Analyze blob geometry🔗

Calculates geometric properties for labeled objects. All measurements are made in world coordinates.

Inputs🔗

  • labels: A labeled image. Each connected blob in the output image is marked with a distinct numeric label. Pixels that belong to the first detected blob are ones, the pixels that belong to the second one with twos and so on. Background is zero.

  • aligned: If this flag is true, the size, upperLeft, upperRight, lowerLeft, lowerRight and frame output parameters are calculated after aligning the bounding box of a blob according its major axis. Otherwise, the measurements are made from a bounding box that is aligned to the x and y axes of the world coordinate system.

  • preferredAngle: If aligned measurements are enabled, this parameter determines the preferred direction of the blob’s aligned x axis in the world coordinate system, in degrees. For example, if the blob is approximately horizontally aligned, setting preferredAngle to 0 would ensure its frame would be attached to the upper left corner. Setting preferredAngle to 180 would attach the frame to the lower right corner and turn the coordinate system upside down.

Outputs🔗

  • area: The number of pixels on each blob. A N-by-1 matrix.

  • centroid: The center-of-mass point (x,y) for each blob. A N-by-2-matrix.

  • upperLeft: The upper left corner of the blob’s bounding box. Each row in the matrix contains the (x,y) coordinates of a point. A N-by-2 matrix.

  • upperRight: The upper right corner of the blob’s bounding box.

  • lowerLeft: The lower left corner of the blob’s bounding box.

  • lowerRight: The lower right corner of the blob’s bounding box.

  • majorDirection: Normalized major direction vector (x,y) for each blob. A N-by-2 matrix.

  • minorDirection: Normalized minor direction vector (x,y) for each blob. A N-by-2 matrix.

  • majorVariance: Relative size of each blob along the major direction vector in a statistical sense. A N-by-1 matrix.

  • minorVariance: Relative size of each blob along the minor direction vector in a statistical sense. A N-by-1 matrix.

  • majorMinorRatio: Ratio of major and minor variances. A N-by-1 matrix.

  • size: The size of the bounding box of each detected blob in world coordinates (width, height). A N-by-2 matrix.

  • frame: A coordinate frame for each detected blob. Each frame is a 4-by-4 matrix totaling in a 4N-by-4 matrix.