diff --git a/scikits/image/io/_plugins/_colormixer.pyx b/scikits/image/io/_plugins/_colormixer.pyx
index 48450473..25767f66 100644
--- a/scikits/image/io/_plugins/_colormixer.pyx
+++ b/scikits/image/io/_plugins/_colormixer.pyx
@@ -185,6 +185,8 @@ def gamma(np.ndarray[np.uint8_t, ndim=3] img,
 
     cdef int i, j
 
+    if gamma == 0:
+        gamma = 0.00000000000000000001
     gamma = 1./gamma
 
     with nogil:
@@ -199,7 +201,7 @@ def gamma(np.ndarray[np.uint8_t, ndim=3] img,
                 img[i,j,2] = <np.uint8_t>(pow(b, gamma) * 255)
 
 
-
+@cython.cdivision(True)
 cdef void rgb_2_hsv(float* RGB, float* HSV) nogil:
     cdef float R, G, B, H, S, V, MAX, MIN
     R = RGB[0]
@@ -261,7 +263,7 @@ cdef void rgb_2_hsv(float* RGB, float* HSV) nogil:
     HSV[1] = S
     HSV[2] = V
 
-
+@cython.cdivision(True)
 cdef void hsv_2_rgb(float* HSV, float* RGB) nogil:
     cdef float H, S, V
     cdef float f, p, q, t, r, g, b
diff --git a/scikits/image/io/_plugins/util.py b/scikits/image/io/_plugins/util.py
index 40f6e92b..a9936bdc 100644
--- a/scikits/image/io/_plugins/util.py
+++ b/scikits/image/io/_plugins/util.py
@@ -202,21 +202,21 @@ class ThreadDispatch(object):
             self.chunks.append((img, stateimg))
 
         elif self.cores >= 4:
-            self.chunks.append((img[:(height/2), :(width/2), :],
-                                stateimg[:(height/2), :(width/2), :]))
-            self.chunks.append((img[:(height/2), (width/2):, :],
-                                stateimg[:(height/2), (width/2):, :]))
-            self.chunks.append((img[(height/2):, :(width/2), :],
-                                stateimg[(height/2):, :(width/2), :]))
-            self.chunks.append((img[(height/2):, (width/2):, :],
-                                stateimg[(height/2):, (width/2):, :]))
+            self.chunks.append((img[:(height/4), :, :],
+                                stateimg[:(height/4), :, :]))
+            self.chunks.append((img[(height/4):(height/2), :, :],
+                                stateimg[(height/4):(height/2), :, :]))
+            self.chunks.append((img[(height/2):(3*height/4), :, :],
+                                stateimg[(height/2):(3*height/4), :, :]))
+            self.chunks.append((img[(3*height/4):, :, :],
+                                stateimg[(3*height/4):, :, :]))
 
         # if they dont have 1, or 4 or more, 2 is good.
         else:
-            self.chunks.append((img[:, :(width/2), :],
-                                stateimg[:, :(width/2), :]))
-            self.chunks.append((img[:, (width/2):, :],
-                               stateimg[:, (width/2):, :]))
+            self.chunks.append((img[:(height/2), :, :],
+                                stateimg[:(height/2), :, :]))
+            self.chunks.append((img[(height/2):, :, :],
+                               stateimg[(height/2):, :, :]))
 
         for i in range(self.cores):
             self.threads.append(ImgThread(func, self.chunks[i][0],