| 摘要 |
1290971 Spatial filtering ENTREPRISE DE RECHERCHES ET C'ACTIVITIES PETROLIERES 2 June 1970 [10 June 1969] 26619/70 Heading G2J [Also in Division H4) Information, e.g. seismic data, is optically processed by illuminating a transparency 16 containing the information with a parallel beam of coherent mono-chromatic light, forming a power spectrum of the transparency in the Fourier transform plane 17 of a lens 7 and locating in said plane 17 a filter consisting of a screen having a transparency which varies over its surface as the auto-cavelation function of the spectrum of the transparency 16, and reconstituting the filtered image 25 of the transparency. In one embodiment the Fourier transform plane 17 is associated with a single spherical transform lens 7 and a spherical reconstituting lens 8. In an alternative embodiment both the transform and reconstituting lens systems 7, 8 comprise a spherical lens 26 or 28 and a cylindrical lens 27 or 29. The image focal planes of lenses 26, 27 coincide in the transform plane 17. The generatrices of cylindrical lenses 27, 29 are vertical and disposed parallel, e.g. to bands on the transparency. Thus the Fourier transform is formed as a series of vertical straight line spectra. The filter is formed as follows: The transparency is placed in the object plane of lens 7 and the spectrum formed in the transform plane is photographed to record the first order power spectrum; this photograph is then placed in the object plane of lens 7 and the process repeated to get a second order power spectrum record; Using this second record the process is again repeated to obtain a positive third order power spectrum record the transparency of which varies as the auto-correlation function of the first order spectrum. In the first and second operations to form the filter the photographic record produced, which is a positive, is reversed in polarity, that is a photographic plate is printed in contact with the film, to give a negative. The positive filter obtained is used to non-periodic random elements from the information in the transparency. If this filter is made as a negative it filters out periodic elements.
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