Page 133 - Enhancing CAD Drawings with Photoshop

4386.book Page 116 Monday, November 15, 2004 3:27 PM

116 CHAPTER 4 YOU AND YOUR ENTOURAGE

9. Select the Edge Touchup tool (press T) and drag along the edges of the main trunk. The tree
bark looks harder. Click OK to accept all the changes you have made up to this point, and close
the Extract dialog box. Notice how the Background layer was automatically converted to Layer 0,
which now contains pixels of the foreground object surrounded by transparency.

Now that you have completed the extraction, you can do several things to improve the image
before it becomes part of your entourage. Whenever you are working on a layer with trans-
parency (such as Layer 0), create a Backdrop layer to help you see the fringes of the object.
It is wise to view your prospective entourage against both black and white backdrops alter-
nately as you are refining the extraction. Most images have bright or dark pixels that do not
belong with the foreground object; these pixels are visible only against a contrasting backdrop.
10. Create a new layer (press Shift+Ctrl+N). Give the new layer the name Backdrop. Drag this layer
below Layer 0 in the Layers palette. Reset the default colors (press D). Fill the Backdrop layer
with the foreground color (press Alt+Backspace). Now the backdrop layer is black. Click Layer 0
to make this the current layer for editing.

The Magic Eraser is a tool that you must be careful using. Each time you click the Magic Eraser,
you have the power to erase many similar pixels in the image to transparency. It is safer (and
slower) to work in Contiguous mode, where the tool will affect only similar pixels that are con-
nected to the point you click. If you do not use the Contiguous option, the Magic Eraser will
work on all similar pixels in the image at once.
11. Choose the Magic Eraser tool from the toolbox; this is under the Eraser tool, and you can also
access it by pressing Shift+E multiple times to cycle through the three types of Eraser tools in
Photoshop. On the Options bar, choose a Tolerance of 15, check Anti-aliased, leave Contiguous
and All Layers unchecked, and leave Opacity at 100%. Finally, press the Caps Lock key.

TIP Pressing the Caps Lock key activates the precise cursor, which appears as cross hairs centered on
the tool’s hot spot. The hot spot is where the tool takes effect in the image. Most tools have icons
whose hot spots vary in position relative to the pointer.
Each time you click the Magic Eraser, you erase many pixels in the tree image. The Magic
Eraser is sensitive to the exact pixel color you select. If you think too many pixels disappear
when you use this tool, undo and try again. You can also adjust Tolerance to a lower value to
affect fewer pixels.
12. Now that you have a black backdrop, white fringe areas will be evident around some of the
leaves. Using the Magic Eraser with the precise cursor, carefully click a white pixel. All similar
pixels are erased to transparency. Repeat this step until you are satisfied that the white fringe
has disappeared, all the while being careful not to erase any important parts of the foliage (see
Figure 4.19).