Photoshop CS5 All 5_10 by odiaworld

VIEWS: 4 PAGES: 10

									                                          Introducing Alpha Channels                469

they appear white in the alpha channel. If an alpha channel includes gray
areas, those areas are partially selected (or partially unselected, depending
on whether you think the glass is half full or half empty).


               Original image                             Alpha channel mask




                                                                                                      Book VI
                                                                                                     Chapter 1




                                                                                                           Using Channels
                                                                              Corbis Digital Stock
Figure 1-10: The alpha channel makes selecting this shape much easier than using the Lasso
or Magic Wand tool.


You can create a mask by first duplicating a color channel and then editing
that channel with painting and editing tools and filters. (See Book VI,
Chapter 3 for the details.) You can also create an alpha channel by saving a
selection you’ve created. After you create a channel mask or save a selection
as an alpha channel, you can load that channel to use it as a selection in any
image. The following sections explain how to save a selection as an alpha
channel and load a selection.


Saving a selection as an alpha channel
One of the great things about alpha channels is that you can save them and
then retrieve them time and time again, which can be especially handy if
you’ve taken a lot of time and effort to create the selection. Why reinvent the
wheel if you want to select the element again in the future? Sure, you can
create a mask by using Quick Mask mode and Color Range (see Book VI,
Chapter 2), but those masks are only temporary.

After you make the initial selection, saving it is a piece of cake. Follow these
steps:

 1. Make a selection in your image. (See Book III for help.)
 2. Choose Select➪Save Selection.
    You can also click the Save Selection as Channel button (a circle on a
    square icon) at the bottom of the Channels panel. A new channel
    appears with the default name of Alpha 1, bypassing Steps 3 and 4.
470   Introducing Alpha Channels


          3. Select a destination image in the Document pop-up menu.
             You can select your current image, any other open image that has the
             same pixel dimensions, or a new image.
          4. Select a destination channel from the Channel pop-up menu.
             You can select a new channel, an existing             Composite     Alpha channel
             alpha channel, or a layer mask. (See Book VI,
             Chapter 3 for more on layer masks.)
              • If you select New, name the channel.
              • If you select an existing alpha channel or
                layer mask, select your desired opera-
                tion: Replace, Add To, Subtract From, or
                Intersect. These commands add to, sub-
                tract from, or intersect your current
                selection with the existing alpha channel.
          5. Click OK.
                                                                Figure 1-11: Saving your
             Your alpha channel is complete and appears      selection as an alpha channel
             in the Channels panel, as shown in Figure 1-11. allows you to efficiently reuse
                                                                the selection.

         Loading an alpha channel
         If you’ve gone through the trouble of creating an alpha channel, it’s no doubt
         because you want to easily load (or access) the selection again and again. To
         load an alpha channel, use any one of these many methods:

          ✓ Choose Select➪Load Selection. In the Load Selection dialog box, select
            your document and channel. Click Invert to swap selected and
            unselected areas. If your image has an active selection, choose how you
            want to combine the selections.
          ✓ Select the alpha channel in the Channels panel, click the Load Channel
            as Selection icon at the bottom of the panel, and then click the compos-
            ite channel.
          ✓ Drag the channel to the Load Channel as Selection icon.
          ✓ Ctrl-click (Ô-click on the Mac) the alpha channel in the Channels panel.
          ✓ Ctrl+Shift-click (Ô+Shift-click on the Mac) to add the alpha channel to an
            active selection.
          ✓ Ctrl+Alt-click (Ô+Option-click on the Mac) to subtract the alpha channel
            from an active selection.
          ✓ Ctrl+Alt+Shift-click (Ô+Option+Shift-click on the Mac) to intersect the
            alpha channel with an active selection.
                                                 Using the Channel Mixer           471

      Adding channels can start to bloat your file size, so use them judiciously.
      The Photoshop native format and TIFF format compress channel information
      and therefore are good file formats to use when working with a lot of chan-
      nels. The only formats that preserve alpha channels are Photoshop, TIFF,
      PDF, PICT, Pixar, Photoshop Raw. BMP, TGA (Targa), and PSB (Photoshop
      large format).



