The proper syntax is `dcrf.DenseCRF2D(img.shape[1], img.shape[0], M)`.

This has to do with C-ordering versus Fortran ordering, also known as https://en.wikipedia.org/wiki/Row-major_order

This bug appears with the following parameters:

d.addPairwiseGaussian(sxy=3, compat=0)
d.addPairwiseBilateral(sxy=3, srgb=5, rgbim=img, compat=50)

And this is confirmed by this other Python wrapper for densecrf:

see the order (D, W, H) at this line:
https://github.com/mbickel/DenseInferenceWrapper/blob/master/denseinference/lib/libDenseCRF/densecrf.cpp#L139

while the original 2D code is (H,W).

dense_inference.py

@@ -20,7 +20,7 @@ output = sys.argv[3]
 M = labels.max() + 1  # number of labels
 
 # Setup the CRF model
-d = dcrf.DenseCRF2D(img.shape[0], img.shape[1], M)
+d = dcrf.DenseCRF2D(img.shape[1], img.shape[0], M)
 
 # Certainty that the ground truth is correct
 GT_PROB = 0.5