Method for anti-aliasing of electronic ink

• US 6,559,858 B1
• Filed: 05/30/2000
• Issued: 05/06/2003
• Est. Priority Date: 05/30/2000
• Status: Expired due to Fees

• Current Assignee: International Business Machines SA (International Business Machines Corporation)
• Original Assignee: International Business Machines Corporation
• Inventors: Chee, Yi-Min, Schneider, Bengt-Olaf
• Primary Examiner(s): Luu, Matthew
• Application Number:
  US09/580,127
• Time in Patent Office: 1,071 Days
• Field of Search: 345/611, 345/613, 345/614, 345/617, 345/173
• US Class Current: 345/611
• CPC Class Codes: G06T 11/001 Texturing; Colouring; Generation of texture or colour inpainting G06T5/77
• CPC Class Codes: G06T 2200/12 involving antialiasing
• CPC Class Codes: G09G 5/28 for enhancement of character form, e.g. smoothing
• CPC Class Codes: G09G 5/393 Arrangements for updating the contents of the bit-mapped memory

Abstract

A procedure is embodied as program code on a medium that is readable by a computer. The program code is used to direct operation of the computer to render lines corresponding to samples, from a digitizer tablet, that map onto a same pixel of a display screen. The program code includes a code segment for subdividing a display screen pixel into a plurality of sub-pixels; a code segment, responsive to each sample that maps onto a current pixel, for mapping the sample onto a sub-pixel center; a code segment for computing a bounding box that is centered on the sample; a code segment, responsive to a size and position of the bounding box, for determining those pixels in a neighborhood of the current pixel that are overlapped by the bounding box; and a code segment for varying an intensity of the overlapped pixels according to the amount of overlap. The code segment that determines pixels in a neighborhood of the current pixel preferably operates to store overlap-related information, for all of the samples that map onto the current pixel, within an auxiliary array. The code segment that varies the intensity then uses the contents of the auxiliary array to vary the intensity of corresponding pixel locations in a frame buffer that has an output coupled to the display screen. The code segment that varies the intensity is responsive to a sub-pixel location of the sample, and to a precomputed summed area table (SAT), for determining an amount by which to vary the intensity.

Claims

1. A method for creating anti-aliased line images for digitizer tablet samples that map onto a same display screen pixel, comprising steps of:

for each sample that maps onto the same display screen pixel, determining a contribution of the sample to other pixels according to an amount that the sample overlaps other pixels that form a neighborhood of the same display screen pixel; and

adding the contribution to the pixels that form the neighborhood.

2. A method as in claim 1, wherein the step of determining includes a step of storing the contributions in an auxiliary array, and wherein the step of adding adds the contents of the auxiliary array to pixel locations in a frame buffer.

3. A method as in claim 1, wherein a size of the neighborhood is a function of a desired line thickness.

4. A method for creating anti-aliased line images for digitizer tablet samples that map onto a same display screen pixel, comprising steps of:

subdividing a display screen pixel into a plurality of sub-pixels;

for each sample that maps onto the same display screen pixel, mapping the sample onto a sub-pixel center;

computing a bounding box that is centered on the sample;

based on the size and position of the bounding box, determining those pixels in a neighborhood of the same display screen pixel that are overlapped by the bounding box; and

varying an intensity of the overlapped pixels according to the amount of overlap.

5. A method as in claim 4, wherein the step of determining includes a step of storing overlap-related information, for all of the samples that map onto the same display screen pixel, within an auxiliary array, and wherein the step of varying uses the contents of the auxiliary array to vary the intensity of corresponding pixel locations in a frame buffer.

6. A method as in claim 4, wherein a size of the neighborhood is a function of a desired line thickness.

7. A procedure embodied as program code on a medium that is readable by a computer, the program code being used to direct operation of the computer to render lines corresponding to samples, from a digitizer tablet, that map onto a same pixel of a display screen, comprising:

a code segment for subdividing a display screen pixel into a plurality of sub-pixels;

a code segment, responsive to each sample that maps onto a same display screen pixel, for mapping the sample onto a sub-pixel center;

a code segment for computing a bounding box that is centered on the sample;

a code segment, responsive to a size and position of the bounding box, for determining those pixels in a neighborhood of the same display screen pixel that are overlapped by the bounding box; and

a code segment for varying an intensity of the overlapped pixels according to the amount of overlap.

8. A procedure as in claim 7, wherein the code segment that determines pixels in a neighborhood of the same display screen pixel operates to store overlap-related information, for all of the samples that map onto the same display screen pixel, within an auxiliary array, and wherein the code segment that varies the intensity uses the contents of the auxiliary array to vary the intensity of corresponding pixel locations in a frame buffer that has an output coupled to the display screen.

9. A procedure as in claim 7, wherein the code segment that varies the intensity is responsive to a sub-pixel location of the sample, and to a precomputed summed area table (SAT), for determining an amount by which to vary the intensity, wherein determining the amount includes clamping a value of the amount to a predetermined maximum value.

10. A procedure as in claim 7, wherein a size of the neighborhood is a function of a desired line thickness.

11. Apparatus for creating anti-aliased line images for digitizer tablet stroke samples, comprising a controller, operable for each sample that maps onto a same display screen pixel, for controlling operation of a datapath for determining a contribution of the sample to other pixels according to an amount that the sample overlaps other pixels that form a neighborhood of pixel being considered, and further controlling adding the contribution to the pixels that form the neighborhood, the storage of the contributions into an auxiliary array, and the addition of the contents of the auxiliary array to pixel locations in a frame buffer.

12. Apparatus as in claim 11, wherein a size of the neighborhood is a function of a stored value defining a desired line thickness.

13. Apparatus as in claim 11, where said datapath comprises a plurality of registers for storing a linewidth with which a stroke is to be displayed, an integer portion of the current sample coordinates and a fractional portion of the current sample coordinates.

14. Apparatus as in claim 13, where said datapath further comprises a pixel address generator, responsive to the linewidth and to the fractional portion of the current sample coordinates, for addressing a lookup table that stores a precomputed filter function for determining, for all pixels potentially overlapped by the current sample, the current sample'"'"'s contribution to those pixels.