Working with masks and channels

Out of the camera, a digital image is an opaque rectangle. To combine part of that image with others, you hide the area outside the subject. Or you might want to apply an adjustment layer or filter only to certain areas of a layer. The recommended way to do both is by using a mask, a way to mark areas of a layer as transparent.

Using a mask is more useful than deleting unwanted areas of a layer, because it’s reversible: For example, if you notice that you accidentally trimmed off part of the subject, a mask lets you restore the trimmed area to correct the mistake.

In addition to color channels, an image can contain alpha channels, useful for saving and reusing selections and marking transparent areas for an entire document.

It can be challenging to paint or draw a mask or channel edge that precisely follows a nonsharp border of a subject, such as fuzzy hair. Photoshop provides automated tools to help you quickly create complicated selections and masks.

Getting started

First, you’ll view the image that you’ll create using masks and channels.

1. Start Photoshop, and then simultaneously hold down Ctrl+Alt+Shift (Windows) or Command+Option+Shift (macOS) to restore the default preferences. (See “Restoring default preferences” on page 5.)

2. When prompted, click Yes to delete the Adobe Photoshop Settings file.

3. Choose File > Browse In Bridge to open Adobe Bridge.

   Note

   If Bridge isn’t installed, the File > Browse In Bridge command in Photoshop will start the Creative Cloud desktop app, which will download and install Bridge. After installation completes, you can start Bridge.

4. Click the Favorites tab on the left side of the Bridge window. Select the Lessons folder, and then double-click the Lesson06 folder in the Content panel.

5. Study the 06End.psd file. To enlarge the thumbnail so that you can see it more clearly, move the thumbnail slider at the bottom of the Bridge window to the right.

In this lesson, you’ll create a graphic for a podcast. The model was photographed in front of a different background. You’ll use Select And Mask to quickly isolate the model over the final background. You’ll also tilt the model’s head up a little more and create a pattern for the background.

6. Double-click the 06Start.psd thumbnail to open it in Photoshop. Click OK if you see an Embedded Profile Mismatch dialog box.

7. Choose File > Save As, rename the file to 06Working.psd, and click Save. Click OK if the Photoshop Format Options dialog box appears.

Saving a working version of the file lets you return to the original if you need it.

Using Select And Mask and Select Subject

Photoshop provides a set of tools focused on creating and refining masks, collected in a task space called Select And Mask. Inside Select And Mask, you’ll use the Select Subject tool to get a fast head start on the mask that will separate the model from the background. Then you’ll refine the mask using other Select And Mask tools, such as the Quick Selection tool.

1. In the Layers panel, make sure both layers are visible and the Model layer is selected.

2. Choose Select > Select And Mask.

Select And Mask opens with the image. A semitransparent “onion skin” overlay indicates masked areas. For now, the checkerboard pattern covers the entire image, because you haven’t yet identified the areas to unmask.

3. Click the View menu in the View Mode section of the Properties panel, and choose Overlay. The masked area is now shown as a semitransparent red color instead of the onion skin checkerboard. It’s solid because nothing is masked yet.

   Tip

   When a selection tool is active, you can enter Select And Mask by clicking the Select And Mask button in the options bar instead of having to find the command in the menus.

   

   Tip

   Quickly cycle through the View Modes by pressing the F key. Viewing different modes helps you spot selection mistakes that might not be obvious in other modes.

The different View Modes are provided so that you can see the mask more easily over various backgrounds. In this case, the red overlay will make it easier to see missed areas and edges where loose hair isn’t properly masked.

4. In the options bar, click the Select Subject button.

   Note

   In the Select Subject button drop-down list, you can choose where to process the selection. Cloud processing may produce better results, using a larger machine learning model on a powerful remote computer. Processing on your device is usually faster. Changing this setting affects the next image only; you can set this permanently in the Image Processing panel of the Preferences dialog box.

   

Using advanced machine learning technology, the Select Subject feature is trained to identify typical subjects of a photo, including people, animals, and objects, and then create a selection for them. The selection may not be perfect, but it’s often close enough for you to refine easily and rapidly with other selection tools.

5. Click the View menu in the View Mode section of the Properties panel, and choose Black & White. This View Mode helps make the mask edge easier to see.

   Tip

   You don’t have to be in the Select And Mask dialog box to use the Select > Subject command. It’s available even when a selection tool is not active. Also, it’s OK to use Select Subject first and then enter Select And Mask to refine the selection.

6. In the Properties panel, expand the Refine Mode if needed, and click Color Aware. If a message appears, click OK. The mask edge changes.

