JPEG And You: How The Most Popular Photo Format Works

Those around in the early days of the internet are no doubt familiar with GIF. For a time, the GIF image format was the de-facto standard for web-based graphics, used on everything from photographs to dancing babies. But as popular as it was, GIF had a problem — it sort of sucked.

Limited to 256 distinct colors, GIF was a poor choice for photographers and web designers who wanted a richly colored experience. It was a great choice for logos or animations, but less suitable for authentic replications. Obviously, that was a problem that needed to be fixed, and the solution — JPEG — is a format still used today.

JPEG, like most other file formats, was created by a consortium of people, the  Joint Photographic Experts Group, in 1992. Unsatisfied with previous methods for storing digital images — uncompressed bitmaps and GIF formats, for example — the group set out to design a standard suitable for conveying photographic information on par with that of traditional film. The catch was it had to be small. 

For example, raw sensor data from a digital camera today can take up anywhere from 10-15MB or more. While this is hardly an issue with the speed and storage capacity of today's machines, imagine how impractical images that large would have been for images in the early nineties. At a time when many hard drives were still smaller in capacity than that of a CD-ROM, JPEG's goal was to bring that file size down to something far more reasonable. That meant compression.


JPEG has a sliding scale of compression that ranges from 0-100. The lower the value, the smaller your image, but quality will suffer as a result. To give you an idea of how this affects an image, consider all the pixels that compose an image. JPEG works by sampling 8x8 blocks of pixels and applying a compression algorithm to simplify the data each small block of pixels contains. As you'll above, the best compression produces no visible artifacts, but more serious compression can simplify the pixels of an image to the point where its defining details are almost unrecognizable. This is particularly obvious with the difference in detail between the two bowls of candy on the left side of the image.

Used with restraint, a JPEG-compressed image is often indistinguishable from the original copy. However, there are side-effects and downsides to the format's unique algorithm. Brightness data is discarded in order to preserve accurate colors, but produces a washed-out looking image. Also, while JPEG's approach to compression is suitable for wide color gradients and photos, it fails to handle sharp edges quite as well. As a result, text or hard geometric shapes are often distorted more easily, even if little compression is applied — particularly evident in our drawn cartoon example above.
 
The strange thing is, not everyone implements JPEG's quality scale in the same manner. For example, while Adobe Lightroom offers a 0-100 scale of compression, in reality, t hat only scales to 13 different levels of compression. So, for example, compressing your image at 92% produces the same image as one compressed at 100%. Things get more confusing still in Photoshop, where saving a JPEG through the conventional output dialog produces distinctly different output than the design suite's "Save for Web" function. 

Of course, attempts have been made to fix and improve JPEG's compression handling over the years. At the turn of the millennium, JPEG2000 was ratified, promising better compression with less artifacts, and the handy ability to scale quality and resolution depending on the display needs required. But while impressive, users were given little incentive to switch to the new format, if only because JPEG worked so well to begin with. The adoption simply wasn't there.

These days, JPEG might not necessarily be the best format for preserving and storing digital images, with a big shift to RAW occurring in the digital space. However, there's no denying that JPEG's defining features — speed, size and quality — have helped it remain relevant almost twenty years after its inception.      
 
Images via Flickr user Pete Fletch, Wikipedia.