Chapter 11: Sophisticated Visual Design 275

Chapter 11: Sophisticated Visual Design 275 Table 11-1: GIF and JPEG Features GIF (Graphic Interchange JPEG (Joint Photographic Feature Format) Expert Group Format) Compression Type GIF compression is based on limiting the amount of colors to 256 or less. It is considered a lossless compression method because, while restrictive, the compression does not remove data. The fewer colors used the better the compression results. GIFs are typically best for those images or line drawings with flat color, few colors, grayscale images, and no gradients. Restricting the number of colors too much can result in very pixilated, jaggy images JPEG compression is known as lossy. This means that unlike GIF, actual data is lost in the compression process. JPEG can support millions of colors, so it s a far better choice for most photographs, images with subtle light sources, and gradients. If too much compression is applied to a JPEG file, the lost data will show up as faded or blurry blocks referred to as artifacts Transparency Transparency is the ability to define certain areas of a graphic as being transparent so the background color or pattern can be seen through those transparent areas. GIF supports transparency JPEG does not support transparency in any way Progressive Rendering Progressive rendering is a technique that allows portions of the graphic file to be seen as it loads, becoming increasingly more clear as data arrives to the Web browser. Very helpful in those situations where low bandwidth is expected, GIFs support progressive rendering with a feature known as interlacing. All common compression utilities allow you to interlace a GIF Progressive rendering wasn t available in the earliest days of the JPEG format, but has been around for many years and is supported in all contemporary browsers. Depending upon your compression software, you can use a number of options to determine how you d like your JPEGs to render Animation GIF animation became all the rage around 1995, and is now used so much on the Web as to cause some controversy largely due to overuse. But a GIF animation can be practical, as in a banner ad, or fun, as in adding a tasteful or subtle movement to a logo or other visual object on the page. Many utilities exist to create animation. (See Chapter 1, Setting Up a Master Toolbox for more details) There is no support for animation in the JPEG format

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