Abstract: A hyperacuity printing system for rendering bitmapped image data on a photosensitive recording medium, the bitmapped image data being rendered as an array of pixels across the photosensitive recording medium in a fastscan direction, and an orthogonal slowscan direction. This system includes a data source for supplying grayscale input image data and a scanning device for rendering grayscale output image data onto the recording medium. The scanning device has a device for writing scan spots on the recording medium. Further included in this system is transformation circuitry for transforming the grayscale input image data into grayscale output image data. The transformation circuitry includes 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: An image enhancement method in which low-resolution bitmapped images may be enhanced and converted into gray images for printing on high-addressability printing and display systems. The method uses template matching to determine a rendering goal, and converts the bitmap pixel into a numerical, multiple-bit-per-pixel sampled value that is independent of the system it may ultimately be printed on. Unlike previous template matching methods which determined an enhanced pixel pattern output which was sent directly to the photoreceptor of a specific printer, the sampled data value of the present invention will require processing by the printer for its own particular characteristics before being sent to the photoreceptor. The sample data value may be sent directly to a printer imaging processor or stored via a network.

Abstract: A method and apparatus is described for eliminating banding, misregistration and bowing by controlling a composite light intensity profile and phase shifting of a spatial location at which the composite light intensity profile crosses a xerographic threshold in a two dimensional high addressability printer operating in an overscan mode. The contrast, pitch grating and phase shifting are dependent on at least one of a predetermined amount of overlap, an exposure profile and an intensity value of each of the plurality of laser beam spots formed on the photosensitive medium of a two dimensional high addressability printer.

Abstract: A hyperacuity printing system for rendering halftoned image data on a recording medium. The system includes comprising a data source for supplying grayscale input image data and a writing device for writing grayscale output image data onto the recording medium. Also included is halftoning circuitry for transforming the grayscale input image data into the grayscale output image data, the halftoning circuitry including a lookup table for providing the grayscale output image data described as halftone dots arranged as a continuum from a lowest intensity value to a highest intensity value of the grayscale input image data. Finally, included is a modulating device coupled between the halftoning circuitry and the writing device for converting the grayscale output image data from the halftoning circuitry into a form which can be utilized by the writing device.

Abstract: A circuit for using a flying spot scanner of one scan density to produce rasters of a different density in the process direction by using a fractional number of scans per raster. In the usual case, where m scans will be used to create n rasters, the number of scans m will normally be greater than the number of rasters n. Then, there will be m/n scans per raster. This will necessitate dividing some scans into two parts, the first part of the scan being used to scan the video data of the previous raster and the second part of the scan being used to scan the data of the next raster. Therefore, a circuit for switching data to each scan from one line of data to the next as the scan transitions from one raster to the next is required in this system. A process direction encoder can be used to determine when the raster boundaries are reached, and therefore when the data is to be switched.

Abstract: A method and apparatus is described for controlling the contrast, pitch grating of a composite light intensity profile and phase shifting of a spatial location at which the composite light intensity profile crosses a xerograpnic threshold in a two dimensional high addressability printer operating in an overscan mode. The contrast, pitch grating and phase shifting are dependent on at least one of a predetermined amount of overlap, an exposure profile and an intensity value of each of the plurality of laser beam spots formed on the photosensitive medium of a two dimensional high addressability printer.

Abstract: A method for resolution conversion by microaddressing an image transition in a printer includes steps of writing a print bit at zero intensity when a current image bit is in a second state and a displacement distance is greater than or equal to one-half of a pitch distance; writing the print bit at maximum intensity when the current bit is in a first state and the displacement distance is greater than or equal to one-half of the pitch distance; and writing the print bit at less than maximum intensity when the current image bit is in the first state and the displacement distance is less than one-half of the pitch distance, the step of writing the bit bit at less than maximum intensity including a step of intensity modulating a writing device based on a function proportional to a sum of the displacement distance plus one-half of the pitch distance.

Abstract: The contour fidelity of reproduction of images is enhanced by matching groups of pixels with templates based on a hierarchical set of patterns. This is accomplished by isolating a symmetrical window of pixels in the image including a central pixel and matching the groups of pixels in the window with hierarchical templates. Enhancement values for the central pixel are provided based on the results of the comparison. Windows are formed so that each pixel in the image is a central pixel for at least one window. The hierarchial set of patterns is developed so that each pattern in the hierarchy is a combination of an extension pattern and the pattern immediately below it in the hierarchy. This significantly reduces the hardware requirements for implementation of the technique. Templates are developed by creating horizontal, vertical, reversed and inverted permutations of each pattern in the set.

Abstract: An apparatus and method for providing accurate layer registration for multiple layer electronic printing systems discloses a means and a method of reducing the positional scan-to-scan error in a multiple layer electronic printing systems, typically multi-beam laser raster output scanners, in which accurate layer registration is critical. The method comprises determination of a time delay between page sync signal and start-of-scan signal, using this delay to determine delay dependent offset factor called the phase registration parameter, and correctively mapping image data to proper output channels based on the phase registration parameter and the laser number. The phase registration parameter must be determined at the beginning of each scan layer and the offset factors must be re-adjusted based on the new phase delay.

