Adobe Photoshop CS4 - Manual (Page 474)

467 USING PHOTOSHOP CS4
Saving and exporting images
Last updated 1/10/2010
JPEG format
Joint Photographic Experts Group (JPEG) format is commonly used to display photographs and other continuous-
tone images in hypertext markup language (HTML) documents over the World Wide Web and other online services.
JPEG format supports CMYK, RGB, and Grayscale color modes, and does not support transparency. Unlike GIF
format, JPEG retains all color information in an RGB image but compresses file size by selectively discarding data.
A JPEG image is automatically decompressed when opened. A higher level of compression results in lower image
quality, and a lower level of compression results in better image quality. In most cases, the Maximum quality option
produces a result indistinguishable from the original.
Large Document Format
The Large Document Format (PSB) supports documents up to 300,000 pixels in any dimension. All Photoshop
features, such as layers, effects, and filters, are supported. (With documents larger than 30,000 pixels in width or height,
some plug-in filters are unavailable.)
You can save high dynamic range, 32-bits-per-channel images as PSB files. Currently, if you save a document in PSB
format, it can be opened only in Photoshop CS or later. Other applications and earlier versions of Photoshop cannot
open documents saved in PSB format.
Note: Most other applications and older versions of Photoshop cannot support documents with file sizes larger than 2 GB.
More Help topics
“ Save large documents ” on page 448
OpenEXR format
OpenEXR (EXR) is a file format used by the visual effects industry for high dynamic range images. The film format
has high color fidelity and a dynamic range suitable for use in motion picture production. Developed by Industrial
Light and Magic, OpenEXR supports multiple lossless or lossy compression methods. An OpenEXR file supports
transparency and only works with 32 bits/channel images; the file format stores the values as 16 bits/channel floating
point.
PCX
PCX format is commonly used by IBM PC-compatible computers. Most PC software supports version 5 of PCX
format. A standard VGA color palette is used with version 3 files, which do not support custom color palettes.
PCX format supports Bitmap, Grayscale, Indexed Color, and RGB color modes, and does not support alpha channels.
PCX supports the RLE compression method. Images can have a bit depth of 1, 4, 8, or 24.
PDF
Portable Document Format (PDF) is a flexible, cross-platform, cross-application file format. Based on the PostScript
imaging model, PDF files accurately display and preserve fonts, page layouts, and both vector and bitmap graphics. In
addition, PDF files can contain electronic document search and navigation features such as electronic links. PDF
supports 16-bits-per-channel images. Adobe Acrobat also has a Touch Up Object tool for minor editing of images in
a PDF. For more information about working with images in PDFs, see Acrobat Help.
Note: The Touch Up Object tool is mainly for last-minute revisions to images and objects. It’s best to do image editing in
Photoshop before saving as PDF.