Compression is a mathematical process of reducing the file size of an image while retaining as much quality as possible. Compression is especially important when you want to publish images to the Web or share them by E-mail. GIF and JPG, the two file formats commonly used on the Web, are compressed formats.
To reduce file size, the GIF format compresses an image by reducing its colors. An image saved using fewer colors will be substantially smaller than an image saved using more colors.
FotoFinish allows you to automatically save a GIF using an optimized palette. This means FotoFinish will save the image using the minimum number of colors required to retain the original look of the image. For example the image below only requires 2 colors: black and white. Saving it using 256 colors triples the image size unnecessarily.
256-color GIF image: 1,358 Bytes 2-color GIF image: 486 Bytes
As with any compression mechanism, compressing GIFs can be overdone.
256-color GIF image: 6957 bytes 32-color GIF image: 3939 bytes
4-color GIF image: 2434 bytes 2-color GIF image: 1542 bytes
Compressing the image of the rocket to 32 colors reduces the file size considerably without compromising the image quality. However, reducing the image further to 4 or 2 colors results in images significantly different from the original.
JPEG is the format most commonly used for compressing photographs. Digital cameras often use the JPEG format to store images. The JPEG file format offers various levels of compression allowing you to trade image quality for smaller file size.
FotoFinish offers three levels of JPEG compression: Fine, Normal, and Compact. Fine preserves the most quality, but achieves the least reduction in file size. Compact greatly reduces the file size at the expense of some image quality. You will have to experiment to determine which one works best for the particular image you are trying to save.