Exerting greater control with masking in Photoshop
With layer masks in Photoshop, any changes you make to the layer to which the mask is attached will be controlled by the mask: black will conceal and white will reveal. And gray? Well, shades of gray apply the mask at a percentage that corresponds to the level of gray. In other words, as black completely hides the change and white completely shows the change, a gray exactly half-way between black and white will show 50% of the effect of the change. With this in mind you can make some very sophisticated layer masks that will affect only targeted areas of an image. You can also make them so that they mask in varying degrees (shades of gray).
A simple, yet sophisticated mask can be made from one of the three channels: Red, Green, and Blue. If you look at the channels palette you’ll see the gray scale representations of each color channel. Remember, in a layer mask, white reveals and black conceals, and shades of gray reveal to a varying extend. So these channels can be used as layer masks. So let's talk about exerting greater control with masking in Photoshop.
First you need to evaluate your image and decided what areas you need to target for adjustment. Next, go to the Channels Palette and click on one of the channels. You’ll see the black and white representation of the channel replace the color image. Look at the channels and see if one of them is significantly white (or very light) or significantly black (or very dark) in the area you’re targeting.
Now click on the RGB composite at the top of the Channels palette to restore the color image and go back to the Layers Palette.
Depending on what you’re trying to accomplish (tonal changes, sharpening, color changes, etc.) either create an adjustment layer or a duplicate background layer. If you’ve chosen an adjustment layer, take a look at the layer mask that was created with it. What do you see? The channel you just loaded as a selection is now the layer mask. If you’re working on a duplicated layer, click the Layer Mask icon at the bottom of the Layers Palette, the selection will automatically load as a mask.
If you chose a channel with significant whites to target your adjustments, hang on for just a bit.
If you chose a channel with significant blacks to target your adjustments you’ll need to first invert the mask. To do so, first ALT-click on the Layer Mask icon in the Layers Palette. The color image is replaced by the black and white mask. Invert the mask by going to Image>Adjustments> Invert or use the keyboard shortcut Ctrl-I (Cmd-I for Mac).
Now you have a mask that is nearly ready to use: the white areas will apply your changes to the targeted areas. But it’s still a gray scale image, meaning that your changes will be applied to varying degrees throughout the image. To specifically target the brighter areas and not the gray areas you need to edit the mask using either levels or curves. I prefer levels myself. Go to Image>Adjustments>Levels (or Curves if you prefer) or use the keyboard shortcut Ctrl-L (Ctrl-M for curves). Make adjustments so that the whites in the target areas stay white but the non-targeted areas go to black, or as many of them as possible go to black. In Levels, move the black slider to the right to make more stuff black and move the white slider to the left to make more stuff white until you get what you want, or pretty darn close.
You can then use a black brush to further mask areas you want to protect.
You’re going to end up with some abrupt transitions from pure black to pure white, which can cause unnatural looking results. By applying a slight blur to the mask, the transitions will look more natural. Use the Gaussian Blur filter, Filter>Blur>Gaussian Blur as was done in the Blending Tutorial Guide. Blur radius will depend on image content and resolution, so experiment a bit here until you get a feel for it.
Now you’ve got a very sophisticated, very precise mask through which to apply your adjustments.
Alt-Click on the Layer Mask icon to restore the color image and proceed in making changes to the image. In this case I used the Levels Adjustment layer to darken (or burn, if you prefer) down the bright areas of the poppy seed pods. Trying to do this pod by pod with the burn tool or other burning techniques would have taken a long time. By using a mask I was able to affect change to all the pods at once.
Once you’ve done this a few times you’ll see just how easy it can be to make very precise masks very quickly. But these relatively simple masks are just the beginning. There are numerous techniques using channels or the combining of channels to create masks for specific purposes.
To really explore the power of masking, take a look at Tony Kuyper’s tutorials on using Luminosity Masks. If you understand what we just went through using a channel as a mask then you’re ready for some really powerful, really easy to use, techniques that will give you much more control over your image processing.
Tony’s website address is www.thegoodlight.us
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