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Automatic measurement of leaf area

  • Open image file leaves.png, which is present in the Digimizer\Sample Images subfolder in the My Documents folder.
  • Select Contrast autofix in the Image menu. This will automatically maximize the contrast in the image.

    Image of leaves

  • The image contains a ruler which we will use to calibrate our measurements.
  • Select the Zoom in tool.

    Zoom In button

  • Drag a rectangle over the ruler so it is enlarged.
  • Select the Unit tool.

    Unit tool button

  • Click on the small vertical line above the value 0 and next click on the line above the value 10.

    Calibrate using the ruler in the image

  • A dialog box is displayed in which we enter the real length of the unit line: 10 cm.

    Unit dialog box

  • Click the Zoom to fit tool.

    Zoom to fit button

  • Select Binarization in the Binary menu. The following dialog box is displayed:

    Histogram

  • The dialog box displays a histogram of gray levels. A red line indicates the default threshold value.
  • Click Preview. All gray levels below the threshold value will become red (indicating an object), those above white (indicating background).
  • Click OK to accept the threshold value.

    Binarized image

  • Select Analyze Objects in the Binary menu. Complete the dialog box as follows (a minimum area of 3 cm2 is required for an object to be identified as a leaf):

    Analyse objects dialog box

  • The leaves are now outlined.

    Outlined leaves

  • The characteristics of the 6 leaves are displayed in the measurements list, and the mean area and perimeter are displayed in the statistics window:

    Measurements list and statistics

  • Select Hide Binary layer in the Binary menu so you can judge how well the areas fit the leaves.

    Leaves with outline