Using openCV to overlay a transparent image onto another image

Question

How can I apply transparent PNG to another image without losing its transparency using openCV in Python?

import cv2

background = cv2.imread('field.jpg')
overlay = cv2.imread('dice.png')

# Help please

cv2.imwrite('combined.png', background)

Desired Result:

Sources:

Background image

overlay

Answer 1

import cv2

background = cv2.imread('field.jpg')
overlay = cv2.imread('dice.png')

added_image = cv2.addWeighted(background,0.4,overlay,0.1,0)

cv2.imwrite('combined.png', added_image)

Answer 2

import numpy as np
import cv2

# ==============================================================================

def blend_transparent(face_img, overlay_t_img):
    # Split out the transparency mask from the colour info
    overlay_img = overlay_t_img[:,:,:3] # Grab the BRG planes
    overlay_mask = overlay_t_img[:,:,3:]  # And the alpha plane

    # Again calculate the inverse mask
    background_mask = 255 - overlay_mask

    # Turn the masks into three channel, so we can use them as weights
    overlay_mask = cv2.cvtColor(overlay_mask, cv2.COLOR_GRAY2BGR)
    background_mask = cv2.cvtColor(background_mask, cv2.COLOR_GRAY2BGR)

    # Create a masked out face image, and masked out overlay
    # We convert the images to floating point in range 0.0 - 1.0
    face_part = (face_img * (1 / 255.0)) * (background_mask * (1 / 255.0))
    overlay_part = (overlay_img * (1 / 255.0)) * (overlay_mask * (1 / 255.0))

    # And finally just add them together, and rescale it back to an 8bit integer image    
    return np.uint8(cv2.addWeighted(face_part, 255.0, overlay_part, 255.0, 0.0))

# ==============================================================================

# We load the images
face_img = cv2.imread("field.jpg")
overlay_t_img = cv2.imread("dice.png", -1) # Load with transparency

result_2 = blend_transparent(face_img, overlay_t_img)
cv2.imwrite("merged_transparent.png", result_2)

Answer 3

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background = cv2.imread('road.jpg')
overlay = cv2.imread('traffic sign.png')

rows,cols,channels = overlay.shape

overlay=cv2.addWeighted(background[250:250+rows, 0:0+cols],0.5,overlay,0.5,0)

background[250:250+rows, 0:0+cols ] = overlay

, :

ROI

, 400x300 32x32, x [0-32] y [250-282] , , , .

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Answer 4

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import cv2
import numpy as np

def overlay_transparent(background, overlay, x, y):

    background_width = background.shape[1]
    background_height = background.shape[0]

    if x >= background_width or y >= background_height:
        return background

    h, w = overlay.shape[0], overlay.shape[1]

    if x + w > background_width:
        w = background_width - x
        overlay = overlay[:, :w]

    if y + h > background_height:
        h = background_height - y
        overlay = overlay[:h]

    if overlay.shape[2] < 4:
        overlay = np.concatenate(
            [
                overlay,
                np.ones((overlay.shape[0], overlay.shape[1], 1), dtype = overlay.dtype) * 255
            ],
            axis = 2,
        )

    overlay_image = overlay[..., :3]
    mask = overlay[..., 3:] / 255.0

    background[y:y+h, x:x+w] = (1.0 - mask) * background[y:y+h, x:x+w] + mask * overlay_image

    return background

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Answer 5

png, IMREAD_UNCHANGED

Mat overlay = cv::imread("dice.png", IMREAD_UNCHANGED);

, RGB , :

/**
 * @brief Draws a transparent image over a frame Mat.
 * 
 * @param frame the frame where the transparent image will be drawn
 * @param transp the Mat image with transparency, read from a PNG image, with the IMREAD_UNCHANGED flag
 * @param xPos x position of the frame image where the image will start.
 * @param yPos y position of the frame image where the image will start.
 */
void drawTransparency(Mat frame, Mat transp, int xPos, int yPos) {
    Mat mask;
    vector<Mat> layers;

    split(transp, layers); // seperate channels
    Mat rgb[3] = { layers[0],layers[1],layers[2] };
    mask = layers[3]; // png alpha channel used as mask
    merge(rgb, 3, transp);  // put together the RGB channels, now transp insn't transparent 
    transp.copyTo(frame.rowRange(yPos, yPos + transp.rows).colRange(xPos, xPos + transp.cols), mask);
}

:

drawTransparency(background, overlay, 10, 10);

Answer 6

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