GlowIcons (or Glow Icon) is the native icon file format for AmigaOS 3.5–4.0. It is sometimes known as OS35 images or OS3.5 extension icons.
A GlowIcons image is usually 46×46 pixels, with up to 256 colors.
See Amiga Workbench icon for more information about Amiga icons.
A GlowIcons file is (more or less) a valid original format icon file. It contains an icon in the old format, which will be displayed by applications that don't support GlowIcons format. This icon may be a placeholder (a blank 1×1 or 4×4 icon is common), a generic icon, or a low-quality version of the real icon.
A GlowIcons file can also contain an icon in NewIcons format, to be used by applications that support NewIcons but not GlowIcons.
Starting at the position where a file in the original format would be expected to end, the real GlowIcons data begins. Locating this position in the file is nontrivial.
The GlowIcons data is in IFF format, and so begins with the ASCII string "
The icon usually consists of two images. By convention, the second image is outlined with a yellow "glowing" effect.
Each image or palette may be compressed, using a variant of PackBits compression.
As with all the Amiga Workbench icon formats, files begin with bytes
The ASCII string "
FORM" appears somewhere in the file, followed (with 4 intervening bytes) by "
- Wikipedia: NewIcons - Also has information about GlowIcons