The WBMP Image Format

You may have noticed that all the examples of the <img> element in this book have used image names ending with .wbmp . This is a special image format used in WAP. In fact, it’s the only image format most browsers support. All WAP browsers that support images must support WBMP, so it’s the safest choice if you want to include images in your WML.

WBMP stands for wireless bitmap , and it’s a simple image format. Forget things like color, or animation, or even compression. (Image formats such as GIF and JPEG are the two most common on web pages; they compress the data to make the files smaller and faster to download.) WBMP files store only two things about the image: its size and a block of pixels, each of which is either black or white. There may be future versions with more features, but at the moment black and white is all there is.

To create the WBMP files, you need a converter. There are many of these available, some for free download.

One thing to bear in mind about small monochrome images such as these are that direct conversion from large, full-color images doesn’t usually produce results that are anywhere near acceptable. Some company logos are simple images in only a few colors, and these can convert reasonably well, but images with subtle graduations of color convert very badly. The best solution is to use regular graphics touch-up software to convert the image to black and white and only then convert it to the WBMP format.

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