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Automatic measurement of areas of leaves.
In this task Able Image Analyser will measure areas of objects in the image.
Open the file "leaves.jpg".
Spatial Calibration procedure
- To perform scale calibration, select "Spatial Calibration" from Tools menu or press “Spatial calibration” button (left-most button, marked with cross). New dialog appears.
- There is a scale 5 centimeters long in the right bottom part of the image. Left click on the zero of this scale. Left click on 5 in the scale.
- Distance (in pixels) between those two points appears in Spatial Calibration dialog. Now you have to enter number of real world units. In our case enter 5, because the scale is 5 centimetres long.
- Now you have Conversion factor. You can save it to the file, so you won’t have to calibrate the image again other time. Press OK.
If you want computer to automatically count/measure objects, you have to define what is object and what it background of the image. The simplest way of binarisation of the image is thresholding.
Binarisation of the image
Hint: If your image has dark background and light objects then you have to invert colors before Thresholding. Use "Invert" from Image menu.
- Select "Threshold" from the Binary menu. New dialog appears. Click, hold and move mouse in grayscale histogram to change threshold level.
- When all objects are dark and background is white you selected correct threshold. Click OK.
- Result of the operation is black and white image. Objects are represented by black color, background by white color.
Analysis of objects
- Select "Analyse objects" from Binary menu. Window with new options appears:
- Objects with pixel size less than "Minimum particle size" and more than "Maximum particle size" won’t be included in results. It is useful that you select min. particle size more than 1 to get rid of binarisation induced noise. In our example 80 is selected to exclude label in the image.
- When you click OK, it takes some time to analyse the image. Rough results are shown in the message window: "60 objects found, 6 objects meet criteria". If you had "Show outlines" option checked new image with outlines of object appears.
- Detailed results are stored in Spreadsheet (menu Tools->Spreadsheet or click second icon from the left in bottom toolbar). Object number as it appears in outline image is in column A. Columns B and C show average x and y coordinates of pixels representing object. Column D shows true (calibrated) areas of objects.
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