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Saving Selections

Create, save and recall a selection as an alpha channel


Alpha Channels

Alpha channels are a convenient way to create and save selections.  By saving the selection, we can recall the selection whenever we need.  Figure 1 is a review of the Channels panel.  The top four layers are the composite and individual color channels.  The next layer is an alpha channel.  And the bottommost layer is a special alpha channel called Quick Mask.  We can have many alpha channels, but we can only have one Quick Mask.

Channels panel

Figure 1.  Channels Panel

Masks and Selections

A selection is stored in an alpha channel as a grayscale mask, as seen in Figure 2c.  An important principle to remember when dealing with masks is the image area that is totally masked is the area that is not selected.  Areas that are partially masked, are partially selected.  And areas that are not masked, are fully selected.

Figure 2a shows an image as it would normally appear in the Photoshop document window.  When creating an alpha channel selection, as explained below, we will paint over the image in the document window.  Black paint will be used to mask an area.  White paint will be used to select an area.  Gray paint will be used to partially select an area.  Even though the paint being used will be black, white or gray, as we paint we will be either adding to a mask overlay color or erasing it.

In Figure 2b, the overlay color is magenta.  Figure 2b shows what the document window will look like as we paint in an alpha channel.  The image area covered by the magenta overlay color is being masked.  Therefore, it will not be part of the selection.  The area of the image where there is no overlay color, is the area being selected.  Figure 2c shows what the grayscale mask stored in the alpha channel looks like.  The white area is the selected area.  The black area is the masked area.

Document window Figure 2a.  The normal document window

Alpha channel overlay Figure 2b.  The alpha channel overlay mask

Alpha channel mask Figure 2c.  The alpha channel grayscale mask


Creating And Saving A Selection

  1. Make the Channels panel the active panel.
  2. Alt + click (Option + click) the Create New Channel icon New Channel icon at the bottom of the Channels panel.
  3. In the New Channel dialog box, type a relevant name.
  4. If most of the image is to be masked (not selected), click the Masked Areas radio button.  If most of the image is to be selected, click the Selected Areas radio button.
  5. If desired, click the Color box to change the overlay color.
  6. Leave Opacity 50%, unless you desire otherwise.
  7. Click OK.
  8. The document window will be filled with either solid black if Masked Areas was chosen or solid white if Selected Areas was chosen.
  9. Make the composite color channel active by clicking in the visibility area and displaying its eye icon Eye icon.
  10. If Masked Areas was chosen...
    1. The document window will show the image covered by the overlay color.
    2. Type the letter d to make the foreground and background colors the default black and white default black.
    3. If white is not the foreground color, type the letter x until white is the foreground color default white.
    4. Type the letter b to make the Brush tool Brush tool the active tool.
    5. Using a brush size and softness of your choice, paint in the document window.  Wherever you paint with white paint, the mask will be erased.  Any part of the image not covered by the overlay color is being selected.  Painting with gray paint will partially select an area.
  11. If Selected Areas was chosen...
    1. The document window will show the image normally.
    2. Type the letter d to make the foreground and background colors the default black and white default black..
    3. If black is not the foreground color, type the letter x until black is the foreground color.
    4. Type the letter b to make the Brush tool Brush tool the active tool.
    5. Using a brush size and softness of your choice, paint in the document window.  Wherever you paint with black paint, the image will be covered by the overlay color.  Any part of the image covered with the overlay color is being masked, or de-selected.  Painting with gray paint will partially de-select an area.
  12. Repeat steps 2 through 11 as many times as needed to create individual custom selections.
  13. When finished, turn off the visibility of the alpha channel by clicking the alpha channel's eye icon Eye icon.
  14. Make the Layers panel the active panel by clicking the Layers tab.
  15. When the file is next saved, the alpha channel(s) will also be saved.

Modifying a selection

One of the nice features about alpha channel selections is you do not have to keep working on the selection until it is completely done.  Since it is saved as an alpha channel, you can create and add to it over time.  To modify an existing selection, follow these steps.

  1. Make the Channels panel active.
  2. Make the desired alpha channel active by clicking in the visibility area and displaying its eye icon Eye icon.
  3. If for some reason the document window displays the grayscale mask instead of the overlay color, click in the visibility area of the composite color channel to display its eye icon Eye icon.
  4. As described above, paint with black, white and/or gray paint to modify the selection.  Black paint will mask an area.  White paint will select an area.  And gray paint will partially select an area.
  5. When the file is next saved, your changes will also be saved.

Recalling A Selection

To recall a saved selection.

  1. Click Select > Load Selection.
  2. In the Load Selection dialog box, use the Channel drop down box to selection the desired alpha channel.
  3. If you want the resulting selection to be the inverse of what is stored in the alpha channel, check Invert.
  4. If a selection is not currently active, New Selection will be selected.  If a selection is already active, selecting...
    • New Selection will replace the active selection with the selection stored in the alpha channel.
    • Add to Selection will append the selection stored in the alpha channel to the active selection.
    • Subtract from Selection will subtract the selection stored in the alpha channel from the active selection.
    • Intersect with Selection will create a new selection of only those areas where both the active selection and the alpha channel selection overlap.
  5. Click OK.

Quick Mask

Quick Mask is a convenient feature for creating a single alpha channel selection.  However, it is not intuitive as to when Photoshop will save the Quick Mask selection as part of the file and when it will not.  Therefore, I do not use Quick Mask.  I use the method described above to create selections I wish to save.  However, Quick Mask is explained here for those who wish to try it.
 

Create a Quick Mask selection.

  1. Make sure the Layers panel and not the Channels panel is active.
  2. Type the letter d to make the foreground and background colors the default black and white default black.
  3. Type the letter b to make the Brush tool Brush tool active tool.
  4. In the Tools panel, click the Quick Mask icon Quick Mask icon.
  5. To mask an area (not select it), use a brush size and softness of your choice and paint in the document window with black paint.  The area being painted will be covered by the Quick Mask overlay color.
  6. To select an area, paint with white paint.
  7. To partially select an area, paint with gray paint.
  8. If you accidentally paint an area with the wrong color, do not click Select > Deselect.  Instead, paint over the area with the correct color paint.
  9. When the areas you do not want selected are covered with the overlay color, click the Standard Mode icon Standard Mode icon on the bottom of the Tools panel.  Photoshop will replace the overlay color with the typical selection grid.
  10. You can switch back and forth between Standard mode and Quick Mask mode and paint until you get the selection you desire.

 

Key Points

Some important points to remember while working in Quick Mask mode.

 

Saving a Quick Mask Selection

To save a Quick Mask selection, I recommend saving it as a normal alpha channel by clicking Select > Save Selection while in Standard Mode.  Name the selection something meaningful.  By saving it as a normal alpha channel, you are assured the selection will be saved when the file is saved.  But keep in mind that once the selection is saved as a normal alpha channel, you will not be able to use the Quick Mask icon to recall the selection.  However, you can recall the selection by following the Recalling A Selection steps above.