python - OpenCV - 拆分和合并阿尔法 channel 很慢

Question

我正在使用 Python OpenCV 来分割 channel 并像这样删除黑色背景......

    b_channel, g_channel, r_channel = cv2.split(image_1)
    alpha_channel = np.zeros_like(gray)

    for p in range(alpha_channel.shape[0]):
        for q in range(alpha_channel.shape[1]):
            if b_channel[p][q]!=0 or g_channel[p][q]!=0 or r_channel[p][q]!=0:
                alpha_channel[p][q] = 255

    merged = cv2.merge((b_channel, g_channel, r_channel, alpha_channel))

这是可行的，但在仅 200kb 的图像上完成大约需要 10 秒

有没有更有效的方法来做到这一点，或者我可以使用我拥有的代码获得一些速度提升？

Answer 1

使用 for 迭代像素循环实际上非常缓慢且效率低下。此外，根据文档 here ,

cv2.split() is a costly operation (in terms of time). So do it only if you need it. Otherwise go for Numpy indexing.

您可以尝试使用 numpy 进行矢量化和索引，如下所示:

# create the image with alpha channel
img_rgba = cv2.cvtColor(img, cv2.COLOR_RGB2RGBA)

# mask: elements are True any of the pixel value is 0         
mask = (img[:, :, 0:3] != [0,0,0]).any(2) 
#assign the mask to the last channel of the image
img_rgba[:,:,3]  = (mask*255).astype(np.uint8)