Point Counting

Point counting is a technique to measure the amount of each component present in an image. It consists in laying a grid over the image and counting what is under each grid intersection point.

Point counting is an alternative method to quantify image components stochastically, especially when the contrast between the components is poor or when the image is too complex for using the Object Extraction or Background tool.

Grid types

No grid (manual): This mode allows counting objects in an image manually. Each time you click on an object, it is tagged using a colored point of the selected class in the Manual combo box (at the top of the Class panel).
Note: To delete a point or modify its class, select None in the Manual combo box, select the desired point and use the delete command from the contextual menu (right-click).
Random grid: The intersection points are in a uniform random grid, which means that the points are selected randomly. This is the default grid.
Recursive grid: The intersection points are located in a rectangular grid, which is subdivided recursively.

Starting a counting

Make your own list of classes with the Class Editor.
Press the Start button.
In the Point Counting Properties window:
- Grid type: Select a grid (see Grid types above).
- Counting limitation: If necessary, select a limitation of the counting to a background or to a specified object class (see Background or Object Extraction).
  For showing an alert message after a certain number of points, check the box and enter a number.
- Area: Select the area of the counting (see Area Editor).
- Finally, click OK to start the counting.
For displaying several images simultaneously with a particular zoom factor for each image, create different views (see Multiview).
Press the button of the class (or the related keystroke) that matches what is in the center of the pointer. Repeat this operation until the counting is statistically representative (see Stopping the counting below).
Display the results with the Data Viewer.

Reset: Reset the current session.

Floating Bar: Open the Class panel in an independent window. Closing the window will replace the panel in the initial state.

Note: Having the list next to the pointer is more comfortable, because you can focus your eyes on the center of the screen during the counting.

Center Pointer: Replace the pointer in the center of the screen.

The two first Arrow Buttons allow going from a point to another chronologically. The third one allows getting a new position (it can also be used for bypassing a position).

Refresh: Refresh the percentages (e.g. when points have been deleted).

Note: Classes can be added, removed or merged even while counting.

Modifying the class of a point

Navigate with the Arrow Buttons and then click on the desired class button. It is also possible to change the class of a point by double-clicking on the point or by selecting Properties in the contextual menu.

Stopping the counting

There are two ways of stopping the counting:

The first one is simply by fixing a limit of points in the Point Counting Properties. An alert message appears when reaching the limit.
The second one is by observing a stochastic criterion in the Evolution Plot (see image below). When the percentages are getting stable in the plot, the counting can be stopped.

Point Counting preferences

Default grid type and default point limit can be changed in the Point Counting Properties when starting a new counting.

Note: To display the preferences, open the Project Preferences window and select Point Counting.