On other hand, JPEG images use an entirely different compression scheme. JPEG was invented in 1991 by Joint Photographic Experts Group to display photographs and similar type images. JPEG has advantage of allowing 16 million colors. However, JPEG compresses by throwing away pixels.

For example, suppose you have a photograph that is 1024 pixels wide. JPEG compression might be specified to throw away 10% of pixels (every 10th one). When image is decompressed those pixel values are extrapolated from colors of surrounding pixels. This implies that JPEG images tend to become "fuzzy" when optimization values are high.

As it turns out, JPEG is great for photographs and similar things because those types of images tend to have soft edges. In fact, for photographs and art JPEG format is much preferred.

PNG is an up-and-coming, very new image format which is similar in concept to GIF. PNG images allow for 16 million colors and, unlike JPEG, does not lose colors. PNG compression is handle by most graphics editors, at least those that support PNG.

So how do you optimize your images? First, find best format for your applications. PNG is very new and is probably not suitable for most web sites (browser support is sporadic so you may lock out some of your users). GIF is great for line drawings and other things with sharp edges and no more than 256 colors. JPEG is perfect for photographs, art, and similar images.

Second, be familiar with optimization functions of your graphics programs. Save images using various settings and closely examine differences. For example, how does that image look in 2 colors, 16 colors and 256 colors? Find correct setting (the smallest possible file size with least change in image quality) and use it. Remember that this setting will be different for every single image.

What do you gain from all of this work? Faster loading times on your web site, which means your visitors are less likely to hit back key even before your site begins to load.

Additional Information

Graphics Formats - Animated GIFs http://www.internet-tips.net/Graphics/animatedgif.htm Use animated GIFs to create moving images on your web site. Just remember not to overdo it.

Graphics Formats - GIF http://www.internet-tips.net/Graphics/gif.htm The GIF format is an excellent format for many types of graphics.

Graphics Formats - JPG http://www.internet-tips.net/Graphics/jpg.htm JPG is best for images with gradients, blends and inconsistent color variants. It is very efficient but parts of image are lost by compression scheme.

Graphics Formats - PNG http://www.internet-tips.net/Graphics/png.htm The PNG format is a newer, better format than GIF. It may soon be dominant format on internet.

Products - GifClean32 http://www.internet-tips.net/Products/gifclean32.htm GifClean32 allows you to remove comments from GIF images. It is a handy little utility to have around.

PNG, like GIF, supports lossless compression. This means that unlike JPEG, bits of image are not lost or thrown away when image is decompressed. This compression scheme is public domain and improved over algorithm used by GIF.

Images in 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 PNG format is that color pallet is contained within image. Thus, it's important that pallet be made as small as possible, containing only colors that are necessary to display image. Most graphics programs should handle this detail for you when 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, PNG design does not include support for animation. Thus, GIFs must still be used for that purpose.

Most of modern graphics editors support output in 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 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.