Fingertip Detection for Camera Based Multi-Touch Systems

• US 20090128499A1
• Filed: 11/15/2007
• Published: 05/21/2009
• Est. Priority Date: 11/15/2007
• Status: Active Grant

• Current Assignee: Microsoft Technology Licensing LLC (Microsoft Corporation)
• Original Assignee: Microsoft Corporation
• Inventors: Taylor, Stuart, Izadi, Shahram, Hodges, Stephen E.
• Granted Patent: US 8,581,852 B2
• Time in Patent Office: Days
• US Class Current: 345/173
• CPC Class Codes: G06F 2203/04109 FTIR in optical digitiser, i.e. touch detection by frustrating the total internal reflection within an optical waveguide due to changes of optical properties or deformation at the touch location
• CPC Class Codes: G06F 3/0425 using a single imaging device like a video camera for tracking the absolute position of a single or a plurality of objects with respect to an imaged reference surface, e.g. video camera imaging a display or a projection screen, a table or a wall surface, on which a computer generated image is displayed or projected tracking a projected light spot to determine a position on a display surface G06F3/0386
• CPC Class Codes: G06F 3/0428 by sensing at the edges of the touch surface the interruption of optical paths, e.g. an illumination plane, parallel to the touch surface which may be virtual sensing beam interruptions in a planar beam grid of an optical touch-screen G06F3/0421

Abstract

Touch detection systems and methods are described. The system comprises a light guiding sheet, a light source, a reflective layer and a detector. When a fingertip or other suitable object is pressed against the light guiding sheet, light which is undergoing total internal reflection within the sheet is scattered. The scattered light is reflected by the reflective layer and detected by the detector. In an embodiment, the light is infra-red light. The touch detection system may, in some embodiments, be placed on a display and the touch events used to control the display.

Claims

1. A touch detection system comprising:

a light guiding sheet having a touch surface and a rear surface;

a source arranged to couple light into an edge of the light guiding sheet, such that the light is totally internally reflected within the light guiding sheet;

a reflective layer in proximity to the rear surface of the light guiding sheet; and

a detector arranged to detect light emitted by the source which is scattered as a result of a touch event and reflected by the reflective layer.

2. A touch detection system according to claim 1, wherein the source comprises an infra-red source.

3. A touch detection system according to claim 2, wherein the reflective layer reflects infra-red and is transparent to visible light.

4. A touch detection system according to claim 2, wherein the detector comprises an infra-red sensitive detector.

5. A touch detection system according to claim 1, further comprising a display surface in proximity to the reflective layer.

6. A touch detection system according to claim 5, wherein the display surface is the reflective layer.

7. A touch detection system according to claim 5, wherein the display surface comprises one of a liquid crystal display, a whiteboard and a projector screen.

8. A touch detection system according to claim 5, further comprising a computing-based device, the computing-based device comprising:

a processor;

an interface to the display surface;

an interface to the detector; and

a memory arranged to store executable instructions to cause the processor to;

perform image analysis on a signal from the detector to identify a touch event.

9. A touch detection system according to claim 8, wherein the memory is further arranged to store executable instructions to cause the processor to:

control an application based on the touch event.

10. A touch detection system according to claim 9, wherein the memory is further arranged to store executable instructions to cause the processor to:

output data to the display surface via the interface to the display surface, to cause the display surface to display a graphical user interface of the application.

11. A touch detection system according to claim 1, wherein the source comprises an array of sources.

12. A touch detection system according to claim 11, wherein in use the sources are illuminated sequentially.

13. A touch detection system according to claim 1, wherein in use the source is modulated.

14. A method of detecting touch events comprising:

projecting light into a light guiding sheet such that it undergoes total internal reflection; and

detecting light scattered by a touch event on a first surface of the light guiding sheet and reflected by a reflective layer in proximity to a second surface of the light guiding sheet.

15. A method according to claim 14, further comprising:

generating a signal representative of the light detected; and

performing image processing on the signal to identify a touch event.

16. A method according to claim 15, further comprising:

controlling an application based on the touch event.

17. A method according to claim 16, further comprising:

displaying a graphical user interface for the application on a display surface in proximity to the reflective layer.

18. A method according to claim 15, wherein performing image processing on the signal to identify a touch event comprises:

filtering the signal to mask areas outside an area of interest; and

converting the signal into a binary image using a threshold.

19. A touch sensitive user input device comprising:

a light guiding layer;

a source arranged to couple light into an edge of the light guiding layer;

a reflective layer in proximity to a first surface of the light guiding layer and arranged to reflect light scattered by a user touching a second surface of the light guiding layer; and

a detector arranged to detect light reflected by the reflective layer.

20. A touch sensitive user input device according to claim 19, further comprising:

a display in proximity to the reflective layer,

and wherein the reflective layer is arranged to reflect at least one wavelength of light emitted by the source and to be transparent to at least one wavelength of light emitted by the display.