VDisplayGrayImage - displays a gray-level image.
  VDisplayGrayImage(win, data, xloc, yloc, width, height, bits_per_pixel,
			min, max)
  Window win;
  unsigned char *data;
  int xloc, yloc;
  int width, height;
  int bits_per_pixel;
  unsigned long max, min;
  VDisplayGrayImage displays a gray-level image within a rectangle in the
image window or one of its subwindows. If the bits_per_pixel is 8, the data
is assigned a character pointer type; if the bits_per_pixel is 16, the data
is assigned a short pointer type. The pixel values are assigned to colorcells
as in the array returned by the function VGetFreeColorcells in increasing 
order of grey values.
Return Value
  0 - work successfully.
  1 - memory allocation error.
  6 - invalid window ID.
  240 - image displayed is out of window boundary.
  win - the image window ID or one of its subwindows ID.
  data - specifies an array of data to be displayed in the image window.
  xloc, yloc - specifies x and y coordinates of the upper left corner of
        rectangle relative to the origin of the image window.
  width, height - specifies the width and height of the pixels of the image.
  bits_per_pixel - specifies the number of bits per pixel, the value is
        either 8 or 16.
  min, max - the minimum and maximum gray values of the image data.
Side Effects
Entry Conditions
  If the value xloc, yloc, width, height, or bits_per_pixel is not valid, or
data is NULL, or the image to be displayed is totally out of the specified
window boundary, or VCreateColormap is not called earlier, then
VDisplayGrayImage prints an error message to the standard error stream,
produces a core dump file and exits from the current process.
Related Functions
VDisplayColorImage, VPrepareColorImage, VPrepareGrayImage, VPutImage, VGetImage, VRestoreDefaultColormap.