Abstract: An image forming apparatus and method for interlace scanning plural light beams by deflecting the plural beams with a rotating polygon onto a recording medium wherein the spacing between adjacent beams hold the relation ##EQU1## wherein I is an interlace factor equal to the number of reference scans between adjacent beams from a single facet of the polygon on the photoreceptor. The photoreceptor velocity is V.sub.o, w is the polygon angular velocity, f is a number of facets per revolution of the polygon, Q is the number of beams and B is the beam spacing.

Abstract: In a raster output scanner, a method of switching video from one raster to the next during a scan without the creation of a visible artifact. A position encoder is used to determine the position of each raster on the photoreceptor, a first distance above the transition point and a second distance below the transition point, in the process direction. Above the first point the video will be supplied by the first raster, and below the second point the video will be supplied by the second raster. From the first point to the transition point the duty cycle will vary from 100% of data from the first raster to 50% from each raster. From the transition point to the second point the duty cycle will vary from 50% to 100% supplied by the second raster. In this way, there is a gradual, and invisible, transition from one raster to the next.

Abstract: A laser recorder for recording images on a substrate in response to a video signal having a frequency which defines a pixel time (during which a single pixel is imaged) includes a duty cycle modulating digital to analog (D/A) converter which outputs a variable duty cycle high frequency signal, based upon an intensity controlling N-bit input, to a power controller which then controls the intensity of a light beam output by a laser based upon the variable duty cycle high frequency signal. The duty cycle modulating D/A converter outputs a high frequency variable duty cycle bitstream including a repeating cycle of fixed amplitude pulses, a total duration of all of the pulses in each cycle varying based upon the N-bit input signal.

Abstract: Microaddressable printers and other types of display systems are provided for rendering two dimensional images on high gamma, photosensitive recording media. These systems are microaddressable because they are operated in an overscanned mode to render images by scanning one or more intensity modulated scan spots over a high gamma, photosensitive recording medium in accordance with a scan pattern that causes the spot or spots to superimpose multiple discrete exposures on the recording medium on centers that are separated by a pitch distance that is significantly less than the effective spatial diameter of the scan spot or spots (e.g., the full width/half max. diameter of a gaussian scan spot). Overscanned systems have substantially linear addressability responses, so boundary scans that are intensity modulated in accordance with preselected offset values are used by these systems for spatially positioning the transitions that are contained by the images they render to a sub-pitch precision.

Abstract: An arithmetic frequency synthesizer for generating a bit clock for the flying spot scanner of a digital printer includes means for loading a pseudo-random offset value, accm.sub.i ; into its accumulator at the start of each scan. The offset values for successive scans pseudo-randomly vary within a range 0.ltoreq.accm.sub.i <N for all bit clock frequencies required for normal operation of the printer. Thus, the offsets pseudo-randomly phase shift the phase transitions of the bit clock sufficiently to prevent periodic variations in the bit clock duty cycle from spatially aligning with each other in the process direction during the printing of adjacent scan lines.

Abstract: An arithmetic frequency synthesizer having an accumulator for recursively accumulating a R-bit long input word at a predetermined reference frequency to generate a variable frequency bit clock for a flying spot scanner with a rotating polygon for cyclically scanning an intensity modulated light beam across a photosensitive recording medium includes means for arithmetically modulating the value of the accumulator input word on a scan cycle-by-scan cycle basis for adjusting the bit clock frequency to compensate for polygon motor hunt errors. There is a counter which is incremented or decremented during each scan cycle at a frequency which is scaled to the reference frequency, whereby the count accumulated by the counter during each scan cycle is a measure of the average angular velocity of the polygon during that cycle.

Abstract: A method for generating a variable frequency clock pulse for a raster scanner. First, a correction number, which may be the sum of corrections for scan-nonlinearity, polygon signature errors and motor hunt errors, is generated. This number is then added periodically to a running sum. The most significant bit of this sum is then available as the clock pulse output. The frequency of the output clock will be proportional to the correction number. The described circuit uses an accumulating adder and a register loop to form an accumulator circuit. The correction number is then supplied to the other accumulator adder input, and the register is clocked with a fixed frequency sample clock pulse.

Abstract: An arithmetic frequency synthesizer comprises one or more parallel/pipelined systolic computing arrays for performing parallel, recursive accumulation functions. Existing very large scale integrated circuit technology may be used to fabricate such arrays. Such a frequency synthesizer may be utilized, for example, to provide scan non-linearity correction, motor hunt compensation and/or polygon signature correction for laser scanners.

Abstract: A circuit for correcting for polygon drive motor velocity irregularities in a flying spot scanner is described. A crystal controlled oscillator is used to generate the system clock. As the motor speeds up, or slows down, pulses are subtracted, or added, to the stream of clock pulses so that the data bit stream will always occupy the same line length on the page regardless of polygon velocity variations.

Abstract: A circuit for correcting the data rate to compensate for polygon facet irregularities in a flying spot scanner is described. A crystal controlled oscillator is used to generate the system clock. As each facet becomes the current facet, a number of pulses appropriate for that facet are subtracted from the bit clock stream so that there will always be a constant ratio between data speed and scan speed regardless of the scan speed variations between individual facets.