Multi-touch detection in moisture

1. An input device comprising:

a plurality of sensor electrodes configured for capacitive sensing in a sensing region of the input device;

processing circuitry; and

a memory storing instructions that, when executed by the processing circuitry, cause the input device to:

acquire sensor information about the sensing region via the plurality of sensor electrodes;

generate a first capacitive image of the sensing region based on the sensor information;

determine a set of contiguous regions in the first capacitive image;

select, from the set of contiguous regions, one or more contiguous regions that correspond to valid inputs by:

generating a delta image based on differences between the first capacitive image and a plurality of capacitive images previously acquired for the sensing region;

associating each contiguous region in the set of contiguous regions with one or more pixel values from the delta image; and

determining, for each contiguous region in the set of contiguous regions, whether the contiguous region corresponds with a new input based at least in part on the associated pixel values from the delta image; and

process user inputs associated with the selected contiguous regions.

2. The input device of claim 1 , further comprising:

a circular buffer configured to store a number of capacitive images of the sensing region.

3. The input device of claim 1 , wherein execution of the instructions further causes the input device to:

identify a position of a corresponding input in each of the selected contiguous regions based at least in part on the associated pixel values from the delta image; and

report positional information for the identified position in each of the selected contiguous regions.

4. The input device of claim 1 , wherein execution of the instructions further causes the input device to:

detect that one of the selected contiguous regions is associated with two or more inputs based at least in part on the associated pixel values from the delta image; and

split the detected contiguous region into two or more contiguous regions based on the associated pixel values from the delta image.

5. The input device of claim 1 , wherein execution of the instructions to determine whether the contiguous region corresponds with a new input causes the input device to:

compare the associated pixel values with a threshold value; and

when the associated pixel values exceed the threshold value, selectively associate the contiguous region with a new input based at least in part on a number of contiguous regions identified in a previous capacitive image.

6. The input device of claim 5 , wherein execution of the instructions to selectively associate the contiguous region with a new input causes the input device to:

determine a number of contiguous regions corresponding to valid inputs in the previous capacitive image;

compare the number of contiguous regions with a maximum number (M) of inputs detectable by the input device; and

selectively associate the contiguous region with a new input based at least in part on the comparison.

7. The input device of claim 6 , wherein execution of the instructions further causes the input device to:

identify a set of first bounding boxes indicating respective boundaries of each of the contiguous regions corresponding to valid inputs in the previous capacitive image.

8. The input device of claim 7 , wherein the contiguous region is associated with a new input when the contiguous region does not overlap any of the first bounding boxes and the number of contiguous regions is less than the maximum number of inputs detectable by the input device.

9. The input device of claim 7 , wherein the contiguous region is merged with another contiguous region in the set of contiguous regions when the contiguous region overlaps at least one of the first bounding boxes or the number of contiguous regions is equal to the maximum number of inputs detectable by the input device.

10. The input device of claim 7 , wherein execution of the instructions further causes the input device to:

detect a pinch or zoom gesture when two or more of the first bounding boxes intersect and a first contiguous region in the set of contiguous regions overlaps each of the two or more first bounding boxes.

11. The input device of claim 10 , wherein the first contiguous region is formed from a union of two or more contiguous regions corresponding to valid inputs in the previous capacitive image.

12. The input device of claim 7 , wherein execution of the instructions to select the one or more contiguous regions that correspond to valid inputs further causes the input device to:

generate up to M second bounding boxes around one or more contiguous regions in the set of contiguous regions;

pair each of the second bounding boxes with a respective contiguous region in the set of contiguous regions; and

eliminate any contiguous regions, in the set of contiguous regions, not paired with a respective one of the second bounding boxes.

13. The input device of claim 12 , wherein execution of the instructions to pair each of the second bounding boxes with a respective contiguous region causes the input device to:

detect that a particular contiguous region in the set of contiguous regions overlaps two or more of the second bounding boxes; and

determine that the particular contiguous region coincides with one of the two or more second bounding boxes based on an amount of overlap between the particular contiguous region and each of the two or more second bounding boxes.

14. The input device of claim 12 , wherein execution of the instructions to pair each of the second bounding boxes with a respective contiguous region causes the input device to:

detect that a particular bounding box of the second bounding boxes coincides with two or more contiguous regions in the set of contiguous regions;

determine which of the two or more contiguous regions is most likely to correspond with a valid input based on a shape or amplitude of each of the two or more contiguous regions; and

pair the particular bounding box with the contiguous region that is most likely to correspond with a valid input.

