Abstract: A compression and decompression system and process for optimally compressing and decompressing multibit per pixel image regions based on the type of data contained in the image region, e.g., whether the image region contains continuous tone data, including data to be halftoned, or non-continuous tone data, including antialiased text and lineart data. Segmented bytemap data blocks are processed to provide both low spatial resolution continuous tone data and high spatial resolution non-continuous tone data. However, the high spatial resolution non-continuous tone data is generated by quantizing and packing the high resolution bytes across an edge and discarding the high resolution bytes along the edge, i.e., the multibit data is discarded only in directions parallel to the edges of marks to be rendered in the image data. Additional information indicating the directions of the edges in the image data are stored to aid in decompression.

Abstract: An image generating system that warps both the image data and halftone screens of a halftone screen system to minimize moirè patterns. Merely warping image data to minimize moirè patterns results in offsets within the image data which should have a corresponding adjustment or warp in halftone screens used in the image generating system to render the color image separation layers. Therefore, the image generating system provides moirè pattern minimization by warping screens of the halftone screen system to correspond to the warping of the image data. The image generating system uses line screens for halftoning the chromatic image separation layers of color images and a hexagonal dot screen for halftoning the luminescent image separation layer. The halftone screen system uses the relatively large average screen displacement angles offered by line screening while providing a dynamic tone range performance similar to that of the performance of dot screening.

Abstract: An image processing system for performing interpolation includes an image data source for supplying rasters of image data based on laser spot position on a xerographic photoreceptor. A two dimensional resampling interpolator is connected to receive the image data from the image data source and determine a resample value and its associated two dimensional slope information. This information can be used by a thresholder to predict where exposure intensities of lineart will cross a xerographic threshold on the photoreceptor. Alternatively, a halftoner unit that includes a dot generator and a screen generator can use the information from the resampling interpolator to improve control of dot shape and spacing.

Abstract: A method and apparatus for altering a drive signal provided to an image forming element of a printer based on the type of object being printed, e.g., text and/or lineart, halftone, etc., to provide an optimal exposure level for producing the particular object. The apparatus provides an increased drive signal which, for example, provides an increased laser power during text and/or lineart production using a high setpoint and re-normalizes laser power by providing a decreased drive signal which, for example, provides a decreased laser power during halftone production using a low setpoint. This increased power offers improved appearance of text and/or lineart and the re-normalization offers more quantization levels for tone adjustment, better highlight production, and better overall control of tone during halftone production in a write black printer.

Abstract: A modulator drive function, for a hyperacuity laser printer that produces text and line art and halftones from numerically sampled input, incorporates device dependent characteristics, such as xerographic development and laser spot size, to position these edges precisely. The modulation drive function converts r,&thgr; channel coordinates to drive values for each scan within the span of its own channel pitch. A spline-based edge reproduction curve (ERC) compensates for slowscan phase errors and a temporal bias compensates for fastscan spot size. An electronic digital-to-analog converter, pulse width modulator or shift register can be used to control exposure.

Abstract: The two symmetrical halves of halftone shapes that have a central axis of symmetry are selectively intensity modulated for accenting human readable information that is embedded in halftone patterns that are composed of halftone cells having fill patterns conforming to such shapes. This human readable information is defined by clustering these halftone fill patterns so that their accented portions visually blend to form alphanumeric character shapes.

Abstract: A high performance halftone shape for embedding machine readable data in printed documents is based on a hyperbola to accommodate the embedded data over an extended dynamic tone range. The shape enables precise tone control and can used for color printing. By rotating the shape 45-degrees, two alternate "ortho-serpentine" structures can be constructed which can be added to the diagonal structures, creating an embedded data system with four orientations. The quadrature system also allows more and varied patterns, but has the disadvantage of additional noise.

Abstract: Predetermined machine and/or human readable information is embedded in at least one serpentine pattern that is printed on each original document, so that any given instance of such a document can be later verified or refuted as being the original by determining whether this information can be recovered from the document or not.

Abstract: A hyperacuity printing system includes a halftoner (20) which converts pixel intensity values into multi-bit gray values which drive a laser diode (62). The halftoner (20) includes a halftoner memory (22), a phase error look-up table (50), and a modulator (60). The halftoner memory (22) stores a pregenerated halftone dot pattern as a plurality of halftone dot planes or cells (24), each representing an intensity value. The halftoner memory (22) is addressed by the integer portion of a screen coordinate (x,y) and the intensity value, and outputs spatial coordinates (r, .theta.) to an edge of the halftone dot nearest the screen coordinate. The fractional portion (xFRACT, yFRACT) of the screen coordinate (x,y) is combined with the outputted spatial coordinates (r,.theta.) to provide corrected coordinates (r.sub.c,.theta.). The corrected coordinates (r.sub.c,.theta.) address a modulator drive function (56) which generates the multi-bit gray value used to drive the modulator (60).

Abstract: A PDL or other type of line drawing program mathematically generates an edge between white and black regions. For curved edges, the edge is transformed into a plurality of piecewise linear edge segments (20). Pixels (u,v) in the vicinity of the edge are identified (12). Each pixel is assigned a magnitude value in accordance with its distance from the mathematically defined edge relative to a width or gray span (22) of the selected vicinity. The magnitudes in each of a plurality of subregions of the selected vicinity define a sloping plane (42). The threshold (t), such as a value mid-way between the extremes of the selected vicinity, defines a plane (44) which intersects the sloping plane. The line (46) of intersection defines the edge. A hyperacuity printer receives slope of the plane relative to a scan and orthogonal directions of the printer, and a magnitude for each pixel.

