There are many file formats, but I will stick to the most commonly used ones.
When creating pictures for the web, you should only use either .gif or .jpg file formats.
The different files:
.BMP ò pronounced B-M-P or bitmap ò these files are Windows based ò they include 1-24 bit depth ò 4 and 8 bit images are compressed using lossless compression ò 24 bit images are not compressed
.GIF ò stands for Graphics Interchange Format ò these are 1 or 8 bit files typically used for the web ò they are small in size, and allow for fast downloads ò they support animations, interlacing, and transparencies ò they are best used for clip art/cartoon style graphics ò A GIF's color palette is limited to a maximum of 256 colors. ò Avoid using GIF's for images with complex, subtle gradations of color. ò The GIF file format uses lossless compression to keep file sizes as small as possible.
.JPEG (.JPG) ò stands for Joint Photographic Experts Group ò JPEG's are 24 bit colour images and are typically used on the web ò JPEG files are the best choice for photographs and other images with continuous-tone color gradations. ò The JPEG format was developed to reduce the file size of photographic images while maintaining quality. ò JPEG's use lossy compression to manage file size. ò each time you save a JPEG, you lose some data and reduce image quality.
.TIFF (.TIF) ò stands for Tagged Image File Format ò TIFF's are good for the exchange of images between programs and platforms ò 1 bit colour to 24 bit colour ò TIFF's are generally uncompressed or they use lossless compression
.PNG ò pronouced PING ò stands for Portable Network Graphics ò PNG is a very flexible format ò These files can be palette-based, grayscale, or true color images with color resolutions of up to 48 bits. ò PNG uses cross-platform color and gamma correction ò indexed PNG's are almost always smaller than identical GIF files. ò unlike GIF, which only lets you to choose a single color to be transparent, PNG provides full alpha transparency, meaning you can have images with graduated transparency ò PNG's can carry information to compensate for brightness variations between Macintosh and PC monitors. ò however - PNG's are not yet fully supported by the major browsers. Only Netscape 4+ and MSIE 4+ browsers support PNG's, and there are limitations. Gamma correction and alpha transparency are not consistently implemented.
.PSD ò stands for Photoshop Shop Document ò these files are only used to save multiple, maneuverable layers. They can be used to save Merged or Flattened Images but the file is not compressed
Compression Types ò There are 2 different types of compression: LOSSY compression, and LOSSLESS compression
LOSSY Compression: ò reduces file size by removing "unnecessary" data. The data is eliminated based on a number of sophisticated mathematically-based formulae. JPEG's are the only type of file that uses LOSSY compression
LOSSLESS Compression: ò is a type of compression algorithm that reduces file size without losing any data. Typically this is done by finding and eliminating redundant information. .BMP, .GIF, .TIFF, .PNG use LOSSLESS compression
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