15. The input device of claim 12 , wherein execution of the instructions further causes the input device to:

trim the respective contiguous region paired with each of the second bounding boxes based at least in part on the associated pixel values from the delta image.

16. A method of operating an input device, comprising:

acquiring sensor information about a sensing region via a plurality of sensor electrodes configured for capacitive sensing;

generating a first capacitive image of the sensing region based on the sensor information;

determining a set of contiguous regions in the first capacitive image;

selecting, from the set of contiguous regions, one or more contiguous regions that correspond to valid inputs by:

generating a delta image based on differences between the first capacitive image and a plurality of capacitive images previously acquired for the sensing region;

associating each contiguous region in the set of contiguous regions with one or more pixel values from the delta image; and

determining, for each contiguous region in the set of contiguous regions, whether the contiguous region corresponds with a new input based at least in part on the associated pixel values from the delta image; and

processing user inputs associated with the selected contiguous regions.

17. The method of claim 16 , further comprising:

identifying a position of a corresponding input in each of the selected contiguous regions based at least in part on the associated pixel values from the delta image; and

reporting positional information for the identified position in each of the selected contiguous regions.

18. The method of claim 16 , further comprising:

detecting that one of the selected contiguous regions is associated with two or more inputs based at least in part on the associated pixel values from the delta image; and

splitting the detected contiguous region into two or more contiguous regions based on the associated pixel values from the delta image.

19. The method of claim 16 , wherein determining whether the contiguous region corresponds with a new input comprises:

comparing the associated pixel values with a threshold value; and

when the associated pixel values exceed the threshold value, selectively associating the contiguous region with a new input based at least in part on a number of contiguous regions identified in a previous capacitive image.

20. The method of claim 19 , wherein the selectively associating comprises:

determining a number of contiguous regions corresponding to valid inputs in the previous capacitive image;

comparing the number of contiguous regions with a maximum number (M) of inputs detectable by the input device; and

selectively associating the contiguous region with a new input based at least in part on the comparison.

21. The method of claim 20 , further comprising:

identifying a set of first bounding boxes indicating respective boundaries of each of the contiguous regions corresponding to valid inputs in the previous capacitive image.

22. The method of claim 21 , wherein the contiguous region is associated with a new input when the contiguous region does not overlap any of the first bounding boxes and the number of contiguous regions is less than the maximum number of inputs detectable by the input device, and wherein the contiguous region is merged with another contiguous region in the set of contiguous regions when the contiguous region overlaps at least one of the first bounding boxes or the number of contiguous regions is equal to the maximum number of inputs detectable by the input device.

23. The method of claim 21 , further comprising:

detecting a pinch or zoom gesture when two or more of the first bounding boxes intersect and a first contiguous region in the set of contiguous regions overlaps each of the two or more first bounding boxes.

24. The method of claim 21 , wherein the selecting further comprises:

generating up to M second bounding boxes around one or more contiguous regions in the set of contiguous regions;

pairing each of the second bounding boxes with a respective contiguous region in the set of contiguous regions; and

eliminating any contiguous regions, in the set of contiguous regions, not paired with a respective one of the second bounding boxes.

25. The method of claim 24 , wherein the pairing comprises:

detecting that a particular bounding box of the second bounding boxes coincides with two or more contiguous regions in the set of contiguous regions;

determining which of the two or more contiguous regions is most likely to correspond with a valid input based on a shape or amplitude of each of the two or more contiguous regions; and

pairing the particular bounding box with the contiguous region that is most likely to correspond with a valid input.

26. The method of claim 24 , further comprising:

trimming the respective contiguous region paired with each of the second bounding boxes based at least in part on the associated pixel values from the delta image.

27. A non-transitory computer-readable medium storing instructions that, when executed by processing circuitry of an input device, cause the input device to perform operations comprising:

acquiring sensor information about a sensing region via a plurality of sensor electrodes configured for capacitive sensing;

generating a first capacitive image of the sensing region based on the sensor information;

determining a set of contiguous regions in the first capacitive image;

selecting, from the set of contiguous regions, one or more contiguous regions that correspond to valid inputs by:

generating a delta image based on differences between the first capacitive image and a plurality of capacitive images previously acquired for the sensing region;

associating each contiguous region in the set of contiguous regions with one or more pixel values from the delta image; and

determining, for each contiguous region in the set of contiguous regions, whether the contiguous region corresponds with a new input based at least in part on the associated pixel values from the delta image; and

processing user inputs associated with the selected contiguous regions.