Set the background color for a PNG with transparency

user_1196549 0
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I am loading PNG images that have a transparency plane. When converted to grayscale, the transparent areas in the image appear as black, which seems to be the default background. I need them to be white instead. What can I do ?

[This is not the usual question on how to preserve transparency.]

alpha-transparency opencv python
3 Answers

You can use the following code

def read_transparent_png(filename, hexcode):
    image_4channel = cv2.imread(filename, cv2.IMREAD_UNCHANGED)
    alpha_channel = image_4channel[:, :, 3]
    rgb_channels = image_4channel[:, :, :3]
    white_background_image = np.zeros((image_4channel.shape[0], image_4channel.shape[1],3), dtype=np.uint8)
    rgb = tuple(int(hexcode[i:i+2], 16) for i in (0, 2, 4))
    RED, GREEN, BLUE = rgb[0], rgb[1], rgb[2]
    white_background_image[::] = (BLUE, GREEN, RED)
    alpha_factor = alpha_channel[:, :, np.newaxis].astype(np.float32) / 255.0
    alpha_factor = np.concatenate(
        (alpha_factor, alpha_factor, alpha_factor), axis=2)
    base = rgb_channels.astype(np.float32) * alpha_factor
    white = white_background_image.astype(np.float32) * (1 - alpha_factor)
    final_image = base + white
    return final_image.astype(np.uint8)

here hexcode is the hexadecimal code of the colour that you want to set as background for transparent PNG.

user_178645140
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