（转）Python下OpenCV的使用 -- 基本操作
本节我们介绍一下Python-OpenCV处理图像的基本操作。
1. 图片读写和显示操作
安装好OpenCV之后，首先尝试加载一张最简单的图片并显示出来，代码示例如下：
import cv2
import numpy
import matplotlib.pyplot
image = cv2.imread("D:\\ImageNet\\timg4.png")
print(image.shape)
cv2.imshow("image",image)
k = cv2.waitKey(0)
if k == ord('s'): # wait for 's' key to save and exit
cv2.imwrite("D:\\ImageNet\\output1.png",image)
cv2.destroyAllWindows()2. 获取图片属性
示例代码如下：
# -*- coding: utf-8 -*-
import cv2
import numpy
import matplotlib.pyplot
image = cv2.imread("D:\\ImageNet\\timg4.png")
print(image.shape)
if image.shape[2] == 2:
print("Gray Image")
elif image.shape[2] == 3:
print("RGB Image")
print(image.size)
print(image.dtype)3. 输出文本
在处理图片的时候，我们经常会需要把一些信息直接以文字的形式输出在图片上，下面的代码将实现这个效果：
# -*- coding: utf-8 -*-
import cv2
import numpy
import matplotlib.pyplot
image = cv2.imread("D:\\ImageNet\\timg2.jpg")
print(image.shape)
# def putText(img, text, org, fontFace, fontScale, color, thickness=None, lineType=None, bottomLeftOrigin=None):
cv2.putText(image, "I Iove you!", (20,40), 0, 0.8, (0,0,255),2)
cv2.imshow("image",image)
cv2.waitKey(0)
cv2.destroyAllWindows()
4. 图片缩放
下面的例子将实现缩放图片并保存，这个在使用 OpenCV 做图像处理的时候都是很常用的操作：
# -*- coding: utf-8 -*-
import cv2
import numpy
import matplotlib.pyplot
image = cv2.imread("D:\\ImageNet\\timg2.jpg")
print(image.shape)
# def resize(src, dsize, dst=None, fx=None, fy=None, interpolation=None): # real signature unknown; restored from __doc__
#res = cv2.resize(image,None,fx=2, fy=2, interpolation = cv2.INTER_CUBIC)
# or
height, width = image.shape[:2]
res = cv2.resize(image,(2*width, 2*height), interpolation = cv2.INTER_CUBIC)
cv2.imshow("image",res)
cv2.waitKey(0)
cv2.destroyAllWindows()5. 图像平移
# -*- coding: utf-8 -*-
import cv2
import numpy
import matplotlib.pyplot
image = cv2.imread("D:\\ImageNet\\timg2.jpg")
print(image.shape)
rows,cols = image.shape[:2]
M = numpy.float32([[1,0,100],[0,1,50]])
dst = cv2.warpAffine(image,M,(cols,rows))
cv2.imshow("image",dst)
cv2.waitKey(0)
cv2.destroyAllWindows()6. 图像旋转
# -*- coding: utf-8 -*-
import cv2
import numpy
import matplotlib.pyplot
image = cv2.imread("D:\\ImageNet\\timg2.jpg")
print(image.shape)
rows,cols = image.shape[:2]
M = cv2.getRotationMatrix2D((cols/2,rows/2),90,1)
dst = cv2.warpAffine(image,M,(cols,rows))
cv2.imshow("image",dst)
cv2.waitKey(0)
cv2.destroyAllWindows()7. 仿射变换
# -*- coding: utf-8 -*-
import cv2
import numpy
import matplotlib.pyplot
image = cv2.imread("D:\\ImageNet\\timg2.jpg")
print(image.shape)
rows,cols = image.shape[:2]
pts1 = numpy.float32([[50,50],[200,50],[50,200]])
pts2 = numpy.float32([[10,100],[200,50],[100,250]])
M = cv2.getAffineTransform(pts1,pts2)
dst = cv2.warpAffine(image,M,(cols,rows))
cv2.imshow("image",dst)
cv2.waitKey(0)
cv2.destroyAllWindows()8. 通道的拆分、合并处理
对于一张图片的 R、G、B 通道，我们可以很方便的使用 OpenCV 获取并分离或者合并：
(这是将图像灰度化处理的一种方式)
# -*- coding: utf-8 -*-
import cv2
import numpy
image = cv2.imread("D:\\ImageNet\\timg2.jpg")
print(image.shape)
b,g,r = cv2.split(image)
img = cv2.merge((b,g,r))
cv2.imshow("image",img)
cv2.waitKey(0)
cv2.destroyAllWindows()9. 图片添加边距
# -*- coding: utf-8 -*-
import cv2
import numpy
image = cv2.imread("D:\\ImageNet\\timg2.jpg")
print(image.shape)
BLUE = [255,0,0]
replicate = cv2.copyMakeBorder(image,10,10,10,10,cv2.BORDER_REPLICATE)
reflect = cv2.copyMakeBorder(image,10,10,10,10,cv2.BORDER_REFLECT)
reflect101 = cv2.copyMakeBorder(image,10,10,10,10,cv2.BORDER_REFLECT_101)
wrap = cv2.copyMakeBorder(image,10,10,10,10,cv2.BORDER_WRAP)
constant= cv2.copyMakeBorder(image,10,10,10,10,cv2.BORDER_CONSTANT,value=BLUE)
#cv2.imshow("image",replicate)
cv2.imshow("image",reflect)
#cv2.imshow("image",reflect101)
#cv2.imshow("image",wrap)
#cv2.imshow("image",constant)
#cv2.imshow("image",image)
cv2.waitKey(0)
cv2.destroyAllWindows()
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