Skeleton minutiae

Skeleton minutiae, a part of algorithm transparency, are minutiae obtained directly from ridge and valley skeletons during feature extraction, specifically from the last filtering stage of both skeletons. Only skeleton minutiae with exactly one connected ridge (or valley) are considered. Skeleton minutiae from ridge skeleton become endings. Skeleton minutiae from valley skeleton become bifurcations. Skeleton minutiae are subsequently filtered to inner minutiae, have minutia clouds removed, pass through top minutiae filter, and lastly get shuffled before being used to construct edge table.

Visualization

Visualization of skeleton minutiae was constructed from this stage's CBOR data with original fingerprint in the background. Visualization itself is not part of transparency data.

Format

Minutiae are reported as part of an intermediate fingerprint template format only used in algorithm transparency. The intermediate template is a CBOR-encoded data structure:

• size.x - Width of the scaled image, from which the minutiae were extracted.
• size.y - Height of the image.
• minutiae - List of minutiae.

Every minutia has the following fields:

• position.x - Horizontal position of the minutia in pixels. It is zero at the left edge of the image and increases to the right.
• position.y - Vertical position of the minutia in pixels. It is zero at the top of the image and increases towards bottom.
• direction - Angle of the minutia. Ridge endings point towards the ridge. Ridge bifurcations point towards the splitted side of the bifurcation. Angle is measured in radians with zero angle pointing right and increasing clockwise.
• type - Minutia type, either ENDING or BIFURCATION.

Example: 038-skeleton-minutiae.cbor

{
  "size": {
    "x": 388,
    "y": 374
  },
  "minutiae": [
    {
      "position": {
        "x": 146,
        "y": 1
      },
      "direction": 2.5652175,
      "type": "ENDING"
    },
    {
      "position": {
        "x": 169,
        "y": 1
      },
      "direction": 2.8501358,
      "type": "ENDING"
    },
    "... skipped 111 items ...",
    {
      "position": {
        "x": 251,
        "y": 362
      },
      "direction": 3.191551,
      "type": "BIFURCATION"
    },
    {
      "position": {
        "x": 252,
        "y": 372
      },
      "direction": 3.191551,
      "type": "BIFURCATION"
    }
  ]
}