High Performance Images

Chapter 4. JPEG

Yoav Weiss

JPEGs are the Web’s most abundant image file format. According to the HTTP archive, at the time of this writing, they make up 45% of all image requests, and about 65% of image traffic. They are good candidates for full-color images and digital photos, making them the go-to image format whenever people want to share important moments in their lives (e.g., what they are having for brunch) over the Internet. JPEG’s capability of lossily compressing images to save bandwidth (without losing too much quality in the process) has gained the format worldwide adoption.

History

The need for photographic image compression was clear from the early days of personal computing. Multiple proprietary formats were devised in order to achieve that, but eventually, the need to share these images between users made the case for a standard format clear.

Even before the Internet was widespread, corporations shared images with their users over CD-ROMs with limited storage capacity, and wanted the users to be able to view these images without installing proprietary software. In the early days of the Internet (then mostly at 9,600 baud speeds), it was apparent that a standard format could not come soon enough.

A few years earlier, back in 1986, the Joint Photographic Experts Group was formed, and after six years of long debates, it published the ITU T.81 standard in 1992. The group’s acronym was adopted as the popular name of this new format: JPEG.

The JPEG Format

The bytestream ...