Graphics Formats - JPG
JPEG (Joint Photographic Experts Group) is a very efficient, true-color, compressed image format. It uses lossy compression, which means that bits are removed from the image in order to save space. JPEG files support millions of colors (compared with the 256 for GIF).
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JPEG Format |
GIF Format |
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A comparison of the JPG and GIF formats of exactly the same picture. As you can see, JPEG lost some clarity. |
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The JPG format is best for images with gradients, blends, and inconsistent color variations such as photographs or paintings. Images which have well separated tones should be saved in the GIF or PNG format. For example, if you include text in your image, you will notice a definite fuzzing of the characters when you view it.
You have several options when optimizing JPG images. JPG is a lossy format (which means it throws away bits), so with each generation of the image you save you will loose information, and that will degrade the quality of the image.
Any good image editor (Photoshop, Paint Shop Pro and others) will allow you to specify a compression percentage when you save the file. Before you purchase a graphics editor make sure it has a preview pane on the save so you can see what the compressed image looks like when you save it. This is a lot easier than saving a copy, examining it, resaving it and so on.
JPEG supports a concept similar to interlacing in GIF which is called progressive JPEG. This simply means that a rough image is displayed initially, followed by more and more detail as additional bits of the image are received. This is good for displaying large images. Unfortunately, progressive JPEG is a relatively new standard and is not supported by all browsers.
Additional Information
- Graphics Formats - Animated GIFs Use animated GIFs to create moving images on your web site. Just remember not to overdo it.
- Graphics Formats - GIF The GIF format is an excellent format for many types of graphics.
- Graphics Formats - PNG The PNG format is a newer, better format than GIF. It may soon be the dominant format on the internet.
- Graphics Optimization Here are some utilities which allow you to optimize your graphics formats