Multi-touch input discrimination
Techniques for identifying and discriminating between different types of contacts to a multi-touch touch-screen device are described. Illustrative contact types include fingertips, thumbs, palms and cheeks. By way of example, thumb contacts may be distinguished from fingertip contacts using a patch eccentricity parameter. In addition, by non-linearly deemphasizing pixels in a touch-surface image, a reliable means of distinguishing between large objects (e.g., palms) from smaller objects (e.g., fingertips, thumbs and a stylus) is described.
1. A method to discriminate input sources to a touch-surface device, comprising:
obtaining a proximity image;
segmenting the proximity image to identify a plurality of patches;
determining a eccentricity value for each of the plurality of patches;
identifying a first patch as a thumb contact if the eccentricity value of the first patch is greater than a first threshold;
determining a minor radius value for each of the plurality of patches;
ignoring each patch having a minor radius value greater than a second threshold: and
using the identified patch to control an operation of a touch-surface device.
2. The method of claim 1 , further comprising identifying a second patch as a fingertip contact if the eccentricity value of the second patch is less than the first threshold.
3. The method of claim 2 , further comprising identifying the first and second patches as contacts from a right hand if the second patch is detected to the right of the first patch; and
using the identified patch to control an operation of a touch-surface device comprises using the identified first and second patches to control an operation of the touch surface-device.
4. The method of claim 2 , further comprising identifying the first and second patches as contacts from a left hand if the second patch is detected to the left of the first patch; and
using the identified patch to control an operation of a touch-surface device comprises using the identified first and second patches to control an operation of the touch surface-device.
5. The method of claim 1 , wherein the eccentricity value of a patch is determined by taking a ratio of a major radius value of the patch and a minor radius value of the patch.
6. The method of claim 1 , wherein the first threshold comprises a constant value.
7. The method of claim 1 , wherein the first threshold comprises a linear function.
8. The method of claim 1 , wherein the act of ignoring is performed before the acts of identifying.
9. The method of claim 8 , wherein the second threshold comprises a constant value.
10. The method of claim 8 , wherein the second threshold comprises a linear function.
11. The method of claim 1 , wherein the act of using comprises changing an operational mode of the touch-surface device.
12. A method to discriminate input sources to a touch-surface device, comprising:
obtaining a proximity image;
segmenting the proximity image to identify a plurality of patches, each patch having one or more pixels, each pixel having a value;
reducing the value of each pixel in a non-linear fashion;
determining a minor radius value for each of the plurality of patches;
identifying a first patch as a palm contact if the minor radius of the first patch is greater than a specified threshold; and
using the identified patch to control an operation of a touch-surface device.
13. The method of claim 12 , wherein the specified threshold comprises a constant value.
14. The method of claim 12 , wherein the specified threshold comprises a linear function.
15. The method of claim 12 , wherein the act of reducing comprises reducing the value of a pixel to the square-root of the value of the pixel.
16. The method of claim 12 , further comprising determining a centroid value for each of the plurality of patches, wherein the act of determining the centroid value uses pixel values that have not been reduced in a non-linear fashion.
17. The method of claim 12 , wherein the act of using comprises changing an operational mode of the touch-surface device.
18. A method to discriminate input sources to a touch-surface device, comprising:
obtaining a proximity image;
segmenting the proximity image to identify one or more patches, each patch having a plurality of pixels, each pixel have a value;
reducing the value of each pixel in a non-linear fashion;
determining an eccentricity value for each of the plurality of patches;
determining a minor radius value for each of the plurality of patches;
identifying each patch having a minor radius value greater than a first threshold as a palm contact, said patches associated with a first group of patches;
identifying each patch having a minor radius value less than the first threshold and an eccentricity value greater than a second threshold as a thumb contact, said patches associated with a second group of patches;
identifying each patch having a minor radius value less than the first threshold and an eccentricity value less than the second threshold as a fingertip contact, said patches associated with a third group of patches; and
using the identified patches to control an operation of a touch-surface device.
19. The method of claim 18 , further comprising identifying the first, second and third groups of patches as contacts from a right hand if the third group of patches is to the right of the second group of patches.
20. The method of claim 18 , further comprising identifying the first, second and third groups of patches as contacts from a left hand if the third group of patches is to the left of the second group of patches.
21. The method of claim 18 , wherein the first threshold comprises a constant value.
22. The method of claim 18 , wherein the second threshold comprises a constant value.
23. The method of claim 18 , wherein the first threshold comprises a linear function.
24. The method of claim 18 , wherein the first threshold comprises a constant value.
25. The method of claim 18 , wherein the second threshold comprises a linear function.
26. The method of claim 18 , wherein the second threshold comprises a constant value.
27. The method of claim 18 , wherein the act of reducing comprises reducing the value of a pixel to the square-root of the value of the pixel.
28. The method of claim 18 , wherein the act of using comprises changing an operational mode of the touch-surface device.
29. A program storage device, readable by a programmable control device, comprising instructions stored thereon for causing the programmable control device to implement one or more of the methods of claims 1 , 12 and 18 .
30. A touch-surface device, comprising:
a touch-surface adapted to receive touch input;
a processor coupled to the touch-surface; and
memory storing instructions to perform one or more of the methods of claims 1 , 12 and 18 .
31. The touch-surface device of claim 30 , wherein the touch-surface device comprises a mobile telephone.
32. The touch-surface device of claim 30 , wherein the touch-surface device comprises a music device.
33. The touch-surface device of claim 30 , wherein the touch-surface device comprises a video display device.
34. The touch-surface device of claim 30 , wherein the touch-surface device comprises a personal computer.