摘自https://docs.opencv.org/4.2.0/d0/d86/tutorial_py_image_arithmetics.html
Image Addition
You can add two images with the OpenCV function, cv.add(), or simply by the numpy operation res = img1 + img2. Both images should be of same depth and type, or the second image can just be a scalar value.
There is a difference between OpenCV addition and Numpy addition. OpenCV addition is a saturated operation while Numpy addition is a modulo operation.
>>> x = np.uint8([250])
>>> y = np.uint8([10])
>>> print( cv.add(x,y) ) # 250+10 = 260 => 255
[[255]]
>>> print( x+y ) # 250+10 = 260 % 256 = 4
[4]This will be more visible when you add two images. Stick with OpenCV functions, because they will provide a better result.
Image Blending
This is also image addition, but different weights are given to images in order to give a feeling of blending or transparency:
g(x)=(1−α)f0(x)+αf1(x)
By varying α from 0→1, you can perform a cool transition between one image to another.
cv.addWeighted() applies the following equation to the image:
dst=α⋅img1+β⋅img2+γ
dst = cv.addWeighted(img1,0.7,img2,0.3,0)Bitwise Operations
This includes the bitwise AND, OR, NOT, and XOR operations. They will be highly useful while extracting any part of the image, defining and working with non-rectangular ROI's, and etc.
I want to put the OpenCV logo above an image. If I add two images, it will change the color. If I blend them, I get a transparent effect. But I want it to be opaque. If it was a rectangular region, I could use ROI. But the OpenCV logo is a not a rectangular shape.
# Load two images
img1 = cv.imread('messi5.jpg')
img2 = cv.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 = cv.cvtColor(img2,cv.COLOR_BGR2GRAY)
ret, mask = cv.threshold(img2gray, 10, 255, cv.THRESH_BINARY)
mask_inv = cv.bitwise_not(mask)
# Now black-out the area of logo in ROI
img1_bg = cv.bitwise_and(roi,roi,mask = mask_inv)
# Take only region of logo from logo image.
img2_fg = cv.bitwise_and(img2,img2,mask = mask)
# Put logo in ROI and modify the main image
dst = cv.add(img1_bg,img2_fg)
img1[0:rows, 0:cols ] = dst
cv.imshow('res',img1)
cv.waitKey(0)
cv.destroyAllWindows()