Last night I was watching "The Screensavers" on tech TV. They had this Photoshop guru, Bert Monroy on. He was showing alpha channels and layer masks in Photoshop. Here is some of what he talked about. You might find it useful, or you might not. You really had to see it to know what he was showing.Channeling colorsChannels containing color information make up every image, and you can see them on the Channels palette. Open an RGB file and you'll see Red, Blue, and Green channels as well as an RGB composite. Open a CMYK file and you'll see Cyan, Magenta, Yellow, and Black channels as well a composite. Open a Grayscale image and you'll see a single channel.The Alpha dogYou can add a lot of additional channels to a Photoshop file, called Alpha Channels, which contain no color information. You can use these purely grayscale channels as specialized, reusable selections or masks.Select part of an image with any of the selection tools, such as the Lasso, Rectangular Marquee, or Magic Wand. You can also make selections based on color by choosing Color Range from the Select menu. You can select by sampled colors, specific colors, highlights, mid-tones, shadows, or colors out of the Gamut.When you select an area of an image, any modification to the image will apply exclusively to that area. You can colorize it, filter it, scale it, or even duplicate it. Anything you wish to do will be done to that area while leaving the unselected areas of the image untouched.If you deselect it, the selection is gone. If you save the selection to an Alpha channel, you can recall it at any time. To save a selection, choose Save Selection from the Select menu to store it to an Alpha channel.Mess with grayAs a grayscale channel, the Alpha channel contains 256 levels of gray, which can be very useful.Anything white in an Alpha channel exposes the image to an alteration just as the normal selection process does. Black protects the image from any alteration just as the unselected portions of an image are protected.You can apply gradients with the Gradient Tool, paint with the Paintbrush, or use any of the other tools to select areas of your image. (No, they aren't in color.)Pesky file formatsWhen you change the format of your image for output to something else, you'll want to discard the Alpha channels. Some file formats, such as EPS, will automatically strip them away. Always keep a PSD (Photoshop native format) file of your work in your archive so you have all your Paths, Layers, and Alpha channels if you need them later.Expose more of your subjectWhen you apply a Layer Mask to a layer, either from the layer palette or the Layer menu, you allow portions of a layer to be seen. In the Layer Mask, you use any of your tools to apply tones from white to black with two 254 additional grays in between, just like in the Alpha Channel.Where the mask is white, you can see the contents of that layer. Where the mask is black, the contents of the layer are hidden. Where the mask is gray, you see a combination of the masked layer and the layers underneath it. The lighter the gray, the more you see the contents of the layer. The darker the gray, the less you see of the layer.Alpha Channel takes on the Layer MaskThe bottom line: the Alpha Channel and Layer Mask operate in similar ways with different end results. White in the Alpha Channel exposes an image to an effect. White in the Layer Mask exposes how much of an image you see. Black in the Alpha Mask protects an image from change. Black in the Layer Mask hides an image from view.Yours in Railroading,
Jerry
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