You can edit a selection in various ways through the Select menu. Most of the options in this menu are grayed out until you have actually made a selection using one of the selection tools, as you would expect. Here are some of the most important option available through the Select menu.
All selects the whole of the visible window, putting a selection border around it. (Note that it is best not to use this option if it is your intention to edit the whole of the image. Although the image as it stands may occupy only the visible window, it is possible that at some time you may only have a part of the image visible, the rest stretching outside the window boundaries. In this case the selection will always be restricted to just that part of the image that is visible. It is best, therefore, to select the appropriate layer without making a selection within the layer.
None clears any current selection. (Note that on occasions you may try to add color to an image to no avail, even though you are on the right layer and the layer is visible. It is more than likely that in these cases you have not cleared a selection properly, that is, you have clicked on the screen when a selection tool is active and reduced the selection to a barely visible dot, outside of whose boundaries nothing can be done until the selection is cleared.)
Invert reverses the area currently selected in the visible window. If, for example, you have a small circle selected and you then apply Invert, a selection border will appear around the whole of the visible window in addition to the circle selection. This means that the selection is now the area between the circle border and the outer selection, that is everything in the visible window excluding the area within the original selection.
Feather softens the edges of a selection when color is applied at the selection boundaries. In effect, feathering creates a transition area of increasing transparency, which gives an appearance of gradual, gentle succession from the selected to the unselected pixels.
The Feather radius is set in the Radius box in the "Feather" dialog and is measured in pixels. The greater the radius (2 to 50 is the range) the greater the extent of the feathering.
Note that the effects of using Feather are only seen with colors applied after feathering has been applied to a selection. The immediate effect is merely to expand the selection boundaries in accordance with the radius set by you.
Border takes the current selection as a basis for creating a new selection of a specified width. The original selection is then abandoned. The border width is set in the Width box of the "Border" dialog and is measured both in and out from the boundary of the current selection.
If, for example, you have a circular selection and then you apply a border of 5 pixels, the new selection will consist of a circular band with borders 5 pixels in and five pixels out from the original selection, rather like a ring doughnut.
Smooth reduces the rough edges of a selection. Only the selection outline is affected, not the colors within the selection. In the "Smooth Selection" dialog, set the Radius at a value from 2 to 50 pixels. The higher the radius the greater the smoothing that will occur.
Expand increases a selection by expanding its boundaries outwards. The degree of expansion is determined by the value you enter in the Expand by box in the "Expand" dialog. The range is from 2 to 50 pixels.
Contract decreases a selection by contracting its boundaries inwards. The degree of contraction is determined by the value you enter in the Contract by box in the "Contract" dialog. The range is from 2 to 50 pixels.
Transform Selection is used for dynamic editing of selections and actually activates the Transform Selection tool on the Tools bar (see Transform selection tool).
Grow uses a current selection to select adjacent areas of the same color as the selection. Grow works best when the currently selected area contains a single color.
Similar uses a current selection to select the same color throughout an image. The areas of color need not be adjacent. Similar works best when the currently selected area contains a single color.
Selection to Alpha deletes the whole of the image on the current layer except for any areas you have selected.
Alpha to Selection selects all colored areas on the current layer. On a layer which is otherwise transparent there will be as many selections as there are separate areas of color.
Make Pattern uses the current selection to store a pattern in the "Pattern" dialog. This dialog is called upon by several of the tools, especially the Pattern brush.