifier. Nonlinear and space-variant response can also be obtained. Digital optical systems operate on binary rather than analog images. The use of feedback leads to the realization of image thresholding devices and optical flip-flop memories (both of which are vitally important to any digital system) using materials without natural hysteresis or sharp nonlinear characteristics. Existing schemes using dif-ferent materials and configurations will be reviewed.
R. P. Akins,
R. A. Athale,
S. H. Lee,
"Feedback In Analog And Digital Optical Image Processing: A Review," Optical Engineering 19(3), 193347 (1 June 1980). https://doi.org/10.1117/12.7972519