Merge pull request #1079 from blink1073/fix-colorconv

Fix holes in lab conversions and add tests

skimage/color/colorconv.py

@@ -53,6 +53,7 @@ References
 
 from __future__ import division
 
+from warnings import warn
 import numpy as np
 from scipy import linalg
 from ..util import dtype
@@ -552,6 +553,8 @@ def xyz2rgb(xyz):
     mask = arr > 0.0031308
     arr[mask] = 1.055 * np.power(arr[mask], 1 / 2.4) - 0.055
     arr[~mask] *= 12.92
+    arr[arr < 0] = 0
+    arr[arr > 1] = 1
     return arr
 
 
@@ -832,6 +835,8 @@ def lab2xyz(lab, illuminant="D65", observer="2"):
     ValueError
         If either the illuminant or the observer angle are not supported or
         unknown.
+    UserWarning
+        If any of the pixels are invalid (Z < 0).
 
 
     Notes
@@ -854,6 +859,11 @@ def lab2xyz(lab, illuminant="D65", observer="2"):
     x = (a / 500.) + y
     z = y - (b / 200.)
 
+    if np.any(z < 0):
+        invalid = np.nonzero(z < 0)
+        warn('Color data out of range: Z < 0 in %s pixels' % invalid[0].size)
+        z[invalid] = 0
+
     out = np.dstack([x, y, z])
 
     mask = out > 0.2068966

skimage/color/tests/test_colorconv.py

@@ -11,6 +11,7 @@ Authors
 :license: modified BSD
 """
 
+from __future__ import division
 import os.path
 
 import numpy as np
@@ -372,6 +373,26 @@ class TestColorconv(TestCase):
         img_rgb = img_as_float(self.img_rgb)
         assert_array_almost_equal(luv2rgb(rgb2luv(img_rgb)), img_rgb)
 
+    def test_lab_rgb_outlier(self):
+        lab_array = np.ones((3, 1, 3))
+        lab_array[0] = [50, -12, 85]
+        lab_array[1] = [50, 12, -85]
+        lab_array[2] = [90, -4, -47]
+        rgb_array = np.array([[[0.501, 0.481, 0]],
+                              [[0, 0.482, 1.]],
+                              [[0.578, 0.914, 1.]],
+                              ])
+        assert_almost_equal(lab2rgb(lab_array), rgb_array, decimal=3)
+
+    def test_lab_full_gamut(self):
+        a, b = np.meshgrid(np.arange(-100, 100), np.arange(-100, 100))
+        L = np.ones(a.shape)
+        lab = np.dstack((L, a, b))
+        for value in [0, 10, 20]:
+            lab[:, :, 0] = value
+            with expected_warnings(['Color data out of range']):
+                lab2xyz(lab)
+
     def test_lab_lch_roundtrip(self):
         rgb = img_as_float(self.img_rgb)
         lab = rgb2lab(rgb)