Abstract: A half-tone reproduction of an original image is made by exposing an output surface OS such as a film wrapped around a rotating drum to a modulated, multiple-head laser scanning beam. The modulation of each scanning beam SB, SB1 is determined by a control signal derived by generating digital position signals representing the position of the scanning beam within a half-tone dot area DA of an imaginary "electronic" screen grid SG inclined at a screen angle .beta.

Abstract: A rotary printing press includes a laser beam imaging device to enable a rotary printing member to be prepared while it is located in the printing press. This arrangement has particular advantages when it is used with a lithographic or a gravure printing press and especially when used as a proofing press for color lithography or color gravure.

Abstract: A printing member has a print surface formed of a blend of urethane and acetal polymers and is particularly suitable when it is to be engraved by laser engraving to form an intaglio print surface.

Abstract: In an electronic amplifier having a floating output stage (42), a demand signal modulates a high frequency carrier (e.g. 20MHz) and the modulated carrier is applied to the floating output stage through a capacitance (10) of very low value (e.g. 1pf) and is then demodulated. The amplifier is preferably a bridge amplifier and each arm of the bridge may comprise a number of floating output stages, each supplied with the modulated carrier through a low-value capacitor (10). As described, the amplifier drives a crystal (40) for modulating electromagnetic radiation from a laser.

Abstract: A web feeding machine for controlling the feed of a web of material comprises a first pair of rollers which bear against one another to form a first nip, a second pair of rollers which bear against one another to form a second nip downstream from the first nip, means to cause the ratio of the linear speed of the web through the second nip to that through the first nip to be a constant and to have a value greater than one, a variable speed drive for driving the nip rollers, means for monitoring the tension T.sub.1 in the web upstream from the first nip and the tension T.sub.2 between the first and second nips, and control means to control the variable speed drive of the rollers so that the angular velocity .omega. of the rollers satisfies the expression: ##EQU1## where A, B and C are constants.

Abstract: A laser engraving machine for engraving cylindrical intaglio printing members is arranged to turn the surface of a printing member and engrave it simultaneously. This is not only more efficient but ensures that an accurate relationship is maintained between the engraving head and the turned outer surface of the printing member 3. The engraving machine includes a slide-way 2 extending parallel to the axis of rotation of the printing member 3, a traversing carriage 1 mounted for movement along the slide-way 2 and having a primary sliding carriage 4 mounted on it, and the primary sliding carriage has a secondary sliding carriage 5 mounted on it. The primary and secondary sliding carriages carry a turning tool holder 8 and a laser engraving head 10.

Abstract: Apparatus for engraving a rotating cylinder by means of a laser, in which the laser beam is focused onto a small area of the cylinder surface by a lens, including means for defining a path for the flow of compressed air across the path of the laser beam, and a suction device communicating with the region between the lens and the cylinder for extracting air from this region, the flow of air serving to remove debris from the area being engraved and to prevent it from reaching the lens.

Abstract: A color scanner for the graphic arts of the kind in which three uncorrected color-component analogue signals from the scanner are converted into digital form and are applied to the inputs of a three-dimensional look-up table or read-only memory in which are stored corresponding color-corrected signal values for the three colors and, if desired, for black. Individual one-dimensional color-component look-up tables are interposed between the analogue-digital converter and the three-dimensional look-up table. The functions performed by the one-dimensional tables may include logarithmic conversion of the input signals, for example. Preferably, further individual one-dimensional look-up tables are inserted between the outputs of the three-dimensional table and a digital-analogue converter preceding an output scanner.

Abstract: An optical modulator which is capable of passing the greatest intensity of light incident upon it when the light incident upon it is either unpolarized or has a partial or variable state of polarization, comprises a beam splitter (1) to resolve the light beam incident upon it into two plane polarized components having mutually perpendicular polarization states, one or more electro-optic cell or cells (2,18,19,22,23) which is or are arranged to receive both components of the light beam and, in use change the state of polarization of both of the components to a corresponding extent in dependence upon an electrical modulation signal applied to it or them.

Abstract: The invention relates to methods and apparatus for interpolating between coarse stored data to achieve a more accurate answer, and is particularly applicable to color scanning reprographic equipment. Color scanners (5) analyze an original to obtain digital signals (8) representing three primary color intensities. The values for the intensities of each of four printing colors, including black, are functions of all three primary color intensities, and a limited quantity of these sets of four values is stored in a three dimensional matrix (25), consisting of cubes with values at their corners. To obtain values from these coarse stored data corresponding to a point (P) within a cube, an interpolator (26) determines which one, of the three pyramids (e.g. W B G C V in FIG. 2) comprising the cube, contains the point, and interpolates within that pyramid between the values at its five vertices.

