Crosfield Electronics Limited

Alastair Reed

Peter W Stansfield

Martin Rosen

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

Image processing

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.

Method and apparatus for generating composite images

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.

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.

Image movement processing for page planning

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.

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.

A method and apparatus for reproducing a colored original image represented by first signals defining the color content of pixels of the original image in terms of a first set of color components. The colored original image is reproduced using at least two separations representing respective color components of a second set which is different from the first set. The color components of the second set are ranked in order of similarity to each pixel and a value is selected for the highest ranked color component for which each of the first set of color component values defining said selected color component does not exceed the corresponding pixel values. The pixel values are then adjusted to take account of the select value of the color component of the second set. The process is then repeated for each of the remaining color components of the second set in the order of ranking.

Reproduction of colored images

In color printing it is customary to print images in a combination cyan, magneta, and yellow printing inks. However, it is sometimes required in the printing of the final image, to include an ink of a special color, for example a brown ink, which cannot be reproduced by combining cyan, magenta and yellow inks. The present invention is concerned with the preparation of a special color printer for a special printing ink. According to the invention sets of values (C.sub.ROP, M.sub.ROP, Y.sub.ROP, K.sub.ROP) defining the characteristic elements of curves for cyan, magenta, yellow, and black, which curves together correspond to a range of values for the overprinted colored separation, are stored. For each picture element, a combination of color component values for cyan, magenta, yellow and black (C,M,Y,K) are derived and compared with different sets of values (C.sub.ROP, M.sub.ROP, Y.sub.ROP, K.sub.ROP) derived from the stored curve elements, each set corresponding to a different value of the overprinted special color separation (R.sub.OP). A value is selected for the desired special color separation for which each of the stored values of the related set (C.sub.ROP, M.sub.ROP, Y.sub.ROP, K.sub.ROP) is not greater than the corresponding value (C,M,Y,K) derived from the picture element of the original. The stored values (C.sub.ROP, M.sub.ROP, Y.sub.ROP, K.sub.ROP) are then subtracted from the corresponding values (C,M,Y,K) to get residual values (C',M',Y', K'). The residual values (C',M',Y',K') are then modified to give a corresponding set of modified values (C',M',Y',K') and a special color separation value (R) is selected which is overprinted to constitute the selected overprinted special color.

Reproduction of colored images including overprinting for reproduction

A method and apparatus for retouching an image represented by color printing data in the form of a number of sets of input data, one set for each of the printing colors, is described. The apparatus comprises a source (1) of color component image data; a reference data set generator (2;9,10) for generating a reference data set comprising the color components of a limited plurality of reference colors; and a color converter (2;9,10) for generating a temporary data set from the color printing data and the reference data set, the temporary set representing the original image in terms of the reference colors. A refresh store (3) receives the temporary data set and feeds the temporary data set to a monitor (8) via a conversion system. The conversion system includes one or more look-up tables (5) defining printing ink modifying functions and an operator table (6) for controlling the contents of the or each look-up table (5). The arrangement is such that the temporary data set is applied to the monitor (8) via the look-up tables (5) whereby the color components defined by the temporary data set are modified in accordance with the contents of the look-up tables before passing to the monitor (8). Due to the limited plurality of reference colors with which the original image is defined, it is possible for the operator to retouch the image displayed on the monitor (8) in real time and interactively.

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Leighton Buzzard, United Kingdom

Alastair Reed