Adobe PHOTOSHOP CS2, Руководство пользователя

Страница: 692 / 815

684 ADOBE PHOTOSHOP CS2
User Guide
The Photoshop Raw format consists of a stream of bytes describing the color information in the image. Each pixel is
described in binary format, with 0 representing black and 255 white (for images with 16-bit channels, the white value
is 65535). Photoshop designates the number of channels needed to describe the image, plus any additional channels
in the image. You can specify the file extension (Windows), file type (Mac OS), file creator (Mac OS), and header
information.
In Mac OS, the file type is generally a four-character ID that identifies the file—for example, TEXT identifies the file
as an ASCII text file. The file creator is also generally a four-character ID. Most Mac OS applications have a unique
file creator ID that is registered with the Apple Computer Developer Services group.
The Header parameter specifies how many bytes of information appear in the file before actual image information
begins. This value determines the number of zeroes inserted at the beginning of the file as placeholders. By default,
there is no header (header size = 0). You can enter a header when you open the file in Raw format. You can also save
the file without a header and then use a file-editing program, such as HEdit (Windows) or Norton Utilities®
(Mac OS), to replace the zeroes with header information.
You can save the image in an interleaved or noninterleaved format. If you choose interleaved, the color values (red,
green, and blue, for example) are stored sequentially. Your choice depends on requirements of the application that
will open the file.
Note: A Photoshop Raw image is not in the same file format as a camera raw image file from a digital camera. A camera
raw image file is in a camera-specific proprietary format that is essentially a “digital negative,” with no filtering, white
balance adjustments, or other in-camera processing.
See also
“Saving large documents” on page 655
Radiance format
Radiance (HDR) is a 32-bits-per-channel file format used for high dynamic range images. This format was originally
developed for the Radiance system, a professional tool for visualizing lighting in virtual environments. The file
format stores the quantity of light per pixel instead of just the colors to be displayed on-screen. The levels of
luminosity accommodated by the Radiance format are far higher than the 256 levels in 8-bits-per-channel image file
formats. Radiance (HDR) files are often used in 3D modeling.
Scitex CT
Scitex Continuous Tone (CT) format is used for high-end image processing on Scitex computers. Contact Creo to
obtain utilities for transferring files saved in Scitex CT format to a Scitex system. Scitex CT format supports CMYK,
RGB, and grayscale images and does not support alpha channels.
CMYK images saved in Scitex CT format often have extremely large file sizes. These files are generated for input
using a Scitex scanner. Images saved in Scitex CT format are printed to film using a Scitex rasterizing unit, which
produces separations using a patented Scitex halftoning system. This system produces very few moiré patterns and
is often demanded in professional color work—for example, ads in magazines.