Patent GB-1378427-A (GB)
Title: Methods and apparatus for forming images and systms utilizing the same
IPC: G09G3/00
Filed: 1972-02-08
Abstract: 1378427 Recording images WESTERN ELECTRIC CO Inc 8 Feb 1972 [12 Feb 1971] 5764/72 Heading H4F A half-tone pictorial image is recorded as an array of discrete holes in a radiation-absorbent film by means of pulses of coherent radiation each of which has one of at least two energies which differ from each other and are such as to produce holes of different sizes, the image being displayed by projecting light on to said film. The output from an oscillator 233 is modulated by a signal source 234 in which a signal may be produced by scanning a three dimensional or two dimensional object such as a picture. Alternatively signals may be derived from a computer, to control the recording of graphic or alphanumeric information, or from a television system, to record television pictures continuously. The output of mixer 235 is gated in mixer 235<SP>1</SP> by the output from a pulse generator 236 to produce amplitude-modulated pulses which are amplified and applied to an acousto-optical modulator 221 in a 3-mirror laser cavity. A diffracted part of radiation in the resonator produces an amplitude-modulated pulsed output beam 218. This is focused on recording film 251 by way of a scanning mirror 245. The film is curved to compensate for curvature of the image plane, but flat film may be used if focusing lens 243 is placed between mirror 245 and the film. The film is transported between two reels through a block having an aperture through which the recording beam is incident on the film and a further aperture on the opposite side through which material ejected from the film by the recording beam is exhausted. The film preferably consists of a 500 micron thick bismuth film on a transparent polyester substrate, the recording film facing away from the incident recording beam. Display of the image may be effected by transmitting through the film at the recording position, or at an adjacent point, a beam of light which projects the image on to a front- or back-projection screen. Permanent full-size copies may be obtained by photographic or electrostatic copying methods. Alternatively a reflection image may be obtained, possibly with the aid of a reflective aluminium layer on the recording film surface. This image will be a negative unless the record is made negative by inverting the signal from source 234. Stereo pairs or 3 colour separation images may be recorded. Instead of a mirror 245 acoustooptical deflectors may be used for scanning the recording medium. Instead of amplitude modulating the laser output pulses the pulse duration may be varied. Signal source 234 may consist of an array of photodetectors arranged adjacent an object mounted on a rotating drum. A laser light beam is scanned across successive lines on the object by a rotating mirror drum and the responses of the photodetectors to the scattered light at any instant are summed. A flat object may be scanned by a laser light beam deflected by a pair of orthogonally arranged scanning mirrors, the scattered light beam being detected by a twodimensional array of detectors. Alternatively a linear array of light sensitive elements may be sequentially read-out out to scan one line of an object, successive lines being scanned by a moving mirror. Low resolution scanning by a vidicon or silicon camera tube is mentioned. When the system is used for two-way communication, e.g. for permanently recording information transmitted over visual telephone networks, a single laser may be used to scan the object for transmission and to provide the recording beam.