 |
Department of Engineering |
 |
|
JPEG files
JPEG (short for the 'Joint Photographic Experts Group') have produced
produce standards for continuous tone image coding. The "format"
uses lossy compression techniques and allows control over the degree
of `lossy-ness.' Lossy compression causes loss of image information. For
JPEG, this usually means that the image becomes blurred. The degree of blurring is controlled by the quality factor which is normally in the range 50% to
95%. Compression
ratios of 30:1 to 50:1 are not unusual for JPEG.
JPEG compression works well with natural images and badly with cartoon images
or line drawings. This is because the absence of sharp
edges in the former tends to hide the effect of moderate JPEG compression.
Some
examples of using different quality factors are online.
JPEG files are useful for WWW documents. Local users should find
cjpeg (for producing JPEG files),
djpeg (for decompressing JPEG files), and
gimp
(for displaying and processing JPEG files) useful.
xfig
can load JPEG files in too, but it can't edit them.
jpeg2ps can be used to convert JPEG files to postscript level 2
for printing.
The JPEG FAQ covers many
issues.
