GNS | Image Formats for the Web

Web Image Formats

Introduction

There are three image formats that see a majority of use on the World Wide Web. They are: GIF, JPEG (or JPG), and PNG.

GIF

GIF stands for Graphics Iterchange Format, and is by far the most popular. The GIF format was developed by CompuServe circa 1987, and was the first color image format to be available on the Web. GIF images are limited to 256 colors, or more accurately, 256 RGB values, one of which can be set to be transparent. GIF images are typically used for web banners, logos, and other low-res requirements. One of the more prevalent uses of GIF is for animated images, although this isn't as popular as it was once.

JPEG or JPG

JPEG stands for Joint Photographic Experts Group. The JPEG standard specifies both the compression algorithms, or codecs, and the file format, and was officially recognized as a standard circa 1994 by the ISO, or International Standards Organization.

JPEG was developed primarily for displaying photographic images, where a smooth gradient between tones is necessary, something the GIF format cannot support. The compression used in JPEG files also makes them suitable for use on the web, as a comparable GIF or PNG image would typically result in a much larger file size. However, since JPEG is a lossy format, each resizing or editing operation normally results in image degragation.

PNG

PNG stands for Portable Network Graphics, and was developed specifically for use on the web. PNG images are technically 32-bit, being made up of a 24-bit image plus an 8-bit transparency layer, usually referred to as the alpha channel. PNG supports a very wide (48-bit maximum) color palette, enabling each pixel to be set to one of over 16,700,000 colors. Combining this color with the alpha-channel allows for super-smooth gradients and true background transparency. However, not every web browser supports PNG, and those that do are not identical in their rendering of PNG images (Internet Explorer 6 being the chief example).