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Balance of sensitivity and ghost reports

This topic describes the balance of sensitivity and ghost reports for multi-touch devices. This balance is defined through the ROC curve on the false positives (ghost reports) and the false negatives (missed reports). The balance point is determined by a combination of a judicious selection of the signal thresholds and an accurate baseline removing process.

There can be multiple levels of thresholds for events such as finger touch down, up, and non-finger detection. Furthermore, the thresholds may be region dependent if such information can be properly fed back to the firmware.

The baseline removing process should promptly update the baseline to minimize the perceived noise level for the purpose of contact detection.

Partners should see How to Run the Windows HCK Tests for Touch and Pen Devices.

When the activation threshold is too low

Failure Cases when the activation threshold is set too low:

  • Ghost points – unwanted triggering of links due to sensitivity being too high.

  • Software keyboard – unwanted keys tapped.

When the activation threshold is too high

Failure Cases when the activation threshold is set too high:

  • Loss of contacts – dragging of a contact can be lost due to sensitivity being too low at certain areas.

  • Change of contact ID – dragging of a contact changes the contact ID, causing the app to interpret a different gesture.

  • Software keyboard – false double taps.

 

 

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