Xerox Corporation

Other

Brian L Waldron

R Victor Klassen

Reiner Eschbach

William A Fuss

Louis D Mailloux

Keith T Knox

An error diffusion technique seeks to remove artifacts resulting from the diffusion of large errors. This technique removes artifacts resulting from instances where there is little difference between a source color and a target color but there is a large diffused error component. The error diffusion technique clips a combination vector resulting from the combination of a source color with the diffused error component so that the combination vector extends roughly one quarter of the width of a color gamut beyond the boundary of the color gamut. This helps to prevent ever-increasing error vectors and, thus, helps prevent certain artifacts in images that are output.

Error clipping for vector error diffusion

A method of error diffusion selects colorants, from a plurality of colorants defining a color space, to obtain an actual color which represents a desired color for respective pixels. The actual colors are output by an output apparatus. The process first determines the desired color for a pixel. Next, undercolor removal is performed for the desired color, thereby dividing the desired color into first and second components. A scalar error diffusion is then performed for the first component of the desired color, resulting in a first component of the actual color. A vector error diffusion is performed for the second component of the desired color. The vector error diffusion calculates an error as a negative of a distance in the color space between a closest available colorant in a subset of the plurality of colorants and the desired color. The error is added to the desired color to obtain a second component of the actual color. The first and second components of the actual color are combined to achieve the final actual color. The final actual color is output to a color output apparatus.

Error diffusion on moderate numbers of output colors

A notepad has a plurality of stacked notes adapted to be secured to an object. The notes each have a leaf with an edge. Each note also has an adhesive sheet secured along the edge of the leaf. This adhesive sheet has (a) an overlay section overlaying part of the leaf, and (b) a narrowed extension section extending away from the leaf in an extension direction. This extension section is adapted to be secured to the object.

Notepad and notes adapted to be adhesively secured to an object

In a digital printing apparatus in which primary colorants are selected by an error-diffusion process, a method takes into account situations in which a colorant is selectable from within the gamut defined by certain other primary colorants. In the case of a printer in which, in addition to CMYK colorants, a mid-gray colorant is also selectable, the method avoids the problem in which an error-diffusion algorithm mandates the simulation of colors outside the gamut.

Error diffusion in color printing where an intra-gamut colorant is

This invention discloses a method of correcting the measurement of the amount of light reflected by a document that is being processed by a digital image acquisition apparatus. A typical image acquisition apparatus measures the amount of light reflected from the surface of the original document and sets a corresponding set of electrical signals to a printing or storage module. Image acquisition usually requires illuminating the original document with a reflecting cavity, which causes the measurement of the amount of light present on the surface of the document to become distorted. The method disclosed by the present invention corrects this phenomenon by calculating the amount of light that reaches the surface of the original document by being reflected from the illumination system and the surrounding cavity. This allows the measured reflectance to be corrected, and the true reflectance to be used for subsequent output or storage.

Method of correcting the measured reflectance of an image acquired by an

A method of improving the contrast in a natural scene image, in which the image is converted from an original set of color coordinates to an expression where one term has a relationship to overall image intensity. A global histogram of the image is derived for that term, which plots the populations of pixels at each possible level of intensity in the image. The signal describing the histogram is operated on with a filter having the characteristic of weakening strong peaks and valleys in the function, but not effecting flat portions of the signal. The filtered histogram signal is used for controlling the TRC mapping in a device at which the image is to be printed. Contrast is improved in areas likely to have the most image information, using the method described above, and further, dividing the image into a number of segments, each describable by a local histogram signal for that image segment. Each local histogram signal is compared to the global histogram, to determine which signals are flatter. If any of the local histograms have signals flatter than the global histogram, the signals are summed into a relevant histogram signal and directed to the flattening filter in its place.

Image-dependent luminance enhancement

A one dimensional electronic halftone generating system having a source of digital data representative of pixel greyscale, a counter to store the digital data, and pulse producing logic responsive to the counter to activate a laser modulator in accordance with the digital data representative of each pixel. In particular, a six bit data word represents one of 64 greyscale states for a particular pixel. The pulse producing logic responds to the particular data word to produce a pulse of a given duration or width to drive the laser for a given time period. The duration of the pulse, representing one to 64 states for a given pixel, will produce a given discrete greyscale value for each pixel.

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Penfield, NY, United States of America

Brian L Waldron