opencv-图像入门

参考：

1、http://docs.opencv.org/3.3.0/  官方文档api

2、http://docs.opencv.org/3.3.0/d6/d00/tutorial_py_root.html 官方英文教程

3、https://opencv-python-tutroals.readthedocs.io/en/latest/py_tutorials/py_tutorials.html

4、https://github.com/makelove/OpenCV-Python-Tutorial# 进阶教程

5、https://docs.opencv.org/3.3.0/index.html  官方英文教程

6、https://github.com/abidrahmank/OpenCV2-Python-Tutorials

7、https://www.learnopencv.com/

8、http://answers.opencv.org/questions/ OpenCV论坛

注：安装的版本 opencv_python-3.3.0-cp36-cp36m-win_amd64.whl

参考：https://opencv-python-tutroals.readthedocs.io/en/latest/py_tutorials/py_tutorials.html

图像入门

目的

• Here, you will learn how to read an image, how to display it and how to save it back
• You will learn these functions : cv2.imread(), cv2.imshow() , cv2.imwrite()
• Optionally, you will learn how to display images with Matplotlib

使用OpenCV

读取一张图像

Use the function cv2.imread() to read an image.

Second argument is a flag which specifies the way image should be read.

• cv2.IMREAD_COLOR : Loads a color image. Any transparency of image will be neglected. It is the default flag.默认彩色加载  （1）
  
• cv2.IMREAD_GRAYSCALE : Loads image in grayscale mode灰度 （0）
  
• cv2.IMREAD_UNCHANGED : Loads image as such including alpha channel包括透明度通道 （-1）
  

Instead of these three flags, you can simply pass integers 1, 0 or -1 respectively.

import numpy as npimport cv2import matplotlib.pyplot as plt# Load an color image in grayscaleimg = cv2.imread('messi5.jpg',0) # 以灰度图加载print(img.shape)cv2.imshow('image',img)cv2.waitKey(0)cv2.destroyAllWindows()img2=plt.imread('messi5.jpg')plt.subplot(2,1,1)plt.imshow(img2)plt.axis('off')plt.title('img2')plt.subplot(2,1,2)plt.imshow(img)plt.axis('off')plt.title('img')plt.show()

显示一张图像

Use the function cv2.imshow() to display an image in a window. The window automatically fits to the image size.

#!/usr/bin/python3# -*- coding: utf-8 -*-import cv2# Load an color image in grayscaleimg = cv2.imread('messi5.jpg',0) # 以灰度图加载print(img.shape)
cv2.namedWindow('image', cv2.WINDOW_NORMAL) # By default, the flag is cv2.WINDOW_AUTOSIZE.
cv2.imshow('image',img) #默认会创建一个窗体cv2.waitKey(0) # 等待键盘响应时间（单位为 ms）,0表示无限等待# cv2.destroyAllWindows() # 摧毁所有创建的窗口cv2.destroyWindow('image') # 指明要摧毁的窗口

写一张图

Use the function cv2.imwrite() to save an image.

# 第一个参数保存的文件名, 第二个参数要保存的图像.cv2.imwrite('messigray.png',img)

This will save the image in PNG format in the working directory.

总结一下

import numpy as npimport cv2img = cv2.imread('messi5.jpg',0) # 加载成灰度图cv2.imshow('image',img)k = cv2.waitKey(0) # 返回按键的ASCII值  64位机器 要改成  k = cv2.waitKey(0) & 0xFFif k == 27:         # wait for ESC key to exit    cv2.destroyAllWindows()elif k == ord('s'): # wait for 's' key to save and exit   ord 转成ASCII值    cv2.imwrite('messigray.png',img)    cv2.destroyAllWindows()

使用Matplotlib

import numpy as npimport cv2from matplotlib import pyplot as pltimg = cv2.imread('messi5.jpg',0)plt.imshow(img, cmap = 'gray', interpolation = 'bicubic')# to hide tick values on X and Y axis  相当于 plt.axis('off')plt.xticks([]), plt.yticks([])plt.show()

注：Color image loaded by OpenCV is in BGR mode. But Matplotlib displays inRGB mode.

Additional Resources

1. Matplotlib Plotting Styles and Features

Exercises

1. There is some problem when you try to load color image in OpenCV and display it in Matplotlib. Read this discussion and understand it.

import numpy as npimport cv2from matplotlib import pyplot as pltimg = cv2.imread('messi5.jpg',1) # BGR加载b,g,r = cv2.split(img) # 通道分离merged = cv2.merge((r,g,b)) # 合并成RGB# img2=np.append(img[:,:,-1],img[:,:,1],axis=2) # BGR 转成 RGB# img2=np.append(img2,img[:,:,0],axis=2) # BGR 转成 RGBplt.subplot(121)plt.imshow(img)# to hide tick values on X and Y axis  相当于 plt.axis('off')plt.xticks([]), plt.yticks([])plt.subplot(122)plt.imshow(merged)plt.axis('off')plt.show()