Opencv(Python版)-4 图像的算术运算
学习对图像的几种算术运算，如加法，减法，按位运算等。
学习以下函数：cv2.add（），cv2.addWeighted（）等。
图像的加法运算
cv2.addWeighted(m1,w1,m2,w2)，四个参数,m1 m2是两个要相加的图片，w1 w2 表示图片的显示权重，值越大图像越清晰，对比度越高。
import cv2
img1 = cv2.imread('6.png')
img2 = cv2.imread('7.png')
cv2.imshow('6',img1)
cv2.imshow('7',img2)
dst = cv2.addWeighted(img1,0.7,img2,0.3,0)
cv2.imshow('dst',dst)
cv2.waitKey(0)
cv2.destroyAllWindows()
图像的位运算
函数 cv2.threshold(src, thresh, maxval, type) 可对图像二值化处理,这个函数有四个参数，第一个原图像，第二个进行分类的阈值，第三个是高于（低于）阈值时赋予的新值，第四个是一个方法选择参数，常用的有：
- cv2.THRESH_BINARY（黑白二值）
- cv2.THRESH_BINARY_INV（黑白二值反转）
- cv2.THRESH_TRUNC （得到的图像为多像素值）
- cv2.THRESH_TOZERO
- cv2.THRESH_TOZERO_INV
import cv2
# Load two images
img1 = cv2.imread('1.png')
img2 = cv2.imread('2.jpg')
# cv2.imshow('1',img1)
cv2.imshow('2',img2)
# 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,127, 1, cv2.THRESH_BINARY_INV)
cv2.imshow('3',mask)
mask_inv = cv2.bitwise_not(mask)
cv2.imshow('4',mask_inv)
# Now black-out the area of logo in ROI
img1_bg = cv2.bitwise_and(roi,roi,mask = mask_inv)
cv2.imshow('5',img1_bg)
# Take only region of logo from logo image.
img2_fg = cv2.bitwise_and(img2,img2,mask = mask)
cv2.imshow('6',img2_fg)
# Put logo in ROI and modify the main image
dst = cv2.add(img1_bg,img2_fg)
cv2.imshow('7',dst)
img1[0:rows, 0:cols ] = dst
cv2.imshow('res',img1)
cv2.waitKey(0)
cv2.destroyAllWindows()
将 ret, mask = cv2.threshold(img2gray,127, 1, cv2.THRESH_BINARY_INV) 中参数1改为255
简单的拼接
将小图片赋值到对应大图片的位置上
import cv2
import numpy as np
img1 = cv2.imread('1.png')
img2 = cv2.imread('2.jpg')
rows,cols,channels = img2.shape
img1[0:rows,0:cols] = img2;
cv2.imshow('res',img1)
cv2.waitKey(0)
cv2.destroyAllWindows()
