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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.
- The image contains a ruler which we will use to calibrate our measurements.
- Select the Zoom in tool.
- Drag a rectangle over the ruler so it is enlarged.
- Select the Unit tool.
- Click on the small vertical line above the value 0 and next click on the line above the value 10.
- A dialog box is displayed in which we enter the real length of the unit line: 10 cm.
- Click the Zoom to fit tool.
- Select Binarization in the Binary menu. The following dialog box is displayed:
- 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.
- 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):
- The leaves are now outlined.
- The characteristics of the 6 leaves are displayed in the measurements list, and the mean area and perimeter are displayed in the statistics window:
- Select Hide Binary layer in the Binary menu so you can judge how well the areas fit the leaves.