The Magic Wand tool in Paint.NET is a quick and easy way to select areas of an image that are of a similar color. The results aren't always perfect and they can depend on the type of image that is being worked upon, but it can achieve results that would be impossible or very time consuming to achieve manually.
To use the Magic Wand, when you have set the options appropriately, you just click upon the image and other areas of the image that are a similar color to the clicked point are included within the selection.
The Magic Wand tool shares the same Selection Mode options as the other selection tools, but it also has two other options which are Flood Mode and Tolerance.
The default setting for this option is Replace. In this mode, any existing selections in the document are replaced with the new selection.
When changed to Add (union), the new selection is added to the existing selection. This can be useful if you want to fine tune the selection to include some areas of a different color.
The Subtract mode will remove parts of the original selection that are included within the new selection. Again this can fine tune a selection where areas have been selected that you did not intend to select.
Intersect combines the new and old selections so that only areas that are within both of the selections remain selected.
Finally, Invert (“xor”) adds to the active selection, except when part of the new selection is already selected, in which case those areas are deselected.
This option affects the the scope of the selection that is made. In the Contiguous setting, only areas of a similar color that are connected to the clicked point will be included in the final selection.
When changed to Flood Mode, all areas within the image that are a similar color value are selected meaning that you can have multiple unconnected selections.
Though perhaps not immediately obvious, this is a slider that allows you to change the setting by clicking and/or dragging the blue bar. The Tolerance setting affects how similar a color must be to the color clicked in order to be included within the selection. A low setting means that fewer colors will be considered similar, resulting in a smaller selection. You can increase the Tolerance setting to produce a larger selection that includes more colors.
The Magic Wand can be a very powerful tool allowing you to make complex selections that might not be possible otherwise. Making full use of the various Selection Modes and adjusting the Tolerance setting can give you a reasonable degree of flexibility to fine tune the selection as required.