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).
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.
PNG
There is a new format which is threatening the supremacy of GIF and JPEG.
That format is called PNG (Portable Network Graphics).
PNG, like GIF, supports lossless compression. This means that unlike JPEG,
bits of the image are not lost or thrown away when the image is
decompressed. This compression scheme is public domain and improved over the
algorithm used by GIF.
Images in the PNG format may be made partially transparent. This is
necessary for displaying good looking graphics on a web page.
Finally, PNG supports color depth of 24 bits or greater. This makes it a
much better format than GIF for images which must have lots of colors.
An important thing to remember about the PNG format is that the color pallet
is contained within the image. Thus, it's important that the pallet be made
as small as possible, containing only the colors that are necessary to
display the image. Most graphics programs should handle this detail for you
when the file is saved.
Note that JPG is still superior for large images because it's compression
scheme is better suited for that purpose.
In addition, the PNG design does not include support for animation. Thus,
GIFs must still be used for that purpose.
Most of the modern graphics editors support output in the PNG format. These
editors include Paint Shop Pro, which is my personal favorite.
Personally, I think it's a little early to go and replace all of your
graphics with PNG graphics. Support within the different browsers is still
very new, and you would be depriving many of your visitors of your graphics
by including PNG images. However, in a few years I expect to see this format
more and more.
About the Author
Richard Lowe Jr. is the webmaster of Internet Tips And Secrets. This
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