78. Expand or Shrink a Selection
Before You Begin
70 About Making Selections
79 Add Areas Similar to the Current Selection
81 Move the Selection Marquee
83 Select Everything But the Current Selection
After making an initial selection, you can modify it in a variety of ways. You can expand or contract a selection by a specific number of pixels. For example, you could select an object, expand the selection by a few pixels, and after adding a new layer, fill the new expanded selection with some color. Assuming that the new layer is below the layer containing the selected object, you now have an object with a border around it.
Make Initial Selection
Open the image you want to select in the Editor in Standard Edit mode and save it in Photoshop (*.psd) format. In the Layers palette, choose the layer that contains the data you want to select, and then use any selection tool to make the initial selection in the image.
Choose Expand or Contract
Choose Selection, Modify, Expand to expand the selection, or Selection, Modify, Contract to shrink it. The Expand Selection or Contract Selection dialog box appears; both are remarkably similar.
Enter Pixel Amount and Click OK
In the Expand Selection or Contract Selection dialog box, enter the number of pixels you want to expand or contract by, and then click OK. The selection is immediately modified.
You can refine a selection by adding to or subtracting from it, or by creating a new selection from the intersection of two selections, using the buttons on the Options bar for most of the selection tools (Selection Brush excluded). To build a selection, you can switch from selection tool to selection tool freely, using each tool to your advantage when trying to snag a particular area.
View the Result
After you're satisfied with the selection, make changes to the area within the selection, copy or cut its data to another image or layer, or delete the data within the selection. Save the PSD file and then resave the file in JPEG or TIFF format, leaving your PSD image with its layers (if any) intact so that you can return at a later time and make different adjustments if you want.
Suppose that you've applied one of the frame effects to an image, and you decide after the fact that you want to add a mat. You could undo everything and follow the steps in 166 Frame a Photograph to add a mat and a frame in sequence, or you could press Ctrl and click the image thumbnail in the Layers palette, which selects the image area. Save this selection by following the steps in 84 Save a Selection for Reuse. Then shrink the selection by the width of the mat you want, add a feather, and finally subtract this new selection from the saved selection as explained in that task. Reload this modified selection and you have a perfect area that fits just inside your frame, which you can fill with your chosen mat color.
I loved how my daughter and her Grandma Ria looked peeking out of this cardboard box, and I couldn't resist trying to make something of it. So, I selected them and copied them to a new image (File, New, Image from Clipboard.) I returned to the original image, expanded the selection and filled it with red, and then copied and pasted the red selection to the new image (Edit, Paste). The red selection appeared on its own layer, which I moved to the bottom of the layer stack on the Layers palette. This action placed a nice red border around my two "girls." I added a gradient fill layer, placed that layer on the very bottom of the layer stack and added some text. Finally, I added a drop shadow layer style to the text and the red layer, making everything pop off the gradient background.