Luminosity Masks and Sepia Toning
"Luminosity mask" is one of those terms that can confound the brain by its mere sound. But here's an easy explanation: A luminosity mask uses the brightness values in an image as a mask. If you've ever copied a grayscale image into a channel, and then loaded the channel as a selection, you've done luminosity masking.
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.
Let's let our *eyes* discover what a luminosity mask is: Open a single-layer RGB image such as a color portrait. Press ctrl-alt-~ (Windows) or opt-cmd-~ (Mac). This loads the luminosity mask. Now under the Select menu, choose Save Selection: Channel: New. Name the new channel "Luminosity Mask." Press ctrl-D (Windows) or cmd-D (Mac) to drop the selection. Now open the channels palette, scroll through the channels, and click on "Luminosity Mask." Surprise! What you see should be a grayscale version of your starting image. So a luminosity mask is just the brightness information from an image, acting as a selection or mask.
If you want to produce really handsome sepia tones, luminosity masking is your friend. Let's see how it works. We'll use two different methods: one lightning fast, the other slower, but more controlled. Before we start, open an image that has a full range of tones and makes an attractive candidate for sepia toning (such as a portrait). If the image is in graycale mode, change to RGB mode. If the image is in color, desaturate it (Image: Adjust: Desaturate).
SEPIA TONING: METHOD 1 (FAST)
1. Set the foreground color to R162/G138/B101.
2. Press ctrl-alt-~ (Windows) or opt-cmd-~ (Mac) to load the luminosity mask.
3. Under the Select menu, choose Inverse.
4. Press ctrl-H (Windows) or cmd-H (Mac) to hide the marching ants.
5. Under Edit: Fill, make the following choices:
That's it!! If you like the result, it could be because: 1. The hue is not too gaudy and the color not too saturated. 2. We applied the color through an inverted luminosity mask, so the shadows absorbed the most color, the midtones were lightly tinted, and the highlights remained white.
SEPIA TONING: METHOD 2 (CONTROLLED)
1. Set the foreground color to R162/G138/B101.
2. Click on the New Layer icon to make a new layer.
3. Under Edit: Fill, make the following choices:
4. Under the Layer menu, choose Add Layer Mask: Hide All.
5. In the Image: Apply Image dialog, make the following choices:
6. Change the Layer 1 blending mode to Color. (At this point, your sepia tone should look just like the one you did using the "fast" method..)
7. Use New Adjustment Layer: Hue/Saturation to create a new adjustement layer above Layer 1. Opacity 100%, Mode: Normal. Play with the sliders to get a color effect you like. If you prefer the original color, press alt (Windows) or opt (Mac), and click on Reset. When you're done with Hue/Saturation, click OK.
8. Click on the Background. Use New Adjustment Layer: Levels to create a new adjustement layer above the background.
9. Step back and look at your image.
You have lots of control and can tweak the settings interactively. If the underlying image needs rebalancing, you can use the Levels adjustment layer. If you want to change the way the layer mask affects the sepia toning, you can click on the layer mask and use levels, curves, or brightness/contrast. If you want to experiment with different toning colors, you can work in the Hue/Saturation adjustment layer. You can also try out different Layer 1 blending modes, and then rebalance using the Levels adjustment layer.
Tutorial Copyright © 2001 Outcast125, Used by permission of author
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