Compression is the process by
which data is selectively removed from a file in order to reduce
its total size.
most common compression format is the JPEG (pronounced jay-peg).
It works on the principle that small color changes in an image are
almost imperceptible to the human eye: some pixels can be deleted without effecting the
overall image quality to a significant degree. The keywords,
obviously, being significant degree.
All forms of JPEG compression are "lossy," meaning that data is
lost, and the image quality is degraded somewhat.
Digital cameras today offer
several image file size settings as part of their basic menu, in order
to allow more pictures to be stored on a single
But it is important to note that a small, compressed image can
never be enlarged to a high-resolution image. The reverse
is not true.
Since the cost of memory cards
has plummeted dramatically, it is strongly recommended that the
maximum "quality" setting is chosen at the onset: large,
high-resolution images can always be reduced later for emailing.
In some cases, compression is
imperceptible. JPEG compression ratio can be controlled, and the
images below demonstrate the relationship between compression,
image quality and file size.