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import io
import struct
import PIL.Image
class ImageHash(object):
"""A hash on the contents of an image. This disregards mode, depth and meta
information. Note that due to limitations in PIL and the image format
(interlacing) the full contents are stored and decoded in hexdigest."""
maxsize = 1024 * 1024 * 32
# max memory usage is about 5 * maxpixels in bytes
maxpixels = 1024 * 1024 * 32
def __init__(self, hashobj):
"""
@param hashobj: a hashlib-like object
"""
self.hashobj = hashobj
self.imagedetected = False
self.content = io.BytesIO()
def update(self, data):
self.content.write(data)
if self.content.tell() > self.maxsize:
raise ValueError("maximum image size exceeded")
if self.imagedetected:
return
if self.content.tell() < 33: # header + IHDR
return
curvalue = self.content.getvalue()
if curvalue.startswith(b"\x89PNG\r\n\x1a\n\0\0\0\x0dIHDR"):
width, height = struct.unpack(">II", curvalue[16:24])
if width * height > self.maxpixels:
raise ValueError("maximum image pixels exceeded")
self.imagedetected = True
return
raise ValueError("not a png image")
def copy(self):
new = ImageHash()
new.hashobj = self.hashobj.copy()
new.imagedetected = self.imagedetected
new.content = io.BytesIO(self.content.getvalue())
return new
def hexdigest(self):
if not self.imagedetected:
raise ValueError("not a png image")
hashobj = self.hashobj.copy()
pos = self.content.tell()
try:
self.content.seek(0)
try:
img = PIL.Image.open(self.content)
except IOError:
raise ValueError("broken png header")
width, height = img.size
pack = lambda elem: struct.pack("BBBB", *elem)
# special casing easy modes reduces memory usage
if img.mode == "L":
pack = lambda elem: struct.pack("BBBB", elem, elem, elem, 255)
elif img.mode == "RGB":
pack = lambda elem: struct.pack("BBBB", *(elem + (255,)))
elif img.mode != "RGBA":
img = img.convert("RGBA")
try:
for elem in img.getdata():
hashobj.update(pack(elem))
except (SyntaxError, IndexError, IOError): # crazy stuff from PIL
raise ValueError("error reading png image")
finally:
self.content.seek(pos)
return "%s%8.8x%8.8x" % (hashobj.hexdigest(), width, height)
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