Python 图像预处理（图像非形变操作和图像归一化）

图像预处理（图像非形变操作和图像归一化）"/>

Python 图像预处理（图像非形变操作和图像归一化）

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（一）图像非形变操作

>>>>>>Python代码：

import os
import cv2
import numpy as np
import time
# 非形变图像处理函数
def letterbox(img,height = 416,augment = False, color = (127.5,127.5,127.5)):# Resize a rectangular image to a padded squareshape = img.shape[:2] # shape = [height,width]ratio = float(height) / max(shape) # ratio = old / new 得到缩放比例new_shape = (round(shape[1] * ratio),round(shape[0] * ratio))dw = (height - new_shape[0]) / 2 # width paddingdh = (height - new_shape[1]) / 2 # height paddingtop,bottom = round(dh - 0.1),round(dh + 0.1)left,right = round(dw - 0.1),round(dw + 0.1)# resize imgif augment: # 数据增强interpolation = np.random.choice([None,cv2.INTER_NEAREST,cv2.INTER_LINEAR,None,cv2.INTER_NEAREST,cv2.INTER_LINEAR,cv2.INTER_AREA,cv2.INTER_CUBIC,cv2.INTER_LANCZOS4])if interpolation is None:img = cv2.resize(img,new_shape)else:img = cv2.resize(img,new_shape,interpolation = interpolation)else:img = cv2.resize(img,new_shape,interpolation=cv2.INTER_NEAREST)# print("resize time:",time.time()-s1)img = cv2.copyMakeBorder(img,top,bottom,left,right,cv2.BORDER_CONSTANT,value = color) # padded squarereturn img,ratio,dw,dhif __name__ == '__main__':path = './images/' # 图片路径img_size = 416 # 生成非形变图像的最终的尺寸，长和宽都是相等的for f_ in os.listdir(path):# 遍历文件夹中的图片img_o = cv2.imread(path+f_) # 加载图片文件img,_,_,_ = letterbox(img_o,height=img_size) # 非形变图像处理print("------------------->>>>")print("img_o shape:",img_o.shape)print("img shape:",img.shape)cv2.namedWindow("img_o",0) # 图像窗口的申明，参数: 窗口的尺寸可以通过鼠标去拉取改变，参数1:则固定为原尺寸，不可改变cv2.imshow("img_o",img_o)cv2.namedWindow("img",0)cv2.imshow("img",img)cv2.waitKey(0)

实验效果：

原图                                   补边图

 

           原图                                                    补边图

（二）图像归一化：

img = img/255. 

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