Basics - GIMP 2.6 for Photographers: Image Editing with Open Source Software - page 12

1.3.4 Important File Formats for Practical Work
When saving an image, you should select a file format that corresponds to the
requirements of the image as well as your stylistic intentions. This section will
introduce you to the most commonly used file formats.
XCF: GIMP's Native File Format
GIMP's XCF format was created for the primary purpose of saving images with
layers ; however, it can also be used to save images that aren't finished yet. The
XCF format saves image layers by employing a lossless compression method. So
the file size of an XCF formatted image will be smaller than most other image
file formats and about 30 percent smaller than the PSD format, described later.
Since overly large files are cumbersome and can be unmanageable,
GIMP's native XCF format is the best choice for storing images with layers. The
only drawback of GIMP's current version is that XCF files cannot be opened in
another image editing program. If you want to export an XCF file into another
program, you must first convert a copy of it into JPEG, PNG, or TIF. If you plan
to consistently use other programs in conjunction with GIMP 2.6, you should
save images with layers in the PSD format.
XCF Characteristics
• 16.78 million colors, 24-bit color depth
• Alpha transparency (color gradient from transparent to opaque)
• Lossless compression
• Supports layers
PSD: Adobe Photoshop's Native File Format
PSD (PhotoShop Document) is the native file format of Adobe Photoshop, one of
the most popular image editing programs. This file format is considered a de-facto
standard and can be used by almost all other image editing programs, including
GIMP. It is a high-quality format that is frequently used to export images with layers.
The downside of saving images in PSD is that the files are often quite
large because the format provides no compression options.
Since GIMP 2.4, Photoshop layer masks are readable, and it can even write
in the PSD format. However, GIMP does not support some PSD formats such
as smart objects or smart filters.
PSD Characteristics
• 16.78 million colors, 24-bit color depth
• Alpha transparency (color gradient from transparent to opaque)
• Supports layers