PIL 在圖像上繪制半透明方形疊加層

Question

from PIL import Image
from PIL import ImageDraw 
from io import BytesIO
from urllib.request import urlopen

url = "https://i.ytimg.com/vi/W4qijIdAPZA/maxresdefault.jpg"
file = BytesIO(urlopen(url).read())
img = Image.open(file)
img = img.convert("RGBA")
draw = ImageDraw.Draw(img, "RGBA")
draw.rectangle(((0, 00), (img.size[0], img.size[1])), fill=(0,0,0,127))
img.save('dark-cat.jpg')

這給了我一個巨大的黑色方塊。 我希望它是一個帶有貓的半透明黑色方塊。 有任何想法嗎？

Answer 1

對不起，我關於它是一個錯誤的評論是不正確的，所以......

您可以通過創建一個臨時圖像並使用Image.alpha_composite() ，如下面的代碼所示。 請注意，它支持黑色以外的半透明方塊。

from PIL import Image, ImageDraw
from io import BytesIO
from urllib.request import urlopen

TINT_COLOR = (0, 0, 0)  # Black
TRANSPARENCY = .25  # Degree of transparency, 0-100%
OPACITY = int(255 * TRANSPARENCY)

url = "https://i.ytimg.com/vi/W4qijIdAPZA/maxresdefault.jpg"
with BytesIO(urlopen(url).read()) as file:
    img = Image.open(file)
    img = img.convert("RGBA")

# Determine extent of the largest possible square centered on the image.
# and the image's shorter dimension.
if img.size[0] > img.size[1]:
    shorter = img.size[1]
    llx, lly = (img.size[0]-img.size[1]) // 2 , 0
else:
    shorter = img.size[0]
    llx, lly = 0, (img.size[1]-img.size[0]) // 2

# Calculate upper point + 1 because second point needs to be just outside the
# drawn rectangle when drawing rectangles.
urx, ury = llx+shorter+1, lly+shorter+1

# Make a blank image the same size as the image for the rectangle, initialized
# to a fully transparent (0% opaque) version of the tint color, then draw a
# semi-transparent version of the square on it.
overlay = Image.new('RGBA', img.size, TINT_COLOR+(0,))
draw = ImageDraw.Draw(overlay)  # Create a context for drawing things on it.
draw.rectangle(((llx, lly), (urx, ury)), fill=TINT_COLOR+(OPACITY,))

# Alpha composite these two images together to obtain the desired result.
img = Image.alpha_composite(img, overlay)
img = img.convert("RGB") # Remove alpha for saving in jpg format.
img.save('dark-cat.jpg')
img.show()

這是將其應用於測試圖像的結果：

Answer 2

鑒於每當我想用 PIL 繪制一個透明矩形時我都會回到這個問題，我決定進行更新。

如果我只更改一件事，您的代碼對我來說非常有用：以 PNG 格式而不是 JPEG 格式保存圖像。

所以當我跑步的時候

from io import BytesIO
from urllib.request import urlopen
from PIL import Image
from PIL import ImageDraw

url = "https://i.ytimg.com/vi/W4qijIdAPZA/maxresdefault.jpg"
file = BytesIO(urlopen(url).read())
img = Image.open(file)
draw = ImageDraw.Draw(img, "RGBA")
draw.rectangle(((280, 10), (1010, 706)), fill=(200, 100, 0, 127))
draw.rectangle(((280, 10), (1010, 706)), outline=(0, 0, 0, 127), width=3)
img.save('orange-cat.png')

我得到了這個美妙的圖像：

Answer 3

如果您只想使整個圖像變暗，有一種更簡單的方法：

img = Image.eval(img, lambda x: x/2)