Selecting pixels in a bitmapped image can be a tricky business. That's why Adobe Photoshop offers so many ways of making selections. There are selection tools, modifier icons and keyboard shortcuts. Once you've made a selection, you will often want to preserve it so that you can use the same selection in the future; especially if it's taken you a lot of effort. There are two ways of saving a selection: as a path or as an alpha channel.
To save a selection as an alpha channel, use the Save Selection command, which is found in the Select menu. When you save a selection in this way, Photoshop creates an alpha channel, a special type of channel which can be viewed by going to the Channel window and clicking on its name. Alpha channels are just greyscale images which use a visual code to represent selections: the black areas on the channel represent areas which will not be highlighted when the channel is loaded as a selection and white areas represent those areas which will be highlighted; or vice versa, since the user can set his or her preferences by double-clicking the channel thumbnail in the Channel window.
Since the different levels of grey within an image represent different levels of selection, alpha channels are ideal for saving selections with feathering and fades. By contrast, paths are incapable of representing different degrees of masking and selection. Paths are vector shapes which can be manipulated using a series of tools imported from Illustrator, Adobe's vector-based drawing program.
To change a selection into a path, choose Make Work Path from the Paths panel menu. Photoshop will then ask you to enter a number representing the tolerance setting that the program should use in creating the vector path. The acceptable range is from 0.5 to 10. Lower numbers give a very detailed trace resulting in shorter line segments and many points. Higher numbers give a less precise trace with fewer points. A number between 1 and 2 usually yields good results for most selections. Having converted your selection to a work path, remember to save it. A work path is only temporary, so always choose Save Path from the Paths panel menu and either accept the default name or enter a new one.
By using the imported Adobe Illustrator vector-based editing tools, you can modify paths to very precisely correspond to edges around elements within the image. This make paths ideal for creating cut-outs of products and similar subjects within photographs.
To save a selection as an alpha channel, use the Save Selection command, which is found in the Select menu. When you save a selection in this way, Photoshop creates an alpha channel, a special type of channel which can be viewed by going to the Channel window and clicking on its name. Alpha channels are just greyscale images which use a visual code to represent selections: the black areas on the channel represent areas which will not be highlighted when the channel is loaded as a selection and white areas represent those areas which will be highlighted; or vice versa, since the user can set his or her preferences by double-clicking the channel thumbnail in the Channel window.
Since the different levels of grey within an image represent different levels of selection, alpha channels are ideal for saving selections with feathering and fades. By contrast, paths are incapable of representing different degrees of masking and selection. Paths are vector shapes which can be manipulated using a series of tools imported from Illustrator, Adobe's vector-based drawing program.
To change a selection into a path, choose Make Work Path from the Paths panel menu. Photoshop will then ask you to enter a number representing the tolerance setting that the program should use in creating the vector path. The acceptable range is from 0.5 to 10. Lower numbers give a very detailed trace resulting in shorter line segments and many points. Higher numbers give a less precise trace with fewer points. A number between 1 and 2 usually yields good results for most selections. Having converted your selection to a work path, remember to save it. A work path is only temporary, so always choose Save Path from the Paths panel menu and either accept the default name or enter a new one.
By using the imported Adobe Illustrator vector-based editing tools, you can modify paths to very precisely correspond to edges around elements within the image. This make paths ideal for creating cut-outs of products and similar subjects within photographs.
About the Author:
Author is a developer and trainer with Macresource Computer Solutions, a UK IT training company offering Adobe Photoshop training courses at their central London training centre.
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