FAST (Features from Accelerated Segment Test)

• It's a fast corner detection method often used in real-time applications due to its speed and simplicity.

 

 

To determine if a pixel p is a corner, FAST uses:

• A circle of 16 pixels around the candidate pixel p.
• These pixels are tested to see if a segment of N contiguous pixels on the circle are all brighter or all darker than p by a threshold.

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• Select 4 key pixels around p (in this example: pixels 1, 5, 9, 13).
• Check any 3 out of these 4 first:
  • If not enough contrast, skip (early rejection).
  • If contrast is good, check the full circle of 16 pixels.
• If at least 12 contiguous pixels are all brighter or all darker than p, then:
  • Pixel p is classified as a corner.

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•  Why is this fast?

• Early rejection: Only a few checks are needed in most cases.
• It reduces computation by quickly rejecting non-corners before checking all 16 pixels.