带有 alpha 通道背景的 Python 文本

Question

我正在使用Python 2.7.3和PIL/Pillow库，想在一个带有透明背景的PNG图片上添加带透明度的文字。这里是我的代码，但结果并不是我想要的：

from PIL import Image
from PIL import ImageDraw
from PIL import ImageFont
from PIL import ImageEnhance

width=854
height=480
opacity=0.8
text='copyright'
filename = 'result.png'
black = (0,0,0)
white = (255,255,255)

font = ImageFont.truetype('verdana.ttf',15)
wm = Image.new('RGBA',(width,height),white)
im = Image.new('L',(width,height),0)

draw = ImageDraw.Draw(wm)
w,h = draw.textsize(text, font)
draw.text(((width-w)/2,(height-h)/2),text,white,font)

en = ImageEnhance.Brightness(wm)
#en.putalpha(mask)
mask = en.enhance(1-opacity)
im.paste(wm,(25,25),mask)

im.save(filename)

结果：

下面的代码是我想要的效果，但背景完全透明：

import PIL
from PIL import ImageFont
from PIL import Image
from PIL import ImageDraw

width = 854
height = 480
black = (0,0,0)
text = "copyright"
white = (255,255,255)
font = ImageFont.truetype("Arial.ttf",40)
img = Image.new("RGBA", (width,height),white)
draw = ImageDraw.Draw(img)
w, h = draw.textsize(text, font)
draw.text(((width-w)/2,(height-h)/2),text,black,font=font)
draw = ImageDraw.Draw(img)
#img.putalpha
img.save("result.png")
#img.show

结果：

Answer 1

这个问题是因为 wm 的颜色和文字是一样的，所以如果你把文字画到上面，就看不见了。你可以把 wm 的颜色改成透明，就像我下面做的那样（并且在设置宽度、高度和透明度的时候去掉逗号）：

from PIL import Image
from PIL import ImageDraw
from PIL import ImageFont
from PIL import ImageEnhance

width=854
height=480
opacity=0.8
text='copyright'
filename = 'result.png'
black = (0,0,0)
white = (255,255,255)
transparent = (0,0,0,0)

font = ImageFont.truetype('verdana.ttf',15)
wm = Image.new('RGBA',(width,height),transparent)
im = Image.new('RGBA',(width,height),transparent) # Change this line too.

draw = ImageDraw.Draw(wm)
w,h = draw.textsize(text, font)
draw.text(((width-w)/2,(height-h)/2),text,white,font)

en = ImageEnhance.Brightness(wm)
#en.putalpha(mask)
mask = en.enhance(1-opacity)
im.paste(wm,(25,25),mask)

im.save(filename)