Adobe Illustrator CS3 Manual de usuario descargar pdf (Pagina 264)

ILLUSTRATOR CS3

User Guide

258

Importing bitmap images

About bitmap images

Bitmap images—technically called raster images—use a rectangular grid of picture elements (pixels) to represent

images. Each pixel is assigned a specific location and color value. When working with bitmap images, you edit pixels

rather than objects or shapes. Bitmap images are the most common electronic medium for continuous-tone images,

such as photographs or digital paintings, because they can more efficiently represent subtle gradations of shades and

color.

Bitmap images are resolution-dependent—that is, they contain a fixed number of pixels. As a result, they can lose

detail and appear jagged if they are scaled to high magnifications on-screen or if they are printed at a lower resolution

than they were created for.

Example of a bitmap image at different levels of magnification

Bitmap images sometimes require large amounts of storage space, and often need to be compressed to keep file sizes

down when used in certain Creative Suite components. For instance, you compress an image file in its original appli

cation before you import it into a layout.

Note: In Adobe Illustrator, you can create bitmap effects in your artwork using filters, effects, and graphic styles.

See also

“About vector graphics” on page 52

Image resolution guidelines for final output

Bitmap images contain a fixed number of pixels, usually measured in pixels per inch (ppi). An image with a high

resolution contains more, and therefore smaller, pixels than an image of the same printed dimensions with a low

resolution. For example, a

1-inch-by-1-inch image with a resolution of 72 ppi contains a total of 5184 pixels (72

pixels wide x 72 pixels high = 5184). The same 1-inch-by-1-inch image with a resolution of 300

ppi would contain a

total of 90,000 pixels.

For imported bitmap images, image resolution is determined by the source file. For bitmap effects, you can specify

a custom resolution. To determine the image resolution to use, consider the medium of final distribution for the

image. The following guidelines can help you determine your requirements for image resolution:

Commercial printing Commercial printing requires 150 to 300 ppi (or more) images, depending on the press (dpi)

and screen frequency (lpi) you’re using; always consult your prepress service provider before making production

decisions. Because commercial printing requires large, high-resolution images, which take more time to display

while you’re working with them, you may want to use low-resolution versions for layout and then replace them with

high-resolution versions at print time.

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Adobe Illustrator CS3 Manual de usuario Pagina 264