python代码可运行但有误检查不出来

写了一个python的代码，正确结果应该是原图直方图、线性拉伸直方图、原图、线性拉伸图
但是运行完显示的结果，线性拉伸图的位置显示的还是原图，检查了好多遍也没发现错误，可以帮忙检查哪里错啦吗
（我也不会像别人呢样直接上传一键复制的代码）

import cv2
import numpy as np
import matplotlib.pyplot as plt

def linear_img(img):
img = img
w, h = img.shape[:2] # 读取灰度图高宽

maxout = 80
minout = 20

gray_new = (img - img.min()) / (img.max() - img.min())  # 归一化到0-1

gray_out = gray_new * (maxout - minout)  # maxout=255 minout=0
gray_out = np.uint8(gray_out)

def GrayHist( img ):
# 计算灰度直方图
height, width = img.shape[:2]
grayHist = np.zeros([256], np.uint64)
for i in range(height):
for j in range(width):
grayHist[img[i][j]] += 1
return grayHist

if name == 'main':
# 读取原始图像
img = cv2.imread("img",0)

#线性拉伸
gray_out = linear_img(img)

#计算原图灰度直方图
origin = GrayHist(img)
linear = GrayHist(gray_out)
x = np.arange(256)
# 绘制灰度直方图
plt.figure( num = 1 )
plt.subplot( 2, 2, 1 )
plt.bar(x, origin,color='blue')
plt.title("Origin")
plt.ylabel("number of pixels")

plt.subplot( 2, 2, 2 )
plt.bar(x, linear,color='blue')
plt.title("linear")
plt.ylabel("number of pixels")

plt.subplot( 2, 2, 3 )
plt.imshow( img,cmap = plt.cm.gray)
plt.title( 'Origin' )

plt.subplot( 2, 2, 4 )
plt.imshow( gray_out, cmap = plt.cm.gray)
plt.title( 'linear')
plt.show()

什么鬼代码
linear_img没有返回值的吗
那gray_out 又是什么，全局变量吗，为什么在linear_img函数里会直接给他赋值
你格式乱糟糟就罢了，代码也不全

我先给你把代码格式化再看问题

import cv2
import numpy as np
import matplotlib.pyplot as plt

def linear_img(img):
    img = img
    w, h = img.shape[:2] # 读取灰度图高宽
    maxout = 80
    minout = 20
    gray_new = (img - img.min()) / (img.max() - img.min())  # 归一化到0-1
    gray_out = gray_new * (maxout - minout)  # maxout=255 minout=0
    gray_out = np.uint8(gray_out)

def GrayHist( img ):
    # 计算灰度直方图
    height, width = img.shape[:2]
    grayHist = np.zeros([256], np.uint64)
    for i in range(height):
        for j in range(width):
            grayHist[img[i][j]] += 1
    return grayHist

if name == 'main':
    # 读取原始图像
    img = cv2.imread("img",0)

    #线性拉伸
    gray_out = linear_img(img)
     
    #计算原图灰度直方图
    origin = GrayHist(img)
    linear = GrayHist(gray_out)
    x = np.arange(256)
    # 绘制灰度直方图
    plt.figure( num = 1 )
    plt.subplot( 2, 2, 1 )
    plt.bar(x, origin,color='blue')
    plt.title("Origin")
    plt.ylabel("number of pixels")
     
    plt.subplot( 2, 2, 2 )
    plt.bar(x, linear,color='blue')
    plt.title("linear")
    plt.ylabel("number of pixels")
     
    plt.subplot( 2, 2, 3 )
    plt.imshow( img,cmap = plt.cm.gray)
    plt.title( 'Origin' )
     
    plt.subplot( 2, 2, 4 )
    plt.imshow( gray_out, cmap = plt.cm.gray)
    plt.title( 'linear')
    plt.show()