当应用于3D直方图到cv2.calcBackProject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）。有没有人知道为什么以及如何在OpenCV python上应用3D直方图反投影？
....
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！