Analyze Shape Characteristics of Object¶

Shape analysis outputs numeric properties for an input object (contour or grouped contours), works best on grouped contours.

plantcv.analyze_object(img, obj, mask, filename=False)

returns shape data headers, shape data, image with shape data

• Parameters:
  • img - RGB or grayscale image data for plotting.
  • obj - Single or grouped contour object.
  • mask - Binary image to use as mask for moments analysis.
  • filename - False (default) or image name. If defined print image.
• Context:
  • Used to output shape characteristics of an image, including height, object area, convex hull, convex hull area, perimeter, extent x, extent y, longest axis, centroid x coordinate, centroid y coordinate, in bounds QC (if object touches edge of image, image is flagged).

• Example use:

  • Use In VIS Tutorial
  • Use In NIR Tutorial
  • Use In PSII Tutorial


• Output Data Units:

  • Object Area - object area, pixels (units)
  • Convex-Hull Area - area of convex-hull, pixels (units)
  • Solidity - Ratio, object area divided by convex hull area.
  • Object Perimeter Length - pixels (units)
  • Object Width (extent x) - pixels (units)
  • Object Height (extent y) - pixels (units)
  • Longest Axis - pixels (units)
  • Center of Mass-X - x-coordinate, pixels (units)
  • Center of Mass-Y - y-coordinate, pixels (units)
  • Hull Vertices - number of convex-hull vertices
  • In Bounds - True or False (if False the object is touching top of image)
  • Object Bounding Ellipse Center-X - x-coordinate, pixels (units)
  • Object Bounding Ellipse Center-Y - y-coordinate, pixels (units)
  • Object Bounding Ellipse Major Axis - length of major axis of bounding ellipse, pixels (units)
  • Object Bounding Ellipse Minor Axis - length of minor axis of bounding ellipse, pixels (units)
  • Object Bounding Ellipse Angle - rotation of ellipse in degrees
  • Object Bounding Ellipse Eccentricity - ratio, 'roundness' of object (a perfect circle is 0, ellipse is greater than 0 but less than 1)

Original image

from plantcv import plantcv as pcv

# Set global debug behavior to None (default), "print" (to file), or "plot" (Jupyter Notebooks or X11)

pcv.params.debug = "print"

# Characterize object shapes

shape_header, shape_data, shape_img = pcv.analyze_object(img, objects, mask, "/home/malia/setaria_shape_img.png")

Image with identified objects

Image with shape characteristics