How do I replace the alpha channel of any image (png, jpg, rgb, rbga) with specified background color? It must also work with images that do not have an alpha channel.
3 Answers
This can be done by checking if the image is transparent
def remove_transparency(im, bg_colour=(255, 255, 255)):
# Only process if image has transparency (http://stackoverflow.com/a/1963146)
if im.mode in ('RGBA', 'LA') or (im.mode == 'P' and 'transparency' in im.info):
# Need to convert to RGBA if LA format due to a bug in PIL (http://stackoverflow.com/a/1963146)
alpha = im.convert('RGBA').split()[-1]
# Create a new background image of our matt color.
# Must be RGBA because paste requires both images have the same format
# (http://stackoverflow.com/a/8720632 and http://stackoverflow.com/a/9459208)
bg = Image.new("RGBA", im.size, bg_colour + (255,))
bg.paste(im, mask=alpha)
return bg
else:
return im
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4In modern versions of Pillow you can probably use
.getchannel('A')
instead of.split()[-1]
.– gpsCommented Jun 9, 2018 at 18:52 -
5After pasting the image onto the background, I had to also convert to RGB using
bg.convert('RGB')
Commented Jan 4, 2019 at 14:03
I'd suggest using Image.alpha_composite
.
This code can avoid a tuple index out of range
error if png has no alpha channel.
from PIL import Image
png = Image.open(img_path).convert('RGBA')
background = Image.new('RGBA', png.size, (255,255,255))
alpha_composite = Image.alpha_composite(background, png)
alpha_composite.save('foo.jpg', 'JPEG', quality=80)
I also recommend you inspect both results with a image.show()
.
Credits for this answer goes to shuuji3 and others who helped build a vast answers repertoire in this other question.
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If the source image is always a PNG, this should be fine, but if it may encounter an image type that doesn't have transparency, e.g. a .jpg, this produces an
OSError: cannot write mode RGBA as JPEG
. I added a check when opening the image to resolve this.– alstrCommented May 23, 2022 at 14:03
I updated Vincius M's code with the user, tutuDajuju, suggestion to make [height, width, 3] matrix (not [height, width, 4]):
from PIL import Image
import numpy as np
png = Image.open(img_path).convert('RGBA')
background = Image.new('RGBA', png.size, (255,255,255))
alpha_composite = Image.alpha_composite(background, png)
# if you check the matrix dimension, channel, it would be still 4.
h, w, channel = np.asarray(alpha_composite).shape
alpha_composite_3 = alpha_composite.convert('RGB')
# if you check the matrix dimension, channel, it would be 3.
h, w, channel = np.asarray(alpha_composite_3).shape
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1You need to add the
.shape
to the numpy array to accesstheh, w, channel
variables. Commented Jul 10, 2023 at 16:43 -
@jegertor Thanks for correction. Next time, please go head to edit. Commented Jul 10, 2023 at 17:33