GIF, an abbreviation of Graphics Interchange Format, is one format for bitmap image data files. Its extension is “.gif.”
This file format, which utilizes the LZW data compression technique, supports 8-bit (256 color) indexed color. Because it only supports 8-bit (256 color) indexed color, it is not well suited for continuous-tone images such as photographs; it is best suited for flat-color and solid-color images. Before the creation of the PNG (Portable Network Graphics) format, GIF was the standard format for flat-color images, such as illustrations and logos, on the Internet.
PNG was developed in response to patent controversy over the use of the LZW data compression technique in GIFs (and in software that utilizes GIFs) that arose between 1994-1999. (LZW’s patent expired in 2003.) PNG can handle 24-bit full color, but can also be created with indexed color up to 8 bits. While there were some problems with PNG in the past, such as whether it had sufficient compatibility with web browsers, when it comes to flat-color images such as illustrations and logos, PNG is currently on the rise in terms of usage.
Another special characteristic of the GIF format is that a single file is able to display an animated sequence of multiple GIF images (animated GIF); during the early years of the Internet, animated GIFs were synonymous with simple animation on the web. Also, GIF files have the ability to render a predetermined color as transparent (transparent GIF).
When creating an image using 24-bit color, saving it as a GIF file will reduce the number of colors. When editing the bitmap data, one must use a lossless file format, such as the native file format of the image creation software (such as the PSD format in the case of Adobe Photoshop); it is best to save the files in GIF format only once, after the editing process is complete.
- Adobe Photoshop "Save for Web" screen. With files created using index color, such as GIF or PNG-8, an appropriate number of colors should be chosen, and an appropriate color table should be set based on the image's contents. This allows for attractive indexed color images to be produced while limiting size of file.