Abstract: An apparatus for correcting color images in an electrophotographic printing machine in which a first image is developed on a photoconductive surface, the second and subsequent images are superimposed over the first developed image. The apparatus includes an input device for inputting an image signal having a plurality of color components. An image processing unit processes the inputted signal. The image processing unit includes an adaptive exposure processor that modulates the exposure level of a raster output scanner (ROS) for a given pixel as a function of toner previously developed at the pixel site, thereby allowing toner layers to be made independent of each other.

Abstract: A hybrid halftone cell selection method enables selection of gray levels in halftone printing algorithms to minimize the effects of noise resulting in nonuniformities, such as, for example, halftone banding. The method requires selection of hybrid halftone cells possessing structures wherein the total number of gray pixels are limited. The number of gray pixels having any given intermediate reflectance level in any halftone cell is also limited. The cell selection method thus reduces the number of TRC gray steps to some minimum required number by eliminating the most noise sensitive cells (i.e. those cells having the highest percentage of gray level pixels). The intermediate reflectance values of the gray pixels in the selected cells are then selected to produce uniform gray steps and reduce variability in the TRC.

Abstract: Improvements in bit-image quality in printing systems is achieved by providing several different pattern matching processors. Each pattern matching processor comprises a lookup table of patterns and corresponding replacement image patterns. A source image is modified by replacing areas in the source image that match patterns with the corresponding image patterns. Pattern matching processors are chosen depending on: the type of image being processed, input from the operator (user), feedback from the xerographic processor, and the color of the image. A user interface is provided which allows a user to download template and pattern data for each pattern matching processor. Pattern matching can be used to correct single-bit, half-bit, line-growth, xerographic effects and aliasing errors, and to provide control of print quality to the user.

Abstract: A pulsed imaging, facet tracked, Raster Output Scanner utilizes pulse width modulation in conjunction with spatial filtering to form three exposure levels at the surface of a charged photoreceptor medium, one of the levels associated with a specific color. This type of scanner with a nominal video rendering experiences a color line growth in the process direction. The line growth problem is caused by a coherent optical effect. The resultant output print has bolded color lines in the process direction. Several techniques are set forth to compensate for this line growth. In a preferred technique, the video data stream is modified by locating or positioning video pulses representing white information at the start of an associated pixel time period. When the color pixel is imaged, it will therefore, always abut an adjoining white pulse and will be inhibited from spreading into the adjacent pixel period.

Abstract: A pulsed imaging Raster Output Scanner utilizes pulse width modulation in conjunction with spatial filtering to form three exposure levels at the surface of a recording medium, one of the levels associated with a specific color.

Abstract: A multiple diode laser array used in a ROS scanning system is modified to reduce the effects of undesirable spatial exposure variation at the surface of certain type of layered, semi-transparent photoreceptors. The spatial absorption variation is later manifested as a "plywooding" pattern formed on output prints derived from the exposed photoreceptor. The laser array is modified to form a merged scanning beam at the photoreceptor surface of two or more diode outputs, each output operating at a different wavelength than the other. In one embodiment, a plurality of diodes, each at a different wavelength, are sequentially addressed, and an image of each diode is scanned across the photoreceptor which results in an exposure distribution that would be similar to that formed by an incoherent beam.

Abstract: A multi-beam laser ROS print system is described which is adapted to minimize banding in output prints. Multiple beams from a laser source are separated by a distance which causes the beam to scan consecutive lines in a non-consecutive scan; e.g., according to a particular beam interlacing sequence. It has been found that as a general proposition, banding decreases with increasing interlacing orders and, furhter, that once a print system error frequency, or another frequency of interest has been identified, there are a number of interlacing orders, each an optimum value, which can be introduced to reduce banding which would ordinarily result from the particular frequency error.

Abstract: A document feeder is provided for presenting documents to the platen of a copier for copying with a vacuum belt platen transport system having document transporting belts movable under a substantially planar vaccum plenum backing. Also included is a vacuum system for applying a partial vacuum to a document sheet being transported by the movable belts over the platen. Show-through and show-around problems are reduced by optically mtching the belts and the plenum backing. In the preferred embodiment, the background surface is slightly roughend and made to be approximately 92% reflective to light during image exposure. The belts are composed of a urethane material which is approximately 16% transmissive but provides a 91% reflectance when moving along the plenum surface.

Abstract: A printing system employing a raster output scanning device is compensated for the effects of motion of the medium upon which an image is being printed. An amplitude transmittance spatial filter is positioned either in an exit pupil of the "slow scan" optics of the system or in the first Fourier transform plane of a lens positioned between the scanning device and the recording medium. Several preferred transmittance functions are provided.

