Với hình ảnh JPEG, những gì được nén để lưu trữ phải được giải nén để xem. Khi một hình ảnh JPEG trên trang web của bạn được truy cập bởi trình duyệt của khách truy cập, hình ảnh đầu tiên phải được tải về trình duyệt và sau đó giải nén trước khi nó có thể được xem. | 324 Part II Web Design and Layout With JPEGs what is compressed for storage must be uncompressed for viewing. When a JPEG picture on your Web page is accessed by a visitor s browser the image must first be downloaded to the browser and then uncompressed before it can be viewed. This dual process adds additional time to the Web-browsing process but it is time well spent for photographic images. JPEGs unlike GIFs have neither transparency nor animation features. A newer strand of JPEG called Progressive JPEG gives you the interlacing option of the GIF format however. Although not all browsers support the interlacing feature of Progressive JPEG they render the image regardless. PNG The latest entry into the Web graphics arena is the Portable Network Graphics format or PNG. Combining the best of both worlds PNG has lossless compression like GIF and is capable of rendering millions of colors like JPEG. Moreover PNG offers an interlacing scheme that appears much more quickly than either GIF or JPEG as well as superior transparency support. One valuable aspect of the PNG format enables the display of PNG pictures to appear more uniform across various computer platforms. Generally graphics made on a PC look brighter on a Macintosh and Mac-made images seem darker on a PC. PNG includes gamma correction capabilities that alter the image depending on the computer used by the viewer. Before the versions the various browsers supported PNG only through plugins. After PNG was endorsed as a new Web graphics format by the W3C both versions of Netscape and Microsoft browsers added native inline support of the new format for Windows. On Macs PNG format is supported in Internet Explorer and up Netscape browsers still require the plugin. Perhaps most important however Dreamweaver was among the first Web authoring tools to offer native PNG support. Inserted PNG images are previewed in the Document window just like GIFs and JPEGs. Browser support for all PNG features is .
