Patent GB-1114130-A (GB)
Title: Improvements in or relating to the registration of photographic images
IPC: G01C11/00
Filed: 1965-08-26
Abstract: 1,114,130. Photo-electric cartographic devices. ITEK CORPORATION. 26 Aug., 1965 [4 Sept., 1964 (2)], No. 36730/65. Heading H4D. [Also in Division G1] In a photogrammetric mapping machine, registration between a pair of stereo-photographs 57a, 57b is obtained by the use of two flying spot scanner cathode-ray tubes 74a, 74b co-operating with two photo-multiplier tubes 76a, 76b, the output signals of which are fed to two viewing cathode-ray tubes 75o, 75b located in a binocular viewer, timing differences between the two signals from the photomultiplier tubes being detected by a correlation system 70 to detect parallaxes between the two photographs 57a, 576, the correlation system feeding a transformation system 71 which distorts the rasters of the two flying spot scanners 74a, 74b to allow for these parallaxes, so that the two images on the viewing cathoderay tubes 75a, 75b will be rectified, undistorted and will be a true stereo-pair. Mechanical components.-The two photographs 57a, 57b are in the form of transparencies and are mounted in two carriers movable on a plane glass plate surface the carriers being guided by two bars disposed at right-angles to one another at the edges of the plate. The glass plate is made so as to obstruct the light rays passing therethrough as little as possible and as such is too thin to be able to support itself without sagging over its entire area. To this end it is supported on a table by air pressure fed to rubber pads under the plate; apertures being provided in the region of the photographs 57a, 57b. The photograph carriers are mounted on the plate by pads fed with air pressure so as to suspend the carriers above the plate for ease of movement. The air supply can be cut off under control of the operator when the desired positions for the photographs have been reached allowing the carriers to rest on the glass plate. The image forming surfaces of the two viewing cathode-ray tubes 75a, 75b are arranged facing each other, and the images are viewed in the binocular viewer using two angularly disposed mirrors 92a, 92b reflecting these images. Raster generator.-The raster formed on each of the flying spot scanner tubes 74a, 74b and the viewing cathode-ray tubes 75a, 75b is in the form of a square generated by interlaced diagonal scanning lines in which each point within the raster is scanned four times for each frame. The frame repetition frequency is approximately 30 per second, and to achieve this a 7À5 Mc/s. crystal oscillator is used in the raster generator and the output of this oscillator is divided in the ratio of 511: 509 and these divided signals are fed to the X and Y deflection plates of the cathode-ray tubes after suitable shaping. This arrangement gives 509 lines to one diagonal and 511 to the other forming the required interlaced diagonal raster. The signals fed to the viewing cathode-ray tube deflection plates are delayed to allow for the delay incurred in processing the signals from the flying spot scanners before they reach the viewing cathode-ray tubes. Scanning system.-Scanning light beams from the flying spot tubes 74a, 74b are transmitted through the pair of stereo-photo transparencies 57a, 57b and become image modulated before reaching the photo-multiplier tubes 76a, 76b. The photo-multiplier tubes are of the dynode type and are each provided with a regulator 186a, 186b to maintain the average current output thereof constant. The signals from the photomultiplier tubes are fed to the viewing cathode-ray tubes by way of two video processing circuits 69a, 69b, which function as an automatic gain control to enhance the video images seen by the operator but these circuits also include edge enhancing networks and, if desired, a signal inverter which enables negative transparencies 57a, 57b to be used, these giving positive images on the viewing cathode-ray tubes. A pair of screen noise feedback control assemblies comprising photo-multiplier tubes 188a, 188b and amplifiers 189a, 189b are also provided to maintain a uniform light intensity from point to point in the faces of the scanning cathode-ray tubes. Correlation system 70.-The purpose of this system is to detect timing differences in the image-modulated signals from the photomultiplier tubes, and thus develop registration error signals which are then used to distort the scanning rasters of the tubes 74a, 74b to remove these registration errors on the images formed on the viewing cathode-ray tubes 75a, 75b. The system 70 comprises five similar systems each arranged by use of filter networks, to detect signals in different frequency ranges. Each of these systems comprises a series of detector modules each including an exclusive OR gate fed with an appropriate signal from one of the video processors 69a, 69b, and with a corresponding reference signal from the raster generator 68. The signals fed to each of the gates are processed to enable the gates to give distinguishing outputs to detect one of ten first or second order transparency distortions or of registration displacement between the two transparencies defined in the Specification. The signals corresponding to each of these errors are fed to the transformation unit 71. Transformation unit 71.-This unit is fed with error signals developed in the correlation unit 70 and also with reference signals from the raster generator 68. The unit comprises a series of modulator circuits coupled to adding points to enable the error signals developed in response to each of the detected registration errors to be added to give four composite output signals which may be fed to the X and Y deflection plates of the scanning tubes 74a, 74b to distort the rasters generated thereon so that the signals fed to the viewing cathode-ray tubes 75a, 75b will be free from such errors. It is also stated in the Specification that if desired the rasters of the viewing cathode-ray tubes may be distorted to allow for these errors, but it is preferred to use the above-described arrangement in order that the square shape of the rasters on the viewing cathode-ray tubes may be preserved.