Adobe photoshop cs2 Manuale Utente
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ADOBE PHOTOSHOP CS2
User Guide
File formats
About file formats
Graphics file formats differ in the way they represent image data (as pixels or as vectors), in compression technique,
and in which Photoshop and ImageReady features they support. With a few exceptions (for instance Large
Document Format (PSB), Photoshop Raw, and TIFF), most file formats cannot support documents larger than 2 GB.
and in which Photoshop and ImageReady features they support. With a few exceptions (for instance Large
Document Format (PSB), Photoshop Raw, and TIFF), most file formats cannot support documents larger than 2 GB.
Note: If a supported file format does not appear in the appropriate dialog box or submenu, you may need to install the
format’s plug-in module.
format’s plug-in module.
See also
About file compression
Many file formats use compression to reduce the file size of bitmap images. Lossless techniques compress the file
without removing image detail or color information; lossy techniques remove detail. The following are commonly
used compression techniques:
without removing image detail or color information; lossy techniques remove detail. The following are commonly
used compression techniques:
RLE (Run Length Encoding)
Lossless compression; supported by some common Windows file formats.
LZW (Lemple-Zif-Welch)
Lossless compression; supported by TIFF, PDF, GIF, and PostScript language file formats.
Most useful for images with large areas of single color.
JPEG (Joint Photographic Experts Group)
Lossy compression; supported by JPEG, TIFF, PDF, and PostScript
language file formats. Recommended for continuous-tone images, such as photographs. JPEG uses lossy
compression. To specify image quality, choose an option from the Quality menu, drag the Quality pop-up slider, or
enter a value between 0 and 12 (Photoshop) or 0 and 100 (ImageReady) in the Quality text box. For the best printed
results, choose maximum-quality compression. JPEG files can be printed only on Level 2 (or later) PostScript
printers and may not separate into individual plates.
compression. To specify image quality, choose an option from the Quality menu, drag the Quality pop-up slider, or
enter a value between 0 and 12 (Photoshop) or 0 and 100 (ImageReady) in the Quality text box. For the best printed
results, choose maximum-quality compression. JPEG files can be printed only on Level 2 (or later) PostScript
printers and may not separate into individual plates.
CCITT
A family of lossless compression techniques for black-and-white images; supported by the PDF and
PostScript language file formats. (CCITT is an abbreviation for the French spelling of International Telegraph and
Telekeyed Consultive Committee.)
Telekeyed Consultive Committee.)
ZIP
Lossless compression; supported by PDF and TIFF file formats. Like LZW, ZIP compression is most effective for
images that contain large areas of single color.
PackBits (ImageReady)
Lossless compression that uses a run-length compression scheme; supported by the TIFF
file format in ImageReady only.
Photoshop format (PSD)
Photoshop format (PSD) is the default file format and the only format, besides the Large Document Format (PSB),
that supports most Photoshop features. Because of the tight integration between Adobe products, other Adobe appli
cations such as Adobe Illustrator, Adobe InDesign, Adobe Premiere, Adobe After Effects, and Adobe GoLive can
directly import PSD files and preserve many Photoshop features. For more information, see Help for the specific
Adobe applications.
that supports most Photoshop features. Because of the tight integration between Adobe products, other Adobe appli
cations such as Adobe Illustrator, Adobe InDesign, Adobe Premiere, Adobe After Effects, and Adobe GoLive can
directly import PSD files and preserve many Photoshop features. For more information, see Help for the specific
Adobe applications.