Local Colour Map

 A Local colour Map is optional and defined here for future use.   If the
 'M' bit of byte 10 of the Image Descriptor is set, then a colour map
 follows the Image Descriptor that applies only to the  following  image.
 At the end of the image, the colour map will revert to that defined after
 the Screen Descriptor.  Note that the 'pixel' field of byte  10  of  the
 Image  Descriptor  is used only if a Local colour Map is indicated.  This
 defines the parameters not only for the image pixel size, but determines
 the  number  of colour map entries that follow.  The bits per pixel value
 will also revert to the value specified in the  Screen  Descriptor  when
 processing of the image is complete.