Abstract: The present invention is a method for efficiently processing an image to detect antialiased pixels using reduced buffering memory. The method stores, in a scanline buffer memory, a predefined number of scanlines of data including data for a target pixel position and, in a tag buffer memory, a plurality of binary antialiasing tags, including at least a previously estimated tag for the target pixel position. Then using the stored pixel data and previously estimated tag, an antialiasing tag for the target pixel position is generated.

Abstract: An image-processing system (20) for mapping full-color images to highlight-color images includes an image-input terminal (30). The image-input terminal (30) reads an image represented in a full-color scheme defined by a three-dimensional color space. An image-processing unit (40) samples the image to obtain a sample color. The image-processing unit (40) maps the sample color from the full-color scheme to a highlight-color scheme. The highlight-color scheme is defined by a two-dimensional color space that includes a highlight-color component and a base-color component. The image-processing unit (40) includes at least a first two-dimensional look-up table (42), which is used in mapping the sample color from the full-color scheme to the highlight-color scheme. Finally, an image-output terminal renders the image in the highlight-color scheme.

Abstract: The present invention is a method for the color correction of digital images that have been compressed. In a preferred embodiment, aspects of the color correction are carried out on the compressed image data to improve computational efficiency. One of a number of alternative methods is employed to accomplish the color correction on lossy or losslessly compressed images. The color transformation process accomplishes color correction on compressed image data in conjunction with compression or decompression operations. A second, simplified phase of the color correction may be applied subsequently to the decompressed image data in certain embodiments.

Abstract: A vector error diffusion system for quantizing pixel value in color images, which initially determines whether any pixel should be white or colored, and subsequently determines whether the pixel should be a primary color, a secondary color or black.

Abstract: An apparatus for bi-directionally rendering an image includes a bi-directional printer (10) having an input (12) which receives data corresponding to the input image. A printhead (14), in accordance with the data, renders the image on a medium (M) in swaths as it passes horizontally over the medium (M) in opposing first and second directions. A medium advance device (16) advances the medium (M) vertically past the printhead (14) between horizontal passes of the printhead (14) in the first direction and horizontal passes of the printhead (14) in the second direction. Horizontal swaths of the image are segmented into a line of columns (20) such that the columns (20) are made up of vertical arrays of pixels. A detector circuit (18) detects for breaks (22) in each of the columns (20) of each swath. Transition regions are defined for columns (20) having no vertical breaks (22) therein.

Abstract: An image data modification technique addresses certain image defects characteristic of still images derived from original video sources, such as television or videotape. Color bleeding, caused by an inability of chrominance signals to change from pixel to pixel as quickly as luminance signals, is addressed by processing the chrominance signal to have slopes closer to a change in the luminance signal for the same small area of the image. The technique can be employed on the image data for a single frame of video image, and does not require information from previous or subsequent frames.

Abstract: A method for color error diffusion using semi-vector quantization is proposed that simplifies error diffusion calculations. When three color separations are used, the two separations with the most visually perceptive color output are compared with one another to determine their output colors, while the third, least visually perceptive separation, is treated separately. A correction term may be applied to the third separation based on the color output of the first two separations to insure uniformity of ink coverage. This method yields results close to vector quantization and also minimizes fluctuation in the two most visually perceptive output colors. Of course, this method may be used with more than three color separations. For example, when four color separations are used, the least visually perceptive color is processed differently than the three other color separations.

Abstract: In this proposal a method of multilevel halftoning is described that allows the definition of halftone patterns using more than two gray levels at a time. This feature can be employed to eliminate the texture contours produced when shades formed by a pattern of two levels blends into a shade formed by a single gray level. The method also gives control over the degree to which a given output gray level is used. This can be employed to limit ink coverage when certain levels require more ink to produce than do others. According to the method: initial pixel intensity ranges are obtained; the initial pixel intensity ranges are compared to at least two overlapping threshold arrays; and selection of enhanced pixel intensity levels are determined for halftone cells according to the comparison results of the initial pixel intensity ranges to at least two overlapping threshold arrays wherein the enhanced pixel intensity levels are a function of results from the comparison.

Abstract: The present invention is a method for the color correction of digital images that have been compressed. In a preferred embodiment, aspects of the color correction are carried out on the compressed image data to improve computational efficiency. One of a number of alternative methods is employed to accomplish the color correction on lossy or losslessly compressed images. The color transformation process accomplishes color correction on compressed image data in conjunction with compression or decompression operations. A second, simplified phase of the color correction may be applied subsequently to the decompressed image data in certain embodiments. Accordingly, the technique has application to any number of color imaging systems, including digital printers and copiers where there is a necessity to color correct compressed digital images.

Abstract: In a color-management system, such as for a color digital printer, digital codes describing combinations of two colors are retained in a specific format. The three primary-color stimuli forming each color of the color pair are described as binary numbers, and the binary numbers are combined to yield a single orderable number. With this format, codes describing color pairs can be readily retained in a searchable table, preferably an AVL-balanced tree.

