Convert hardware-specific image data to float or integer array.

This class used to be ALWAYS there when reading an image, but now the ToHost object only needs to be used when data are used straight from the hardware. The ImageReader classes now take care that valid data arrays are always passed whenever data are read from a file. The code here is horribly duplicated from the ImageReaders!

Frame ( self,  data )

HeaderInfo ( self,  header )