Web graphics are important part of web designing. Though there are many file formats for graphics only few are used for web purposes. It is important to familiarize with them so that you can choose the best that suits your purpose.
GIF (Graphic Interchange Format):
In 1980 CompuServe Information Service popularized the Graphic Interchange Format as an efficient way to transmit images across data networks. It was adopted in 1990 by the World Wide Web due its efficiency and widespread familiarity. Majority of images on the Web are now in GIF format, and the format is supported by all web browsers.
GIF files use a compression scheme to keep file sizes at a minimum, and they are limited to 8-bit (256 or fewer colors) color palettes. Also the GIF compresses large fields of homogeneous color better than pictures with many colors and complex textures.
With conventional (non-interlaced) GIF graphics, the browsers downloads one line of pixels at a time from top to bottom, display each line of the image as it gradually builds on the screen.
In interlaced GIF files the image data is stored in a format that allows browsers to build a low-resolution version of the full-sized GIF picture on the screen while the file is downloading. It gives the reader a idea of the full area of the picture while the picture downloads.
The GIF file format also allows you to combine multiple GIF images into a single file to create animation. The animations can be made to play again and again and again if looping is allowed. GIF animations are used in many a banners over the web
JPEG (Joint Photographic Experts Group):
This graphic file format commonly used on the Web to minimize graphics file sizes is the Joint Photographic Experts Group (JPEG) compression scheme. Unlike GIF graphics, JPEG images are full-color image or true color images.
JPEG can achieve incredible compression ratios, squeezing graphics down to as much as one hundred times smaller than the original file. But increasing the JPEG compression progressively can degrade the details of the image:
Once an image is compressed using JPEG compression, data is lost and cannot be recovered from that image file. It is always better to save an uncompressed original file of your graphics or photographs as backup.
Portable Network Graphic (PNG):
Portable Network Graphic is an image format developed by a consortium of graphic software developers as a open source alternative to the GIF image format.
PNG graphics offer a range of attractive features including a full range of color depths, support for sophisticated image transparency, better interlacing, and automatic corrections for display monitor gamma. PNG images can also hold a short text description of the image’s content, which allows Internet search engines to search for images based on these embedded text descriptions. At this moment almost all of the major browser support PNG format.
For practical purposes all formats are good and a difference is usually not appreciated by common eye. You can choose any of the three web graphics you are comfortable with.