Anti-aliased inking for pen computers

• US 6,201,528 B1
• Filed: 11/16/1994
• Issued: 03/13/2001
• Est. Priority Date: 11/16/1994
• Status: Expired due to Fees

• Current Assignee: International Business Machines Corporation
• Original Assignee: International Business Machines Corporation
• Inventors: Rhyne, James Rush II, Lucas, Bruce D., Wolf, Catherine G.
• Primary Examiner(s): CHANG, KENT WU
• Application Number:
  US08/340,561
• Time in Patent Office: 2,309 Days
• Field of Search: 345/179-183, 345/199, 345/173, 345/136, 345/141-144, 345/147, 345/114, 345/16-17, 345/137, 345/138, 345/150, 345/153, 395/143, 395/132, 395/135, 178/18.01, 178/18.03
• US Class Current: 345/611
• CPC Class Codes: G06T 11/001 Texturing; Colouring; Generation of texture or colour inpainting G06T5/77
• CPC Class Codes: G09G 5/28 for enhancement of character form, e.g. smoothing

Abstract

An anti-aliased inking method and apparatus for pen computers is presented. The invention eliminates aliased imaging of pen strokes by a number of techniques, including a “replace-if-darker” method in the event of overlapping strokes, a “multiplication” method for strokes drawn against backgrounds of various intensities; and a combination of replace-if-darker and multiplication for strokes drawn against colored backgrounds.

Claims

1. A computer system comprising:

a digitizing tablet;

a display;

a stylus;

means responsive to movement of the stylus across the digitizing tablet for producing an anti-aliased ink image of the path of the stylus on the display.

2. A method for producing an anti-aliased image on the display of a pen computer, comprising:

(a) moving a stylus along a desired path on the surface of a digitizing tablet, the digitizing tablet having a plurality of locations corresponding to pixel locations on an attached display;

(b) producing in response to step (a) an electrical signal indicative of the location of the stylus at a given time;

(c) generating on the display an anti-aliased visual display of the path, the visual display comprising a plurality of pixels, comprising the steps;

displaying as line segments each group of proximately disposed pixels corresponding to locations traversed by the stylus, a plurality of the line segments constituting a representation of the path of the stylus;

displaying each of the line segments on the display such that the ends of adjacent line segments overlap.

3. The method of claim 2, further comprising:

providing a color table having a plurality of indexed color value entries indicative of various colors that can be displayed;

reserving one or more color table entries for representing lines to be drawn on the display;

storing an initial color table index for each background pixel position of the display;

assigning a color value to the line to be produced;

while moving the stylus, comparing the color value of the line with the color value of each pixel location that is traversed by the stylus;

if the color table index value of a pixel traversed by the stylus is one of the reserved color table index values, computing a blended pixel color for that pixel using a replace-if-darker method;

if the color value of a pixel traversed by the stylus is not one of the reserved color values, computing a blended pixel color value using a multiplication method;

assigning a color to the traversed pixel based on the results of the replace-if-darker and multiplication methods.

4. The method of claim 3, wherein the replace-if-darker method comprises:

assuming a fixed background color;

computing the red, green and blue components of a blended pixel value as follows;

5. The method of claim 4, wherein intensity is computed using a linear combination of the color values of the pixel.

6. The method of claim 4, wherein it is assumed that r=b=g=1.

7. The method of claim 3, wherein the multiplication method comprises:

assuming a color for the line;

computing a blended color for each pixel traversed by the stylus as follows;

8. The method of claim 7, wherein the geometric relationship between the line and the pixel is the proportion of the pixel covered by the line.

9. The method of claim 7, wherein it is assumed that r_foreground=b_foreground=g_foreground=0.

10. The method of claim 2, further comprising:

producing a border along the length of a line produced by the stylus, the border having an intensity level between the intensities of the background and the line.

11. The method of claim 10, wherein the intensity of the border is computed as follows:

derive from the colors of the line and background pixels a blended intensity level as follows;

assume a fixed intensity value for the background;

for each pixel traversed by the line, let intensity_pixel=(1−

p)*intensity_foreground+P*I;

where intensity_foreground represents the intensity of the foreground, I equals the assumed value of the intensity of the background, P represents the proportion of the pixel covered by the line, and intensity_pixel represents the resultant intensity of the blended pixel;

determining the intensity of the actual traversed pixel;

comparing the intensity of each blended pixel color with the intensity of the actual traversed pixel; and

replacing each traversed pixel with the blended pixel if the intensity of the blended pixel is less than that of the actual traversed pixel.

12. The method of claim 11, further comprising:

producing a border pixel with a gray value with an intensity equal to intensity_pixel.

13. The method of claim 11, wherein I=1.

14. The method of claim 10, wherein the intensity of the border color is computed as follows:

derive from the colors of the line and background pixels a blended intensity level as follows;

assume an intensity value for the line;

for each pixel traversed by the line, let;

intensity_pixel=(1−

p)*I+P*intensity_background, where intensity_background represents the intensity of the background, I equals the assumed line intensity, P represents the proportion of the pixel covered by the line, and intensity_pixel represents the resultant intensity of the border pixel.

15. The method of claim 14, further comprising:

producing a border pixel with a gray value having the computed intensity.

16. The method of claim 14, wherein I=0.

17. A system for producing an anti-aliased image on the display of a pen computer, comprising:

a stylus;

a display;

a digitizing tablet coupled to the display having a plurality of locations corresponding to pixel locations on the display;

means for producing in response to stylus movement across the surface of the digitizing tablet an electrical signal indicative of the location of the stylus at a given time;

means for generating on the display an anti-aliased visual display of the path, the visual display comprising a plurality of pixels.