Example 3. Reading the Raster Image

This example illustrates the use of the routine GRreadimage/mgrdimg
to read the image and its subsets.

In this example, the program reads the image written by
Example 1 and modified by Example 2 in the file "General_RImages.hdf".
Recall that this image has two components and has 5 rows and 10 columns.
The program first reads the entire image, then reads a subset of
the image, 3 rows and 2 columns starting at the 2nd row and the
4th column, and finally reads the image skipping all the even rows
and all the odd columns.  Reading patterns are applied to all components.
