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Graphics for the web: JPG and PNG Files
 Category |
: Web Development |
 Times Read |
: 71 |
 Date |
: 05 February. 2008 20:42 |
JPEG (Joint Photographic Experts Group) is a very efficient, true-color,compressed image format. It uses lossy compression, which means that bitsare removed from the image in order to save space. JPEG files supportmillions of colors (compared with the 256 for GIF).The JPG format is best for images with gradients, blends, and inconsistentcolor variations such as photographs or paintings. Images which have wellseparated tones should be saved in the GIF or PNG format. For example, ifyou include text in your image, you will notice a definite fuzzing of thecharacters 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 yousave you will loose information, and that will degrade the quality of theimage.Any good image editor (Photoshop, Paint Shop Pro and others) will allow youto specify a compression percentage when you save the file. Before youpurchase a graphics editor make sure it has a preview pane on the save soyou can see what the compressed image looks like when you save it. This is alot easier than saving a copy, examining it, resaving it and so on.JPEG supports a concept similar to interlacing in GIF which is calledprogressive JPEG. This simply means that a rough image is displayedinitially, followed by more and more detail as additional bits of the imageare received. This is good for displaying large images. Unfortunately,progressive JPEG is a relatively new standard and is not supported by allbrowsers. PNGThere 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 isdecompressed. This compression scheme is public domain and improved over thealgorithm used by GIF.Images in the PNG format may be made partially transparent. This isnecessary for displaying good looking graphics on a web page.Finally, PNG supports color depth of 24 bits or greater. This makes it amuch 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 palletis contained within the image. Thus, its important that the pallet be madeas small as possible, containing only the colors that are necessary todisplay the image. Most graphics programs should handle this detail for youwhen the file is saved.Note that JPG is still superior for large images because its compressionscheme 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. Theseeditors include Paint Shop Pro, which is my personal favorite.Personally, I think its a little early to go and replace all of yourgraphics with PNG graphics. Support within the different browsers is stillvery new, and you would be depriving many of your visitors of your graphicsby including PNG images. However, in a few years I expect to see this formatmore and more.
About the Author
Richard Lowe Jr. is the webmaster of Internet Tips And Secrets. Thiswebsite includes over 1,000 free articles to improve your internetprofits, enjoyment and knowledge.Web Site Address: http://www.internet-tips.netWeekly newsletter: http://www.internet-tips.net/joinlist.htmDaily Tips: mailto:internet-tips@GetResponse.com
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