The two Refine Modes interpret potential subject edges differently. Color Aware can work well on simple backgrounds like the one in this lesson. Object Aware may work better on more complex backgrounds. If you want to compare the two results, choose Edit > Toggle Last State to switch between them.

7. Click the View menu in the View Mode section of the Properties panel, and choose Overlay to better compare the edge to the actual image.

Notice that there are a few areas over the chest that were missed by Select Subject. You can easily add them to the selection using the Quick Selection tool.

8. Make sure the Quick Selection tool () is selected. In the options bar, set up a brush with a size of 15 px.

9. Drag the Quick Selection tool over the missed areas (without extending into the background) to add the missed areas to the selection. Notice that the Quick Selection tool fills in the selection as it detects content edges, so you don’t have to be exact. It’s okay if you release the mouse button and drag more than once.

   Tip

   When editing a selection, increase the magnification if it helps you see missed areas.

   

Where you drag teaches the Quick Selection tool which areas should be revealed and are not part of the mask. Do not drag the Quick Selection tool over or past the model’s edge to the background, because this teaches the Quick Selection tool to include part of the background in the mask, and you don’t want that. If you accidentally add unwanted areas to the mask, either choose Edit > Undo or reverse the edit by painting over it with the Quick Selection tool in Subtract mode. To enable Subtract mode for the Quick Selection tool, click the Subtract From Selection icon () in the options bar.

As you drag the Quick Selection tool over the model, the overlay disappears from the areas that you are marking to be revealed. Don’t worry about total perfection at this stage.

10. Click the View menu in the View Mode section again, and choose On Layers. This shows you how the current Select And Mask settings look over any layers that are behind this layer. In this case, you’re previewing how the current settings will mask the Model layer over the Episode Background layer.

    

Inspect the edges around the model at a high magnification, such as 400%. Some of the original light background may still show between the model’s edge and the podcast background, but overall the Select Subject and Quick Selection tools should have created clean edges for the shirt and face. Don’t be concerned about edge gaps or imperfect hair edges, because you’ll take care of those next.

Creating a quick mask

To change the color of the glasses frames, you’ll use a quick mask, because you won’t need the mask after you’re done with this one task and so that you can create the mask by painting. First, you’ll clean up the Layers panel.

1. Hide the Episode Background layer so you can concentrate on the model. Make sure the Model copy layer is selected.

   

2. Click the Edit In Quick Mask Mode button near the bottom of the Tools panel. (Until now, you have been working in the default Standard mode.)

   

   Note

   If you are using a small display and the Tools panel is in single-column mode, the Quick Mask Mode button may be past the bottom of the screen. If the Tools panel is in two-column mode, the Quick Mask Mode button is at the bottom-left corner of the panel.

In Quick Mask mode, a red overlay appears as you make a selection, masking the area outside the selection the way a rubylith, or red acetate, was used to mask images in traditional print shops. (This idea is similar to the Overlay view mode you saw in Select And Mask.) You can apply changes only to the unprotected area that is visible and selected. Notice that the highlight color for the selected layer in the Layers panel is red, indicating you’re in Quick Mask mode.

3. In the Tools panel, select the Brush tool ().

4. In the options bar, make sure that the mode is Normal. Open the Brush pop-up panel, and select a small brush with a diameter of 13 px and a Hardness of 100%. Click outside the panel to close it.

5. Paint the earpiece of the glasses frames. (Magnify the view if it helps you paint more precisely.) The area you paint will appear red, creating a mask.

6. Continue painting with the Brush tool to mask the earpiece of the frames and the frame around the lenses. Reduce the brush size to paint around the lenses. You can stop where the earpiece goes under the hair.

   Tip

   Here, you’re making a selection by painting the area you want to select. Compare this to Chapter 3, where you made selections using tools that create a selection marquee.

   

In Quick Mask mode, Photoshop treats the red overlay as a grayscale mask, where shades of gray correspond to degrees of mask transparency. When using a painting or editing tool in Quick Mask mode, keep these principles in mind:

• Painting with black adds to the mask (the red overlay), subtracting from the selected area.

• Painting with white erases the mask, adding to the selected area.

• Painting with gray or reduced opacity adds semitransparent areas to the mask, where darker shades are more transparent (more masked).

7. Click the Edit In Standard Mode button (), which is the same as the Enter Quick Mask Mode button.

Exiting Quick Mask mode converts the Quick Mask into a selection.

8. Choose Select > Inverse to select the area you originally masked.

   Tip

   If you want to keep the selection for future use, save it as an alpha channel (Select > Save Selection); otherwise, it will be lost as soon as the area is deselected.

