imagewbmp() outputs or save a WBMP version of the given image.
An image resource, returned by one of the image creation functions, such as imagecreatetruecolor().
The path to save the file to. If not set or
NULL, the raw image stream
will be outputted directly.
You can set the foreground color with this parameter by setting an identifier obtained from imagecolorallocate(). The default foreground color is black.