A combined dot density and size modulation system uses dispersed dot halftoning in conjunction with dot size modulation to produce a halftone image in which both the density and size of the dots are modulated to control overall gray level. The dot density and size modulation system offers advantages over pure dot density modulation systems or pure dot size modulation systems because it allows an extra degree of flexibility which can be used to increase the visual quality of the halftoned pattern and/or increase the robustness of the halftoning to printer artifacts and variations. An input pixel value is used to independently produce a dot density value and a dot size value. The dot density value and dot size values may be obtained from, e.g., look up tables that have been optimized for print quality and printer stability. Dispersed dot halftoning is used to provide a halftone value for the desired pixel location using the dot density value. The dispersed dot halftoning may be, e.g., tone dependent error diffusion. The halftone value and the dot size value for the pixel location is then used to generate a modulated code, e.g., a pulse width modulated code, to the printer. The modulated code may include both the pulse width of the desired dot for the pixel location as well as the justification, e.g. left, center, or right, for the pixel location. The dot density and size modulation system is particularly useful in modern electrophotographic printing systems that allow the printed dot size to be almost continuously varied through the specification of a pulse width modulation (PWM) code.
A method of printing a test pattern including printing cyan or magenta in a test region using a default printer half-tone, printing a yellow in a reference area portion of the test region using a coarse clustered dot half-tone, and printing different levels of yellow in test patch regions of the test region using a default printer half-tone.
The methods and systems presented herein use well-known logic devices in combination with one or more pulse-width-modulation (PWM) devices in order to create left- and right-justified width-modulated pulses. In some embodiments, justification ability is added without the need to alter an existing PWM device. In some embodiments, the generation of justified pulses is accomplished by a logic circuit in combination with an inherently left- or right-justified PWM device. Some embodiments of the present invention may include, for example, any combination of logical selectors, inverters, and flip-flops. In some embodiments, a justification circuit may receive as input any combination of one or more bits of pixel data, one or more bits of justification selection data, and one or more clock signal. In some embodiments, a justification circuit may output one more signals representing left or right-justified pulses.
Xerox Reference No. D/A0639A system and method for improving xerographic halftoning by magnifying a threshold array, interpolating the in-between values, enabling multiple thresholds to be accessed simultaneously and presented to multiple comparators, to cause multi-bit output. A threshold array is sampled at distinct locations separated by the sparse sampling distance to allow warping of the threshold array dots by adjusting the sampling distance in small, fractional portions (deltas) of the magnified distance. By adding more thresholds, amplitude or intensity modulation is used to move dot edges in a process direction for further flexibility in printing irrational or warpable screens.
A combined dot density (FM) and dot size (AM) modulation halftoning method and system produces a halftone in which both the density and size of the dots are modulated. In addition to modulating the dot size and density, the halftoning method can also explicitly control the size of dot clusters and different intensity levels.
Exemplary methods for estimating an orientation angle and a translation values for scanned images are disclosed. The methods described herein may be embodied as logic instructions on a computer-readable medium. In one exemplary implementation meaningful image information is removed from a scanned image, resulting in a transformed image that comprises alternating, parallel lines disposed at an orientation angle relative to an orthogonal axis. The orientation angle may be determined using geometric techniques or statistical correlation techniques, and statistical correlation techniques may be implemented to determine translation values.
