Pillow ImageDraw绘制部分不透明文本

示例：绘制部分不透明文本

from PIL import Image, ImageDraw, ImageFont
# get an image
base = Image.open("Pillow/Tests/images/hopper.png").convert("RGBA")

# make a blank image for the text, initialized to transparent text color
txt = Image.new("RGBA", base.size, (255,255,255,0))

# get a font
fnt = ImageFont.truetype("Pillow/Tests/fonts/FreeMono.ttf", 40)
# get a drawing context
d = ImageDraw.Draw(txt)

# draw text, half opacity
d.text((10,10), "Hello", font=fnt, fill=(255,255,255,128))
# draw text, full opacity
d.text((10,60), "World", font=fnt, fill=(255,255,255,255))

out = Image.alpha_composite(base, txt)

out.show()