Abstract: An image processing apparatus has a memory device for storing pixel image data including both halftone image data such as data of image of a photograph having a gradation and line image data such as data of text containing characters. The storage is conducted on the basis of blocks each having a predetermined number of pixels. The mean information quantity of the halftone image data per pixel stored in the memory means is not greater than the information quantity of the line image data per pixel stored in the memory means. The halftone image data being compressed on the basis of the block. Therefore, both the halftone image data and line image data can be stored in a small memory by using common addresses, without causing any degradation of the image quality.

Abstract: A method of color halftone reproduction with reduced moire patterns and simplified calculations of color densities is disclosed. The method entails dividing a reproduction surface into an array of abutting halftone cells having centers aligned at a screen angle, preferably 45.degree. , with halftone cells in adjacent rows. The halftone cells each cover an area of M abutting horizontal dots long by N abutting vertical dots wide. The various system colors are applied to the pels, as required, in color patterns centered within the halftone cells. The patterns overlap one another to adjust the hue of the reproduction at the halftone cell location to the desired hue. The method is usable with permanent reproductions, such as printed paper, or with transient reproductions, such as the image on a CRT screen.

Abstract: A method and associated apparatus is implemented in a halftone printing system that permits a halftone dot of the type that is represented by an envelope that is formed from a combination of straight lines that are drawn from tangent points to be position modulated by a displacement engine to introduce noise into the screener.

Abstract: The present invention is a method and apparatus for processing a color document for moire-free printing, the color document including a plurality of color separations each defined with a set of image signals representing optical density with m possible density levels, while a printer is capable of rendering density with n density levels. The invention employs a spatial resolution scaler to produce m-bit signals at a spatial resolution that is a function of the halftone screen angle, base dot pitch, and desired halftone cell size. Subsequently, the m-bit signals at the desired spatial resolution (frequency and angle) are halftoned to produce n-bit signals that are printed with a raster output scanning-type printer suitable for printing at selectively variable spots per inch in both the fast and slow scan directions.

Abstract: The invention relates to a method and apparatus for automatic high-speed generation of digital angled halftone screens, specially suited for obtaining screens approximating the irrational angles which are generally required by high-quality color reproduction. The method enables color separations to be generated which minimize Moire effects, interferences and artifacts by applying discrete one-to-one rotations to digital halftone screens of the required period in order to reach the final screen angle. Dither tiles incorporating assemblies of the basic screen element are rotated by one-to-one discrete rotation and transformed into a new type of dither array, the scanning dither array. The scanning dither array is composed both of dither thresholds and of displacement vectors, providing the means to scan the dither array at image generation time.

Abstract: An image processing system for preparing a color document for printing, each discrete area or pixel in the image described by a signal having a number of possible states greater than can be rendered by a selected printer, in which each separation of the image is halftoned, with at least one of the separations processed with a non-periodic halftoning method, and at least one of the remaining separations processed with a periodic pattern. Preferably, in a printer printing with colorants approximating cyan, magenta, yellow and black, one of the non-yellow separations is processed with the non-periodic halftoning method.

Abstract: Apparatus and method for descreening and for performing resolution changes and correction of misregistration on a color half-tone image in order to produce a color continuous tone image. The apparatus includes filter apparatus for removing screen information from the half-tone image including a plurality of different filters each providing interpolation and screen removal functions and a controller for selecting per pixel of the continuous tone image and in accordance with sensed misregistration and as a function of desired resolution changes, one of the filters for operation on a neighborhood of the pixel.

Abstract: A method of halftone printing in four colors using, for cyan, magenta and black, halftone screens that will result in screening angles of 15, 45 and 75 degrees, as is the standard process in the art, and a halftone screen for yellow that will result in screening angles of 0, +60 and -60 degrees. This combination will diminish the 2 color moire patterns that result from the interaction between the yellow and one of the other colorants. The 0 and + or -60 degree screening angles are generated by using a screen that produces a four-centered cell having dots that are spaced to form hexagons, when the nearest neighbors of a central dot are connected by lines, as opposed to the conventional trapezoidal orientation.

Abstract: A method of reproducing on a substrate an image incorporating metallic inks involves scanning (18) the image to be reproduced and creating (20) four color separations of the scanned image. Metallic gold and/or metallic silver color separations (22, 24) are created by electronically selecting any color area where the effect is desired. Next, the color separations are edited by creating (26) an electronic yellow mask of the image and adjusting (28) the desired tonal range of the metallic areas. The mask edges of each color separation can also be softened (34). The scanner then outputs (36, 38) the separations to film. The image is then reproduced by printing each of the process color separation films (44, 48) and the metallic separation films (42, 46) onto a substrate.