Abstract: A hyperacuity printing system for rendering image data on a recording medium, the image data being rendered as an array of pixels across the recording medium in a fastscan direction, and an orthogonal slowscan direction. The system includes a data source for supplying grayscale input image data and a scanning device for rendering grayscale output image data, the scanning device having a writing device for writing scan spots on the recording medium at a writing pitch in the slowscan direction and a writing pitch in the fastscan direction. The system also includes transformation circuitry for transforming the grayscale input image data into grayscale output image data, the transformation circuitry including a halftoner, a thresholder, and a selection device, where the selection device selects either the thresholder or the halftoner to provide the grayscale output image data.

Abstract: A system for correcting registration errors in a printer. The system includes a memory device for storing sequential rasters of image data and an interpolator coupled to the memory device, the interpolator using the rasters of image data from the memory device in conjunction with multiplication factors to calculate an interpolated resample value. The system also includes addressing circuitry for providing address signals to the memory device, the addressing circuitry also providing the multiplication factors to the two dimensional interpolator. Finally, included is a correction device for providing adjustment values to the addressing circuitry, the adjustment values being used to correct for the registration errors.

Abstract: An apparatus and method for producing a halftone image generates halftone cells based on grayscale image data and bitmap code. A human readable pattern is embedded within the halftone image. Each of the halftone cells is formed from dot patterns having one of a plurality of predetermined shapes. The predetermined shapes of the halftone cells form the human readable pattern. The halftone cells are written onto a recording medium to produce the halftone image. Rotation of the halftone cells allows data to be encoded within each of the halftone cells without varying the tone of the image. The tone of the image may be controlled by selectively varying a thickness of the dot patterns within the halftone cells.

Abstract: An apparatus and method for producing a halftone image which generates halftone cells based on grayscale image data values. Each of the halftone cells is formed from serpentine dot patterns. The serpentine dot patterns form two separate arcs. The halftone cells are written onto a recording medium to produce the halftone image. Rotation of the halftone cells allows data to be encoded within each of the halftone cells without varying the tone of the image.

Abstract: A printing device (10) is commanded to print a reference set of intensity values from almost white or highlight regions through almost dark or shadow regions. A measuring device (12) measures the actual outputted printer intensity levels from the printing device (10). An interpolator (14) interpolates the printer intensity levels into a best fit smooth curve plotted against the reference set of intensity levels which produces a non-linear function. A mapping means and converter (24a, 24b) calculate a set of fractional intensity values and densities which produce a linear function when mapped with the printer intensity levels. A dot area parameter calculator (28) calculates a set of dot parameters defining a configuration of a halftone dot required to fill an area within the halftone cell corresponding to each intensity level. For each position of each halftone cell, a measurement processor (30) determines a distance between a current scan position (a,b) and a nearest edge defined by the dot parameters.

Abstract: A system for performing interlace scanning with plural light beams. The system includes a data source for supplying sequential lines of image data and a memory device for sequentially storing a plurality of the lines of image data, where the memory device has an input port for receiving the lines of image data from the data source. The memory device also has plural output ports where each of the plural output ports corresponds with one of the plural light beams. The system further includes addressing circuitry for addressing the memory device, where the addressing circuitry provides plural sets of slowscan output address signals corresponding to the plural output ports for providing an address value. The address value of each of the slowscan output address signals are offset from other of the address values by an offset amount provided by the addressing circuitry to enable interlacing of the plural light beams.

Abstract: An image processing system for performing thresholding. The system includes a source of image data, where the source of image data provides an image value and associated two dimensional slope information for that image value. And, the system includes thresholding circuitry utilizing the image value and the two dimensional slope information for determining a thresholded value from the thresholding circuitry.

Abstract: Image data (10) is represented by a plurality of scan lines (30). Each scan line (30) includes a line of pixels (32) along a fast scan access. Each pixel (32) represents an optical density for a specific location in the image data (10). Pairs of pixels in the fast scan direction of odd numbered scan lines (30) are grouped in even/odd pixel pairs by logic circuit (12). Pairs of pixels of even numbered scan lines (3) are grouped in odd/even pixel pairs such that the groupings in adjacent lines are offset. Each pixel pair contains n addressability units defining a halftone cell. The addressability units of the pixel pair are combined. A propagated error value from a previous pixel pair and the data values of each pixel pair are combined and used to address a memory location in a look-up table (14). The memory location contains a corresponding binary data value representing an intensity level for each pixel of the pixel pair. The binary data is outputted to a gray modulator (16) to be printed by a printer (18).

Abstract: An image forming apparatus and method use interlace scanning of plural light beams by deflecting the plural beams with a rotating polygon onto a recording medium. Corrections are made to the scan envelope to compensate for errors due to perceived imperfections in the spot profile or aberrations in the optical and mechanical systems used to scan the spot. The corrections are performed by adjusting intensity of gaussian components of the envelope according to a look up table.

Abstract: A printing system for receiving grayscale input image data and rendering halftoned image data having embedded data on a recording medium includes an addressable three dimensional memory system. The memory system has a first set of address lines defining an x dimension, a second set of address lines defining a y dimension, and a third set of address lines providing an intensity dimension, and halftoning circuitry for receiving and transforming grayscale input image data into multi-bit value output data. A look-up table is used to match multi-bit value output data representing x dimension, y dimension, and intensity, to grayscale input image data. The system uses addressing circuitry for addressing the three dimensional memory system, with the first set of address lines and the second set of address lines defining a screen stored in the memory system, the first set of address lines and the second set of address lines providing x and y address values defined at a desired screen angle.