如何使用 Python 中的 OpenCv 将图像添加到视频中？

Question

I was trying to add a logo to my video using OpenCv by modifying a code that I found online (that was made for merging two pictures). The process worked somehow but the added logo was displayed only like a quarter of it, not full. So my questions are:

• How do I change the size and the cropping of the added logo?
• Is it possible also to change it's position on the video (like in the bottom)?

Any help or documentation (for beginner) would be appreciated.

The code I used:

import cv2
import numpy as np
 
foreground = cv2.imread('logo.jpg')
cap = cv2.VideoCapture("video.mp4")
alpha = 0.4
while True:
    ret, background = cap.read()
    background = cv2.flip(background,1)
    added_image = cv2.addWeighted(background[150:250,150:250,:],alpha,foreground[0:100,0:100,:],1-alpha,0)
    background[150:250,150:250] = added_image
    font = cv2.FONT_HERSHEY_SIMPLEX
    cv2.putText(background,'alpha:{}'.format(alpha),(10,30), font, 1,(255,255,255),2,cv2.LINE_AA)
    cv2.imshow('a',background)
    k = cv2.waitKey(10)
    if k == ord('q'):
        break
    if k == ord('a'):
        alpha +=0.1
        if alpha >=1.0:
            alpha = 1.0
    elif k== ord('d'):
        alpha -= 0.1
        if alpha <=0.0:
            alpha = 0.0
cap.release()
cv2.destroyAllWindows()

Answer 1

I added comments and some ease-of-use stuff to your code to help make it easier to understand what each part is supposed to be doing. The overall structure is the same, but hopefully this helps you figure out why the overlay looks the way it does.

import cv2
import numpy as np
 
# load image and start video
foreground = cv2.imread('logo.jpg')
cap = cv2.VideoCapture("video.mp4")

# init font
font = cv2.FONT_HERSHEY_SIMPLEX

# position of logo on video
top_left = [0, 0] # the top-left corner of your logo goes here
tx = top_left[0] # less typing later
ty = top_left[1]

# crop of logo
left = 0
right = 100
top = 0 # y = 0 is the top of the image
bottom = 100

# calculate width and height of logo crop
width = right - left
height = bottom - top

# main loop
alpha = 0.4
while True:
    # read image
    ret, background = cap.read()

    # horizontal flip to create mirror image
    background = cv2.flip(background,1)

    # quick primer on 2d image slicing:
    # images are [y,x]
    # crop = image[0:100, 300:500] will be a 200x100 image (width x height) 
    # the logo slice should give you a decent idea of what's going on

    # WARNING: there are no out-of-bounds checks here, make sure that
    # tx + width is less than the width of the background
    # ty + height is less than the height of the background
    # right is less than the width of the foreground
    # bottom is less than the height of the foreground

    # get crops of background and logo
    background_slice = background[ty:ty+height, tx:tx+width]; 
    logo_slice = foreground[top:bottom, left:right]; 

    # since we don't change our crop, we could do the logo slice outside the loop
    # but I'll keep it here for clarity

    # add slice of logo onto slice of background
    added_image = cv2.addWeighted(background_slice,alpha,logo_slice,1-alpha,0)
    background[ty:ty+height, tx:tx+width] = added_image

    # draw alpha value
    cv2.putText(background,'alpha:{}'.format(alpha),(10,30), font, 1,(255,255,255),2,cv2.LINE_AA)

    # show image
    cv2.imshow('a',background)
    k = cv2.waitKey(10)

    # process keypresses
    if k == ord('q'):
        break
    if k == ord('a'):
        alpha +=0.1
        if alpha >=1.0:
            alpha = 1.0
    elif k== ord('d'):
        alpha -= 0.1
        if alpha <=0.0:
            alpha = 0.0

# close
cap.release()
cv2.destroyAllWindows()