Abstract: An apparatus records a halftone area and a solid area in a single image with respective, different screen angles. Encoders (13, 14) and a coordinate value generator (16) generate coordinate values (U, V) on an image plane on a recording drum. An address generator (17), a pattern data memory (18) and a comparator (19) generate a first halftone dot signal (S.sub.da) for the halftone area. An address generator (22) and a pattern data memory (23) generate a second halftone dot signal (S.sub.db) for the solid area. A threshold data setter (20) and a comparator (21) generate a detection signal (S.sub.s) which indicates whether or not an image signal (S.sub.i) corresponds to the solid area. One of the first and second halftone dot signals (S.sub.da or S.sub.db) is selected by a selector (24) according to the detection signal (S.sub.s).

Abstract: A method and an arrangement for producing rastered printing forms having rasters with arbitrary raster angles on the basis of at least one recording beam moving across a recording medium. The recording beam is switched on or, respectively, off corresponding to the size and position of raster dots. A switch signal for the recording beam is generated by a signal comparison between the image signal, which represents the tonal values of an original, and stored raster thresholds, which represent the periodic basic structure of a raster mesh. Coordinate increments corresponding to the proceeding recording are accumulated dependent on the screen angle to form coordinate values. A plurality of most significant binary places of the coordinate values form addresses for reading out the stored raster thresholds. Random numbers are superimposed on the coordinate values.

Abstract: A method of and system for rendering a halftone image of a gray scale image by utilizing a pixel-by-pixel comparison of the gray scale image against a blue noise mask is disclosed in which the gray scale image is scanned on a pixel-by-pixel basis and compared on a pixel-by-pixel basis to an array of corresponding data points contained in a blue noise mask stored in a PROM or computer memory in order to produce the desired halftoned image. Both digital and optically implemented halftone methods are disclosed. Application specific modifications of the blue noise mask as well as its use for producing halftoned color images are also disclosed.

Abstract: Apparatus and method for descreening and for performing resolution changes on a half-tone image in order to produce a continuous tone image. The apparatus includes filter apparatus for removing screen information from the half-tone image including a plurality of different filters each providing interpolation and screen removal functions and a controller for selecting per pixel of the continuous tone image and as a function of desired resolution changes, one of the filters for operation on a neighborhood of the pixel.

Abstract: A screen system used in the electro-optical reproduction of half-tone pictures in multicolor prints are generated by an algorithm which simulates a continuous tone image. There is disclosed partial screens and screen systems produced by an algorithm for use with a digitized image which provides a means of simulating a continuous tone image containing a range of gray shades from black to white or a color separation. The "Threshold equation" is the key of the invention as it calculates a threshold gray value that is compared to the desired local image value to determine whether that particular point should be "on" or "off". Which points (spots) are "on" and which are "off" is determined by the function that assigns a "threshold" value (the shade at which a pixel changes from "off" to "on") based on a pixels "x" and "y" coordinates.

Abstract: An image processing apparatus has a memory device for storing pixel image data, including both halftone image data such as data of image of a photograph having a gradation, and line image text data such as data, containing characters. The storage is conducted on the basis of blocks each having a predetermined number of pixels. The mean information quantity of the halftone image data per pixel stored in the memory means is not greater than the information quantity of the line image data per pixel stored in the memory means. The halftone image data is compressed on the basis of blocks. Therefore, both the halftone image data and line image data can be stored in a small memory by using common addresses, without causing any degradation of the image quality.

Abstract: A halftone screen pattern generation system for computing halftone screened images with rotated screens including multiple angle and ruling combinations, including irrational tangent angles, is disclosed. A screen pattern is generated by storing an oversized strip from an ideal angled screen pattern, and then assembling a sequence comprising selected scan line segments of the oversized strip. Each selected scan line segment corresponds to one of a plurality of offsets of the oversized strip. The error between the actual generated screen and ideal desired screen is computed. Each subsequent scan line segment is selected from the plurality of scan line segments corresponding to the plurality of offsets so as to minimize the accumulated error. In accordance with one aspect of the present invention, the measure of error between the actual generated screen and the ideal angled screen is the length of a vector in a transformed UV space between the actual screen sample point and the ideal screen sample point.

Abstract: A technique for generating a screened reproduction of an image including the steps of providing a representation of an original containing information representing the input density values of the original, storing information representing only part of at least one printing dot, and exposing a recording medium to record the image by using the stored information to compose complete printing dots depending on the input densities of the representation at the location of the printing dots. Apparatus for carrying out this and other techniques is also disclosed.

Abstract: A set of halftone screens and a write white xerographic system for generating halftone images with a minumum of artifacts. The screens used in a four color printer have at least 64 pixels per pattern and are distributed to creat fourcentered dots that are at either -14, 0,+14 or +45 degrees. The xerographic process involves charging the photoreceptor, partially discharging the photoreceptor with a scanning beam to create an image, and then using toner which adheres to the charged portions of the photoreceptor to create the hard copy.