Using the Channel Mixer
      The Channel Mixer actually does what its name implies — it mixes color
      channels. This feature lets you repair bad channels and produce grayscale              Book VI
      images from color images. It also allows you to create tinted images and              Chapter 1
      more intense special effects. Finally, it allows you to do the more mundane
      tasks of swapping or duplicating channels.




                                                                                                  Using Channels
      Although some Photoshop elitists worldwide tout the Channel Mixer as an
      advanced feature not to be mucked with by amateurs, I say, “Give it a whirl.”
      Intimidation is a nasty roadblock to creative fun. Just make a backup copy of
      an image before diving into the mix by following these steps:

       1. Select the composite channel in
          the Channels panel.
          If you have an RGB image, the com-
          posite channel is the RGB channel;
          for CMYK images, it’s the CMYK
          channel.
       2. Choose Image➪Adjustments➪
          Channel Mixer.
          The Channel Mixer dialog box
          appears, as shown in Figure 1-12.
       3. If desired, select a Preset from the
          pop-up menu.
          CS5 provides an assortment of
                                                Figure 1-12: Among its many capabilities,
          Black and White presets you can
                                                the Channel Mixer enables you to repair
          use to convert your color images
                                                bad channels.
          to grayscale. This is a great conver-
          sion method because it preserves
          detail and provides very good contrast control.
       4. For Output Channel, select the channel in which to blend one or more
          source (existing) channels.
472   Using the Channel Mixer


             For example, if your Blue channel is lousy, select it from the Output
             Channel drop-down list. Note that if you’re using one of the black and
             white presets, you have only the Gray channel available.
          5. Drag any source channel’s slider to the left to decrease the channel’s
             effect on the Output channel or drag to the right to increase the effect.
             Because my Blue channel contains artifacts and dithering picked up by
             the scanner, I’m raising the Red and Green values from 0% to 25% and low-
             ering the Blue value from 100% to 50%. To retain good contrast, try to use
             a combo of Red, Green, and Blue values that add up to close to 100%.
             You can also enter a value from –200% to +200%. Using a negative value
             inverts the color data of the source channel.
          6. Tinker with the Constant option to add a Black or White channel of
             varying opacity.
             This option adjusts the grayscale value of the selected Output channel.
             Drag the slider to a negative value to get a Black channel. Positive values
             give a White channel.
             This option brightens or darkens the overall image, but it may cause
             strange color shifts if adjusted to the extreme. I recommend leaving it at
             0 most of the time. But try it. It may help.
          7. Select Monochrome to apply the same settings to all output channels,
             producing a color image that has only values of gray.
             This is another great way to produce a grayscale image from a color
             image. Adjust the individual sliders to mix the values until you’re satis-
             fied with the contrast.
             You can save (and load) any of your custom settings by clicking the
             Preset Option button just to the left of the OK button.
          8. Click OK to exit the Channel Mixer.
             After you exit the Channel Mixer, choose Image➪Mode➪Grayscale to
             complete the conversion.
             If you select and then deselect the Monochrome option, you can modify
             the blend of each channel separately. By doing so, you can create color
             images that appear to be hand-tinted with color inks. Go for the subtle
             treatment or a more intensely colored look.
             Swapping color channels can produce some bizarre color effects. For
             example, try selecting the Red channel from the Output Channel drop-
             down list. Set the Red source channel to 0 and then set the Green source
             channel to 100. Try other combinations, Green for Blue, Blue for Red,
             and so on. Sometimes, they can be downright freakish, but occasionally
             you may stumble on one that’s worthy.
                                                       Using the Channel Mixer               473

Putting It Together

      Giving Flat Art Highlights and Shadows
      Sometimes, you need to give your art — whether it’s a photo or another type of image —
      a little shine and shadow to bring it to life. You can do this by creating and saving your
      selections as alpha channels and filling them with translucent color. The great thing
      about alpha channels is that because you save them with your document, you can use
      them time and time again. Just follow these steps:

