image formats

by Workshop, 8 July 1998

image file formats
In the 80's and early to mid 90's, all web browsing was text based - first using a browsing system called gopher and then using the HTML based text browser Lynx. Around the same time as the introduction of the graphical browser, the Internet exploded into a worldwide communications medium. This is directly related to the introduction of the graphical browser and highlights the importance of visual impact on the web.

As discussed in the section site layout/file types, there are a number of different file types for images that are used on the web. These file types are .gif, .jpeg (or.jpg), and .png. The reason that three different file types are used on the Internet is because each file type stores the image in a different way. In other words, some file types work better for certain types of images. A discussion on which file type to use is presented below.

.jpeg (jpg) files
This file format was developed by the Joint Photographic Experts Group (hence the file extension .jpeg) to provide a file format suitable for storing photographs. You may notice that there are two file extensions for a JPEG file (.jpeg, and .jpg). It does not matter which one of these is used. Both will still work for a JPEG file. JPEG files are suitable for images that have a very high number of unique colors. JPEG files are often unsuitable for images with large blocks of single colors and images that have lines in them (Line Art images).

.gif files
This file format is the most popular file format on the Internet at present. It is suitable for images that have a smaller number of unique colors (less than 256) and have large blocks of a single color. This image file type also lets you have a transparent background in your image (you need a paint program such as Paint Shop Pro to do this). The .gif format is suitable for Line Art images (images with lines in them). You can also make your images animated using a program such as GIF Construction Set although this can be quite complicated.

.png files
This image file format was designed to replace the .gif file format. Portable Network Graphics (PNG) files are smaller than .gif files in nearly all cases (for the same image) and include more features than gif (such as being able to have more than 256 colors in an image). Unfortunately, this file format is not fully supported on the Internet yet with the major browsers not implementing this image file format properly. For more information on this file format, see the PNG home page below.

examples
The following image has large blocks of a single color, and has a low number of colors (7 unique colors). This example demonstrates a situation where using .gif format is superior to using .jpg format for storing images.


example image in .jpg format


example image in .gif format

more information?
PNG image file format home page