Abstract: A method of modifying a digital representation of an image in which digital data defines the content of pixels of the image. The method comprisesa) determining whether a predetermined degree of compression can be achieved if data defining a block of pixels is compressed by applying a predetermined compression algorithm; and, if not,b) discarding a portion of the data in the block, andrepeating steps a and b on the most recently modified block until the predetermined degree of compression is achieved, and generating a compressed version of the image.

Abstract: A method of and an apparatus for interactively controlling the display of an image on a monitor screen has the image stored in digital data form defining the color content of pixels of the image. The method includes displaying a representation of the image of the monitor screen; selecting a first point on the image and a first point on the monitor screen at which the first image point is to be located; selecting with a cursor a second point on the image; moving the cursor relative to the monitor screen; and, during the cursor movement, repeatedly adjusting the representation of the image displayed according to one or more predetermined algorithms so that the second image point remains coincident with the cursor position while the first image point is fixed at the first screen point.

Abstract: A method of mounting a transparency for use in an input scanner comprises first inserting a transparency into an envelope. Within the envelope a film of liquid of substantially the same refractive index as the transparency is spread over the transparency. The liquid may be provided in a rupturable pod within the envelope. The transparency holder is sealed by either an integral seal or adhesive tape. The transparency holder protects the transparency from dust and scratches and helps to prevent Newtons rings occuring in the image produced when mounted in the scanner.

Abstract: A manual position indicating device comprises a body portion (1) that can be moved by hand across a surface; and a support member (4) movably mounted to the body portion. The support member includes a graticule (13) and associated signal generating or detecting circuitry for interaction in use with position determining apparatus, whereby the relative positions of the graticule (13) and the body portion (1) are selected by suitably moving the support member and body portion relatively to one another. A cooperating ball (11) and notch system (10) is provided for locking the support member (4) relative to the body portion (1) in a number of different positions.

Abstract: Radiation scanning apparatus comprises a record medium support (10); and a rotatably mounted scanning device (1) on which a modulated radiation beam (6) is incident in use. The device splits the incident beam into at least two subsidiary beams (17,21) which scan in turn across a record medium on the support during relative rotation between the scanning device and the support, each subsidiary beam exposing a respective scan line on the record medium in accordance with the beam modulation. The support (10) and device (1) are relatively movable such that the scan lines are offset in the direction of relative movement.

Abstract: Apparatus for synchronizing a clock signal to a pulse comprises a clock signal generator (1) for generating a first clock signal having a frequency equal to that of a desired clock signal. A delay circuit (2) to which the first clock signal is fed generates a number of time delayed versions of the first clock signal, each time delay being less than the period of the first clock signals. Logic (9) compares the time delayed versions of the first clock signal and the original clock signal at the time of occurrence of the pulse and selects as the desired clock signal, a version of the first clock signal which has changed state close to the time of occurence of the pulse.

Abstract: Apparatus for modulating a radiation beam during relative scanning movement between the beam and the record medium. The apparatus comprises a beam modulator which is operable to modulate the power level of the beam in accordance with a binary control signal so as selectively to expose the record medium in use to record and image on the record medium. Each bit of the control signals corresponds to a respective output pixel of the image. An exposure control system determines, prior to the modulation step, the pattern of control signal bits corresponding to image pixel in an area containing the pixels to be exposed, and causes the modulator to modulate the radiation beam to take up an output power level corresponding to the determined pattern during exposure of that pixel.

Abstract: A method and apparatus for generating a half-tone version of an image represented by a first set of digital data defining the colour content of abutting pixels of the image at a first resolution. The apparatus comprises a radiation beam generator (8); a recond medium support (11), wherein the radiation beam and the support are relatively moveable such that the radiation beam scans a record medium (10) mounted on the support in a series of abutting scan lines; a radiation beam modulator (7) for modulating the radiation beam in response to a control signal (CS); and a control signal generator (5) for generating the control signal. The radiation beam is modulated selectively to expose a record medium on the support (11) at a second, finer resolution, the control signal generator (5) being adapted to interpolate the second set of digital data from the first set of digital data and to generate the control signal by comparing the second set of digital data with half-tone information.

Abstract: A method of and apparatus for detecting a register mark on an elongate web (3) is described. The web (3) carries a number of copies of an image (4) spaced apart along the web (3) and a region of the path along which the web (3) moves is irradiated with infra-red radiation by a source (5). The region is viewed with a series of detectors (1D-1F) as the web (3) passes through the irradiated region and the output levels of the detectors (1D-1F) are monitored for changes in their output levels. An edge extending transverse to the direction of movement (2) of the web (3) is then selected within the image (4) when the monitored changes in the output levels of all the detectors (1D-1F) satisfy predetermined criteria. The edge is then used for subsequent register control.