      1.   Create a simple piece of artwork to
           use as a basis for your shadows and                                                      Book VI
           highlights.                                                                             Chapter 1
           I created a pool ball by creating
           two layers. On each layer, I used




                                                                                                         Using Channels
           the Elliptical Marquee tool to
           create different-sized circles.
           I filled each circle with a separate
           color, as shown in the figure.
           To follow along with these steps,
           you can download this image
           from this book’s Web site. (See
           the Introduction for details.)
      2.   Choose Window➪Channels.
           The Channels panel appears.
           Be sure to keep this panel visible because you’ll be creating new channels for the
           highlights.
      3.   Select the Pen tool from the Tools panel and create a path for the highlight.
           I created a path for the highlight on the top-left portion of the ball in my example,
           assuming that the light source is coming from the upper-left corner. If the Pen tool
           seems like a foreign object to you, check out Book III, Chapter 2.
      4.   Choose Window➪Paths.
           The Paths panel appears.
      5.   Click the Load Path as Selection icon (a dotted circle) at the bottom of the Paths
           panel.
           Your work path disappears and a selection marquee appears.
      6.   Choose Select➪Save Selection.
           The Save Selection dialog box appears.
                                                                                       continued
474   Using the Channel Mixer


  continued
         7.   Name the channel. Make sure to select New Channel under Operation and
              click OK.
              An additional channel appears in the Channels panel, as shown in the preceding
              figure. This new channel is the alpha channel — your saved selection.
         8.   Click the Create a New Layer icon (the dog-eared page) in the Layers panel.
              Double-click the layer name and rename it.
              I named mine large highlight.
              Putting your highlights and shadows on separate layers is important so that you
              can apply different opacity settings and also retain the ability to tweak them later,
              if needed.
         9.   Choose Edit➪Fill, select the White option for Contents, and leave all the other
              options at their default settings. Click OK to close the Fill dialog box.
              Your highlight is now filled with white. Don’t worry; it won’t stay this opaque.




        10.   In the Layers panel, adjust the Opacity setting to 50%.
              The highlight now appears translucent. (Refer to the preceding figure.)

        11.   Select the Pen tool and create a path for the
              highlight on the bottom of the object, as shown
              in the figure.
              Make sure the path matches up to the edge of the
              object. Use the Direct Selection tool if you need
              to adjust the anchor points or curve segments of
              the path.
        12.   In the Paths panel, click the third icon from the left
              at the bottom of the panel.
              The work path disappears, and a selection marquee appears.
                                                  Using the Channel Mixer              475


13.   Choose Select➪Save Selection. In the Save Selection dialog box that appears,
      name the channel. Make sure to select New Channel under Operation and
      click OK.
      Mine is called bottom highlight. Another alpha channel appears in the Channels
      panel.
14.   Repeat Steps 8 through 10, but adjust the opacity
      to only 30% as shown in the figure.
15.   Use the Pen tool to create a path for the smaller
      shadow.
                                                                                              Book VI
      For example, I created a path on the bottom-right                                      Chapter 1
      portion of the ball.
16.   Load the path as a selection in the Paths panel and




                                                                                                   Using Channels
      choose Select➪Modify➪Feather. In the Feather
      Selection dialog box, enter 3 pixels and click OK.
      The idea is to give the shadow a softer edge.
17.   Repeat Steps 6 through 10, but fill the selection
      with black, rather than white, and adjust the
      opacity to 20%.
      The shadow is shown in the figure.
18.   Use a selection tool to add a cast shadow.
      In my example, I used the Elliptical Marquee tool to
      create an ellipse at the base of the ball by holding
      down Alt (Option on the Mac) and dragging the
      mouse. The resulting selection is shown in the figure.
      Then, I feathered the selection 25 pixels before I saved the selection.
      The cast shadow needs to have really fuzzy edges, thus the large number of pixels
      for the feather.
19.   Repeat Steps 8 and 9, filling the selection with black.
      My highlighted and shadowed pool ball is ready to roll, shown in the figure.
      If your cast shadow layer is above your object, you have to change the stacking
      order and move your shadow layer so that it’s below your object.
      Now that you’ve spent all this time on the front end creating your alpha channels,
      you can save time on the back end by using those alpha channels to apply highlights
      and shadows to similar artwork.
                                                                                continued
476   Using the Channel Mixer

