ENH: Check that float images are between 0 and 1.

skimage/util/dtype.py

@@ -63,6 +63,8 @@ def _convert(image, dtype):
                  "%s to %s" % (dtypeobj_in, dtypeobj))
 
     if kind_in == 'f':
+        if np.min(image) < 0 or np.max(image) > 1:
+            raise ValueError("Images of type float must be between 0 and 1")
         if kind == 'f':
             # floating point -> floating point
             if itemsize_in > itemsize:

skimage/util/tests/test_dtype.py

@@ -67,6 +67,13 @@ def test_unsupported_dtype():
     assert_raises(ValueError, img_as_int, x)
 
 
+def test_float_out_of_range():
+    too_high = np.array([2], dtype=np.float32)
+    assert_raises(ValueError, img_as_int, too_high)
+    too_low = np.array([-1], dtype=np.float32)
+    assert_raises(ValueError, img_as_int, too_low)
+
+
 if __name__ == '__main__':
     np.testing.run_module_suite()