Progressive Vs. Nonprogressive JPEG

When computer users download standard, nonprogressive JPEGs, no part of the image is displayed until all the data is received. When they download progressive JPEGs, they are able to see a preview of the image based on the data received, long before all the data is received. Many image-editing programs offer the option to create progressive JPEG images.

Progressive Levels

Progressive JPEG files are downloaded in a number of stages, known as progressive levels. The software component responsible for decoding JPEG images, known as a decoder, makes multiple decoding passes on the image as each progressive level is downloaded. Each level is set to an increasingly higher resolution. Resolution describes the total number of picture elements, or pixels, in an image, so the details of the image are filled in, bit by bit, until all the image data is received. The number of progressive levels and the resolution of each level depend on the way in which the progressive JPEG was encoded initially.

Advantages

From the point of view of computer users, progressive JPEG files appear to load faster than their nonprogressive counterparts because users have something to look at as soon as the initial image data arrives at their Web browser. This, in itself, can greatly enhance their Web browsing experience and makes it possible for them to decide whether a particular image is of interest. If not, they can navigate to another Web page without waiting for the entire image to download.

Disadvantages

Progressive JPEG can be useful for viewing images from the Internet or any other data source where the speed of data transfer, or bandwidth, is limited. However, although progressive JPEG images appear to load faster than nonprogressive JPEG images, they actually take longer to load completely. They also require more RAM to view and are not handled well by all Web browsers.