Abstract: A system for detecting image black and white points for a digital image.

Abstract: A printer driver operates a printer capable of multiple dot-placement geometries or resolutions and multiple inks per color channel. It maps a continuous-tone cyan pixel-component value to continuous-tone light- and dark-cyan values, which it separately halftones to respective binary pixel values that respectively indicate whether an associated pixel will receive light- and dark-cyan ink dots. It similarly generates binary values that respectively indicate whether an associated pixel will receive light- and dark-magenta ink dots. In performing the halftoning, the driver separately performs error diffusion through different interleaved sub-images of the image to be printed so that the error-diffusion process is performed for images whose pixel geometry is that for which the process was designed even though the overall image's pixel geometry is not.

Abstract: A multi-stage, preprocessing technique increases the quality of a monochrome or colored mixed-mode document printed on a binary-type printer. The document is preferably apportioned into a plurality of small tiles, each of which provides information to the inventive technique for eventually defining the modes as either text or images. The multi-stage technique comprises a first stage for normalizing a non-ideal histogram of the mixed-mode document to a histogram having an ideal distribution of selected pixel values. A second stage classifies each tile as either text, image or background, while a third stage collates groups of tiles in both vertical and horizontal directions to remove variances in the document. Those portions of the document classified as images are then halftone processed, while the text areas are threshold processed to thereby significantly improve the reproduction quality of the printed document.

Abstract: An ink-jet-printer driver employs clustered-dot dither to generate binary image signals that represent an image that has been adjusted for the ink-duty limit that must be imposed to avoid bleeding on some print media. Some image values that would result in ink duties that exceed the limit without adjustment are actually reduced by more than needed to meet the ink-duty limit. The resultant adjusted value is an increasing function of unadjusted value even for unadjusted values that exceed the ink-duty limit. To impose the limit, a Bayer dither process (94) receives an input that represents the ratio of ink-limit-adjusted ink duty to unadjusted ink duty. A gating operation (96) permits an ink request only at those locations where both dither processes (92 and 94) indicate that an ink is permitted.

Abstract: To impose a total-ink duty-cycle limitation by an ink-jet printer that substitutes black ink for simultaneous occurrences of cyan, magenta, and yellow, a printer driver determines a component-value adjustment as a function of the difference between a color's maximum and average component values. Adjusting the color values when this quantity is high but not when it is low enables one to prevent violation of the total-ink duty-cycle limit without unduly limiting black-ink use.

Abstract: An ink-jet-printer driver employs clustered-dot dither to generate binary image signals that represent an image that has been adjusted for the ink-duty limit that must be imposed to avoid bleeding on some print media. To impose the limit, a Bayer dither process (94) receives an input that represents the ratio of ink-limit-adjusted ink duty to unadjusted ink duty. A gating operation (96) permits an ink request only at those locations where both dither processes (92 and 94) indicate that an ink is permitted.

Abstract: A controller for an ink-jet printer (26) half-tones three color-component values in clustered-dot dither operations (80, 82, and 84) that employ respective dither arrays whose cluster centers are displaced from each other. Additionally, a half-toning operation (86) is performed on a fine-resolution black value obtained from the color-component values in an undercolor-removal operation (59) in which the resultant black value is less, throughout most of the component-value range, than the minimum of the color-component values from which the black value is derived. The banding effects that would otherwise result from ink bleeding are thereby greatly reduced. The banding effects can be further reduced by performing black-component half-toning in a non-cluster-dot-dither operation, without detracting significantly from the intended clustered-dot dither effect.

Abstract: An adaptive filtering and thresholding arrangement provides a set of error filters having different sizes and associated weighted coefficients for diffusing quantization errors among neighboring pixels in predetermined tonal areas of an image to achieve a smooth halftone image quality. Each error filter circuit is optimally applied to a particular pixel area depending upon the grayscale tone of that area and the desired output print resolution. The arrangement further provides for the addition of "noise" errors to threshold values at selected input image pixel ranges and at the intersection of two differently filtered areas to eliminate visible pattern distortion.

Abstract: A printer driver for a color printer employs an error-diffusion-type half-toning process in which different quantization thresholds are employed for different ones of the color components. The color component whose value is highest after augmentation by accumulated error is compared with a relatively low threshold to determine the binary output value for that component. The lowest error-augmented component value is compared with a relatively high quantization threshold, and the component whose value is between those of the other two is compared with an intermediate-valued quantization threshold. Varying the thresholds in this manner tends to discourage coincidences of different-colored imaging agents at the same pixels and thus tends to result in light colors' having a smoother appearance.

Abstract: An image preprocessing method and apparatus processes image data line-by-line using an error diffusion process to generate a halftoned image. The method and apparatus varies the processing direction from line-to-line to minimize the presence of worm-type artifacts in a halftoned image where the processing direction of each line in the image is dependent on the content of the image. More particularly, the processing direction of each line in the image is dependent upon the grayscale value and/or the quantization error associated with one or more pixels of a previously processed line in the image.