9. Choose Image > Adjustments > Hue/Saturation. The commands on the Adjustments menu affect pixels directly, without creating an adjustment layer.

10. In the Hue/Saturation dialog box, change the Hue to +70. The new green color fills the glasses frame. Click OK.

    

11. Choose Select > Deselect.

Manipulating an image with Puppet Warp

The Puppet Warp feature gives you flexibility in manipulating an image. You can reposition areas, such as hair or an arm, just as you might pull the strings on a puppet. Place pins wherever you want to control movement. You’ll use Puppet Warp to tilt the model’s head back so she appears to be looking up.

1. Zoom out so you can see the entire model.

2. With the Model Copy layer selected in the Layers panel, choose Edit > Puppet Warp.

A mesh appears over the visible areas in the layer—in this case, the mesh appears over the model. You’ll use the mesh to place pins where you want to control movement (or to ensure there is no movement).

3. Click to add pins around the body and along the base of the head, as shown below. Each time you click, Puppet Warp adds a pin. About 10 to 12 pins should work.

   

The pins you’ve added around the shirt will keep it in place as you tilt the head.

4. Select the pin at the nape of the neck. A blue dot appears in the center of the pin to indicate that it’s selected.

   

5. Press Alt (Windows) or Option (macOS). A larger circle appears around the pin, and a curved double arrow appears next to it. Continue pressing Alt or Option as you drag the pointer to rotate the head backwards. You can see the angle of rotation in the options bar; you can enter 170 there to rotate the head back.

   Note

   Be careful not to Alt-click or Option-click the dot itself, or you’ll delete the pin.

   

6. When you’re satisfied with the rotation, click the Commit Puppet Warp button () in the options bar, or press Enter or Return.

   

7. Save your work so far.

Using an alpha channel to create a shadow

Just as different information in an image is stored on different layers, channels also let you access specific kinds of information. Alpha channels store selections as grayscale images. Color information channels store information about each color in an image; for example, an RGB image automatically has red, green, blue, and composite channels.

To avoid confusing channels and layers, think of channels as containing an image’s color and selection information, and think of layers as containing painting, shapes, text, and other content.

You’ll first convert the transparent areas of the Model copy layer to a selection and then fill it with black on another layer to create a shadow. Because the selection will be altered to make the shadow, you’ll now save the current form of the selection as an alpha channel so that you can load it again later if needed.

1. In the Layers panel, Ctrl-click (Windows) or Command-click (macOS) the layer thumbnail icon for the Model Copy layer. The masked area is selected.

2. Choose Select > Save Selection. In the Save Selection dialog box, make sure New is chosen in the Channel menu. Then name the channel Model Outline, and click OK.

   

Nothing changes in the Layers panel or in the document window. However, a new channel named Model Outline has been added to the Channels panel. The selection is still active.

3. Click the Create A New Layer icon () at the bottom of the Layers panel. Drag the new layer below the Model Copy layer so that the shadow will be below the image of the model. Double-click the new layer’s name, and rename it Shadow.

   Note

   Some image file formats offer the option to save an alpha channel with the image document. If you use this option, Photoshop creates an alpha channel that includes all areas of the composite image that are not occupied by an opaque pixel.

4. With the Shadow layer selected, choose Select > Select And Mask. This loads the current selection into the Select And Mask task space.

5. Click the View menu in the View Mode section of the Properties panel, and choose On Black.

6. In the Global Refinements section, move the Shift Edge slider to +36%.

7. In the Output Settings section, make sure Selection is selected in the Output To menu, and then click OK.

   

8. Choose Edit > Fill. In the Fill dialog box, choose Black from the Contents menu, and then click OK.

   

The Shadow layer displays a filled-in black outline of the model. Shadows aren’t usually as dark as the person who casts them, so you’ll reduce the layer opacity.

9. In the Layers panel, change the layer opacity to 30%.

   

The shadow is in exactly the same position as the model, where it can’t be seen. You’ll shift it.

10. Choose Select > Deselect to remove the selection.

11. Choose Edit > Transform > Rotate. Rotate the shadow by hand, or enter −15^° in the Rotate field in the options bar. Then drag the shadow to the left, or enter 545 in the X field in the options bar. Click the Commit Transform button () in the options bar, or press Enter or Return, to accept the transformation.

    

12. Click the eye icon for the Episode Background layer to make it visible, and delete the Model layer (the one without the mask).

    

13. Choose File > Save to save your work so far.

Creating a pattern for the background

The design for the episode graphic incorporates a pattern into the background. You’ll quickly create the pattern by customizing a vector graphic shape.