TST: skel3d: redo 3D test images

Remove ad-hoc images from morphology/tests/data folder.
Add a FIJI generated image to skimage/data.

The image was generated via
>>> img = binary_blobs(32, 0.05, n_dim=3, seed=1234)
>>> img = img.astype(np.uint8)*255
>>> img = img[:-2, ...]

then saved as a sequence of png frames, read into FIJI as an image sequence,
and skeletonized via Plugins -> Skeletonize (2D/3D).

skimage/morphology/tests/test_skeletonize_3d.py

@@ -11,7 +11,7 @@ import scipy.ndimage as ndi
 
 import skimage
 from skimage import io, draw, data_dir
-#from skimage import draw
+from skimage.data import binary_blobs
 from skimage.util import img_as_ubyte
 
 from skimage.morphology import skeletonize_3d
@@ -162,30 +162,15 @@ def test_two_hole_image():
     assert_equal(res, img_f)
 
 
-# trivial 3D images
-def test_simple_3d():
-    for fname in ['3/stack', '4/stack']:
-        yield check_skel_3d, fname
-
-
-# 'slow' test: Bat Cochlea from FIJI collections.
-def test_large():
-    for fname in ['bat/bat-cochlea-volume']:
-        yield check_skel_3d, fname
-
-
-def get_data_path():
-    # XXX this is a bad temp hack
-    return os.path.join(os.path.split(skimage.__file__)[0],
-                        'morphology',
-                        'tests',
-                        'data')
-
-def check_skel_3d(fname):
-    img = io.imread(os.path.join(get_data_path(), fname + '.tif'))
-    img_f = io.imread(os.path.join(get_data_path(), fname + '_fiji.tif'))
+def test_3d_vs_fiji():
+    # generate an image with blobs and compate its skeleton to
+    # the skeleton generated by FIJI
+    img = binary_blobs(32, 0.05, n_dim=3, seed=1234)
+    img = img[:-2, ...]
+    img = img.astype(np.uint8)*255
 
     img_s = skeletonize_3d(img)
+    img_f = io.imread(os.path.join(data_dir, "_blobs_3d_fiji_skeleton.tif"))
     assert_equal(img_s, img_f)