Negative Pixel Compensation

• US 20110175823A1
• Filed: 01/21/2010
• Published: 07/21/2011
• Est. Priority Date: 01/21/2010
• Status: Active Grant

• Current Assignee: Apple Inc.
• Original Assignee: Apple Inc.
• Inventors: VIETA, William Matthew
• Granted Patent: US 8,581,879 B2
• Time in Patent Office: Days
• US Class Current: 345/173
• CPC Class Codes: G06F 2203/04104 Multi-touch detection in digitiser, i.e. details about the simultaneous detection of a plurality of touching locations, e.g. multiple fingers or pen and finger
• CPC Class Codes: G06F 3/0412 Digitisers structurally integrated in a display
• CPC Class Codes: G06F 3/0418 for error correction or compensation, e.g. based on parallax, calibration or alignment
• CPC Class Codes: G06F 3/04182 Filtering of noise external to the device and not generated by digitiser components
• CPC Class Codes: G06F 3/0443 using a single layer of sensing electrodes
• CPC Class Codes: G06F 3/0446 using a grid-like structure of electrodes in at least two directions, e.g. using row and column electrodes

Abstract

Negative pixel compensation in a touch sensor panel is disclosed. A method can compensate for a negative pixel effect in touch signal outputs due to poor grounding of an object touching the panel. To do so, the method can include determining at least one bound for a negative pixel compensation factor based on touch signal values, estimating the compensation factor within the determined bound based on the touch signal values that are negative, where the negative values indicate the presence of the negative pixel effect, and applying the estimated compensation factor to the touch signal outputs to compensate the touch signal values for the negative pixel effect.

Claims

1. A method comprising:

determining at least one bound for a compensation factor based on touch image values;

estimating the compensation factor within the determined bound based on the touch image values that are negative; and

applying the estimated compensation factor to the touch image values to compensate the touch image values.

2. The method of claim 1, wherein determining the at least one bound comprises:

determining an upper bound for the compensation factor based on at least one of a maximum attainable touch image value or a sum of expected touch image values; and

determining a lower bound for the compensation factor to be about zero.

3. The method of claim 1, wherein estimating the compensation factor comprises:

estimating a compensation factor for each negative touch image value;

calculating a weight factor for each estimated compensation factor; and

applying the calculated weight factors to the corresponding estimated compensation factors to produce the compensation factor within the determined bound.

4. The method of claim 3, wherein calculating the weight factor comprises:

calculating a difference between the corresponding negative touch image value and zero; and

associating the weight factor with the calculated difference.

5. The method of claim 3, wherein calculating the weight factor comprises:

calculating a probability of the corresponding compensation factor adjusting the corresponding negative touch image value to zero; and

associating the weight factor with the calculated probability.

6. The method of claim 1, wherein applying the estimated compensation factor comprises:

calculating correction image values indicative of correction to be made to the touch image values; and

adding a product of the estimated compensation factor and the calculated correction image values to the touch image values.

7. The method of claim 1, comprising subtracting noise bias from the touch image values.

8. The method of claim 1, comprising applying a scale factor to at least one of the touch image values or the compensated touch image values for image consistency.

9. The method of claim 1, wherein the touch image values indicate a grounding condition.

10. A method comprising:

analyzing negative pixel values of a touch image to determine a compensation factor;

applying the determined compensation factor to the touch image to produce a compensated image absent substantially all the negative pixel values; and

selectively scaling the compensated image or the touch image to provide image display consistency.

11. The method of claim 10, wherein selectively scaling the compensated image or the touch image comprises scaling the compensated image so that an overall energy of the compensated image is substantially the same as an overall energy of the touch image.

12. The method of claim 11, wherein scaling the compensated image comprises:

choosing a scale factor that scales high pixel values of the compensated image to high pixel values of the touch image; and

applying the scale factor to all of the pixel values of the compensated image.

13. The method of claim 10, wherein selectively scaling the compensated image or the touch image comprises scaling the touch image so that an overall intensity of the touch image is substantially the same as an overall intensity of the compensated image.

14. The method of claim 13, wherein scaling the touch image comprises:

choosing a scale factor that scales high pixel values of the touch image to high pixel values of the compensated image; and

applying the scale factor to all of the pixel values of the touch image.

15. A touch sensitive device comprising:

a touch sensor panel comprising multiple touch locations for sensing a touch on the panel; and

a processor in communication with the panel and configured to

capture an image of the sensed touch,

identify negative values in the captured image,

determine a bound of a compensation factor based on the identified negative values for adjusting the captured image,

estimate the compensation factor within the determined bound, and

adjust the identified negative values to about zero using the estimated compensation factor.

16. The device of claim 15, wherein adjusting the identified negative values is based on a nonlinear relationship between the captured image and the compensation factor.

17. The device of claim 15, wherein adjusting the identified negative values is based on a linear relationship between the captured image and the compensation factor.

18. The device of claim 15 incorporated into at least one of a mobile telephone, a digital media player, or a personal computer.

19. A method comprising:

determining at least one characteristic associated with a touch sensor panel; and

selectively applying negative pixel compensation to an image captured by the panel based on compatibility of the compensation with the determined characteristic.

20. The method of claim 19, wherein selectively applying the negative pixel compensation comprises:

selecting at least one of negative pixel compensation based on a maximum touch signal that can be sensed by the panel or negative pixel compensation based on a sum of touch signals expected in an image free of negative pixels; and

applying the selected negative pixel compensation to pixels in the captured image.

21. The method of claim 19, wherein the characteristic is panel design.

22. The method of claim 19, wherein the characteristic is touch type.

23. A computer readable storage medium having stored thereon a set of instructions for compensating for a negative pixel effect in a touch sensor panel, that when executed by a processor causes the processor to:

determine a bound for a compensation factor based on values of a touch image captured by the panel;

estimate the compensation factor within the determined bound based on the touch image values that are negative, indicative of the negative pixel effect; and

apply the estimated compensation factor to the touch image values to compensate for the negative pixel effect.

24. The medium of claim 23, wherein the processor applies the estimated compensation factor to the negative touch image values to set the negative touch image values to about zero.

25. The medium of claim 23, wherein the processor applies the estimated compensation factor to the touch image values that are positive to boost the positive touch image values in a positive direction.