Abstract: A color printing process, printing a color image in which out-of-gamut original colors are present. For each pixel defined by an original color which is determined to be out of gamut, a gamut remapping process is applied to map each pixel to a color which is within a printer gamut, remapping said pixels to colors within an output printer gamut. For a given set of gamut remapped pixels, gamut remapped pixel colors are compared with said original pixel colors, to derive a comparison metric. Using the comparison metric, a corrected set of gamut remapped colors is generated. The comparison metric may be subjected to an adaptive filtering process, which strengthens the comparison metric in high frequency image regions to increase its impact on the gamut remapped colors, and weakens the comparison metric in low frequency areas, to weaken its impact on the gamut remapped colors.

Abstract: A method for digital image compression of a raster image is disclosed which uses different compression methods for selected parts of the image and which dynamically adjusts compression and segmentation parameters to control tradeoff of image quality and compression. The image is encoded into a single data stream for efficient handling by disk, memory and I/O systems. This system provides a stable feedback loop that manages to a fine granularity (typically 8×8 pixel blocks) the compression of image data so as to be compliant with a plurality of compression constraints; the management of an incremental bias toward more aggressive compression that selectively applies the more aggressive compression methods to blocks that are the most tolerant with respect to visible artifacts; and the adjustable segmentation and compression parameters used to control the image compression.

Abstract: A method and apparatus for compressing and decompressing electronic documents, with improved compression and reduced history memory size requirements. The method includes receiving scan line ordered raster documents ordering the raster data, and compressing the data with a lossless dictionary compression method. The ordering of raster data into vectors accounts for the correlation of pixel data between scan lines, improving the compression. This ordering also reduces the history window size requirements in a sliding window dictionary compression method.

Abstract: A color printing process, printing a color image in which out-of-gamut original colors are present. For each pixel defined by an original color which is determined to be out of gamut, a gamut remapping process is applied to map each pixel to a color which is within a printer gamut, remapping said pixels to colors within an output printer gamut. For a given set of gamut remapped pixels, gamut remapped pixel colors are compared with said original pixel colors, to derive a comparison metric. Using the comparison metric, a corrected set of gamut remapped colors is generated. The comparison metric may be subjected to an adaptive filtering process, which strengthens the comparison metric in high frequency image regions to increase its impact on the gamut remapped colors, and weakens the comparison metric in low frequency areas, to weaken its impact on the gamut remapped colors.

Abstract: The present invention is a method and apparatus for reducing two-color moiréoften found during the rendering of full color images using halftoning techniques, by providing shared screen angles between distinct color separations.

Abstract: A method and apparatus for the control of darkness/lightness in a digital image rendered by a printing system. An original image containing antialiased edges is initially thresholded and filtered to determine an edge map. With knowledge of the edge via the edge map, darkness adjustment is applies to the digital image. Gray-edge compaction is applied thereafter to adjust the position of the edge.

Abstract: A method and apparatus for operating a color ink jet printer of the type which prints a swath of the image at a time with each transit across a sheet. An image may be optionally preprocessed with undercolor removal, so that each color pixel in the image is defined by black and, at most, two colored inks. Color will be deposited to print the image on forward and return transits of a multiple color printhead across a sheet. The colors and location printed in each transit are determined prior to the first transit, by determining first, which colors may be printed in the second transit irrespective of their order of deposit. The result of this determination is logically ANDed with a checkerboard pattern to determine printing locations. Then, the other required colors and locations for the image which will not be printed with the second transit are printed on a first transit. Each swath is printed with forward and reverse transits, with checkerboarding of the reverse transit to prevent head signature artifacts.

Abstract: A method for calibrating a printer includes printing a set of color samples with the printer, the set of samples or calibration target generated dynamically in response to selected printer variables, and reflecting at least a portion of the printer gamut. Each printed color sample in the set of samples is measured calorimetrically, to determine the printer's response thereto, so that a calibration table can be generated, taking into account printer variables selected by a user.

Abstract: A color printing process, printing a color image in which out-of-gamut original colors are present. Each pixel is reviewed in context of its neighbors prior to remapping, so that a remapping function may take local area information into account in the remapping process.

