Abstract: Correction data is produced for density errors in prints produced using a printer. While printing a test image, the periods of rotation of one or more rotatable imaging members arranged along a receiver feed path in the printer are measured using respective period sensors. The printed test image is measured along a selected measurement direction and a reproduction error signal representing deviation from aim density is determined. For each period sensor, the autocorrelation of the reproduction error signal for the corresponding period is determined. If the determined autocorrelation exceeds a selected threshold, the reproduction error signal is decomposed at the corresponding period to extract the variation from the measured component. The remaining error signal is separated by frequency terms. The variations from the data at measured periods and the remaining error signal are used to produce a correction signal.

Abstract: Methods are provided for automatic cross-track density correction for a print engine having a print head that forms lines of picture elements on a receiver based upon lines of pixel values. In one aspect of the method, the print engine is caused to print a first print having a plurality of different areas along a cross-track direction with target densities and data is received from which measured densities for different ones of the plurality of different areas can be determined. A line density adjustment function is based upon a functional relationship between a cross track position of different ones of the areas and a difference between the measured density and the target density at the different ones of the areas. A production print is subsequently printed according to lines of pixel values for the production print modulated by the line density adjustment function.

Abstract: Printers are provided having a print engine having a print head that forms lines of picture elements on a receiver based upon lines of pixel values and a controller that causes the print engine to print a first print having a plurality of different areas along a cross-track direction with target densities and that receives data from which measured densities for different ones of the plurality of different areas can be determined. The controller determines a line density adjustment function based upon a functional relationship between a cross-track position of different ones of the areas and a difference between the measured density and the target density at the different ones of the areas and subsequently prints a production print according to lines of pixel values for the production print modulated by the line density adjustment function.

Abstract: Electrophotographic (EP) streaking compensation is performed. A tonescale is measured for each column and a per-column gain computed to compensate for variations. An adjustment tonescale is determined and a per-column adjustment-tonescale gain computed to correct for remaining error after the per-column gain is applied. The two corrections are used together to provide improved compensation quality.

Abstract: Compensation is performed for nonuniformity in a printer. The printer has a photoreceptor and a print head with a plurality of different light sources, each light source capable of producing a plurality of different levels of light. A plurality of stored gain control signals for each light source are related to the light output of that light source. Print job data includes screened pixel levels and a halftone screen specification. The stored gain control signals are adjusted based on the halftone screen specification. The screened pixel levels are modified using the adjusted gain control signals to provide engine pixel levels. Those levels are provided to corresponding light sources to expose the photoreceptor in respective pixel areas with light corresponding to the compensated pixel levels.

Abstract: Screened hardcopy reproduction apparatus for applying toner to a receiver using a print engine that may not apply toner uniformly, so the toner applied to the receiver has a non-uniformity. A controller receives an input pixel level and a corresponding input pixel location; a tone-reproduction unit calculates an output pixel level from the input pixel level and a corresponding output pixel location from the input pixel location; a compensator calculates a compensated pixel level from the output pixel level and the output pixel location; and a screening unit calculates a screened pixel level and a screened pixel location from the compensated pixel level, the output pixel location, and a selected screening pattern. The print engine applies an amount of the toner corresponding to the screened pixel level and the non-uniformity to the receiver at a toner location corresponding to the screened pixel location to compensate for the non-uniformity.

Abstract: A method of calculating compensation data for compensating for spatial print engine non-uniformity of an image applied by a print engine to a receiver. A test target has two test areas of different output densities, each with a single output pixel level. A relationship between output density and output pixel level for the print engine is determined, and is used to calculate the output pixel level for each test area from the respective output density. The test target is printed, and the reproduced densities of the test areas are measured at a plurality of different locations in each area. A processor is used to calculate the compensation data using the measured densities. The compensation data defines a relationship between an output pixel location on the receiver, an output pixel level, and a compensated pixel level.

Abstract: One or more printers or printing systems are connected to a scanning device. Each printer includes one or more color modules that are used during a printing operation. A printer prints a target for each color module or color channel. The printed targets are then scanned by the scanning device. The printed targets may be rotated to any angle and then scanned by the scanning device. The scanned raster data is processed by a controller to detect non-uniformities in at least one density image and to generate one or more correction profiles for the printer. When an image is to be printed, one or more controllers receive the image data and use the one or more correction profiles to correct or compensate for the non-uniformities during the exposure process.

Abstract: A method for calibrating a printer including a light-emitting diode (LED) printhead for non-uniformity on an image plane. The LED recording elements are arranged in a plurality of arrays. A plurality of characteristics (102, 104, 106, 108, 110) associated with each recording element are measured and from the measured characteristics a plurality of parameters (112, 114, 116, 118, 120) associated with each recording element is determined. Adjustment factors for a plurality of parameters are combined mathematically to determine an adjusted power density (122) for each recording element on the image plane. Correction factors (130) are then assigned to each recording element to correct for the adjusted power density (122). The correction factors (130) are stored in a memory (132) associated with the LED printhead.

Abstract: The invention adjusts the calibration of each light emitting element, such as a light emitting diode (LED) by storing data representative of the difference between a linear or non-linear characteristic of the LED. In a printer or copier, a print engine uses LEDs to form a latent image on a photosensitive member. A linear regression identifies the differences between the slope of the individual LED and the average LED. A further, non-linear regression identifies the curvature of the individual LEDs. The differences in linear slope and/or curvature are stored and used to correct the calibration of each LED when the LED is recalibrated during operation and in response to a global calibration signal, GREF.

Abstract: An electrophotographic recording apparatus and method wherein an electrophotographic recording medium is continuously moved in a first direction relative to a row of light-emitting recording elements such as LEDs. A beam shifter assembly is located within an optical path between the LEDs and the recording medium. The beam shifter assembly is operable in a first mode to pass light from the LEDs without substantial lateral shifting and in a second mode to pass light with substantial shifting of said light in a lateral direction having a directional component parallel to the row of LEDs. A control is provided for controlling the beam shifter assembly in different modes on alternate recording time lines of exposure. This helps minimize in-track artifacts. The apparatus is also operable in a multiaddress mode that is automatically instituted when a higher resolution image scanner is used or when a higher resolution character font library is input for recording.

Abstract: A heterodyne type interferometer utilizing two optically aligned photoelac modulators driven at the same frequency and in phase quadrature.

Abstract: A digital phase meter to measure the phase difference between an input signal and a reference signal and output this phase information in the form of an eight bit number. The input signal and the reference signal, which are sinusoidal, are conditioned to a more defined leading edge by a high speed differential voltage comparator and a dual/differential line receiver. A series of uniquely configured D flip-flops are used to detect the leading edge of both the signal input and the reference input. An AND gate then acts as a switch that is activated on the leading edge of the signal input. The time interval between the two positive leading edges of the input signal and reference signal specifies the phase difference. The AND gate is in the high state for this duration. The phase difference is converted into an 8-bit binary number via two 4-bit cascaded counters. The high output of the AND gate is used to enable the counters for the duration of the phase difference.