The gradient mask allows the image to blend between the grayscale and color image.
This technique of adding a mask can also be used on one layer to create a gradual fade to transparency or to a different layer stacked beneath.
Using a Channel
Often, a channel will get you very close to a perfect Layer Mask. This technique works particularly well when the subject is against a high-contrast background (such as a sky or a wall), and it works very well with fne details like hair. The image can be masked so it is ready for integration into a composite image. For example, a masked image could be used to add a palm tree to another photo. Let’s give it a try.
- Open the Channel_Mask.tif file.
- Switch to the Channels panel and examine the Red, Green, and Blue channels.
Look for one with high contrast from the background. Although all three channels are fairly high contrast, the Blue channel stands out the most.
- Duplicate the Blue channel by dragging it onto the New Channel icon at the bottom of the Channels panel (it looks like a pad of paper).
- Rename the new channel Selection by double-clicking its name.
- With the Selection channel selected, press Command+L (Ctrl+L) to invoke a Levels adjustment. Levels is a powerful command that allows you to adjust the gamma (gray) point as well as the black and white points.
- Move the black slider to the right, setting the Input Level to around 60. The black in the channel should get crisper.
- Move the white slider to the left, setting the Input Level to around 190. The gray areas in the channel should switch to pure white.
- Move the middle (gray) slider to refne any gray spots in the channel. A value of 1.5 should be approximately correct.
- Click OK to apply the Levels adjustment.
- Command-click (Ctrl-click) on the Selection channel’s thumbnail to load the selection (you’ll see the marching ants).
- Choose Select > Inverse to reverse the selected area from the sky to the palm tree.
- Turn on the visibility for the RGB channels by clicking the RGB composite channel’s visibility icon. Turn off visibility for the Selection channel.
- Switch to the Layers panel.
- Click the Add layer mask button at the bottom of the Layers panel to turn the palm tree into a layer with a mask added.
This command uses channel data to create a new alpha channel. You can then refine the channel to create an accurate selection. You can also take this one step further to make a high-quality Layer Mask. Let’s give it a try.
- Open the file Calculations.tif.
- Turn the Background layer into a floating layer by double-clicking its name in the Layers panel. Name the layer Banana Tree.
- Call up the Channels panel and closely examine the channels for a high contrast between the tree and the background. Although all three channels have contrast between the sky and the tree, the Blue channel has the best.
- Invoke the Calculations command by choosing Image > Calculations.
- Set Source 1 to the Blue channel, set Source 2 to the Red channel, and select the Invert check box. The Red channel differs most from the Blue channel in this image, so it will create a good matte.
- Experiment with different blending modes so you get a clearer separation between the tree and the sky. In this case, the Vivid Light mode works best to create a new channel. Click OK.
- The new channel will need a little touch-up. You can get the channel near perfect with a Levels adjustment. Press Command+L (Ctrl+L) to invoke the Levels dialog box.
- Adjust the black, white, and gray points for Input Levels to improve the matte. Click OK when you’re satisfied. You then need to reverse the channel so the area you want to discard is black. Press Command+I (Ctrl+I) to invert the channel.
- Soften the selection by blurring it. Choose Filter > Blur > Gaussian Blur, set it to a value of 1 pixel, and click OK.
- Load the channel as a selection by Command-clicking (Ctrl-clicking) the channel’s thumbnail.
- Turn on the visibility icon for the RGB channels and turn it off for the alpha channel.
- Switch to the Layers panel and select the Banana Tree layer.
- Click the Add layer mask button to apply a mask to the selected layer.
Tip: The Masks Panel Is Essential
The Masks panel offers several other useful commands. You can load a mask as a selection, apply a mask, disable its visibility, or discard it. Additionally, you can use the Color Range or Invert command to further refine the selection. The Masks panel consolidates all the masking commands into a single location, which can save you valuable time.
Don‘t miss the next Photoshop article on Graphics.com. Get the free Graphics.com newsletter in your mailbox each week. Click here to subscribe.
|Excerpted from Understanding Adobe Photoshop CS6: The Essential Techniques for Imaging Professionals by Richard Harrington. Copyright © 2012. Used with permission of Pearson Education, Inc. and Peachpit Press.|