Adobe Photoshop CS5 for Photographers - Martin Evening [197]
Selections
There are many ways you can create a selection in Photoshop. You can use any of the main selection tools such as the lasso tool or the Select Color Range command, or convert a channel or path to a selection. Whenever you create a selection, you will notice that it is defined by a border of marching ants (Figure 9.1). It is important to remember that selections are only temporary – if you make a selection and accidentally click outside the selected area with the selection tool, the selection will be lost, although you can always restore a selection by using the Edit Undo command ( ). As you work on a photo in Photoshop, you will typically use selections to define specific areas of an image where you wish to edit the image or maybe copy the pixels to a new layer and, when you are done, you'll deselect the selection. If you end up spending any length of time preparing a selection, you will maybe want to save such selections by storing them as alpha channels (also referred to as ‘mask channels’). To do this, go to the Select menu and choose ‘Save Selection…’. The Save Selection dialog box then asks if you want to save the selection as a new channel (Figure 9.2). If you select a pre-existing channel from the Channel menu you will have the option to add, subtract or intersect with the selected channel. You can also create new alpha channels by clicking on the ‘Save selection as a channel’ button at the bottom of the Channels panel, which will convert a selection to a channel. If you look at the Channels panel shown in Figure 9.3, you will notice how a saved selection has been added as a new alpha channel (this will be channel #6 in RGB mode, or #7 if in CMYK mode). You can also click on the ‘Create new channel’ button, then fill the empty new channel with a gradient or use the brush tool to paint in the alpha channel using the default black or white colors. Once you create a new channel it is preserved when you save the image.
Figure 9.1 A selection is represented in Photoshop using marching ants.
Figure 9.2 To save a selection as a new alpha channel you can choose Select Save Selection and select the New Channel button option.
Figure 9.3 When you save a selection it is added as a new alpha channel in the Channels panel. Channels can be viewed independently by clicking on the channel name. However, if you keep the composite channels selected and click on the empty space next to the channel (circled), you can preview a channel as a quick mask overlay.
To load a saved channel as a selection, choose ‘Load Selection…’ from the Select menu and select the appropriate channel number from the submenu. Alternatively, you can -click a channel in the Channels panel, or highlight a channel and click on the ‘Load channel as a selection’ button.
Recalling the last used selection
The last used selection is often memorized in Photoshop. Just go to the Select menu and choose ‘Reselect’ ( ).
Omitting channels in a save
As was pointed out in the main text, channels are automatically saved when you save an image. However, if you choose ‘Save As…’ you do have the option to exclude saving alpha channels with an image should you wish to do so.
The marching ants indicate the extent of an active selection and any image modifications you carry out are applied within the selected area only. Remember though, all selections are only temporary and can be deselected by clicking outside the selection area with a selection tool or by choosing Select Deselect ( ). If you find the marching ants to be distracting you can temporarily hide them by going to the View menu and selecting ‘Extras’. This and the keyboard shortcut can be used to toggle hiding/showing the marching ants.
Quick Mask mode
You can also preview and edit a selection in Quick Mask mode where the selection will be represented as a transparent colored mask overlay (Figure 9.4). If a selection has a