NF: add guard for unexpected bit widths

From comment by Eric L

Author: matthew-brett

nibabel/parrec.py

@@ -567,7 +567,11 @@ def __init__(self, info, image_defs, permit_truncated=False):
         # functionality
         # dtype
         bitpix = self._get_unique_image_prop('image pixel size')
-        # REC data always little endian?
+        if bitpix not in (8, 16):
+            raise PARRECError('Only 8- and 16-bit data supported (not %s)'
+                              'please report this to the nibabel developers'
+                              % bitpix)
+        # REC data always little endian
         dt = np.dtype('uint' + str(bitpix)).newbyteorder('<')
         Header.__init__(self,
                         data_dtype=dt,

nibabel/tests/test_parrec.py

@@ -534,3 +534,11 @@ class TestPARRECImage(tsi.MmapImageMixin):
 
     def write_image(self):
         return parrec.load(EG_PAR), EG_PAR
+
+
+def test_bitpix():
+    # Check errors for other than 8, 16 bit
+    hdr_defs = HDR_DEFS.copy()
+    for pix_size in (24, 32):
+        hdr_defs['image pixel size'] = pix_size
+        assert_raises(PARRECError, PARRECHeader, HDR_INFO, hdr_defs)