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. Documents saved
in the Photoshop Raw format can be of any pixel or file size, but
they cannot contain layers.
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
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 non-interleaved 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.