Digital photos are computer files. They are stored
either on the camera memory or on a computer hard disk. Like any other
computer file digital photos are saved in well known formats. One of
those standard formats is known as JPEG. Here is some useful
information on JPEG files.

Digital photo files are at their core
a collection of bits and bytes. A file format is a description of how
these bits and bytes are ordered. Using standard file formats allows
one device like a digital camera to save a file that can be later on
processed by another device for example a personal computer running a
digital photo viewer software. JPEG files are a format that allows the
storage of digital photos in a compressed format. Such format saves
storage space, allows for faster transmission of files over the
Internet and also for faster performance when viewing photos.

JPEG
stands for Joint Photographic Experts Group. The original JPEG file
format goal was to allow for the compression and storage of high
quality digital photos. The JPEG file format was successful and was
widely used. It later became an official ISO standard. JPEG files are
also known as JPG file named after their common three letter file
extension. JPEG files are the de-facto standard for storing digital
photos and are used by virtually all digital cameras and computer
software.

JPEG files store digital photos in a compressed format.
There are two types of compression algorithm: Lossy and lossless.
Lossless compression means that when opening a compressed file the
extracted data is exactly the same as the original. Lossless
compression is used for example to compress large documents. Lossy
compression on the other hand means that the extracted data is a bit
different than the original. At first it seems that the loss of data
typical to lossy compression algorithms is a problem. But for some data
like digital photos such loss can be negligible. The advantage of lossy
compression is much higher compression ratios.

Using lossless
algorithms with digital photos is limited and provides very poor
compression ratios. Lossy algorithms on the other hand provide very
high compression ratio while the quality degradation due to data loss
is minimal and in most cases not noticeable. JPEG files support both
lossy and lossless compression algorithms but since lossless
compression is inefficient for digital photos it is hardly used. In
most cases JPEG files use lossy compression to efficiently compress
digital photos.

An example can help to understand why high
compression ratios are so important even on the expense of a slight
quality degradation. Digital photos files are arrays of pixels. Each
pixel has a value that represents its color and intensity and is
usually 3 bytes long. A digital photo taken with an 8 mega pixels
digital camera has 8,000,000 pixels and the corresponding image file
size would be 8,000,000*3=24,000,000 or 24Mbytes. 24Mbytes is a very
big file. Big files are hard to manipulate they take a long time to
send by email, they occupy large storage space and they take longer to
load. If JPEG was used to compress and save the same digital photo a
typical result would be a file size of about 3Mbytes. The quality of
the JPEG photo would be lower than the original but the difference
would not be noticeable to the viewer.