Abstract: A method and apparatus for modifying the phase characteristics of a coherent beam of radiation (7) are described. The apparatus comprises a laser (6) for generating a coherent beam of optical radiation (7). A support (1) for a record medium (1') sensitive to the radiation is provided, the beam of radiation (7) and the record medium (1') being relatively movable whereby the beam of radiation scans the record medium. First modulation means including an E/O modulator (8) and beam computer (9) is provided for modulating the beam (7) in accordance with image information. Second modulation means including an A/O modulator (10) or phase diffraction grating is responsive to a control function generated by a control function generator (11). The control function has a frequency which is repeatedly swept through a range of frequencies at a relatively fast rate to control the transmission characteristics of the grating.

Abstract: A method and apparatus for decoding a digital codeword of a codeword system comprising digital codewords of varying length in which no short codeword forms the prefix of a longer codeword in the same system comprises detecting with means (26) whether the codeword has a predetermined prefix, the predetermined prefix being shorter than any codeword containing it. Further means (26) are provided for decoding only the suffix of the codeword or the entire codeword respectively according to whether or not the predetermined prefix is detected.

Abstract: To produce a plurality of parallel light beams from a single input beam, the input beam is incident on a partially transmissive face of a triangular prism, the other two faces of which are silvered. The input beam strikes the partially-transmissive face at such a position and at such an angle of incidence that it gives rise to only two parallel emitted beams, part of the emitted light arising from internal reflections at both silvered faces. A number of such prisms may be arranged in series so that the n.sup.th prism receives 2.sup.n-1 beams and emits only 2.sup.n parallel output beams.The partially-transmissive face or faces may be coated to give rise to output beams of substantially equal intensity. In one form, each beam entering each prism has equal S- and P-polarization components.

Abstract: Angle measuring apparatus, particularly for measuring doctor blade angle, comprises an elongate support (1); a horizontal level detecting device (4) pivotally connected to an upper surface of the support (1); and means (5, 8) for determining the angle between the support (1) and the horizontal level detecting device (4). An under surface of the support (1) includes a pair of projecting feet (13, 14), the arrangement being such that when the apparatus is placed on a cylinder, the upper surface of the support (1) is substantially parallel with a chord of the cylinder.

Abstract: Method and apparatus for generating a half-tone dot representation of an original image which has been previously generated as one or more color separations each comprising a plurality of cells (12), each cell being digitally encoded in accordance with the color density at that point is described. The apparatus comprises a record medium support (8); a plurality of scanning beam generators arranged side by side, the scanning beams (B1-6) and the record medium support (8) being relatively movable. First control means controls the scanning beams during relative movement between the scanning beams and the record medium support (8) in response to the digital information and half-tone dot information to generate a plurality of half-tone dots (14) at a first rate, each dot corresponding to one or more of the plurality of cells (12).

Abstract: A method and apparatus for coding signals representing a stream of digital data groups (for example run lengths) for transmission or storage, each group representing a numerical quantity, is described. The signals are supplied via input and modify registers (4,6) and an encode latch (11) to a set of encode PROMs (12). The PROMs (12) generate for each data group a code representing the group, the code comprising a terminator codeword and, where necessary, one or more make-up codewords. The codewords are based on one or more multiplicative modifiers. The codewords are fed in parallel to output registers (13,14) and then serially shifted out of the output registers for subsequent transmission, storage, or further processing.

Abstract: In a video retouching system having an image source (40), a refresh store (42) fed from the image source, and a monitor (46) supplied from the refresh store, an image modifier (44) is interposed between the refresh store and the monitor and is controlled by a modifying store having a multi-bit location for each picture element. The stored multi-bit values may be used, for example to modify the display to obtain a vignetting effect, or to lighten or darken picture elements or modify chrominance. Preferably a mask store (48) having one bit per pixel defines those pixels which may be modified and those which must not be modified. In one form, the store with a multi-bit location for each picture element controls the merging of two images.

Abstract: A method and apparatus for detecting digital codewords or predetermined portions of digital codewords in a stream of codewords is described. The apparatus comprises a shift register (21) having a length at least one bit greater than the length of the longest codeword or predetermined codeword portion to be detected; and means including an inverter (24) for loading the shift register (21) with the logical complement of the leading bit of the stream of codewords. A clock (25) is provided to cause data in the data stream to be serially shifted into the shift register (21). The contents of the shift register after each shift are then used to address one or more PROMs (26) to determine whether the data in the shift register (21) upstream of the first change between data in the shift register of one type and data in the shift register of the complementary type comprises a codeword or a predetermined codeword portion.

Abstract: This concerns retouching a set of n input image signals (1), one for each of the image printing colors, by converting these signals into a set of signals in a format (R, G, B) suitable for displaying the image on a monitor (3) to be viewed by an operator controlling the retouching. The converter (21) simulates the effect of the characteristics of the printing inks. In the present invention, for a rapid monitor response during retouching, the operator first generates, outside the main signal path from the image source to the monitor, a record (A) of n one-dimensional modifying functions corresponding respectively to the n printing colors. These printing-color modifying functions are converted into monitor-format modifying functions for storing in respective one-dimensional stores (B) in the said main signal path, where they modify the monitor-format image signals and therewith the displayed image.

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).