如何用PIL确定ICO图像的透明色彩指数？

Question

具体来说，这是来自一个.ico文件，所以没有像您在gif中获得的“透明”“信息”属性。下面的例子说明了如何使用我猜测的正确的透明度索引“0”将雅虎的favicon转换为png。如何检测ico实际上是透明的，并且透明度指数是0？

import urllib2 
import Image 
import StringIO 

resp = urllib2.urlopen("http://www.yahoo.com/favicon.ico") 
image = Image.open(StringIO.StringIO(resp.read())) 

f = file("test.png", "w") 

# I guessed that the transparent index is 0. how to 
# determine it correctly ? 
image.save(f, "PNG", quality=95, transparency=0) 

Answer 1

看起来像有人认为，PIL并没有真正读ICO正确的（我可以看到调和其源代码的ICO格式一些研究之后，同样的事情 - 有它决定透明度和位图） 并想出了这个扩展名：

http://www.djangosnippets.org/snippets/1287/

，因为这是对非Django应用程序非常有用，我已经有一些调整，它的异常这里转贴抛出：

import operator 
import struct 

from PIL import BmpImagePlugin, PngImagePlugin, Image 


def load_icon(file, index=None): 
    ''' 
    Load Windows ICO image. 

    See http://en.wikipedia.org/w/index.php?oldid=264332061 for file format 
    description. 
    ''' 
    if isinstance(file, basestring): 
     file = open(file, 'rb') 

    try: 
     header = struct.unpack('<3H', file.read(6)) 
    except: 
     raise IOError('Not an ICO file') 

    # Check magic 
    if header[:2] != (0, 1): 
     raise IOError('Not an ICO file') 

    # Collect icon directories 
    directories = [] 
    for i in xrange(header[2]): 
     directory = list(struct.unpack('<4B2H2I', file.read(16))) 
     for j in xrange(3): 
      if not directory[j]: 
       directory[j] = 256 

     directories.append(directory) 

    if index is None: 
     # Select best icon 
     directory = max(directories, key=operator.itemgetter(slice(0, 3))) 
    else: 
     directory = directories[index] 

    # Seek to the bitmap data 
    file.seek(directory[7]) 

    prefix = file.read(16) 
    file.seek(-16, 1) 

    if PngImagePlugin._accept(prefix): 
     # Windows Vista icon with PNG inside 
     image = PngImagePlugin.PngImageFile(file) 
    else: 
     # Load XOR bitmap 
     image = BmpImagePlugin.DibImageFile(file) 
     if image.mode == 'RGBA': 
      # Windows XP 32-bit color depth icon without AND bitmap 
      pass 
     else: 
      # Patch up the bitmap height 
      image.size = image.size[0], image.size[1] >> 1 
      d, e, o, a = image.tile[0] 
      image.tile[0] = d, (0, 0) + image.size, o, a 

      # Calculate AND bitmap dimensions. See 
      # http://en.wikipedia.org/w/index.php?oldid=264236948#Pixel_storage 
      # for description 
      offset = o + a[1] * image.size[1] 
      stride = ((image.size[0] + 31) >> 5) << 2 
      size = stride * image.size[1] 

      # Load AND bitmap 
      file.seek(offset) 
      string = file.read(size) 
      mask = Image.fromstring('1', image.size, string, 'raw', 
            ('1;I', stride, -1)) 

      image = image.convert('RGBA') 
      image.putalpha(mask) 

    return image