cv2.calcBackProject对于三维柱状图失败

Question

当应用到cv2.calcBackProject的三维直方图时，输出只是一个空白（即，它没有失败，但返回没有投影的空白屏幕）。有人知道为什么以及如何在opencvpython上应用3D直方图反投影吗？在

....

dims = 3 # cv2.calcBackProject works if dims is set to a value less than 3 (i.e. not return blank)
channels = list(xrange(dims))
size = [4] * dims
ranges = [0, 255] * dims

hist = cv2.calcHist([roi], channels=channels, mask=None, histSize=size, ranges=ranges)
projection = cv2.calcBackProject([image], channels=channels, hist=hist, ranges=ranges, scale=1)

...

谢谢你！在