This is the generic interface to be implemented by all image file (or other resource) readers for different image file formats.

       <p>An ImgReader behaves as an ImgData object. Whenever image data is
       requested through the getInternCompData() or getCompData() methods, the
       image data will be read (if it is not buffered) and returned. Implementing
       classes should not buffer large amounts of data, so as to reduce memory
       usage.</p><p>This class sets the image origin to (0,0). All default implementations
       of the methods assume this.</p><p>This class provides default implementations of many methods. These
       default implementations assume that there is no tiling (i.e., the only tile
       is the entire image), that the image origin is (0,0) in the canvas system
       and that there is no component subsampling (all components are the same
       size), but they can be overloaded by the implementating class if need
       be.</p>