GB1445119A - Direct electronic fourier transform of optical images - Google Patents

Abstract

1445119 Television RESEARCH CORP 26 Sept 1973 [29 Dec 1973] 45011/72 Heading H4F A device for converting an optical image into electrical signals which are spatial Fourier transform representations of the optical image uses a medium having an electrical property which varies as a function of an incident optical image and strain disturbances, the electrical property being measured as a plurality of varying strain disturbances are sequentially caused in the medium to provide a like plurality of electrical signals, each representing one term in the Fourier transform. In one embodiment, Fig. 5, for a one-dimensional image projected by a projector 18 the medium is formed by a film 12 on a substrate 10, surface acoustical waves being generated by a transducer 20 fed by a sweep frequency generator 24. A constant voltage from source 28 is applied between electrical contacts, 14, 16, changes in the conductivity of the film 12 being detected by a detector 34 which also receives a frequency-related input from generator 24. Several of the devices of Fig. 5 may be connected in parallel (Fig. 6, not shown) for two-dimensional images, using interdigitated tooth-like contacts. In an alternative embodiment voltage changes across a semi-conductor or metal bar (36, Fig. 7, not shown) receiving a onedimensional image and being subjected to bulk wave vibrations are detected. In a further embodiment, Fig. 8, for twodimensional images an image is projected by a projector 70 through a substrate 56 vibrated by transducers 72 to a photo-cathode film 58, emitted electrons being collected at 60, the voltage across a resistor 64 being measured to derive the output signals. In an alternative embodiment the image is projected on a selected area of a substrate (56, Fig. 9, not shown) vibrated by two transducers. The vibrating medium in each of the above devices may vibrate at a fundamental frequency and simultaneously at one or more harmonics, the signals relating to these different frequency being separated by electronic filters (106a- 106c, Fig. 11, not shown). For deriving signals from a colour image three devices (114a-114c, Fig. 12, not shown) may be used, each receiving a different primary colour image component. To reproduce an image from the derived signals the signals are fed to transducers (92, 94, Fig. 10, not shown) coupled to an elasto-optical plate (88) positioned between crossed polarizers, light being shone on one end of this assembly, the plate causing local changes in the angle of polarization of light passing through it. The light transmitted by the assembly can be stored, as a signal, in an acoustic delay line which adds up the Fourier components; an electronic shutter or flash tube can then illuminate the sound wave complex to derive a total optical image.