Abstract: A method for calibrating a printer includes printing a first set of color samples with the printer, reflecting at least a portion of the printer gamut. Each printed color sample in the set of samples is measured calorimetrically, to determine the printer's response thereto. The colorimetric response is compared with a predictive model of printer behavior for that portion of the printer gamut. In a portion of the printer gamut wherein the calorimetric response differs from predicted printer behavior, the printer generates a new set of color samples, for printing. The new set of color samples is secondarily measured to determine the printer's colorimetric response thereto; and using the initial measurements and the secondary measurements, a color calibration table is generated for use by the printer in converting device independent colors to device dependent colors.

Abstract: A color printing systems which deposits colors on a separation by separation basis is calibrated to determine a printed color responsive to a requested color, based on a mapping of device independent colors to printer output colors. The system provides trapping to correct misregistration between printer output colors due to imperfect placement of said separation color. Such a system includes calibration data stored in a device memory mapping a set of device independent colors to printer output colors; a trapping processor, using calibration data to determine device independent colors for printer colors. Also included is a trapping calculation processor, converting device independent colors to a color space in which equivalent color differences in human color perception are approximately equivalent values, determining whether to trap, a trap color, and a trapping location for the trapping color.

Abstract: An improved technique for compressing a color or gray scale pixel map representing a document using an MRC format including a method of segmenting an original pixel map into two planes, and then compressing the data or each plane in an efficient manner. The image is segmented such that pixels that compress well under a lossy compression technique are placed on one plane and pixels that must be compressed losslessly are placed on another plane. Lossy compression is then applied to the lossy pixel plane while lossless compression is applied to the lossless pixel plane.

Abstract: A processing system for preparing a plural separation document image for printing, including a process for mitigation or reduction of three color moiré. An approximation of moiré amplitude is calculated, and compared to a reference. Where three color moiré mitigation is desirable, black is removed and replaced with other separation colors.

Abstract: A processing system for preparing a plural separation document image for printing, including small feature enhancement of the image, preventing halftoning damage thereto, including detecting small features in the document image; and in a detected small feature region, setting any output image signals corresponding to said small feature region to ON in at least one of the at least two separations.

Abstract: A method of quantizing pixels from a first pixel depth to a second includes adding to an original value of each pixel to be quantized, an error value resulting from quantization of any previous pixels, to generate a modified pixel value; comparing each modified pixel with threshold varying in accordance with the gray difference that a printed mark would make to a neighborhood pixels and outputting second depth pixels responsive to said comparison; and determining a halftoning error as a function of the modified pixel values, the gray difference, and the binary signals, and distributing say error to other gray level pixels in an image.

Abstract: A document containing colored strokes or lines is reproduced in a way to preserve the color intent if the reproduced document is copied on a black-and-white device. Dashed lines are generated for insertion into the stroke, with dashing patterns that reflect the original color of the stroke. Outlining in black or white, dependent on the stroke color, may be provided. If the stroke is wide enough, the color within the stroke may alternatively be reproduced with a black and white reproducible pattern.

Abstract: A document containing colored text is reproduced in a way to preserve the color intent if the reproduced document is copied on a black-and-white device. For small text, the fact that it is colored, is conveyed by reproducing it bold, and for medium size text, by reproducing it outlined. For large text, both the fact that it is colored and the color used can be conveyed by filling the interior of the characters with patterns that correspond directly to the color.

Abstract: An error diffusion processor for preparing a document image for printing. Shadows and highlights regions stress error diffusion processes, because accumulated error cannot be easily compensated for in these regions. Edge enhancement emphasizes the problem by locally increasing error in order to maintain spatial detail of the image. The arrangement described puts an additional term into the error calculation that is a function of local intensity, with substantial value only in shadow and highlight regions to correct for edge enhancement artifacts.

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 method for processing compressed digital data derived from an original image sequence, the data being organized as a set of image frames, each image frame comprising a set of blocks, each block including a string of bits corresponding to an area of the original image frame in the original image sequence. A cost function is derived as a number related to the amount of bits spent to encode a block, sets of blocks, an image frame, or sets of image frames. A segmentation technique is applied to the map with cost functions. Temporal segmentation is performed by analyzing cost functions associated with each image frame. In both cases auxiliary functions can be used to improve the segmentation quality. The segmented regions of a image frame or sets of image frames can be identified, replaced, printed, or processed in special manners.