Abstract: A method and apparatus for processing digital data representing the color content of abutting blocks of pixels defining an image. The method comprises, for each block(i) determining a measure of the variation in color content of pixels in the block; and,(ii) if the variation lies within a predetermined range, applying a compression algorithm to the digital data defining the block.

Abstract: Apparatus for generating a composite image from a plurality of subsidiary images comprises first stores for storing signals representing at least two subsidiary images. Second stores store at least two arrays of mask data, each array having a mask pixel corresponding to each pixel of the composite image. A control system is responsive to each array of mask data to generate for the pixels of the composite image signals defining a weighted sum of the subsidiary images.

Abstract: A method of generating a composite image on a record medium at a first resolution resulting from two subsidiary images defined by pixels at a second resolution lower than the first. The method comprises generating an array of control data at the second resolution, the control data indicating the relative locations of the subsidiary images in the composite image at the first and second resolutions, generating data defining the composite image at the second resolution under the control of the control data, interpolating the second resolution composite image up to the first resolution, the relative locations of the subsidiary images at the first resolution being determined in accordance with the control data, and causing the first resolution composite image to be recorded on the record medium.

Abstract: A method and apparatus for processing a first (e.g. half-tone) image constituted by a second (e.g. continuous tone) image convolved with a periodic (screen) function, to produce the second image is described. The invention is particularly suited to handling digitally represented half-tone images. The apparatus comprises a microcomputer (17) for determining digital data defining a frequency filter characteristic adapted to suppress the frequency or frequencies of the periodic function. A fast Fourier transform circuit (11) transforms the image data into the frequency domain and a multiplier (12) multiplies the transformed data by the frequency characteristic stored in a store (13). The resultant multiplied data is inversely transformed back into the image of spatial domain by a fast Fourier transform circuit (14) to generate the second image.

Abstract: Apparatus for generating a two-dimensional coloured display in which there is a variation of colour across the display in a predetermined manner, the colour of each pixel in the display being defined by one or more colour components. The apparatus comprises, for each colour component, a memory for storing a pair of gradation curves (X(i), Y(i)) representing the variation in intensity of the color component in orthogonal directions X, Y across the display; a monitor; and processing apparatus. The processing apparatus determines a resultant colour component value V(i,j) for a pixel to be displayed at a location (i,j) on the monitor in accordance with the following formula:V(i,j)=f[a(X(i))b(Y(j))+c(X(i))d(Y(j))]where the pixel has coordinates i,j and k is a normalizing constant, and where a, c, are functions of X(i), b, d are functions of Y(j) and f is an output function, the functions being chosen such that V(i,j) exhibits no discontinuities for all values of X(i), Y(j).

Abstract: Apparatus for processing a first signal representing a color component of a pixel of an image in which the signal defines the value of the color component as one of a first set of values defining a first scale of color component values. The apparatus comprises a first Look-up Table addressed by the color component value for generating a second signal representing a modified color component value chosen from a set of modified color component values defining a second scale coarser than the first scale.

Abstract: Apparatus for modifying part of an image represented digitally in the frequency domain comprises a first memory for storing a representation of the image digitally in the frequency domain as at least one first block of data locations containing frequency coefficient data. A second memory is provided for storing a representation of the image part in the frequency domain by second blocks of data locations containing frequency coefficient data, the first and second blocks representing, after conversion to the spatial domain, spatially shifted versions of the image part relative to a fixed spatial co-ordinate system. A suitably programmed computer applies a predetermined shift function defined in the frequency domain to the (or each) first block of data stored in the first memory to generate the (or each) second block, and stores the resultant second blocks of data in the second memory.

Abstract: A method and apparatus for processing original data defining the values of pixels of an original colored image represented in a spatial domain by two or more color separations each color separation defining the respective color component content of pixels arranged in a two dimensional array extending in X and Y directions. The apparatus comprises a store 6 for storing the original data; and a frequency transform circuit 8 for performing a three dimensional transformation on the store representation to generate transformed data representing the original image in three dimensional frequency space. Two of the three dimensions represent the variation in pixel value in the X direction and the Y direction respectively and the transformed data has a single zero order frequency term.

Abstract: A method and apparatus for processing a screened separation comprises an analyze scanner for scanning the separation at a resolution higher than the screen ruling to generate a binary value for each high resolution pixel of the separation; a processor for generating signals representing single values for respective blocks of the high resolution pixels from the binary data in the blocks; and a descreening system to which the signals from the processor are fed, the descreening system generating signals representing a descreened version of the original separation.

Abstract: A method of detecting the position of a feature, such as a register mark, in a color separation comprises printing the color separation on a substrate with an ink containing a pigment corresponding to the color of the separation and a dye which is detectable only when exposed to radiation outside the visible range. The printed color separation is exposed to the said radiation and the position of the feature in the printed color separation is determined by detecting radiation, such as fluorescence, from the dye.