Abstract: A system of curve generation takes a sequence of control points and constraint codes for each control point, and outputs a curve in which each of the constraints is satisfied. The set of constraints is chosen from the tangent angle, curvature, first derivative of curvature, and second derivative of curvature. The interactive curve design uses as its primitive, a curve whose curvature is a polynomial function of arclength (whose intrinsic equation is a polynomial). At each control point, a choice of G2 curvature continuity (tangent angle and curvature) or G4 curvature continuity (tangent angle and curvature plus first and second derivatives of curvature are continuous) is input. The desired curve is expressed as the solution to the chosen set of constraints.

Abstract: A halftone screening method includes a method of moire suppression, in which the input image is first screened in a trial screening module. The input image is then subtracted from the trial screened image to produce an error image which contains both the trial screen pattern and the moire pattern introduced by the trial screening process. The error image is filtered in a lowpass filter to remove the trial screen pattern, leaving only the moire pattern, which is then subtracted from the input image to produce a compensated image. Finally, the compensated image is then screened in a final screening module. The moire image component of the compensated image tends to cancel the moire pattern introduced by the final screening module so as to suppress moire patterns in the final screened image. In two alternate embodiments, filter refinements are provided to reduce grayscale distortions and improve moire suppression in the extreme light and shadow regions of the image.

Abstract: In an error diffusion halftone screen generation system, improved image smoothness in the highlight and shadow areas is obtained by calculating the distance to the nearest previously generated output dot. The square of the distance to the nearest previously generated dot is used as a bias value to effectively modulate the error diffusion threshold. The resulting output provides a halftone with a more uniform texture in the highlight and shadow areas of the screened image. The resulting pattern resembles the pattern of dots produced by tightly packing imaginary circles in the image plane, and placing an output dot at the center of each such tightly packed imaginary circle.

Abstract: In the generation of screened halftones of photographic images for low resolution marking devices, conventional screen techniques are too coarse, and adaptive dither techniques are too fine. The present invention preserves the advantages of the adaptive dither techniques, while creating screen patterns with an adjustable degree of coarseness. The invention applies a hysteresis constant and recursion techniques previously limited to adaptive screening with fixed dot patterns to vary the size of dots in the screened image, thereby allowing adjustment of the image coarseness by adjusting the hysteresis constant.