Photoshop Tutorial for Fashion Design (Part 19)
Alpha Channels, Masks, Advanced Selections

I want you to recall the Quick Mask mode we covered in the Toolbox segment. We used it to create a selection by masking the image with freehand brush strokes. What I didn’t mention at the time: when we are working in that mode, Adobe Photoshop creates a Quick Mask channel. The Quick Mask channel can be hidden and deactivated by clicking on the RGB channel. In this case, you can go back to your image and work in it as if Quick Mask didn’t exist.

At anytime, you can go back to the Quick Mask channel and convert it into a selection using the Channels palette instead of exiting the Quick Mask mode. And of course, Quick Mask can be moved using the Move tool and deleted. It is a very handy way to preserve selections. However, there is a catch: it’s called Quick Mask for a reason. You can have only one Quick Mask channel and it can only be preserved in the Quick Mask mode. As soon as you exit the Quick Mask mode the channel will be deleted. So, Adobe Photoshop offers you an alternative: Alpha Channels.

Instead of a Quick Mask channel that is stored only in the Quick Mask mode you can use an alpha channel to store a mask in the regular mode and it works just like Quick Mask. You can create an alpha channel from an already existing selection by clicking on the “Save selection as channel” icon at the bottom of the palette or you can create a new channel to start a new mask.

You can double-click on the channel to choose a different mask color and set its options. You can use the Blur tool to soften the edges. You can delete masked areas by switching foreground to white and background to black. And finally, load the channel as a selection. As you can see, loading as a selection doesn’t affect the channel.

You will be the using alpha channels to preserve a mask so that you can load it as a selection for future use. The channel will be saved with your document as long as you’re saving it in an alpha channel supporting format like Adobe Photoshop’s native PSD or TIFF. Note that the common JPEG format does not support alpha channels.

You’ve probably noticed that as opposed to a single Quick Mask channel, you can create multiple alpha channels to store different selections in the same document. This is very helpful when you’re editing textured or multi-colored parts of the artwork. This scanned image from a magazine is a good example for mask use. It has multi-colored pixels distributed all over the image so there is no way I can make a selection using conventional selection tools like Magic Wand that works with colors. On top of that, some of the parts are too small for the Polygon Lasso tool. It could take too long to select. So I would use a combination of selection techniques selecting larger parts with the Polygon Lasso tool, then creating a channel out of the selection and using mask for smaller parts. On the job, you will be dealing with files like this quite often. It will take you time and work to isolate parts of your images so I strongly recommend to create and keep alpha channels to store your selections.

To deactivate an alpha channel click on the RGB on the top of the palette. Click on the eye icon to hide the alpha channel completely. If you want to go back to the alpha channel, just click on it to activate. Adobe Photoshop will automatically hide RGB showing only the active alpha channel. Don’t get scared: to preview your image simply click on the RGB eye section to unhide. Your alpha channel is still active but you also have a visual of your image.

And of course you can duplicate the channel. Just click and drag into the New Channel icon. You can delete the channel, click and drag to the trash can. To change channel options, double-click on the channel or choose it from the menu list. And just like with any palette, you can access channel commands in a number of ways. You can use the icons at the bottom of the palette, you can right-click on the channel, or choose the appropriate command in the palette menu.

And to make it even more convenient and sometimes more confusing, Adobe Photoshop offers a number of ways to save your selection. First, you can right-click on your selection and make sure that a selection tool is in use then choose “Save Selection”. Keep document name as is, channel as “New” and you can even give it a name. And click “OK”. Now your new channel will show in the Channels palette. The second option is to use the Select menu in the menubar. Choose “Save Selection”, keep document as is, channel as “New”, give it a name and click “OK”. And once again you’ll find your channel in the Channels palette. You can double-click to change it to a different color And you’re already familiar with the third option when you simply click on “Save selection as channel”. It will be automatically named as “Alpha 3″ because we already have “Alpha 1″ and “Alpha 2″.

Something to keep in mind: selections, paths, quick and alpha masks are not layer specific. They belong to the entire document. You can create them based on the pixels of one layer and use for editing on another layer. Now, that could sound confusing so let me give you an example.

I’m going to use an existing alpha channel to load a selection. The next step is to activate RGB and select a new layer. You can see that although I’ve selected a new layer, alpha channel masks and selection are still visible because they are not a part of a specific layer: they belong to the entire document. I’m going to hide the alpha channel for now. Now, using the Selection tool, I can move the selection around to find a specific pattern placement and do all kinds of editing. I can also convert that selection into path and then stroke or fill that path on yet another layer.