How Touchscreens Use Math to Recognize Your Fingers
Apple's patent on using mathematical ellipses to track and identify individual fingers and palms on a touch-sensitive surface.
Original patent title: “Ellipse fitting for multi-touch surfaces”
Apple's patent on using mathematical ellipses to track and identify individual fingers and palms on a touch-sensitive surface. Granted to Apple Inc in 2010 with 38 claims and 93 forward citations, and it is expected to expire in 2027.
Coverage
What does this patent actually cover?
This patent describes a method for a touchscreen to interpret raw electrical data as distinct physical objects. It takes a 'proximity image'—a grid of data from electrodes—and groups nearby pixels together to represent a touch. The system then mathematically fits an ellipse to these pixel groups to estimate the shape, size, and orientation of the finger or palm. By tracking these ellipses over time, the device can distinguish between a thumb and a fingertip or detect if a hand is resting on the screen.
The gap
What does this patent NOT cover?
- Does not cover touch detection methods that do not use ellipse fitting (e.g., simple centroid or bounding box tracking).
- Does not cover hardware that lacks a proximity-sensing electrode grid.
- Does not cover software gestures that are not derived from the calculated ellipse parameters.
These exclusions are unique to PatentBrief — derived from the actual claim language, not patent-office boilerplate.
Key facts
What made this novel
Instead of treating a touch as a single point (an X,Y coordinate), the inventors treated it as a shape with orientation, using eigenvectors and eigenvalues to calculate the ellipse that best fits the contact area.
The Patent Drawing
Schematic visualization of the patent's claim structure. Hand-drawn diagrams in progress for each landmark patent.
Where you've seen this
Real-world examples
Apple MacBook trackpads
iPhone and iPad multi-touch displays
Modern laptop touchscreens with palm rejection
Why it matters
The bigger picture
This technology was foundational for the transition from simple single-touch screens to the sophisticated multi-touch interfaces found in modern smartphones and trackpads. By allowing the software to 'understand' the difference between a finger and a palm, it enabled features like palm rejection, which prevents accidental clicks while typing.
Filed
February 22, 2007
Granted
October 12, 2010
Market context
Who's building on this
Companies in this space
Apple continues to refine these methods in their latest trackpad and display hardware. Other major consumer electronics manufacturers, including Samsung and Microsoft, utilize similar proximity-sensing and shape-fitting algorithms to manage multi-touch input and palm rejection.
Market impact
This patent helped define the standard for high-fidelity multi-touch interaction. It provided a technical roadmap for manufacturers to move beyond simple 'tap' interfaces toward complex, ergonomic input devices that can handle multiple simultaneous contacts without error.
Claim 1 — Plain English
What this patent covers
This patent describes a method for a touchscreen to interpret raw electrical data as distinct physical objects. It takes a 'proximity image'—a grid of data from electrodes—and groups nearby pixels together to represent a touch. The system then mathematically fits an ellipse to these pixel groups to estimate the shape, size, and orientation of the finger or palm. By tracking these ellipses over time, the device can distinguish between a thumb and a fingertip or detect if a hand is resting on the screen.
The clever bit
Instead of treating a touch as a single point (an X,Y coordinate), the inventors treated it as a shape with orientation, using eigenvectors and eigenvalues to calculate the ellipse that best fits the contact area.
What it does not cover
- Does not cover touch detection methods that do not use ellipse fitting (e.g., simple centroid or bounding box tracking).
- Does not cover hardware that lacks a proximity-sensing electrode grid.
- Does not cover software gestures that are not derived from the calculated ellipse parameters.
Patent timeline
Application submitted to the patent office
Application published, typically 18 months after filing
Patent officially issued
Patent enters public domain
PatentBrief Score
Impact Score
High impact
Citation count
39/40
Highly cited
Claim breadth
20/20
Very broad protection
Recency
5/20
Granted 10–20 years ago
Assignee scale
20/20
Major company or institution
PatentBrief Impact Score — based on citation count, claim breadth, recency, and assignee scale. Not a legal assessment.
Heuristic Value Estimate
What this patent might be worth
$86K – $276K
Midpoint $173K · expired or expiring · industry ×1.6
Heuristic only — blends forward/backward citation counts, claim scope, time remaining, litigation history, and CPC-derived industry baseline. Real valuations need a professional appraisal.
Patent Claims
0 independent claims · 1 dependent
Claims are the legal boundaries of the patent. An independent claim stands alone. A dependent claim adds limitations to its parent, narrowing — but not broadening — the scope.
The original legal language
Original claims
38 claims as filed with the patent office.
Concepts involved
Citations
Patent lineage
Cite this patent
Westerman, W., & Elias, J. G. (2010). How Touchscreens Use Math to Recognize Your Fingers (U.S. Patent No. 7,812,828). U.S. Patent and Trademark Office. https://patentbrief.org/patent/us/7812828/ellipse-fitting-for-multi-touch-surfaces
Auto-generated from the patent record. Double-check author order and the issue date against the official USPTO document before submitting.
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Common Questions
Frequently Asked Questions
What does How Touchscreens Use Math to Recognize Your Fingers cover?
Apple's patent on using mathematical ellipses to track and identify individual fingers and palms on a touch-sensitive surface.
Who owns patent US 7812828?
Apple Inc owns this patent, granted in 2010.
When does this patent expire?
This patent is expected to expire on February 22, 2027, when the invention enters the public domain.
What is patent US 7812828 cited by?
This patent has been cited by 93 later patents that build on its ideas.
What problem does this patent solve?
This technology was foundational for the transition from simple single-touch screens to the sophisticated multi-touch interfaces found in modern smartphones and trackpads. By allowing the software to 'understand' the difference between a finger and a palm, it enabled features like palm rejection, which prevents accidental clicks while typing.
What does this patent NOT cover?
Does not cover touch detection methods that do not use ellipse fitting (e.g., simple centroid or bounding box tracking).
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