Adobe Illustrator CS3 - Manual (Page 377)

ILLUSTRATOR CS3
User Guide
371
To understand how Illustrator divides objects into pixels, open a file that contains vector objects, choose View > Pixel
Preview, and magnify the artwork so that you can see its individual pixels. The placement of pixels is determined by
an invisible grid that divides the artboard into 1-point (1/72 inch) increments. If you move, add, or transform an
object, you’ll notice that the object snaps to the pixel grid. As a result, any anti-aliasing along the “snapped” edges of
the object (usually the left and top edges) disappears. Now deselect the View
> Snap To Pixel command, and move
the object. This time, you’ll be able to position the object between the grid lines. Notice how this affects the anti-
aliasing of the object. As you can see, making very minor adjustments can affect how the object is rasterized.
Pixel Preview off (top) compared to on (bottom)
Important: The pixel grid is sensitive to the ruler origin (0,0). Moving the origin of the ruler will change how Illustrator
rasterizes artwork.
See also
“About bitmap images” on page 258
Slices and image maps
About slices
Web pages can contain many elements—HTML text, bitmap images, and vector graphics, to name a few. In
Illustrator, you can use slices to define the boundaries of different web elements in your artwork. For example, if your
artwork contains a bitmap image that needs to be optimized in JPEG format, while the rest of the image is better
optimized as a GIF file, you can isolate the bitmap image using a slice. When you save the artwork as a web
page
using the Save For Web & Devices command, you can choose to save each slice as an independent file with its own
format, settings, and
color panel.
Slices in an Illustrator document correspond to table cells in the resulting web page. By default, the slice area is
exported as a image file that is enclosed in a table cell. If you want the table cell to contain HTML text and a
background color instead of an image file, you can change the slice type to No Image. If you want to convert
Illustrator text to HTML text, you can change the slice type to HTML Text.