If you register for free, you will be able to post threads, vote on polls and lots more. If you have problems with the registration or logging in, please contact the administrator.
I have been given a tutorial on Luminosity Masking. The technique is used to bring out detail either in the image's highlights or in its shadows dependiing on how it's used.
You use the keyboard shortcut Crtl + Alt + ~ (Command + Option + ~ for the Mac) to select the highlights of the image. Inverting the mask selects the images shadow areas. A new layer is created with Crtl + J and its blend mode is set to Multiply (for highlights) or Screen (for shadows). The layers opacity control adjusts the effect.
My question for you gurus is what exactly does the Crtl + Alt + ~ shortcut do? I have been unable to find a definition in Adobe manuals, PS7 help, the PS7 Bible, etc.
Now I think I understand. Your replies pointed my to the right experiment. The Crtl + Alt + ~ shortcut seems to match what I get when I (1) Switch to LAB color, (2) select the L (Lightness) channel, (3) choose the Magic Wand tool, (4) set its Tolerance to 50%, and (5) click in an obvious highlight.
The complete lightness channel is exactly the same as the selection with Ctrl+Alt+~
You're confused because of the marching ants; these show you an area that is at least 50% selected.
You're also confused about the magic wand tool. Somewhere clicking in the lightness channel with the magic wand and using 50% tolerance isn't the same like Ctrl+Alt+~
Also, the tolerance is not a percentage, it's a value between 0-255 (similar colors)
When you press ctrl-alt-~ (Windows) or opt-cmd-~ (Mac), Photoshop loads the luminosity mask for the currently active layer. That means Photoshop looks at the layer as if it were grayscale, and calculates a selection based on the light and dark values (luminosity). White areas are selected, black areas are unselected, and gray areas are partially selected. It doesn't matter if the layer is color. Photoshop just averages the color channels to create an 8-bit grayscale mask, and loads it as a selection. What you see is "marching ants," but those marching ants represent the layer's luminosity mask.
When some people hear that you press a key combo and Photoshop "loads the luminosity mask," they think: "I didn't know there *was* a luminosity mask. How come I've never seen it? Where is it stored?" Well, once you realize that the mask is just a grayscale version of the layer itself, you can understand that the luminosity mask is implicit in the layer. It's just the grayscale average of the color channels. So it doesn't have to be stored anywhere. Photoshop calculates it for you on the fly when you ask for it.
Need keyboard shortcut definition 
Linear Mode
