Adobe illustrator 10 Manuale Utente

When designing graphics for the Web, you must consider different issues than when 
designing graphics for print. Here are some things to keep in mind: 

Color Color is often a key aspect of artwork. However, the colors you see on your artboard 
aren’t necessarily the colors that will appear in a Web browser. You can prevent dithering 
and other color problems by taking a few precautionary steps when creating Web 
graphics. First, always work in RGB color mode. Second, try to use Web-safe colors. 
(See 

.) 

File size Creating small graphics files is essential to distributing images on the Web. With 
smaller files, Web servers can store and transmit images more efficiently, and viewers can 
download images more quickly. You can view the size and the estimated download time 
for a Web graphic in the Save for Web dialog box. (See 

.)

File format The format in which you save a Web graphic determines the size and display 
characteristics of the file. In general, Web graphics formats fall into two categories: bitmap 
and vector. The bitmap formats—GIF, JPEG, and PNG—describe artwork as a series of 
colored dots called pixels. Each pixel in a bitmap image has a fixed size and is therefore 
resolution-dependent, meaning that dimensions of the image depend of the resolution of 
the monitor on which it is viewed. The vector formats—SVG and SWF—describe artwork 
mathematically, as a set of geometric objects. Because of this, vector graphics are 
resolution-independent and can be scaled up or down in a Web browser. 

Each Web file format has its own characteristics and uses. JPEG preserves the broad range 
and subtle variations in brightness and hue found in photographs and other continuous-
tone images. GIF and PNG-8 efficiently compress solid areas of color while preserving 
sharp detail, such as that in line art, logos, or illustrations with type. SVG and SWF maintain 
high-quality, vector artwork and produce smaller file sizes than bitmap formats. Both of 
these formats are ideal for creating animation frames and sophisticated Web effects. 

When you save artwork in a bitmap format—such as JPEG, GIF, or PNG—Illustrator 
rasterizes the artwork at 72 pixels per inch. You can preview how objects will appear when 
rasterized using pixel preview mode. This is especially helpful when you want to control 
the precise placement, size, and anti-aliasing of objects in a rasterized graphic.