Optical touch screens
Activating a plurality of light emitters and light detectors around a screen, each emitter-detector pair corresponding to a light path crossing the screen, wherein some of the light paths are blocked when one or more objects touch the screen, providing a look-up table, listing, for each cell from a plurality of cells, those light paths that traverse that cell when no object is touching the screen, wherein the cells partition the screen, for each cell: accessing the look-up table to identify those light paths that traverse that cell, determining whether the thus-identified light paths are blocked during the activating and, if affirmative, recognizing that cell as being a touched cell, and combining adjacent touched cells into a common touch location, thereby calculating one or more touch locations wherein each touch location is a combination of one or more constituent touched cells.
1. A method for calculating multiple touch locations on a screen comprising:
activating a plurality of light emitters and light detectors around the perimeter of a screen, each emitter-detector pair corresponding to a light path crossing the screen, wherein some of the light paths are blocked when one or more objects touch the screen;
providing a look-up table, listing, for each cell from a plurality of cells, those light paths that traverse that cell when no object is touching the screen, wherein the cells partition the screen;
for each cell:
accessing the look-up table to identify those light paths that traverse that cell; and
determining whether the thus-identified light paths are blocked during said activating and, if affirmative, recognizing that cell as being a touched cell; and
combining adjacent touched cells into a common touch location, thereby calculating one or more touch locations wherein each touch location is a combination of one or more constituent touched cells.
2. The method of claim 1 , wherein the cells are of different sizes.
3. The method of claim 1 , wherein each cell surrounds a point of intersection between two light paths.
4. The method of claim 1 , further comprising calculating an area for each touch location according to the sum of the areas of that touch location's constituent cells.
5. The method of claim 4 , further comprising:
providing a range of values for the area of a touch location; and
validating those touch locations whose calculated area is within the range.
6. The method of claim 5 , further comprising associating each touch location whose calculated area exceeds the range, with a plurality of objects touching the screen at that location.
7. A method for calculating multiple touch locations on a screen comprising:
activating a plurality of light emitters and light detectors around the perimeter of a screen, each emitter-detector pair corresponding to a light path crossing the screen, wherein some of the light paths are blocked when one or more objects touch the screen;
providing a look-up table, listing, for each light path, those cells from a plurality of cells, that are traversed by that light path when no object is touching the screen, wherein the cells partition the screen;
for each light path that is not blocked during said activating, accessing the look-up table to identify those cells that the identified light path traverses, and recognizing the thus-identified cells as being untouched cells;
classifying those cells that are not recognized as being untouched cells, as being touched cells; and
combining adjacent touched cells into a common touch location, thereby calculating one or more touch locations wherein each touch location is a combination of one or more constituent cells.
8. The method of claim 7 , wherein the cells are of different sizes.
9. The method of claim 7 , wherein each cell surrounds a point of intersection between two light paths.
10. The method of claim 7 , further comprising calculating an area of each touch location according to the sum of the areas of that touch location's constituent cells.
11. The method of claim 10 , further comprising:
providing a range of values for the area of a touch location; and
validating those touch locations whose calculated area is within the range.
12. The method of claim 11 , further comprising associating each touch location whose calculated area exceeds the range with a plurality of objects touching the screen at that location.