imagewbmp() creates the WBMP file in filename from the image image. The image argument is the return from the imagecreate() function.
The filename argument is optional, and if left off, the raw image stream will be output directly. By sending an image/vnd.wap.wbmp content-type using header(), you can create a PHP script that outputs WBMP images directly.
Note: WBMP support is only available if PHP was compiled against GD-1.8 or later.
Using the optional foreground parameter, you can set the foreground color. Use an identifier obtained from imagecolorallocate(). The default foreground color is black.