Check for valid data in `addPairwiseBilateral` and bail.

README.md

@@ -101,6 +101,10 @@ d.addPairwiseGaussian(sxy=3, compat=3)
 d.addPairwiseBilateral(sxy=80, srgb=13, rgbim=im, compat=10)
 ```
 
+An important caveat is that `addPairwiseBilateral` only works for RGB images, i.e. three channels.
+If your data is of different type than this simple but common case, you'll need to compute your
+own pairwise energy using `utils.create_pairwise_bilateral`; see the [generic non-2D case](https://github.com/lucasb-eyer/pydensecrf#generic-non-2d) for details.
+
 ### Compatibilities
 
 The `compat` argument can be any of the following:

pydensecrf/densecrf.pxd

@@ -90,3 +90,5 @@ cdef class DenseCRF:
 
 cdef class DenseCRF2D(DenseCRF):
     cdef c_DenseCRF2D *_this2d
+    cdef int _w
+    cdef int _h

pydensecrf/densecrf.pyx

@@ -96,6 +96,11 @@ cdef class DenseCRF2D(DenseCRF):
         if type(self) is DenseCRF2D:
             self._this = self._this2d = new c_DenseCRF2D(w, h, nlabels)
 
+        # Unfortunately, self._this2d.W_ and .H_ are protected in C++ and thus
+        # we cannot access them from here for sanity-checks, so keep our own...
+        self._w = w
+        self._h = h
+
     def addPairwiseGaussian(self, sxy, compat, KernelType kernel=DIAG_KERNEL, NormalizationType normalization=NORMALIZE_SYMMETRIC):
         if isinstance(sxy, Number):
             sxy = (sxy, sxy)
@@ -109,6 +114,11 @@ cdef class DenseCRF2D(DenseCRF):
         if isinstance(srgb, Number):
             srgb = (srgb, srgb, srgb)
 
+        if rgbim.shape[0] != self._h or rgbim.shape[1] != self._w:
+            raise ValueError("Bad shape for pairwise bilateral (Need {}, got {})".format((self._h, self._w, 3), rgbim.shape))
+        if rgbim.shape[2] != 3:
+            raise ValueError("addPairwiseBilateral only works for RGB images. For other types, use `utils.create_pairwise_bilateral` to construct your own pairwise energy and add it through `addPairwiseEnergy`.")
+
         self._this2d.addPairwiseBilateral(
             sxy[0], sxy[1], srgb[0], srgb[1], srgb[2], &rgbim[0,0,0], _labelcomp(compat), kernel, normalization
         )