Abstract: An image preprocessing method and apparatus processes image data line-by-line using an error diffusion or dithering process to generate a halftoned image in which the radius of a dot representing a pixel is /dpi.ltoreq.r.ltoreq..sqroot.2/dpi The method and apparatus selectively performs the halftone process on every other pixel to reduce in consumption and computation time while maintaining a high resolution.

Abstract: A vivid color correction technique eliminates artifacts from a predetermined tonal area of a halftone image to thereby improve the color vividness of that image. According to this technique, pixel tonal values associated with input colors are initially examined to determine a maximum color value. After error diffusion halftoning, the resulting binary pixel values are collectively processed to generate inter-color information for comparison with a selected harmonic color cluster. If the inter-color information specifies a color that does not match one of the colors of the selected harmonic cluster, the inter-color information is "corrected" to reflect an acceptable output color.

Abstract: An image preprocessing method and apparatus processes image data line-by-line using an error diffusion or dithering process to generate a halftoned image in which the radius of a dot representing a pixel is /dpi.ltoreq.r.ltoreq..sqroot.2/dpi. The method and apparatus selectively performs the halftone process on every other pixel to reduce in consumption and computation time while maintaining a high resolution.

Abstract: A K separation screen comprises a grid of dots located at fixed positions, with the screen angle for each color, including black, maintained at 45.degree.. All of the primary color dots are printed at a predetermined screen frequency at predetermined locations. The black dots are also printed at a fixed screen frequency at predetermined locations. However, the black dots are printed in a different screen phase from the other colors, in particular, the phase offset is equal to one-half the screen frequency. Apparatus and a method are disclosed for generating the K separation screen using a cluster dot dithering array and offsetting the array pattern used to generate the colored halftone dots from the array pattern used to generate the black halftone dots.

Abstract: An image preprocessing method and apparatus processes image data line-by-line using an error diffusion or dithering process to generate a halftoned image in which the radius of a dot representing a pixel is /dpi.ltoreq.r.ltoreq..sqroot. 2/dpi The method and apparatus selectively performs the halftone process on every other pixel to reduce in consumption and computation time while maintaining a high resolution.

Abstract: Disclosed are printing methods and apparatus that process image source data into printed output visually superior to that obtained by conventional predistortion. In accordance with a first aspect of the invention, multibit source data representing the density variations of an original or source image is modified by a filter function. The filtered data is then processed by a halftoning routine that converts the data into a raster of single-bit data suitable for transfer to a printing device. The raster data specifies a density pattern lighter than that of the source image in highlight and upper midtone regions and darker than that of the source image in shadow and lower midtone regions. In accordance with a second aspect of the invention, an analogous filter is applied to parameters associated with the halftone processing algorithm rather than to the source data.

Abstract: An existing void-and-cluster method for generating dither arrays for halftoning grayscale images on binary printing devices is improved by including additional steps which both homogenize the starting pattern used in the void-and-cluster method and correct the starting pattern for the effects of oversized dots generated by the printing devices. More particularly, a constant gray starting pattern is first subjected to an error diffusion halftoning process before void and cluster processing to produce a starting binary pattern as a more homogeneous starting point. In addition, after the starting binary pattern has been created, it can be modified to take into account that most printers print "oversized dots" in order to avoid white areas between dots. In particular, from the starting binary pattern, a starting gray pattern is created which uses oversized dot information to assign grayscale values to the "0" pixels surrounding a "1" pixel.

Abstract: Adaptive preprocessing is performed on the three primary color signals generated during the scanning of a color image in order to enhance the perceived saturation of the dominant primary color. This preprocessing is performed by removing a small increment from the least intense primary color and adding the same increment to the most intense primary color. In this manner the overall brightness of the pixel is preserved, but the perceived saturation is increased. The increment that is effectively transferred from the least intense primary color value to the most intense primary color value is based on the relations of the three primary color values to each other in order to avoid visible color artifacts.

Abstract: A gray balance correction technique eliminates artifacts, caused by the accumulation of diffusion errors, from a predominantly "gray" tonal area of a halftone image. According to the technique, pixel tonal values associated with three input colors are initially examined to detect a condition that specifies production of a gray image area. Upon detecting this condition, errors from previously processed pixels are averaged prior to being "diffused" among these input color pixels. Thereafter, the input pixels are processed in accordance with conventional halftoning operations and the resulting binary pixel values are passed to an output buffer for printing. Averaging of the errors prior to error diffusion ensures that the detected condition is maintained throughout preprocessing of those input color pixel values.

Abstract: A practice for producing a halftone reproduction wherein a predetermined screen function is used to process the gray levels of the scanned original and wherein the halftone reproduction is made capable of exhibiting gray levels over the entire gray tone range of 0 (black) to 255 (white) by selecting the screen frequency in the screen direction so as to result in a screen frequency in the print direction which is other than a sub-multiple of the print frequency.