Object detection in touch systems
A signal processor implements a technique for detecting objects on a panel which transmits signals inside the panel such that the objects are allowed to interact with (e.g. attenuate) the signals by contact with a touch surface of the panel. The signal processor operates to define cells that have a given location on the touch surface and are associated with a respective set of intersecting paths for the signals across the touch surface. The signal processor operates to obtain ( 90 ) an output signal from a signal detection arrangement that measures a signal property for each path; process ( 91 ) the output signal to obtain an interaction value for each path; and generate ( 93 - 95 ′) a cell value of a selected cell among the cells as either a robust measure of central tendency (e.g. a median) or a minimum/maximum among the interaction values for the intersecting paths. The signal processor determines ( 97 ) presence or absence of an object in the selected cell based on the cell value.
1. A method of detecting objects on a panel, wherein signals are transmitted across the panel such that the objects are allowed to interact with the signals by contact with a touch surface of the panel, said method comprising:
obtaining an output signal from a signal detection arrangement;
processing the output signal to obtain an interaction value for each transmission path;
generating a two-dimensional distribution of values representative of the interaction on the touch surface by operating an image reconstruction algorithm on the interaction values for at least a portion of the transmission paths;
identifying one or more touch candidates from the two-dimensional distribution of values, the one or more touch candidates each having a location on the touch surface;
selecting reconstruction cells, from a plurality of reconstruction cells, corresponding to each location of the identified one or more touch candidates on the touch surface, wherein the plurality of reconstruction cells are defined with respect to the touch surface, each of the plurality of reconstruction cells having a given location on the touch surface and being intersected by a respective set of transmission paths for the signals across the touch surface;
generating a cell value for the selected reconstruction cells based on the interaction values for the set of transmission paths that intersect the selected reconstruction cells;
processing each cell value of the selected reconstruction cells to validate the one or more touch candidates; and
detecting objects on the panel based on the validation of the one or more touch candidates;
wherein the cell value is generated as a function of a subset of the interaction values.
2. The method of claim 1 , wherein interaction between one of the objects and the signals on the transmission paths is represented by interaction values of a given sign.
3. The method of claim 1 , wherein the interaction values for the transmission paths are generated to represent interactions between one of the objects and the signals on the transmission paths by one of exclusively non-negative values and exclusively non-positive values.
4. The method of claim 1 , wherein the generating a cell value comprises:
extracting one of a single interaction value, a percentile value, and an average of interaction values within a percentile among the interaction values for the set of transmission paths that intersect the selected reconstruction cell.
5. The method of claim 1 , further comprising:
validating a touch candidate by comparing the corresponding cell value to a threshold, the validation indicating presence or absence of one of the objects in the selected reconstruction cell.
6. The method of claim 1 , further comprising:
measuring, by the signal detection arrangement, energy of light that has propagated along the transmission paths inside the panel by internal reflections between a front surface and an opposing surface of the panel, wherein
the front surface defines the touch surface and allows the light to be attenuated by interaction with the objects.
7. A method of detecting objects on a panel, wherein signals are transmitted across the panel such that the objects are allowed to interact with the signals by contact with a touch surface of the panel, said method comprising:
obtaining an output signal from a signal detection arrangement;
processing the output signal to obtain an interaction value for each transmission path such that the interaction between the objects and the signals on the transmission paths is represented by interaction values that are larger and smaller than a target value that represents absence of interaction;
generating a two-dimensional distribution of values representative of the interaction on the touch surface by operating an image reconstruction algorithm on the interaction values for at least a portion of the transmission paths;
identifying one or more touch candidates from the two-dimensional distribution of values, the one or more touch candidates each having a location on the touch surface;
selecting reconstruction cells, from a plurality of reconstruction cells, corresponding to each location of the identified one or more touch candidates on the touch surface, wherein the plurality of reconstruction cells are defined with respect to the touch surface, each of the plurality of reconstruction cells having a given location on the touch surface and being intersected by a respective set of transmission paths for the signals across the touch surface;
generating a cell value for the selected reconstruction cells based on the interaction values for the set of transmission paths that intersect the selected reconstruction cells;
processing each cell value of the selected reconstruction cells to validate the one or more touch candidates; and
detecting objects on the panel based on the validation of the one or more touch candidates;
wherein the cell value is generated as a robust measure of central tendency among at least part of the interaction values for the set of transmission paths.
8. The method of claim 7 , wherein the robust measure of central tendency is computed to represent a median value among said at least part of the interaction values.
9. The method of claim 7 , wherein the generating a cell value is performed for a plurality of selected reconstruction cells within a region of interest on the touch surface.
10. The method of claim 9 , further comprising:
processing the two-dimensional distribution to identify said region of interest.
11. The method of claim 10 , wherein said region of interest is identified in the two-dimensional distribution to contain at least one candidate touch.
12. The method of claim 10 , wherein the region of interest is a coherent region of values that indicate presence of an object.
13. The method of claim 7 , wherein an interaction value, among the interaction values, is generated to represent a change in interaction with respect to a reference value for a corresponding transmission path.
14. The method of claim 7 , further comprising:
measuring, by the signal detection arrangement, energy of light that has propagated along the transmission paths inside the panel by internal reflections between a front surface and an opposing surface of the panel; wherein
the front surface defines the touch surface and allows the light to be attenuated by interaction with the objects.
15. A device for detecting objects on a panel, the objects allowed to interact, by contact with a touch surface of the panel, with signals transmitted across the panel, said device comprising:
at least one processor configured to execute computer-readable instructions to
obtain an output signal from a signal detection arrangement,
process the output signal to obtain an interaction value for each transmission path,
generate a two-dimensional distribution of values representative of the interaction on the touch surface by operating an image reconstruction algorithm on the interaction values for at least a portion of the transmission paths;
identify one or more touch candidates from the two-dimensional distribution of values, the one or more touch candidates each having a location on the touch surface;
select reconstruction cells, from a plurality of reconstruction cells, corresponding to each location of the identified one or more touch candidates on the touch surface, wherein the plurality of reconstruction cells are defined with respect to the touch surface, each of the plurality of reconstruction cells having a given location on the touch surface and being intersected by a respective set of transmission paths for the signals across the touch surface;
generate a cell value for the selected reconstruction cells based on the interaction values for the set of transmission paths that intersect the selected reconstruction cells, the cell value generated as a function of a subset of the interaction values and without tomographic reconstruction,
process each cell value of the selected reconstruction cells to validate the one or more touch candidates; and
detect objects on the panel based on the validation of the one or more touch candidates.
16. A touch-sensitive apparatus including a device according to claim 15 , the touch-sensitive apparatus further comprising:
the panel, wherein the panel is configured to conduct the signals from a plurality of peripheral incoupling points to a plurality of peripheral outcoupling points, thereby defining transmission paths that extend across the touch surface on the panel between pairs of incoupling and outcoupling points;
at least one emitter configured to generate the signals at the incoupling points; and
the signal detection arrangement, wherein the signal detection arrangement is configured to generate an output signal based on detected signals at the outcoupling points.