Saving Photoshop Selections As Paths And Alpha Channels
Selecting pixels in a bitmapped image can be a tricky process. That's why Adobe Photoshop offers so many different ways of making selections. There are the selection tools, the four modifier icons and the keyboard shortcuts. Once you've made your selection, you will often want to preserve it so that you can reuse the same selection in the future; especially if it's taken you a lot of time and effort. You can save a selection in two ways: as a path or as an alpha channel. To save a selection as an alpha channel, choose Save Selection from the Select menu. When you save a selection in this way, Photoshop creates an alpha channel which is simply a special type of channel that can be viewed by going to the Channel window and clicking on its name. Alpha channels are greyscale images which use a visual code to represent selections and masks: the black areas on the channel represent masked (non-selected) areas and white areas represent those areas which will be highlighted when the channel is loaded as a selection. (The reverse can also be true: the user can set his or her preferences by double-clicking the channel thumbnail in the Channel window.) The different levels of grey inside the alpha channel represent different levels of selection, making alpha channels ideal for saving selections with feathers and fades. Paths, by contrast, are incapable of representing different degrees of masking and selection. Paths are really vector shapes, superimposed on the bitmapped image, which can be manipulated using a series of tools imported from Illustrator, Adobe's vector-based drawing program. To covert a selection into a path, choose Make Work Path from the Paths panel menu. You will be asked to enter a number representing the tolerance setting that Photoshop should use in creating the vector path. The permitted range is from 0.5 to 10. Lower numbers lead to a very detailed trace resulting in shorter line segments and many points. Higher numbers lead to a less precise trace with fewer points. A number somewhere between 1 and 2 normally yields good results for most selections. Having converted the selection to a work path, it is important to save it since a work path is only temporary. Simply choose Save Path from the Paths panel menu. With the use of the imported Adobe Illustrator vector-based editing tools, paths can be modified to very precisely correspond to edges around elements within the image. This make them ideal for creating cut-outs of products and other subjects within photographs.About the Author:
The The writer of this article is a trainer and developer with Macresource Computer Solutions, a UK IT training company offering Adobe Photoshop Classes at their central London training centre.
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