opencv 图像基本操作

目录：读取图像，获取属性信息，图像ROI，图像通道的拆分和合并

1.  读取图像

　　像素值返回：直接使用坐标即可获得， 修改像素值：直接通过坐标进行赋值

　　能用矩阵操作，便用，使用numpy中的array.item()以及array.itemset()会加快速度，逐渐修改像素会慢

import cv2
import numpy as np
img = cv2.imread("test.jpg")
#获取像素值
px = img[100,100]
blue = img[100,100,0]
print(px, blue)
#修改像素值
img[100,100] = [255,255,255]
print(img[100,100])
#使用item
print(img.item(10,10,2))
img.itemset((10,10,2),100)
print(img.item(10,10,2))

2.  图像属性： 行、列、通道、数据类型、像素数目

print(img.shape)
#(342,548,3)   (342,548)  图像是灰度时，只有行和列
print(img.size, img.dtype)
#562248 uint8  图像像素数目， 图像数据类型，  注意：运行代码时数据类型是否一致

3.  图像ROI

ROI = img[y1:y2,x1:x2]

4. 拆分以及合并图像通道

b,g,r = cv2.split(img)
img = cv2.merge(bgr)
b = img[:,:,0]
#修改时能尽量用numpy索引就用，用split比较耗时

5.  图像加法及混合

cv2.add(x, y)
cv2.addWeighted(img1, 0.7, img2, 0.3, 0)   #dst = a* img1 + b*img2 + c

6.  图像掩码

import cv2
import numpy as np
# Load two images
img1 = cv2.imread('messi5.jpg')
img2 = cv2.imread('opencv-logo-white.png')

# I want to put logo on top-left corner, So I create a ROI
rows,cols,channels = img2.shape
roi = img1[0:rows, 0:cols ]

# Now create a mask of logo and create its inverse mask also
img2gray = cv2.cvtColor(img2,cv2.COLOR_BGR2GRAY)
ret, mask = cv2.threshold(img2gray, 10, 255, cv2.THRESH_BINARY)
mask_inv = cv2.bitwise_not(mask)

# Now black-out the area of logo in ROI
img1_bg = cv2.bitwise_and(roi,roi,mask = mask_inv)

# Take only region of logo from logo image.
img2_fg = cv2.bitwise_and(img2,img2,mask = mask)

# Put logo in ROI and modify the main image
dst = cv2.add(img1_bg,img2_fg)
img1[0:rows, 0:cols ] = dst

cv2.imshow('res',img1)
cv2.waitKey(0)
cv2.destroyAllWindows()