How to Compute the Area of Irregular Shapes using ImageJ ?

The ImageJ is an open source software that is provided for free by National Institutes of Health (US), and it is used widely in the world.

The ImageJ is a handy tool that can be used in many fields such as the area of a cell (biology), the area of a river (geography), the size of a hole in the material, the area of a leave. It can be used to compute the area for a macro or micro image.

Demo of Using ImageJ on a Irregular Circle

The traditional method is to measure the diameter using a ruler. However, in most cases, the center of the circle cannot be found. ImageJ can then be very helpful. You take the picture, compute its area then compute the equivalent diameter, which is effective and accurate.

Click The fifth button under dropdown menu (Straight) to select the known distance in the picture then set the scale to tell the ImageJ the real distance.

Set scale.

The default unit of distance is mm.

Convert the image to 8-bit (which is black and white). This will convert the image to grayscale from 0 to 255.

Change the threshold of the grayscale.

Choose Over/Under mode, scroll until the green region covers the entire target shape. Click apply to continue.

The shape now turns into black and white, with its obvious boundary shown.

Choose the ‘Wand’ button and the target boundary of the shape will be recognized.

Click the target shape (black), ImageJ will mark the boundary in yellow line.

Choose the ‘Measure’ from the ‘Analyze’ sub menu..

The result will be shown immediately. The area is in the unit of mm, so that you can convert to a approximate diameter which is around 137 mm.

Click HERE to download the software ImageJ.

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