Apart of pixel classification perClass Mira provides object segmentation. In order to segment objects (connected components), one needs to set one or more classes as "foreground":
1. In the class list, use right click to open the context menu on the desired class and select Set class as foreground (or press F key)
2. On the toolbar, press the Objects button (or press O key)
Selected class/classes will be segmented out and each connected component will be visualized with a randomly selected color.
You may notice that small objects got removed from the segmentation result. The minimum size of accepted objects is adjustable in the Objects pannel or via Classification / Set minimum objects size menu.