如何使用Pillow從圖像中提取Alpha通道

Question

如何使用Pillow從PNG導出Alpha模板？

理想情況下，結果將是表示alpha通道的灰度圖像。

Answer 1

# Open the image and convert it to RGBA, just in case it was indexed 
image = Image.open(image_path).convert('RGBA') 

# Extract just the alpha channel 
alpha = image.split()[-1] 

# Unfortunately the alpha channel is still treated as such and can't be dumped 
# as-is 

# Create a new image with an opaque black background 
bg = Image.new("RGBA", image.size, (0,0,0,255)) 

# Copy the alpha channel to the new image using itself as the mask 
bg.paste(alpha, mask=alpha) 

# Since the bg image started as RGBA, we can save some space by converting it 
# to grayscale ('L') Optionally, we can convert the image to be indexed which 
# saves some more space ('P') In my experience, converting directly to 'P' 
# produces both the Gray channel and an Alpha channel when viewed in GIMP, 
# althogh the file sizes is about the same 
bg.convert('L').convert('P', palette=Image.ADAPTIVE, colors=8).save(
                   mask_path, 
                   optimize=True)