You can move a selection border around an image, hide a selection border, and invert a selection so that the previously unselected part of the image is selected.
To move the selection itself, not the selection border, use the Move tool. See Move a selection.
from
the options bar, and position the pointer inside the selection border.
The pointer changes 
to indicate
that you can move the selection.
You can apply geometric transformations to change the shape of a selection border. (See Apply transformations.)
Do one of the following:
You can use this option to select an object placed against a solid-colored background. Select the background using the Magic Wand tool and then invert the selection.
You can use the selection tools to add to or subtract from existing pixel selections.
Before manually adding to or subtracting from a selection, you may want to set the feather and anti-aliasing values in the options bar to the same settings used in the original selection.
Select the Add To Selection option 
in
the options bar, and drag to add to the selection.
Hold down Shift, and drag to add to the selection.
A plus sign appears next to the pointer when you’re adding to a selection.
Select the Subtract From Selection option 
in
the options bar, and drag to intersect with other selections.
Hold down Alt (Windows) or Option (Mac OS), and drag to subtract another selection.
A minus sign appears next to the pointer when you’re subtracting from a selection.
Select the Intersect With Selection option 
in the options bar, and drag.
Hold down Alt+Shift (Windows) or Option+Shift (Mac OS) and drag over the portion of the original selection you want to select.
An “x” appears next to the pointer when you’re selecting an intersected area.
The border is increased or decreased by the specified number of pixels. (Any portion of the selection border running along the canvas’s edge is unaffected by the Expand command.)
The Border command lets you select a width of pixels inside and outside an existing selection border. This can be useful when you need to select a border or band of pixels around an image area, rather than the area itself, for example to clean up a halo effect around a pasted object.
The new selection frames the original selected area, and is centered on the original selection border. For example, a border width of 20 pixels creates a new, soft-edged selection that extends 10 pixels inside the original selection border and 10 pixels outside it.
Do one of the following:
To increase the selection in increments, choose either command more than once.
You cannot use the Grow and Similar commands on Bitmap mode images or 32‑bits-per-channel images.
For each pixel in the selection, Photoshop examines the pixels around it, to the distance you specify in the radius setting. If more than half of these surrounding pixels are selected, the pixel remains in the selection, and the unselected pixels around it are added to the selection. If less than half the surrounding pixels are selected, the pixel is removed from the selection. The overall effect is to reduce patchiness and smooth sharp corners and jagged lines in the selection.
The Select and Mask option improves the quality of selection edges, letting you extract objects with ease. You can also use Select and Mask to refine a layer mask. (See Adjust mask opacity or edges.)
Click Select and Mask in the options bar, or choose Select > Select and Mask.
For details, see Select and Mask.
You can smooth the hard edges of a selection by anti-aliasing and by feathering.
Anti-aliasing
Smooths the jagged edges of a selection by softening the color transition between edge pixels and background pixels. Because only the edge pixels change, no detail is lost. Anti-aliasing is useful when cutting, copying, and pasting selections to create composite images.
Anti-aliasing is available for the Lasso tool, the Polygonal Lasso tool, the Magnetic Lasso tool, the Elliptical Marquee tool, and the Magic Wand tool. (Select a tool to display its options bar.)
You must specify this option before using these tools. After a selection is made, you cannot add anti-aliasing.
Feathering
Blurs edges by building a transition boundary between the selection and its surrounding pixels. This blurring can cause some loss of detail at the edge of the selection.
You can define feathering for the Marquee tools, the Lasso tool, the Polygonal Lasso tool, or the Magnetic Lasso tool as you use the tool, or you can add feathering to an existing selection.
Feathering effects become apparent only after you move, cut, copy, or fill the selection.
A small selection made with a large feather radius may be so faint that its edges are invisible and thus not selectable. If you see the message “No pixels are more than 50% selected,” either decrease the feather radius or increase the size of the selection. Or click OK to accept the mask at its current setting and create a selection in which you cannot see the edges.
A. Selection with no feather, same selection filled with pattern B. Selection with feather, same selection filled with pattern
When you move or paste an anti-aliased selection, some of the pixels surrounding the selection border are included with the selection. This can result in a fringe or halo around the edges of the pasted selection. These Layer > Matting commands let you edit unwanted edge pixels:
Color Decontaminate replaces background colors in fringe pixels with the color of fully selected pixels nearby.
Defringe replaces the color of fringe pixels with the color of pixels farther in from the edge of the selection that lack the background color.
Remove Black Matte and Remove White Matte are useful when a selection is anti‑aliased against a white or black background and you want to paste it onto a different background. For example, anti‑aliased black text on a white background has gray pixels at the edges, which are visible against a colored background.
You can also remove fringe areas by using the Advanced Blending sliders in the Layer Styles dialog box to remove, or make transparent, areas from the layer. In this case, you would make the black or white areas transparent. Alt-click (Windows) or Option-click (Mac OS) the sliders to separate them; separating the sliders allows you to remove fringe pixels and retain a smooth edge.
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