如何polyfit()一个opencv calchist()柱状图?

我有这样的东西:

import numpy as np
import cv2 as cv
from matplotlib import pyplot as plt
import numpy.polynomial.polynomial as poly

img = cv.imread('SomeImage.jpg')
color = ('b','g','r')
for i,col in enumerate(color):
    histr = cv.calcHist([img],[i],None,[32],[0,256])
    plt.plot(histr,color = col)
    plt.xlim([0,32])

    x = np.linspace(0,histr.shape[0],1);  # <== ERROR HERE
    poly.polyfit(x, histr, 4)

我得到以下错误:

File "/Users/case/anaconda2/lib/python2.7/site-packages/numpy/polynomial/polynomial.py", line 1438, in polyfit raise TypeError("expected x and y to have same length") TypeError: expected x and y to have same length

我对这个很陌生,但似乎我错过了一些简单的东西?