- Layer Mask Essentials
- Mask Creation Strategies
- Refining Masks
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Mask Creation Strategies
There are many different approaches to creating Layer Masks. The approach you should take will vary based on your source image. Let’s try four different images and techniques to perfect your Layer Masking ability.
Using a Gradient as a Mask
When designing, you may need to gradually blend the edges of an image. This can be easily accomplished by combining a Layer Mask and a gradient. Let’s give it a try:
- Open the file Ch07_Gradient_Mask.tif from the Chapter 7 folder.
- Duplicate the Background layer by pressing Command/Ctrl+J.
- Select the top layer and choose Image > Adjustments > Desaturate.
- With the topmost layer active, click the Add layer mask button at the bottom of the Layers panel. A new, empty Layer Mask is added to the layer.
- Press G to select the Gradient tool.
- Press D to load the default colors of black and white.
- From the Options bar, choose the black-to-white gradient. If it’s not available, choose Reset Gradients from the Gradient Picker’s submenu.
- With the Layer Mask selected, click and drag to create a new linear gradient going from top to bottom in the document window.
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The new Layer Mask will create a gradual blend from the grayscale version to the colored version.
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
Oftentimes, 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 fine 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 file Ch07_Channel_Mask.jpg from the Chapter 7 folder. This image was shot against a night sky using a flash.
- Switch to the Channels panel and examine the red, green, and blue channels. Look for one with high contrast from the background. While all three channels are fairly high contrast, the green channel stands out the most.
- Duplicate the green 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/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 100. The gray areas in the channel should switch to pure white.
- Move the middle (gray) slider to refine any gray spots in the channel. A value of 2.25 should be approximately correct.
- Command/Ctrl-click on the Selection channel’s thumbnail to load the selection.
- Turn off 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.
- Turn the Background layer into a floating layer by double-clicking its name in the Layers panel. Name the layer Palm Tree.
- Click the Add layer mask button at the bottom of the Layers panel.
Using the Color Range Command
Sometimes, a color (or range of colors) will be very present in your image. This color can be used to quickly create an accurate Layer Mask. Even if the color cannot be used to select the object entirely, you can always harness the Brush tool to clean up stray areas.
- Open the file Ch07_Color_Range.jpg from the Chapter 7 folder.
- Turn the Background layer into a floating layer by double-clicking its name in the Layers panel. Name the layer Bees and Flower.
- Choose Select > Color Range to make a selection based on a range of colors. Select the Localized Color Clusters option to reduce the selection area to just the chosen colors.
- With the Eyedropper tool, click within the yellow area of the flower to make an initial selection. Hold down the Shift key and drag through other areas of the flower to add to the selection.
- Leave the Fuzziness set to a low value (30–40). When most of the flower is selected, click OK to create an active selection.
- Click the Add layer mask button for the layer. The petals will display well, but parts of the flower will be missing.
- Add a solid color layer to make it easier to see your edges. Choose Layer > New Fill Layer > Solid Color. A purple layer will help things stand out nicely. Click OK and drag the solid layer below the masked flower.
- Examine the masked layer closely. You will need to paint in part of the center of the flower. Additionally, some of the petals contain unwanted transparency. You may also see some leaves or stems that have bled through. You can fix all these problems quickly using the Brush tool.
- Press D to load the default colors of black and white.
- Select the Layer Mask attached to the Bees and Flower layer.
- Press B to activate the Brush tool. Adjust the size of the brush and its hardness settings so you have a small brush with a gentle edge (an 80-pixel brush with a hardness of 75% is a good place to start). Make sure the brush is set to 100% opacity.
- Paint in spotted or missing areas with white. You can remove any unwanted areas by painting with black.
- When finished, you can save the image as a layered file such as a TIFF or PSD formatted file.
Using Calculations
You explored the Calculations command to create an advanced selection in Chapter 5. 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 Ch07_Calculations.tif from the Chapter 7 folder.
- Turn the Background layer into a floating layer by double-clicking its name in the Layers panel. Name the layer Castle.
- Call up the Channels panel and closely examine the channels for a high contrast between the lamp and the background. While all three channels have contrast between the sky and the castle, 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 castle 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/Ctrl+L to invoke the Levels dialog box.
- Adjust the black, white, and gray points for Input Levels to improve the matte. The results will be closer but not complete. Click OK when satisfied.
- With your Brush tool, paint out the windows with black.
- You then need to reverse the channel so the area you want to discard is black. Press Command/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/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 Castle layer.
- Click the Add layer mask button to apply a mask to the selected layer.
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