Python OpenCV - 使用透明度叠加图像

Question

我想实现的是将一张带有透明度的图片放在另一张图片的上层。就像这样：

我找不到任何解决方法，所以我决定一像素一像素地计算颜色结果。虽然这个方法对我有效，但是速度非常慢。我对OpenCV和Python都很陌生。这是我写的代码：

import numpy as np
import cv2

img1 = cv2.imread("img1.png", -1)
img2 = cv2.imread("img2.png", -1) # this one has transparency
h, w, depth = img2.shape

result = np.zeros((h, w, 3), np.uint8)

for i in range(h):
    for j in range(w):
        color1 = img1[i, j]
        color2 = img2[i, j]
        alpha = color2[3] / 255.0
        new_color = [ (1 - alpha) * color1[0] + alpha * color2[0],
                      (1 - alpha) * color1[1] + alpha * color2[1],
                      (1 - alpha) * color1[2] + alpha * color2[2] ]
        result[i, j] = new_color

cv2.imshow("result", result)
cv2.waitKey(0)
cv2.destroyAllWindows()

还有其他方法吗？更快的方式，更快的方式？ 谢谢。

- Dusan

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请查看此答案。 - Dan Mašek

这导致了与我的代码相同的图像，但速度快得多！谢谢！ - Dusan

可能是如何在实时帧中加入带有alpha /透明度的png的重复问题。 - Elijan9

Answer 1

答案：

import numpy as np
import cv2

from time import time

img1 = cv2.imread("./test_image/rgb.jpg", -1)
img2 = cv2.imread("./test_image/rgba.png", -1) # this one has transparency
h, w, c = img2.shape

img1 = cv2.resize(img1, (w, h), interpolation = cv2.INTER_CUBIC)
result = np.zeros((h, w, 3), np.uint8)

#slow
st = time()
for i in range(h):
for j in range(w):
        color1 = img1[i, j]
        color2 = img2[i, j]
        alpha = color2[3] / 255.0
        new_color = [ (1 - alpha) * color1[0] + alpha * color2[0],
                      (1 - alpha) * color1[1] + alpha * color2[1],
                      (1 - alpha) * color1[2] + alpha * color2[2] ]
        result[i, j] = new_color
end = time() - st
print(end)

#fast
st = time()
alpha = img2[:, :, 3] / 255.0
result[:, :, 0] = (1. - alpha) * img1[:, :, 0] + alpha * img2[:, :, 0]
result[:, :, 1] = (1. - alpha) * img1[:, :, 1] + alpha * img2[:, :, 1]
result[:, :, 2] = (1. - alpha) * img1[:, :, 2] + alpha * img2[:, :, 2]
end = time() - st
print(end)

cv2.imshow("result", result)
cv2.waitKey(0)
cv2.destroyAllWindows()

- Josanghyeon

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请将英语翻译成中文。仅返回翻译的文本：请不要只回答代码，还要添加一些解释为什么这是正确的或您的代码执行什么操作。 - tung

谢谢，这非常有帮助。 - crazjo