Negative Pixel Compensation

• US 20110074725A1
• Filed: 09/30/2009
• Published: 03/31/2011
• Est. Priority Date: 09/30/2009
• Status: Active Grant

• Current Assignee: Apple Inc.
• Original Assignee: Apple Inc.
• Inventors: WESTERMAN, Wayne Carl, O'Connor, Sean Erik
• Granted Patent: US 8,749,512 B2
• Time in Patent Office: Days
• US Class Current: 345/174
• 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 3/041 Digitisers, e.g. for touch screens or touch pads, characterised by the transducing means
• CPC Class Codes: G06F 3/04186 Touch location disambiguation
• CPC Class Codes: G06F 3/044 by capacitive means
• 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. The panel 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 panel can reconstruct a captured touch image to remove negative pixel values indicative of the negative pixel effect and compute a composite image from the captured image and the reconstructed image to replace the captured image. In addition or alternatively, the panel can reconstruct a captured touch image to remove negative pixel values indicative of the negative pixel effect and replace the captured image with the reconstructed image.

Claims

1. A method comprising:

reconstructing a touch image from a touch sensor panel; and

compensating the touch image for a negative pixel effect by computing a composite image of the touch image and the reconstructed touch image, weighting of the touch image and the reconstructed touch image in the composite image being determined based on a magnitude of the negative pixel effect.

2. The method of claim 1, wherein reconstructing the touch image comprises adjusting the touch image to remove touch values affected by the negative pixel effect.

3. The method of claim 1, wherein compensating the touch image comprises:

determining multiple parameters associated with the negative pixel effect;

combining the determined parameters to provide an image mixing factor;

weighting the touch image and the reconstructed touch image using the image mixing factor; and

computing the composite image from the weighted touch image and the weighted reconstructed touch image.

4. The method of claim 3, wherein determining the multiple parameters comprises:

determining a number of fingers captured in the touch image as touching the touch sensor panel, wherein one finger indicates absence of the negative pixel effect and more than one finger indicates presence of the negative pixel effect; and

ending the method if the determination indicates one finger touching the touch sensor panel.

5. The method of claim 3, wherein determining the multiple parameters comprises:

determining an overcompensation ratio indicating a grounding condition of a user touching the touch sensor panel,

wherein, if the determined overcompensation ratio is greater than a threshold, the user is grounded and the negative pixel effect does not apply.

6. The method of claim 3, wherein determining the multiple parameters comprises:

determining a negative pixel ratio indicating a grounding condition of a user touching the touch sensor panel,

wherein, if the determined negative pixel ratio is less than a threshold, the user is grounded and the negative pixel effect does not apply.

7. A touch sensor panel comprising:

multiple pixels configured to generate a touch image; and

a processor in communication with the pixels and configured to

determine a negative pixel effect on the touch image,

reconstruct the touch image, and

compute a composite touch image by combining weighted pixel values of the touch image with weighted pixel values of the reconstructed touch image.

8. The touch sensor panel of claim 7, wherein determining the negative pixel effect comprises determining whether more than one finger is touching the panel according to the touch image, the determination of more than one finger being indicative that the negative pixel effect is present.

9. The touch sensor panel of claim 7, wherein reconstructing the touch image comprises correcting pixel values of the touch image subject to the negative pixel effect.

10. The touch sensor panel of claim 7, wherein computing the composite touch image comprises calculating an image mixing factor indicative of the magnitude of the negative pixel effect as a weight for the touch image and the reconstructed touch image.

11. The touch sensor panel of claim 7 incorporated into at least one of a mobile telephone, a digital media player, or a computer.

12. A method comprising:

computing at least one parameter indicative of a grounding condition of a user of a touch sensor panel;

comparing the computed parameter to a threshold to determine whether a negative pixel effect applies to the touch sensor panel; and

based on the comparison, compensating a touch image of the touch sensor panel for the negative pixel effect by replacing the touch image with a reconstructed touch image having the negative pixel effect substantially reduced.

13. The method of claim 12, wherein computing the parameter comprises computing an overcompensation ratio, wherein a higher overcompensation ratio indicates that the user is grounded.

14. The method of claim 12, further comprising:

computing a second parameter if the computed parameter indicates that the user is not grounded; and

comparing the second parameter to another threshold to determine whether the negative pixel effect applies to the touch sensor panel.

15. The method of claim 14, wherein the second parameter comprises a negative pixel ratio, a lower negative pixel ratio indicating that the user is grounded.

16. The method of claim 12, further comprising:

determining whether more than one finger of the user is touching the touch sensor panel; and

if not, omitting the computing, comparing, and compensating.

17. A touch sensor panel comprising:

multiple pixels configured to generate a touch image; and

a processor in communication with the pixels and configured to

determine whether the touch image indicates a negative pixel effect, and

based on the determination, compensate the touch image for the negative pixel effect by replacing the touch image with a reconstructed touch image in which the negative pixel effect is reduced.

18. The touch sensor panel of claim 17, wherein determining whether the touch image indicates the negative pixel effect comprises determining whether more than one finger is captured in the touch image.

19. The touch sensor panel of claim 17, wherein determining whether the touch image indicates the negative pixel effect comprises determining whether an overcompensation ratio indicates grounding of a user of the touch sensor panel.

20. The touch sensor panel of claim 17, wherein determining whether the touch image indicates the negative pixel effect comprises determining whether a negative pixel ratio indicates grounding of a user of the touch sensor panel.

21. The touch sensor panel of claim 17, wherein compensating the touch image comprises replacing the touch image if the negative pixel effect is determined and to keep the touch image otherwise.

22. 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:

compute at least one parameter indicative of the negative pixel effect in the touch sensor panel; and

compensate pixel values of a touch image generated by the touch sensor panel for the negative pixel effect by applying the computed parameter to the pixel values.

23. The computer readable storage medium of claim 22, wherein the parameter is a touch magnitude computed as a sum of the pixel values above a particular threshold.

24. The computer readable storage medium of claim 22, wherein the parameter is an overcompensation ratio computed as a ratio of a sum of positive pixel values in a reconstructed image to a sum of positive pixel values in the touch image, the reconstructed image being formed from the touch image absent negative pixel values.

25. The computer readable storage medium of claim 22, wherein the parameter is a negative pixel ratio computed as a ratio of negative pixel values to positive pixel values in the touch image.