JPEG Compression

Online Graphic Design Degree Guide: JPEG Compression

If you’ve ever saved a picture off the internet, there’s a very good chance that image was in JPEG format. JPEG is one of the most common file formats for digital images, along with GIF, and the highest quality compression format available for complex images. Almost everybody has used JPEG format at some point, but it’s important to know a little bit about it before you start using it professionally.

History

JPEG is pronounced “jay-peg,” and it stands for Joint Photographic Experts Group. The JPEG committee is a group of experts who are responsible for developing and implementing standards for file compression, and the file format is named after them. The standards were first established in 1991 on behalf of several different software companies who wanted one central file format that would make images easy to store without losing too much visual information. Since then, the committee has met three times annually in order to discuss how to improve the standard, eventually coming out with JPEG2000.

How it Works

Like most compression software, JPEG reduces the size of an image file by eliminating unnecessary visual information, or “noise.” This usually entails selecting small squares of the image called “pixels” and equalizing them, which means that the computer only has to keep track of one color for that tiny square rather than several. The rate at which this compression happens is variable, which means that the user can decide what level of resolution he wants and JPEG will format the image accordingly. The higher the resolution, the clearer the image, but also the bigger the file.

Most of the time, JPEG images are only compressed slightly, so that the difference is virtually indistinguishable on a computer monitor. This is because computers work with pixels, too, so it cannot present the higher quality image the way it’s meant to be seen. If you were to print the images, especially in a large format, it would be another story. When you place the two printed images side by side, you can tell which has been compressed and which hasn’t, because the JPEG image will look slightly boxy, or “pixela

Other Formats

There are several other digital image formats available, some of which are also compression formats. The most common is GIF, which stands for Graphics Interchange Format. GIF is the oldest graphic format on the internet, and it’s hung around for a reason. When presented with images with clearly defined lines and less than 256 colors, GIF can present an almost perfect copy of the original in a much smaller file size. However, when the image is more complex—say, a photo of a waterfall—GIF images will appear pixelated, and the colors will get distorted. That’s why the JPEG format had to be created—to fill the gap GIF left behind.

Another common digital image format is BMP, which is the default format used in MS Paint. It saves higher quality images, and can even keep track of more than one layer of data within that image, but it is also a much bigger format. In fact, BMP files are typically five times bigger than their JPEG counterparts, which means they take up more space and they take quite a big longer to load. For that reason, BMP doesn’t appear very often on the internet.

PNG is a newer format. It stands for Portable Network Graphic, and was designed to replace GIF as the go-to graphic design file format. PNG can do everything GIF can do (except animations), plus transparency, which means that images saved in PNG can be moved over the top of any other image without getting bits of white space in between. Plus, PNG is patent-free, which means that you can get progression software legally for free.

Working with JPEG

While JPEG is a great format for digital graphics, because it is almost impossible to tell the difference between a compressed file and a raw one on a computer monitor, it isn’t perfect. Before you start saving all of your files in JPEG format, you should take a look at a few tutorials, where you can get an idea for what the difference between raw, JPEG, GIF, and other formats are. Here are a few examples to get you started:

Software
Compression software for JPEG format is readily available all across the internet. Here are just a few program downloads:

  • JPEG ReducerAn online tool for shrinking JPEG images to thumbnail size.
  • JPEG ImagerSoftware for compressing images into JPEG format.
  • WinSoft CompressorsCompressor software for a number of different formats, including JPEG.
  • JasPer Project
    Free software that implements the newest JPEG standard, JPEG2000.
  • SimileThe source code for MIT’s JPEG to RDF conversion software.

Additional Resources
JPEG official website

The official website for the Joint Photographic Experts Group.

JPEG FAQ Index
Commonly asked questions about JPEG, and their answers.

JPEG JFIF

A basic overview of the JPEG format from W3.org.

Knowledge Base

A basic overview of JPEG from Indiana University.

Baseline JPEG and JPEG2000

An article exploring the differences between traditional JPEG and the newer JPEG2000, from Columbia University.

Seeing the Difference with JPEG Compression
An explanation of how compression works and what it does to a picture, from PhotoshopEssentials.

The JPEG Still Picture Compression Standard

An article exploring the use of compression technology for digital images, from Communications of the ACM journal.