How to crop an image by its mask

Question

I have this image:

And for the beard, I have this mask:

I want to cut the beard out using the mask with a transparent background like this:

I followed this SO post's attempt. Here it is:

for img in input_images:
    gaberiel = Image.open(path + '/gaberiel-images/' + img)

    beard_mask = imread(path + '/gaberiel-masks/' + 'beard_binary_' + img[:-4] + '.png', cv2.IMREAD_GRAYSCALE)

    gaberiel_x, gaberiel_y = gaberiel.size
    beard_mask_x, beard_mask_y, _ = beard_mask.shape

    x_beard_mask= min(gaberiel_x, beard_mask_x)
    x_half_beard_mask = beard_mask.shape[0] // 2

    mask_beard = beard_mask[x_half_beard_mask - x_beard_mask // 2: x_half_beard_mask + x_beard_mask // 2 + 1, :gaberiel_y]

    gaberiel_width_half = gaberiel.size[1] // 2
    gaberiel_to_mask = gaberiel[:, gaberiel_width_half - x_half_beard_mask:gaberiel_width_half + x_half_beard_mask]
    masked = cv2.bitwise_and(gaberiel_to_mask, gaberiel_to_mask, mask=mask_beard)

    tmp = cv2.cvtColor(masked, cv2.COLOR_BGR2GRAY)
    _, alpha = cv2.threshold(tmp, 0, 255, cv2.THRESH_BINARY)
    b, g, r = cv2.split(masked)
    rgba = [b, g, r, alpha]
    masked_tr = cv2.merge(rgba, 4)

    plt.axis('off')
    plt.imshow(masked_tr)

But this is the error I am getting:

gaberiel_to_mask = gaberiel[:, gaberiel_width_half - x_half_beard_mask:gaberiel_width_half + x_half_beard_mask]
TypeError: 'PngImageFile' object is not subscriptable

I think that my attempt is overall bad. Is there a way I can simplify this process?

[`getdata()`](https://pillow.readthedocs.io/en/stable/reference/Image.html#PIL.Image.Image.getdata) — tevemadar, Feb 22 '22 at 09:46

MD Mushfirat Mohaimin · Accepted Answer · 2022-02-22T03:12:30.620

2

Make sure your mask is of the same size as your image and then use the function as in below:

def apply_mask(image, mask):
    # Convert to numpy arrays
    image = np.array(image)
    mask = np.array(mask)
    # Convert grayscale image to RGB
    mask = np.stack((mask,)*3, axis=-1)
    # Multiply arrays
    resultant = image*mask
    return resultant

image = ...
mask = ...

resultant = apply_mask(image, mask)

Result:

For the code to work, the image array must be in range 0-255 and the mask array must be in binary (either 0 or 1). In the mask array, the area of beard must have pixel value of 1 and the rest 0, so that multiplying the image with the mask will give the desired image as shown above.

Save image as a png with transparent background:

import matplotlib.pyplot as plt
plt.plot(resultant)
plt.savefig('image.png', transparent=True)

edited Feb 22 '22 at 03:12

answered Feb 22 '22 at 01:01

MD Mushfirat Mohaimin

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What if I want the background to be transparent and not black? Also, how do you save this as a png? What is the dtype of resultant? – Onur-Andros Ozbek Feb 22 '22 at 02:54
@oo92 dtype of the resultant will be the dtype of the image array – MD Mushfirat Mohaimin Feb 22 '22 at 03:08
@oo92 I have updated my answer, check it out. – MD Mushfirat Mohaimin Feb 22 '22 at 03:10
The `resultant = image * mask` throws this error: `ValueError: operands could not be broadcast together with shapes (280,300,3) (280,300,3,3) ` – Onur-Andros Ozbek Feb 22 '22 at 03:43
@oo92 that is because your mask is already in RGB, just comment the grayscale-to-RGB conversion line in the `apply_mask` function, and the error will be eliminated – MD Mushfirat Mohaimin Feb 22 '22 at 03:44
When I ran the code, it just gave me image files with nothing but transparency. When I made `transparent = False`, the image files were just white. – Onur-Andros Ozbek Feb 22 '22 at 03:49
@oo92 could you send me a link to an image and the corresponding mask? – MD Mushfirat Mohaimin Feb 22 '22 at 03:51
I got the image of the guy with his corresponding mask in the question. – Onur-Andros Ozbek Feb 22 '22 at 03:55

How to crop an image by its mask

1 Answers1