Merge pull request #2118 from local-minimum/patch-1

Fixing Error and documentation on Otsu Threshold

skimage/filters/tests/test_thresholding.py

@@ -167,7 +167,7 @@ def test_otsu_astro_image():
 
 def test_otsu_one_color_image():
     img = np.ones((10, 10), dtype=np.uint8)
-    assert_raises(TypeError, threshold_otsu, img)
+    assert_raises(ValueError, threshold_otsu, img)
 
 def test_li_camera_image():
     camera = skimage.img_as_ubyte(data.camera())

skimage/filters/thresholding.py

@@ -110,6 +110,11 @@ def threshold_otsu(image, nbins=256):
     threshold : float
         Upper threshold value. All pixels intensities that less or equal of
         this value assumed as foreground.
+        
+    Raises
+    ------
+    ValueError
+         If `image` only contains a single grayscale value.
 
     References
     ----------
@@ -133,9 +138,9 @@ def threshold_otsu(image, nbins=256):
 
     # Check if the image is multi-colored or not
     if image.min() == image.max():
-        raise TypeError("threshold_otsu is expected to work with images " \
-                        "having more than one color. The input image seems " \
-                        "to have just one color {0}.".format(image.min()))
+        raise ValueError("threshold_otsu is expected to work with images " \
+                         "having more than one color. The input image seems " \
+                         "to have just one color {0}.".format(image.min()))
 
     hist, bin_centers = histogram(image.ravel(), nbins)
     hist = hist.astype(float)