Patent GB-1277441-A (GB)
Title: Image processing systems
Inventor: JNR MICHAEL GRASER
IPC: G02B27/44
Filed: 1969-06-20
Abstract: 1277441 Spatial filtering TECHNICAL OPERATIONS Inc 20 June 1969 31440/69 Heading G2J Optical images are processed by illuminating a record of the image with partially spatially coherent light, opening a Fourier transform of the record, forming at least two images of the transform, spatially filtering a first one of the images so that the filtered beam contains only selected portions of the image of the Fourier transform and retransforming the transform images. In one embodiment Fig. 1, a mono-chrome record 70 containing colour coded information is illuminated by partially coherent light. A transform lens 68 forms a Fourier transform of the record coincident with a filter 74, the Fourier transform being a diffraction pattern of spatial frequencies in the record which includes a spectrum of the spatial frequencies convolved with a Dirac delta function associated with the periodic modulation of the record image. The spatial filter 74 passes only desired diffraction orders corresponding to the colour coded information, and images of this transform are erected by lens 78 in separate planes each associated with a respective vidicon tube 88, 96, 98, 100. The plurality of images is formed by semi-reflecting mirror 80 and either semi-reflecting or dichroic mirrors 82, 84. Simultaneously the record 70 is illuminated with a spatially non-coherent light beam from which is formed a transform image containing luminance information of the record. Images of this transform are also erected by lens 78. Spatial filter 128 located in the image plane of vidicon 88 only passes luminance information. The red, blue, green vidicons 96, 98, 100 each have a spatial filter 112, 114, 116 located in their image planes to filter out all but the appropriate colour separation images. A normal colour television system 102, 110 then processes the thus formed electric signals to give a composite signal representing the original coloured scene of the mono-chrome record 70. Alternatively Fig.2 (not shown) a record (144) is illuminated by partially coherent light and a transform made containing all orders of diffraction. Respective images of the transform are fed to vidicon tubes using semi-reflecting plates (152), (154), (156). The luminance vidicon (178) receives all the information. Spatial filters (158), (160), (162) are associated with the other vidicons passing only the desired diffraction orders of desired information. In another embodiment Fig.3 a record 184 is illuminated and a Fourier transform of its spatial frequencies formed in transform plane 188. Transform lens 186 with the aid of a beamsplitter 190 images the transform on lenses 194, 196. These images are recombined in a common image plane 213, by lenses 198, 200 and mirrors 202-212, coincident with an element of photosensitive material. A high pass spatial filter 214 is located in one light path and thus gives rise to an image on 213 whose spectral frequency content is weighted towards the higher frequencies. This image mixed with the unaltered image gives a composite image having enhanced contrast. Reference has been directed by the Comptroller to Specification 1167727.