Adobe Photoshop CS4 - Manual (Page 61)

54 Last updated 1/10/2010
Chapter 3: Opening and importing images
Adobe® Photoshop® CS4 can open and import many types of graphic files. To work effectively, you should understand
basic imaging concepts, and how to acquire, import, and resize images.
Image essentials
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
application before you import it into a layout.
Note: In Adobe Illustrator, you can create bitmap effects in your artwork using effects and graphic styles.
More Help topics
“ About vector graphics ” on page 54
About vector graphics
Vector graphics (sometimes called vector shapes or vector objects) are made up of lines and curves defined by
mathematical objects called vectors, which describe an image according to its geometric characteristics.
You can freely move or modify vector graphics without losing detail or clarity, because they are resolution-
independent—they maintain crisp edges when resized, printed to a PostScript printer, saved in a PDF file, or imported
into a vector-based graphics application. As a result, vector graphics are the best choice for artwork, such as logos, that
will be used at various sizes and in various output media.
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