Creates a 2D image object.  cl_mem clCreateImage2D (
cl_context context,   cl_mem_flags flags,   const
cl_image_format *image_format,   size_t image_width,  
size_t image_height,   size_t image_row_pitch,   void *host_ptr,
  cl_int *errcode_ret)    A valid OpenCL context on which the
image object is to be created.   A bit-field that is used to
specify allocation and usage information about the image memory
object being created and is described in the table List of
supported cl_mem_flags values for clCreateBuffer.   A pointer to
a structure that describes format properties of the image to be
allocated. See cl_image_format for a detailed description of the
image format descriptor.  image_width , image_height  The width
and height of the image in pixels. These must be values greater
than or equal to 1.   The scan-line pitch in bytes. This must be
0 if host_ptr is NULL and can be either 0 or greater than or
equal to image_width * size of element in bytes if host_ptr is
not NULL. If host_ptr is not NULL and image_