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Adobe Photoshop Help
Saving and Exporting Images
Using Help
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Raw (Photoshop)
Raw format is a flexible file format for transferring images between applications and
computer platforms. This format supports CMYK, RGB, and grayscale images with alpha
channels, and multichannel and Lab images without alpha channels.
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). Adobe 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 inter-
leaved, 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.
Scitex CT (Photoshop)
Scitex Continuous Tone (CT) format is used for high-end image processing on Scitex
computers. Contact Scitex 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.
Targa
TGA (Targa
®
) format is designed for systems using the Truevision
®
video board and is
commonly supported by MS-DOS color applications. Targa format supports 16-bit RGB
images (5 bits x 3 color channels, plus one unused bit), 24-bit RGB images (8 bits x 3 color
channels), and 32-bit RGB images (8 bits x 3 color channels plus a single 8-bit alpha
channel). Targa format also supports indexed-color and grayscale images without alpha
channels. When saving an RGB image in this format, you can choose a pixel depth and
select RLE encoding to compress the image.