  continued
        20.   To load alpha channels, choose Select➪Load Selection and select an alpha chan-
              nel from the Channel pop-up menu. Then, repeat the applicable steps for creating
              new layers, filling them with color, and adjusting their opacity.
              In my example, I took the highlights and shadows I created with lucky pool ball
              number 7 and loaded them as alpha channels in pool ball number 5.
Chapter 2: Quick-and-Dirty
Masking
In This Chapter
✓ Using Quick Masks
✓ Working with Color Range
✓ Selecting by erasing



M       asking is essentially just another way of making a selection. Instead
        of defining your selection with a selection outline, masks define your
selection with up to 256 levels of gray, which allows you to have varying lev-
els of selection. Photoshop masks (or protects) unselected pixels from any
commands you execute. Photoshop doesn’t mask selected pixels, making
them fair game to any executed commands.

Different types of masks have different purposes — channel masks, layer
masks, and vector masks. You can use them to temporarily make a selec-
tion, save and load selections, define vector shapes, selectively apply an
adjustment layer or filter, blend one layer into another, and so on.
Although selecting with the Marquee, Lasso, Magic Wand, and
Pen tools can be fine, you’ll soon find that these tools have a
limited repertoire: You can’t use them with much accu-
racy on more complex images. That’s when you turn to
masking.

Most things that pack a powerful punch are either
expensive or hard to master, or both. Well, you
already forked out a pretty penny for Photoshop.
And yes, masking isn’t for those who get their selec-
tions via a drive-thru window. To help you with the
learning curve, in this chapter I ease you into mask-
ing by using Photoshop’s automated masking tools.
Although they aren’t quite as accurate as the hardcore
masking I cover in Book VI, Chapter 3, they’re easier on
you, and with certain images (or a serious time crunch),
the quick-and-dirty masking tools get the job done.
478   Working with Quick Masks



Working with Quick Masks
         As you can probably guess from the name, Quick Masks allow you to create
         and edit selections quickly without having to bother with the Channels
         panel. Although you don’t really create an end-product mask per se, the
         way you go about getting your selection is “masklike.” They’re also user-
         friendly in that they allow you to see your image while you’re working. You
         can begin your Quick Mask by using a selection tool or a painting tool. After
         you have your Quick Mask, you can edit the mask by using any painting or
         editing tool.

         Quick Masks are temporary, so if you create one you really like, be sure to
         choose Select➪Save Selection at the end of the following steps. (Note that
         you have to be out of Quick Mask mode to do this.) That way, you can save
         the selection as an alpha channel. For more on saving selections as alpha
         channels, see Book VI, Chapter 1.

         Follow these steps to create your very own Quick Mask:

          1. Open a new document and, using any selection tool, select the ele-
             ment you want in your image.
             Don’t worry about getting the selection perfect. You can fine-tune your
             selection after you have the Quick Mask in place. Note that you can also
             just paint your mask from scratch. But I think that starting with a selec-
             tion is easier.
          2. Click the Edit in Quick Mask Mode button in the Tools panel (or press
             the Q key).
             If your Quick Mask settings are at the default, a color overlay covers and
             protects the area outside the selection, as shown in Figure 2-1. The
             selected pixels are unprotected.
          3. Refine the mask by using a painting or editing tool.
             Paint with black to add to the mask, thereby making the selection
             smaller. Even though you’re painting with black, your strokes show up
             as a red overlay, as shown in Figure 2-2. This red overlay is a visual car-
             ryover from back in the day when artists used Rubylith (red transparent
             material) to mask portions of their art during airbrushing. Paint with
             white to delete from the mask, making the selection larger. Paint with a
             shade of gray to partially select the pixels. Partially selected pixels take
             on a semitransparent look, perfect for feathered edges.

								
To top