Abstract: A system and method for eliminating luminance false contours within rendered documents by sacrificing chrominance accuracy within printer halftones and for using the reduction of chrominance to improve the luminance correctness for any requested color. Ordinary halftone processes are modified such that small hue shifts are traded off for the ability to eliminate luminance false contours. Luminances of colored inks are created in a manner that turns on only one color spot at a time, instead of all three, within a slowly changing gray area because numerically equivalent steps in chrominance are much less visible in printed form than changes in luminance. Removal of false contours is therefore achieved by chrominance variations rather than by spatial variations in a document.

Abstract: An image data modification technique addresses certain image defects characteristic of still images derived from original video sources, such as television or videotape. A lack of vertical alignment of pixels in a single frame, causing a "wobble" or "jitter" artifact in the image, is detected and corrected by a series of algorithms.

Abstract: A method and apparatus for achieving an ultra-small or compressed image buffer images at half the resolution and then scales by two to achieve the device resolution. Acceptable quality can be maintained by identifying edge and interior portions of the page image and using this information to scale intelligently. A split-level frame buffer provides this identification of the image components. Further, an extension of block-truncation coding can be used with the split-level frame buffer to provide up to a 16 to 1 compression for an overall compression of up to 64 to 1. Actual techniques to scale these encodings are described along with new encodings for graphics and text designed this high compression of the image.

Abstract: An ink-jet printhead in which an orifice for the passage of ink therethrough toward a preselected location on the sheet is shared by two ejectors. Each ejector is capable of emitting ink of a preselected quantity through the orifice. The ejectors may be activated substantially simultaneously, to cause ink of a combined quantity to be emitted through the orifice.

Abstract: A method of applying noise removal to an image so that the areas having the greatest variance have the least correction. First, the variance between each image pixel and its surrounding pixels is determined. Next, for the neighborhood around each pixel, a density of variance is determined. Finally the density of variance for the neighborhood around each pixel is used to correct the original pixel, the direction of correction being toward the mean value in the surrounding pixels. The result is that relatively uniform areas of the image, within which noise is most obvious, will get the most correction and areas that are textured will get the least.

Abstract: A printing machine of the type in which liquid ink is deposited on a recording medium for printing gray scale images. The printing machine includes a printhead having ink ejecting nozzles of different sizes. Nozzles of the same size are arranged in groups and groups of nozzles are offset from one another. Ink drops of one group are deposited at locations corresponding to the points of a grid and ink drops of another group are deposited at locations corresponding to points not on the grid. Gray scale printing is achieved by the variation in drop size produced by different groups of nozzles as well as offsetting nozzles of one or more groups of nozzles from a reference group of nozzles printing on the points of a grid.

Abstract: A method of combining antialiased edges for printing or display at a grey level reproduction device, wherein pixels have shade values determined as a function of their neighbor's shade values and mask values. Shade values are determined by processing each pixel in terms of subpixels forming the pixel. Each of a plurality of subpixels are assigned mask and shade values as a function of their position in the pixel and with respect to the nearest neighbors. The resulting values for each subpixel are averaged to determine a final output value for the pixel.

Abstract: A method and apparatus for blending pictorial and graphical look-up tables is provided. The blended look-up table, addressable by image signals from both pictorial and graphical objects, produces printer signals which are a blend of the output of the pictorial and graphical look-up tables. For image signals that are inside the pictorial gamut of the printer, only the output of the pictorial look-up table is used in the blended look-up table. For image signals that are outside the pictorial gamut, a blend of the output of both pictorial and graphical look-up tables is used in the blended look-up table. To blend the tables, graphical and pictorial image signals are selected from the surface of the graphical and pictorial gamut which have the same hue and luminance as the desired image signal.

Abstract: A liquid ink printing apparatus printing images includes a printhead having a plurality of nozzles wherein a single power pulse causes two or more nozzles to eject ink simultaneously. The printhead includes an ink directing element having a plurality of ink conduits coupled to an array of spaced nozzles and a transducer element aligned with and mated to the ink directing element. The transducers are spaced a distance apart and each transducer is substantially aligned with at least two or more of the nozzles. The printhead is stepped in a direction transverse to the array of spaced nozzles a stepping distance approximately equal to or less than the distance between transducers. The ink directing element includes a silicon wafer having etched ink conduits or channels holding ink for ejection through the nozzles connected thereto.

Abstract: A method for combining foreground objects defined by a mask value and shade value, with a background image defined by a shade value, using high resolution edge information derived from low resolution grey image representations. By treating the object edge pixels in a high resolution grey model, characteristics of an edge represented by an edge pixel can be approximated by reference to surrounding grey elements. Movement of the edge can be approximated by changing the mask values in the high resolution grey model. Changes in the overall grey level of the pixel resulting from the mask changes cause the impression of edge movement in the low resolution edge.