Apple Numbers '08 - Manual (Page 174)

174 Chapter 8 Working with Shapes, Graphics, and Other Objects
3 Click the color you want to make transparent, and then drag slowly over it.
As you drag, the selection grows to include the area that uses the same color. You can
control how much of the image is selected by dragging less or more.
4 Repeat step 3 as many times as you like.
5 Press Return or click outside the image when you’re done.
You can restore the parts removed from the image at any time. To revert to the original
image, choose Format > Remove Instant Alpha. To restore parts of the image removed
using Instant Alpha, choose Edit > Undo Instant Alpha until the parts have been
restored.
Changing an Image’s Brightness, Contrast, and Other Settings
You can change the brightness, contrast, and other settings of images to improve their
quality or to create interesting effects. Adjustments you make don’t affect the original
image; they affect only the image’s appearance in Numbers.
To adjust an image:
1 Select the image.
Dragging selects the
contiguous area that
uses the same color.
Dragging more here...
...selects more of
the image.