276 Part III: Designing Sites for Long-Term Success features of GIF and JPEG formats to assist you in using today s tools to their best end. An interesting outcome of having more sophisticated tools to apply compression to Web graphics is that sometimes you find that the general guidelines, such as using GIF for line drawings and JPEG for anything with light source and color gradation, do not apply. tip For excellent graphic results, use a compression utility that allows you to apply numerous options and preview the resulting look, file size, and download time. Most good compression utilities (check Chapter 1) have features like this, and, of course, Photoshop s Save for Web feature supports this. Balancing the visual quality of the resulting image with its file size will get you the best possible results. Secret #187: Refinding the Lost Promise of PNG Portable Network Graphics (PNG) appeared in 1995 as a reaction to the fact that Unysis, owner of the patent for GIF compression, began to seek licensing fees for use of GIFs. PNG was created to provide a royalty-free means of providing all of the features of GIFs and then some to those wishing to have high-quality graphics that are flexible and well-compressed. PNG has many rich features that appeal toWeb designers, including the following: Combined features of JPEG and GIF compression: Ability to limit colors, to compress grayscale palettes, and compress true colors. This means that you don t have to choose between JPEG or GIF, because PNG takes care of both approaches. Alpha channel support in PNG allows for transparency, something formerly only available in GIF. The transparency technology in PNG is superior to the GIF format, but limitations in browsers have prevented it from becoming widespread for this application. Advanced progressive rendering So, if PNGs provide such flexibility, why have they been so slow to be adopted? Well, the problem is not with the PNG format, nor is the problem support within graphic applications. PNG is available in all major compression utilities these days, and users are convinced, too. It won t come as a surprise that the issue is browser support. It was the major thorn in PNG sside in the years since it was developed, and remains a major thorn when it comes to one browser Internet Explorer (IE). The problem isn t that the file format itself isn t supported, but that the alpha support the portion of the technology required to mask aspects of the image or make them transparent is broken, requiring people to use GIFs for transparency anyway. As a result, PNG has yet to fully achieve its promise through no fault of its own. Can you usePNGconfidently? It depends on the browser base you llbe addressing. Typically speaking, if you aren t using transparency in PNG and are aiming at contemporary browsers, you can use PNG freely with confidence that PNGs will look good in most of those browsers, including IE.
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