Abstract: To record on a single sheet (9) both a picture image and alphanumeric characters, each character to be recorded is stored (24) in the form of signals representing a multi-column pattern of dots which make up that character. Signals derived in synchronism with the scanning of successive lines on the recording sheet are applied to circuits (19, 20, 23, 25) to derive a column address signal for the character store (24), which is also addressed with a data signal representative of a selected character (32). In this way, signals corresponding to a selected column of the required character are taken from store and are applied to a selector circuit which also receives the picture signals and applies either the picture signals or the character signals to the recording head.

Abstract: Longitudinal drive mechanisms are usually provided in combination with a component (17) of a machine which is mounted on a slide way to move the component along the slide way. Such mechanisms usually include a nut (2) running along a screwthreaded shaft or leadscrew (1) and any deviations from staightness or any discrepancies in the pitch of the leadscrew (1) cause extraneous or irregular movement of the component (17) along the slideway. By including a first pair of links (4) pivotally connected to the nut (2) and to a collar (3) and a second pair of links (7 and 8) pivotally connected to the collar (3) and the component (17) inaccuracies in the leadscrew (1) are absorbed by the pivoted links and so not transferred to the component (17).

Abstract: To produce a whole page image from a number of separate images, the input images are separately scanned and reproduced at the required enlargement or reduction to produce pre-prints which are then assembled on a digitizer table in the relative positions required for the finished page; signals representing the boundaries of these positions are generated and stored; the boundary representing signals then control the derivation of output signals suitable for a scanner making the whole-page reproduction, each whole-page line signal including the line signals for each of the input images crossed by the page line, the output signals controlling the treatment of a sheet or surface for use in the preparation of a printed page.

Abstract: For presetting values of parameters in an image-reproducing process, an operator selects a spot on a transparency to be reproduced, for example by visual inspection of a projected image of an area of the transparency illuminated by a defocused light beam. The light beam is then temporarily brought to a focus on the selected spot and the light transmitted through the transparency on a photomultiplier, the signal from which is sampled within a very short period and held, after which the focused light beam is again defocused to enable the operator to select a further spot. The value of the sample signal is used in the presetting of the said parameter values. The period for which the focused light beam falls on the transparency is made small enough to avoid the bleaching of the transparency at the illuminated spot.

Abstract: In a method of image reproduction in which both pictures and test are to be combined in an image on a single sheet for use in the reproduction of a printed page, and in which the signals resulting from the scanning of the pictures are stored prior to the preparation of the sheet, a high resolution is achieved in the reproduction of the text without requiring excessive storage capacity for the picture signals by scanning the text at a resolution which is an integral multiple n of the picture resolution and, when the text and picture signals are merged to control an output scanner operating at the higher resolution, applying each line of picture signals extracted from store n successive times to the output scanner.

Abstract: A beam splitter is disclosed in which a light beam entering a block of light-transmitting material is internally reflected a plurality of times between a pair of parallel sides, one side being coated to enhance such internal reflection and the other side having in the direction of its length a succession of areas which are differently coated to control the amount of the beam which is reflected internallly and the amount of the beam which emerges; a plurality of parallel emergent beams of substantially equal intensity can be obtained in this way. The application of such a beam splitter to an image-reproducing system is described, the beams contributing to the formation of half-tone dots in the image.

Abstract: For the lateral guidance of travelling webs, three photoelectric detectors are arranged under one margin of the web in a transverse line such that the path of light from a light source, on the other side of the web plane, to a first of the detectors is blocked by the web, the light path to a second of the detectors is partially blocked by the web, and the third detector is fully exposed to the light source, when the web is in its normal lateral position. Signals from the three detectors are combined in such a manner that a signal is derived representing the extent to which the second detector is covered by the web, the value obtained being corrected for variations in light source intensity and for web translucence.

Abstract: In an image-reproducing system in which a number of parallel light beams contribute to the formation of half-tone dot areas on a record medium and scan over the record medium together, a reversing prism is included in the beam path to permit the line fit or line overlap to be closely controlled. The prism also adjusts the spacing between beams in the scanning direction which is provided when a coherent light source is used to avoid interference between adjacent beams.

Abstract: In an image-reproducing system in which a number of beams scan over a record medium together and contribute to the formation of half-tone dots, an anamorphic system is included in the beam path to match the beam cross-section to the shape of mask apertures in the light paths and to compress the length of the line of beams, transverse to their direction.

Abstract: For the reproduction of colored originals, a set of standard color patches is scanned with an original to be reproduced and corresponding signals are applied to a display system having controls for adjusting the appearance of the displayed original and color patches. The standard color patch signals applied to the display are gated out and used to adjust a color-modifying means in the signal path between the input scanner and the output scanner, for reproducing the original, in such a manner that the standard color patches if reproduced by the output scanner would simulate the appearance of the displayed standard color patches after the adjustment of the display system.