Adobe Illustrator CS4 Manual do Utilizador descarregar pdf (Página 294)

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USING ADOBE ILLUSTRATOR CS4

Importing, exporting, and saving

• Subsampling Chooses a pixel in the center of the sample area and replaces the entire area with that pixel color.

Subsampling significantly reduces the conversion time compared with downsampling but results in images that are

less smooth and continuous.

• Bicubic Downsampling Uses a weighted average to determine pixel color, which usually yields better results than

the simple averaging method of downsampling. Bicubic is the slowest but most precise method, resulting in the

smoothest gradations.

Compression Determines the type of compression that is used. The Automatic option automatically sets the best

possible compression and quality for the artwork contained in the file. For most files, this option produces satisfactory

results. Use Automatic (JPEG) if you need the greatest compatibility. Use Automatic (JPEG2000) for superior

compression.

• ZIP compression Works well on images with large areas of single colors or repeating patterns, and for black-and-

white images that contain repeating patterns. ZIP compression can be lossless or lossy, depending on the Quality

setting.

• JPEG compression Is suitable for grayscale or color images. JPEG compression is lossy, which means that it removes

image data and may reduce image quality; however, it attempts to reduce file size with a minimal loss of information.

Because JPEG compression eliminates data, it can achieve much smaller file sizes than ZIP compression.

• JPEG2000 Is the new international standard for the compression and packaging of image data. Like JPEG

compression, JPEG2000 compression is suitable for grayscale or color images. It also provides additional advantages,

such as progressive display.

• CCITT and Run Length compression Are only available for monochrome bitmap images. CCITT (Consultative

Committee on International Telegraphy and Telephony) compression is appropriate for black-and-white images and

any images scanned with an image depth of 1 bit. Group 4 is a general-purpose method that produces good

compression for most monochrome images. Group 3, used by most fax machines, compresses monochrome bitmaps

one row at a time. Run

Length compression produces the best results for images that contain large areas of solid black

or white.

Image Quality Determines the amount of compression that is applied. The available options depend on the

compression method. For JPEG Compression, Illustrator provides Minimum, Low, Medium, High, and Maximum

Quality options. For ZIP compression, Illustrator provides 4-bit and 8-bit Quality options. If you use 4-bit ZIP

compression with 4-bit images, or 8-bit ZIP compression with 4-bit or 8-bit images, the ZIP method is lossless; that is,

data is not removed to reduce file size, so image quality is not affected. Using 4-bit ZIP compression with 8-bit data

can affect the quality, however, because data is lost.

Tile Size This option is only enabled when its corresponding Compression setting is JPEG2000. It determines the size

of the tiles for progressive display.

Compress Text And Line Art Applies compression to all text and line art in the file. This method results in no loss of

detail or quality.

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Adobe Illustrator CS4 Manual do Utilizador Página 294