Abstract: Trinary and quaternary halftone reproduction systems for electronic printers in which discrete combinations of either three or four reflectance level pixels having optimum intermediate levels form halftone cells to provide an increased number of gray steps for processing image signals, yielding an optimum Tone Reproduction Curve.

Abstract: In an electronic printer which utilizes an image write bar, a control circuit is provided to compensate for the effects of vibration in a rotating photoconductive member, typically a photoreceptor drum. In one embodiment an encoder is positioned so as to detect spatial displacements of indicia affixed to the photoconductor surface, Correction signals are generated and sent to control circuits which adjust the on/off timing of the write bar operation and/or the intensity of the image bar output. This adjustment results in compensation for the effects of photoconductor vibration.

Abstract: An electrophotographic reproduction device is described which is capable of forming images of an original document modified by information added to or replacing information of the original. A latent image of the document is formed on a photosensitive surface and a portion of the image, in a first embodiment, is maintained at the original charge level. This fully charged section is subsequently discharged in an image-wise pattern by a compact annotator device. The annotator includes an illumination source, an addressable light modulator device such as a liquid crystal panel and a lens array for forming the modulated light pattern onto the photosensitive surface.

Abstract: A gradient index lens array having improved stray light characteristics is enabled by coating the surfaces of the fibers comprising the array with a low transmittance, low viscosity material. The index of this material is matched to that of the fiber surface to prevent Fresnel reflection. The interstitial areas of the lens array comprises a light absorbing material. In another embodiment, stray light caused by light scattering at the end faces of the lens array is reduced by masking the end face with a mask having apertures overlying the fiber faces. The mask apertures have slightly smaller diameters to mask out the rough outer edge of the fibers.

Abstract: Exposure modulation (strobing) at a photoreceptor surface due to mechanical vibration of the photoconductor is eliminated by placing a filter with appropriate transmission characteristics in the optical path. The transmission characteristics necessary to achieve zero strobing include an incidence profile having a zero Fourier transform at the vibration frequencies.

Abstract: An imaging device is disclosed which comprises a noble metal photosensitive glass having formed on the surfaces a plurality of raised spherical surfaces which form an array of thick lenses. The array can be positioned between an object and image plane to project images from the object plane onto the image plane. Lens spherical aberrations are reduced and lens array imaging performance is optimized by an optimum lens aperture radius or an optimum lens numerical aperture.

Abstract: An exemplary two-row design for a reduction/enlargement gradient index lens is provided. The gradient index fibers of each row are aligned in the length direction so that the fiber axis lies along respective symmetrical planes. These planes are tilted with respect to each other and with respect to a plane normal to the object and image planes by some small angle. The array images objects in an object plane onto an image parallel plane of a magnification dependent on the system parameter. In this configuration, the center fiber of one row is aligned such that a plane extending through the axis of the center fiber in the width direction of the lens makes a right angle with the object and image planes. A further characteristic of the two-row array is that adjacent fibers in adjoining rows are offset to provide the required contiguous image at the image plane and to optimize the exposure uniformly.

Abstract: A compact, two-dimensional full-frame document illumination and imaging device is formed by combining a short focal length imaging area array, such as a gradient index fiber lens area array, with a light source formed in the fiber interstitial areas of the array. The light source is addressed to provide a uniform illumination level at a document platen interface. The full document image is reflected back to the array and projected onto a photosensitive image plane.

Abstract: The light output of a fluorescent lamp is controlled and optimized. Both the light output and the lamp voltage peak at nearly the same value of mercury cold spot temperature. Controlling the lamp voltage therefore controls the light output. Thus, when the lamp voltage is continually monitored, any decline from the peak voltage is detected and a signal is generated which reverses the instant mode of operation of a cooling device placed in proximity to the lamp cold spot. With the cooling mode reversed, the lamp voltage will rise towards the peak. The cooling mode remains unaltered until the lamp voltage falls again.

Abstract: A power supply circuit for a flash lamp delivers energy to the lamp in increments rather than in the conventional single charging pulse. A dc voltage power supply is used which has a voltage output considerably higher than the normal lamp voltage. The power supply output is connected across at least two circuits which are adapted to charge to some small increment of the total lamp energy requirements and then to discharge the stored energy into the lamp. Each circuit which contains a low value capacitor is cyclically connected between the lamp and the dc supply so as to create a continuous series of incremental inputs to the lamp, the inputs terminating when the desired lamp energy output is achieved.

Abstract: A gradient index lens array used in an optical imaging system is modified so as to compensate for factors creating a non-uniform image exposure at an image plane. Various parameters of the individual fibers comprising the array, such as index gradient, radii and packing density, are selectively modified so as to obtain a desired exposure profile.