Graphics - The selection tool

The purpose of using a selection tool is to highlight an area of an image so you can edit it. You may want to crop an image, replace a colour or copy an outline. What most users fail to realise is that once an image has been selected, it can be reshaped, resized and subjected to a wide range of other operations.

Selection is such an important aspect of image manipulation that most packages come with at least two or three items on the toolbar to perform various types of selection - and these can be customised further. Examples include the Lasso, Wand, and Mask tools.

The simplest is the rectangular selection tool (also called a Marquee in Photoshop) and typically it appears as a small rectangle on the toolbars of most programs. The procedure for using the tool is also similar: click on the image and hold down the button while dragging. Where you start and let go of the button will determine the far corners of the selection. The program will draw a highlighted line around the selected area (don't worry, this won't appear on the final image).

The Imaging for Windows program that ships with Windows has the most basic version of the tool. You can use this to select parts of an image for copying/cutting. Compared with most other image editing programs, it is very limited. To crop an image you have to select the image, copy the selection to the clipboard, close the existing file and paste the clipboard contents into a new document - very tedious. The free graphic program, Irfanview, also has an unsophisticated select tool, but you can at least crop an image. After selecting the area, choose Crop from the Edit menu (see the cover CD for a copy of this program ).

If all you ever need to do is trim the outside of an image, then Irfanview or the software that ships with most scanners and cameras can do this with little fuss. However, even slightly more serious users will need more options and the perennial favourites Photoshop 6, Paint Shop Pro 7 and, to a lesser degree, Photoshop LE will greatly increase the user's control.

In Photoshop, the Selection/Marquee tool is found in the top left corner of the tools palette. You can change the shape of the selection tool by either right-clicking on the button or left clicking and holding the button for about two seconds. Paint Shop has even more options available in the Tool-Options floating menu.

The first trick to realise with both these programs is that if you hold down the shift key while selecting part of an image you can select different parts of the image at the same time. After making your basic highlights, you are free to further manipulate the selection using the options under the Select Menu (Photoshop) or Selections menu (Paint Shop Pro). In some instances, it is easier to select the opposite of what you want and then use the Invert option (see images 1-3 for an example).

One problem to watch arises when you're using layers. It is quite common to accidentally switch to an empty layer and apparently select part of the image. When you try to paste or edit the selection, either nothing appears or, at best, only part of the selection is pasted. When this happens, always check the layers of the image; or, if layers are not needed, you can merge the layers (see the programs' help file for further instructions).

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Scott Mendham

PC World
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