Correctly define compression rates. Most of the recent versions of the image-editing programs enable you to define the compression rate for JPEG images. For
instance in Paint Shop Pro, click on the Options button of the dialog box Save as.
Webmaster
Design : Web image formats
[ Contents ]
Bernard Jolivalt
The JPG Format
Developed by JPEG (Joint Photographic Expert Group), this format can display up to 16.7 million colours. Animations cannot be created, nor can a transparent colour be defined. The compression results in information loss, as you can see in the following figure. In the image on the right, a high compression rate reveals the loss of data associated with this format.
Figure 3: The JPG format can result in significant data loss.
There is a loss of quality as the compression rate is fairly high (a 50:1 ratio). With a lower compression rate, the quality loss would have been less apparent. It is also possible to avoid the compression entirely by choosing a zero rate, but then be aware that the download time will be longer!
When should one use or not use the JPEG format?
- Suitable for colour photographs.
- Not suitable for images containing typography or geometrical patterns.
- Unusable for silhouetting or animations.
Correctly define compression rates. Most of the recent versions of the image-editing programs enable you to define the compression rate for JPEG images. For
instance in Paint Shop Pro, click on the Options button of the dialog box Save as.