Crosfield Electronics Limited

Wisconsin Alumni Research Foundation

Malcolm D Roe

Michael E Hicks

Richard A Kirk

Michael Slone-Murphy

A method and apparatus for viewing the effect of outputting on the output device an image represented by digital data defining the colour content of pixels of the image. The apparatus comprises a monitor; a store; and a processor to enable a portion of the image to be selected, and for generating and storing in the store data simulating the selected image portion as it would appear after screening by the output device. The monitor is responsive to the stored data to display the simulated, screened image portion.

Method and apparatus for viewing screened images

An apparatus for controlling the exposure of a record medium (4) to a radiation beam (3) during relative scanning movement between the medium and the beam to record half-tone image separations at particular screen angles, includes a control signal generator (6); a controller (8,9); and a store (7) for storing a previously generated half-tone dot map under the control of the controller (9), the control signal generator being responsive to an image signal representing the color content of an image and a signal from the store to generate a binary beam control signal by scanning the map in synchronism with the beam scanning the record medium and comparing the image signal with the current map value, the binary beam control signal being generated in accordance with the result of the comparison. The store (7) is of a size sufficient to enable the half-tone dot map to define a number of adjacent half-tone dot areas, each area corresponding to a half-tone dot and the content of at least some areas being different. The control signal generator (6) is responsive to each area in the map for generating the control signal for adjacent, corresponding areas on the record medium. The controller (8) scans the half-tone dot map in the same direction and in the same increments for all screen angles and supplies corresponding map values to the control signal generator (6).

Methods and apparatus for half-tone imaging utilizing a rotated

A method for generating a binary representation of an image represented in half-tone form is described in which the image is scanned and sampled, and in which each pixel corresponding to a sample of the image is assigned one of two colors. The method comprises, for each group of abutting and non-overlapping sampled pixels, determining the number of pixels in the group which are to be assigned to each of the two colors (step 13); allocating a unique sequence to the pixels (step 15); and assigning one of the two colors to pixels in sequential order until the predetermined number of pixels of that color has been assigned (step 16) and thereafter assigning the other color to the remaining pixels in the group (step 17).

Method and apparatus for generating a binary representation of an image

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.

Modulated beam scanning with pixal exposure control

A method and apparatus for generating a half-tone representation of an original image is described. The apparatus comprises an exposing beam generator (8); a record medium support (11); and a mirror (10) for causing an exposing beam generated by the beam generator (8) to scan a record medium mounted on the support (11). An exposing beam control system (5) generates a two state control signal (CS) to control the condition of the exposing beam, the control signal being generated in accordance with a picture signal (PS) representing color component densities of the original image and half-tone dot information (PV) defining for elemental areas within a dot cell corresponding values representative of color densities whereby elemental areas of the record medium are exposed or not exposed in use according to the control signal taking up a first or second state respectively. The control signal is generated by making use of a probability function which introduces a random element into the choice of elemental areas at the edge of a half-tone dot, but which ensures that, although each half-tone dot will not itself accurately define the required color density, an area of such dot will on average define the required dot density with the further feature that within that area, the dots will have a variety of different shapes.

Generating half-tone representations

An exposure system and method comprising a radiation generator (15'); and a modulator (4) which comprises a device for controlling the transmission of radiation passing through the modulator in accordance with an applied control function, the response characteristic of the modulator to the control function exhibiting a maximum or minimum and onto which radiation from the generator is incident. A microprocessor (19) controls the transmission condition of the modulator (4), and is responsive to predetermined control signals during an exposing stage and, during a compensation stage prior to the exposing stage, generates a test control function having a DC component and a cyclically varying component for application to the modulator. A photodiode (17) monitors radiation transmitted through the modulator, and a phase detector (18) detects the phase relationship between the cyclical component of the transmitted radiation and the cyclically varying component of the test control function and determines the position of the DC component of the test control function along the response characteristic of the modulator. The microprocessor (19) determines a correction function for application to the modulator (4) to compensate for any change in the response characteristic.

Modulators

A method and apparatus for matching the transmission characteristics of two beam modulators (4,4') comprises radiation generating means (30); and the first and second beam modulators (4,4'), the radiation generating means causing beams of radiation (16,16') to impinge on each modulator. Control means (20) generates first and second control functions for application to the first and second modulators (4,4') respectively, the first control function cyclically varying between first upper and lower values (V.sub.1,V.sub.2) and the second control function cyclically varying between second upper and lower values (V.sub.3,V.sub.4) at the same rate and at the same time as the first control function, the range of the first and second control functions being such that the transmission characteristics of the first and second beam modulators overlap. Detecting means (18,19) detects the phase relationship between the radiation transmitted by the first and second beam modulators and having the higher or lower intensity and the first or second control function; and storage means (32) stores the second upper value (V.sub.3) when the detecting means determines a change in the phase relationship.

Growing community of inventors

Herts, United Kingdom

Malcolm D Roe