Ductus Incorporated

Sun Microsystems, Inc.

Oms, Inc.

Jacobo Valdes

Eduardo Martinez

Jeffrey H Hoel

Eduardo D Martinez

A trajectory and a footprint of a hypothetical pen are each divided into sequences of segments, each segment having a slope associated therewith. The segments of the footprint form a closed sequence and those of the trajectory form a sequence with a beginning and an end. Each of the two approximate envolvents of the thick line are calculated in the same way, from the trajectory segments and the footprint segments. An envolvent is initialized to include the first segment of the trajectory starting at an appropriate offset from the trajectory start point, followed by zero or more footprint segments and then followed by the next trajectory segment until each of the trajectory segments are concatenated. In determining how many footprint segments to concatenate before concatenating the next trajectory segment, the slopes of the last concatenated trajectory segment and the next trajectory segment are compared to the slopes of the footprint segments. If any footprint segments have slopes between the slopes of the last and next trajectory segments, those footprint segments are concatenated before the next trajectory segment is concatenated. The selection of one of the two sets of footprint slope vectors, either the clockwise set or the counterclockwise set, determines which envolvent of the two envolvents are generated.

Envolvent approximation using accurate slope information

A method and apparatus for converting multi-level raster shapes into bi-level raster shapes while preserving as much of the visual character of the shape is disclosed. The method and apparatus solve two main problems arising in the task: that of broken continuity (drop-outs) and that of large changes in the width of horizontal and vertical lines on the bi-level raster shape as a result of minute changes on the multi-level shape (stem width aliasing). Drop-outs are handled by identifying certain boundaries between pixels as drop-out warnings. Pixels adjacent to dropout warnings have their coverage values converted from multi-level to bi-level by a process that guarantees that at least one of them will be rounded up. Dropout warnings are found from the outline of the ideal shape used to generate the multi-level shape and represent an approximation to said outline. In a preferred embodiment, the set of drop-out warnings for an outline is the set of pixel boundaries containing the nearest pixel boundary to each intersection of the outline with mid-pixel lines. Stem width aliasing occurs because of rounding errors clustering along horizontal and vertical lines. The present invention minimizes stem width aliasing by a variable threshold technique in which the threshold value used to turn the multi-level coverage value of a pixel into a bi-level value depends on the pixel position. The multiple threshold values are used to scatter the rounding errors over neighboring pixels so that they do not cluster along horizontal or vertical lines and are therefore less apparent to a viewer. In a preferred embodiment, two different threshold values are used in a checkerboard pattern, i.e., the threshold value for every other pixel in the horizontal or vertical direction alternates between the two values.

Multi-level to bi-level raster shape converter

A method of synthesizing multi-level raster shapes directly from outlines describing ideal shapes is disclosed. A raster shape suitable for approximating the ideal shape in a raster display device is synthesized by dividing a plane into a plurality of pixel areas according to a pixel grid, then by representing the shape as one or more arcs in the plane, where the arcs collectively, and in conjunction with an insideness criterium, divide the plane into an inside region and an outside region, and then by separating the pixels into inside pixels, outside pixels, and boundary pixels. The raster shape comprises coverage values assigned to each pixel in the plane, where inside pixels are assigned a coverage value of 1, outside pixels a coverage value of 0 and the boundary pixels a coverage value between 0 and 1 approximating the degree to which the boundary pixel is covered by the inside of the outline. Initially, boundary pixels are assigned a coverage value of 0 or 1 based on a pixel-coverage criterium, and then it is corrected by a correction value resulting in a coverage value between 0 and 1. The correction value for a pixel might be a numerical value indicating the fraction of the pixel covered by the correction region; the correction value may also depend on the geometry of the correction region represented by the valve and the region's location within the pixel. The correction region of a boundary pixel is the signed difference between the region represented by the initial coverage value assigned to the pixel and the actual region of the pixel covered by the inside of the outline.

Raster shape synthesis by direct multi-level filling

A method and apparatus is described which fills in the pixels missed when drop-out occurs during the fill process of character contours. The character contour is decomposed into a series of rook moves. The pixel selected is the one more covered by the actual shape of the portion of the curve where the rook moves are coincident and dropout occurs. This is dependent upon the slope of each of the curves at the location of dropout. Preferably the length of the sequence of colinear consecutive rook moves is used to approximate the slopes of the curves. The target pixel of the longest sequence of colinear rook moves is more covered than its opposite pixel and therefore the target pixel is set. The target pixel for a rook move is the pixel in the winding direction (i.e., left or right direction) along the rook move. Thus the target pixel of the stronger rook moves will be set and added to the bit map image generated using a outline fill process. In the preferred embodiment, the rook moves are examined to determine the length of a sequence, that is the number of rook moves that are sequentially in alignment with one another. A strength value is then assigned to each of those rook moves in a sequence equal to the number of rook moves in the sequence. The strength value of the rook move is then compared to the strength value of the opposite pixel, that is the pixel opposite the target pixel for a particular rook move. If the strength value of the target pixel of the rook move is greater than the strength of the opposite pixel, the opposite pixel value if reset to zero and the target pixel is set to equal the strength of the sequence. This process is performed for each rook move in a sequence and for each sequence of rook moves around the contour of the character. Once all rook moves have been evaluated, the value is assigned to the pixels of the character according to this process, are adjusted to reflect a bit map image to be displayed. This is achieved by turning on all bits which are greater than zero. The bit map generated is then logically ORed with the bit map generated using the contour fill process to provide a filled character in which drop out is eliminated and the distortion to the character is minimized.

Method and apparatus for filling contours in digital typefaces

Disclosed is a page printing system which uses virtual (logical) memory for mapping images. Physical memory which is used for creating a page image bitmap for synthetic graphics is to be allocated as patches. A path in general corresponds to a rectangular area of a page when the page exists in bitmap form. Each patch is represented by a set of non-contiguous segments of logical memory which, when mapped to physical memory, are contiguous.

Growing community of inventors

Palo Alto, CA, United States of America

Jacobo Valdes