Abstract: For register control when printing on a web, signals corresponding to a predetermined hidden pattern of low-amplitude density variations are superimposed on picture signals representing the image to be printed. After printing, light from elements of the printed image, with its hidden pattern, is detected by a register scanning head and the variations are correlated in a signal processor with the known variations of portions of the predetermined hidden pattern. In this way a position error signal is derived and can be used to correct the web position.

Abstract: In colored image reproduction, we have found that for the appearance of some self-colored objects (e.g. human flesh or plant leaves) to be satisfactory, when picture elements of the object are expressed in terms of luminance (L) and two chromaticity signals (CHR1 and CHR2), each chromaticity signal is a single-valued function of the luminance. In this specification, such objects are identified by means of a mask (24) or by a color recognition circuit or both and the corresponding area of the reproduction is made under the control of the luminance signal (L) for the picture elements of the object and two chromaticity signals generated by digital look-up tables (LUT2 and LUT3) having the luminance signal as an input and loaded with functions representing the respective functions relating chromaticity to luminance for that object.

Abstract: A flying spot scanner is used to expose a photosensitive surface to an intensity modulated beam of light to build up an image on the photosensitive surface.

Abstract: In the reproduction of colored images, the "white point", that is to say a point which determines which areas are to be printed with zero-ink, is a critical adjustment. In this invention, signals representing the three color components derived from the original are applied to a NAND gate (14) and when all of these signals simultaneously represent a zero printing color condition, the NAND gate generates a zero-ink signal. This is used to modify the zero-ink or white display on the monitor tube, for example by inhibiting passage of red and blue signals (18R, 18B) to the display tube while allowing the passage of green signals. The green signal to the monitor tube may be periodically interrupted, so that zero-ink areas are shown in pulsating green. The operator then adjusts the white point until the pulsating green areas correspond to the areas of the original which are to be reproduced with zero-ink.

Abstract: In image reproduction, a method of preventing the reproduction of a defect in an area (74) of the image, which has been indicated as including a defect-containing region, comprises comparing pixel values in a region (A.sub.o) of the said area outside the defect-containing region (72) to ascertain the range of the values of picture elements in a defect-free line or region in the neighborhood of the defect-containing region. Next image values for picture elements in a portion (A.sub.1) of the defect-containing region are compared with the said range of values to ascertain whether any such picture element has a value differing sharply from the said range of values.

Abstract: The positive correction of a gravure printing surface is conducted by depositing into the cells of the surface a heat activatable composition that is inert at the temperature of deposition but which, upon heating the surface, causes etching of the cells. When the desired correction has been achieved the etching is terminated, for instance by washing. The compositions are preferably in the form of pastes and include novel compositions comprising alkali metal bisulphate.

Abstract: A holding mechanism for holding a workpiece in position during an operation being performed by an operating device (7) passing along the workpiece includes a toggle linkage (1, 2, 3), a projecting member (9) attached to the device, and a cam track (2) connected to one part of the toggle linkage, the arrangement being such that, towards the end of the pass of the device, after it has completed its operation on the workpiece, the projecting member (9) engages the cam track (2), further movement of the device causes the projecting member (9) to move the middle pivot (3) of toggle linkage to release it and, hence, release the workpiece as the device completes its pass. Preferably the toggle linkage is arranged as an over-center toggle linkage with its other component formed by a telescopic arm (1).

Abstract: An apparatus for controlling the registration between a printed web of material and a downstream processing station comprising a control unit which further controls a web path register to change the web path length as a function of the output of a print detector monitoring the passage of said web and as a function of an encoder coupled to a web processing station to provide an output signal indicative of the operation of the web processing station wherein said apparatus compensates for error resulting in the registration of the printing on the web due to variations in the printed repeated length of the web extending between both (1) the printing station and the print detector and (2) the print detector and a subsequent web processing station.

Abstract: A print surface is formed by photoexposure of a photocurable resin layer through a photomask comprising an image-wise distribution of opaque material on its image surface, and sticking of the image surface to the resin layer during photoexposure is prevented by providing over the image surface a clear thin film of a natural gum or other material that is impermeable to softeners such as alcohols that are liberated from the resin layer. A coated photomask may be made by image-wise laser scanning of a transparent sheet to which opaque material such as graphite is bonded by a binder such as an alkyl cellulose, followed by application of the film over the resultant image-wise distribution of opaque material.

Abstract: A color gravure printing press of simple construction which is easy to set up and operate, and is therefore economic for use in printing short runs comprises printing members (2) for at least two different colors arranged around a common printing cylinder (1), an impression cylinder (3) including means (11) to hold a sheet of substrate (15) to be printed, and at least as many inking assemblies (4) as there are different color printing members (2) arranged around the printing cylinder (1). Each of the inking assemblies (4) includes a doctor blade (35) movable towards and away from the printing cylinder (1). The press is arranged so that each inking assembly (4) applies ink only to its corresponding printing member (2) and each doctor blade (35) contacts only its corresponding printing member (2), and that the substrate (15) is held in a fixed position on the impression cylinder (3) until it has been contacted and printed by all of the different color printing members ( 2).

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.