Abstract: A method and arrangement for reproducing an original image scans an original image to digitize the image so as to produce a digitized image signal, and collects statistical information of dot regions from the digitized image signal. For each dot region of the digitized image signal, a dot type is selected to render that dot region in accordance with the statistical information, the dot type being either a mixed dot type or one of a fixed threshold or a dot type mathematically modified from said mixed dot type. A printer is controlled to print the digitized image signal by rendering the dot regions in accordance with the selected dot type for each dot region, so that an original image that may contain different types of image regions is satisfactorily reproduced. In order to reduce printer moire patterns indexes to the threshold masks may be modified to avoid rigid threshold mask patterns from being used.

Abstract: A document reproduction method and apparatus wherein a scanner scans a document to determine the color components of pixels forming the image information on the document. The color signals generated by the scanner are transformed into lightness space and each pixel is examined as part of a window that includes neighboring pixels. The examination involves a first determination of whether or not the neighboring pixels are white pixels, second and third determinations of whether or not the current pixel is a grey pixel and has high contrast, and a fourth determination of whether or not the window has text structure. In accordance with combination of these determinations, a decision is made to recast the pixel as a pixel to be reproduced with a black colorant to thereby minimize color fringing errors at the edge of text-like information.

Abstract: An image processing system renders halftone images with an increased number of gray level steps without increasing the number of sub-elements in the halftone cells.

Abstract: Method and apparatus for converting gray-scale pixel information into data for rendering dots by a printer, video display, or similar device. A form of error diffusion is used wherein a thresholding error produced during the conversion process for a particular dot is propagated to one or more adjacent dots. The propagated error modifies the comparisons made for the adjacent dots and can be converted into lightness space to linearize the error. The error itself is modified when there is overlap of the propagating dot with an adjacent dot. The overlap modification is dependent upon the density levels being rendered and the amount of overlap between the dots.

Abstract: Methods and apparatus for interpolating existing gray-level pixel data to obtain new pixel values during image reduction and enlargement. A quadratic interpolation equation is used to apply location weighting factors to the density values of neighboring pixels. Edge strength modifying factors are used to modify the weighting factors in the x, y, and diagonal directions. In one embodiment, the modifying factors are set to greater than unity when the corresponding edge strength is greater than a predetermined threshold value. In another embodiment, the modifying factors are a non-linear function of the edge strength. These techniques preserve the sharpness of high contrast edges in the original image.

Abstract: An image processing system for converting gray level, digital, pixel information into binary data. Pixels with digital values close to the threshold value are further processed to determine the binary value to be specified for that pixel. In such cases, the adjacent horizontal pixel is tested and, if that test is inconclusive, the adjacent vertical pixel is tested. Depending upon the tests of whether the adjacent pixels were also close to the threshold value, the current pixel value is assigned the opposite value as the previous adjacent pixel. This has the effect of specifying, for transition areas at the boundaries of text characters and graphic lines, alternating pixels which produce a serrated edge along the borders of the character or line. These edges are of high spatial frequency and are substantially undetectable under ordinary circumstances by an observer. These edges are also smoothed in the printing process by the fusing of the toner to the output medium.

Abstract: False contouring of a screened halftone image without including more sub-elements in each cell, increasing the size of each cell, or decreasing the screen frequency of the image is accomplished by assigning to each sequential sub-element of a halftone cell a weighted probability of being "ON" in accordance with the value of the associated input signal.