Fix opencv for systems without libraries installed.

scikits/image/opencv/opencv_backend.pyx

@@ -6,6 +6,13 @@ from opencv_constants import *
 from opencv_type cimport *
 from _libimport import cv, cxcore
 
+if cv is None:
+    raise RuntimeError("Could not load libcv")
+
+if cxcore is None:
+    raise RuntimeError("Could not load libcxcore")
+
+
 # setup numpy tables for this module
 np.import_array()
 

scikits/image/opencv/opencv_cv.pyx

@@ -14,6 +14,9 @@ from opencv_cv import *
 
 from _libimport import cv
 
+if cv is None:
+    raise RuntimeError("Could not load libcv")
+
 # setup numpy tables for this module
 np.import_array()
 

scikits/image/opencv/tests/test_opencv_cv.py

@@ -12,8 +12,7 @@ with warnings.catch_warnings():
     warnings.simplefilter("ignore")
     from scikits.image.opencv import *
 
-opencv_skip = dec.skipif(cv is None,
-                         'OpenCV libraries not found')
+opencv_skip = dec.skipif(not loaded, 'OpenCV libraries not found')
 
 class OpenCVTest(object):
     lena_RGB_U8 = np.load(os.path.join(data_dir, 'lena_RGB_U8.npy'))