FIX: img_as_ubyte function threw ValueError due to floating point errors in hed2rgb function.

Clipping the output of the hed2rgb function between 0 and 1 seems to correct
the bug without affecting the conversion quality.

skimage/color/colorconv.py

@@ -807,7 +807,9 @@ def hed2rgb(hed):
     >>> ihc_hed = rgb2hed(ihc)
     >>> ihc_rgb = hed2rgb(ihc_hed)
     """
+    from ..exposure import rescale_intensity
+
     hed = dtype.img_as_float(hed)
     logrgb1 = np.dot(-np.reshape(hed, (-1, 3)), rgb_from_hed)
     rgb1 = np.exp(logrgb1)
-    return np.reshape(rgb1 - 1, hed.shape)
+    return rescale_intensity(np.reshape(rgb1 - 1, hed.shape), in_range=(0, 1))

skimage/color/tests/test_colorconv.py

@@ -16,7 +16,7 @@ import os.path
 import numpy as np
 from numpy.testing import *
 
-from skimage import img_as_float
+from skimage import img_as_float, img_as_ubyte
 from skimage.io import imread
 from skimage.color import (
     rgb2hsv, hsv2rgb,
@@ -125,7 +125,7 @@ class TestColorconv(TestCase):
     # RGB<->HED roundtrip with ubyte image
     def test_hed_rgb_roundtrip(self):
         img_rgb = self.img_rgb
-        assert_array_almost_equal(hed2rgb(rgb2hed(img_rgb)), img_as_float(img_rgb))
+        assert_equal(img_as_ubyte(hed2rgb(rgb2hed(img_rgb))), img_rgb)
 
     # RGB<->HED roundtrip with float image
     def test_hed_rgb_float_roundtrip(self):