我在学习python，在csdn复制了一段图像处理的代码，运行后报错：
发生异常: ValueError
the input array must have size 3 along channel_axis, got (771, 1024, 4)
File "D:\python\photo.py", line 14, in
lab_img = color.rgb2lab(cimage)
请问这是什么问题，我查了一圈都没找到解决方法，感谢。
代码如下：
```python
from skimage.io import imread
from skimage import color
import numpy as np
import matplotlib.pyplot as plt
plt.ion()
# 读取图片
cimage = imread('D:\python\photo.jpg')
fig, ax = plt.subplots(figsize=(20, 20))
ax.imshow(cimage)
ax.axis('off')
# RGB转为LAB
lab_img = color.rgb2lab(cimage)
x, y, z = lab_img.shape
# 显示颜色
to_plot = cimage.reshape(x * y, 3)
colors_map = to_plot.astype(np.float) / 256
# 创建数据
scatter_x = []
scatter_y = []
for xi in range(x):
for yi in range(y):
L_val = lab_img[xi, yi][0]
A_val = lab_img[xi, yi][1]
B_val = lab_img[xi, yi][2]
scatter_x.append(A_val)
scatter_y.append(B_val)
plt.figure(figsize=(20, 20))
plt.xlabel("a* from green to red")
plt.ylabel("b* from blue to yellow")
plt.scatter(scatter_x, scatter_y, c=colors_map)
# 显示
plt.show()
```
