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Selecting the Best Format for Graphics

Graphics are pictures, charts, and animations that are often added to websites to draw attention to a particular section or to break up the page. They can be very powerful assets to a website, but they can also detract if misused. There are three common formats of graphics used on websites – they are .gif, .jpg and .png. Web graphics are not, however, limited to just these three formats.

.GIF

.gif (Graphics Interchange Format) is a bitmap image format introduced by CompuServe in 1987. It has become a standard and often preferred format for graphics and animations for web publication. .gif offers 256 colors in compressed format, taking up less space on web servers and reducing user download time more than uncompressed images.

The compression process for .gif is called “lossless,” meaning it does not degrade the quality of the graphics when compressed. Photographs that will not be printed can easily fit into the 256 color limitation of .gif. Photographs tend to be large in size, though, and may not be compressed enough to really reduce download time. .gif is best suited for low-quality images, buttons, diagrams, and images made of text.

One of the unique aspects of .gif images is that the algorithm used to compress graphics to the .gif format is proprietary and any software developers that use the algorithm to create .gif format graphics must pay a royalty to Unisys. The latest patent for .gif format expired in August 2006. .png has become a superior alternative to .gif according to many graphic artists.

.JPG

JPEG (pronounced JAY-peg) and often used as .jpg is the most common format used for graphics on the web. It is most useful for photo images as it compresses much of what won’t be viewed on a computer monitor. JPEG is a process of lossy image compression. The file extension for JPEG formats include .jpg (the most common), .jpeg, .jfif, and .JPE.

.PNG

The Portable Network Graphics (.png) file format is often referred to as “P-N-G” or “ping.” It is very similar to the .gif format, in fact the reason for .png development was in response .gif proprietary state. .png was developed to provide a lossless compression of images without paying royalties to Unisys, who held the patent for .gif format until August 2006.

There were a few additional benefits when using .png instead of .gif format besides being royalty free. First, the color potential for .png formatted graphics is much better. While .gif is limited to just 256 colors (perfectly fine for images to be viewed on a computer only), .png can provide true color into the millions. The higher fidelity of .png is preferred by anyone planning to print quality images.

Another benefit of .png is that the compression results in a smaller file than the same image compressed using .gif if the same number of colors are used. While saving an image with millions of colors will result in a bulkier file size, saving a 256 color image in .png and .gif the .png file will be smaller.

A third advantage of using .png for imagery is the ability to use an alpha channel for transparency. This is not available in .gif or .jpg formats. While Internet Explorer currently does not support transparency, other image viewers do and IE is considering adding transparency support in future updates.

The limitation of .png is evident when working with animations. .gif is still the preferred method for animated graphics, as neither .png nor .jpg support movements. There are other formats available for animations as well, but the .gif is the most commonly used.