ico The .ICO filename extension refers to the ICON image file format originally developed by Microsoft. The extension is used to represent computer icon images of varying sizes designed for the operating system Microsoft Windows. Its use today has extended to developing icons for programs designed using the Microsoft developer's suite Visual Studio and other applications. Similar to other device independent bitmap file formats, the ICON file format is also in the raster graphics class of image formats where each individual pixel is part of an orthogonal dot matrix data structure with support for a limited palette of color information. As a resource file, the .ico file format has its strength in contextual use. This allows for multiple icon images of different color depth or size to be stored within the resource file and used when appropriate.
sgi A .sgi extension file saves images in the original Silicon Graphics Image format. These files are originated from the library of SGI images that were there on every Silicon Graphics machine. SGI files are also referred to as RGB, IRIS or Irix RGB., .sgi image files can be saved in 8-bit color, 16-bit or 32-bit color. GIMP has the compatibility to read and write .sgi extension files and also has a dialog box that pops up to help select the compression type. The preferred compression is RLE and while it reduces the file size, it is advisable to check once it is done to ensure that the file size is indeed reduced as sometimes the size is more than the actual file size.