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