comictagger/comictaggerlib/imagehasher.py

"""A class to manage creating image content hashes, and calculate hamming distances"""

# Copyright 2013 Anthony Beville

# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at

#     http://www.apache.org/licenses/LICENSE-2.0

# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.

import io
import logging
from functools import reduce

try:
    from PIL import Image

    pil_available = True
except ImportError:
    pil_available = False
logger = logging.getLogger(__name__)


class ImageHasher:
    def __init__(self, path=None, data=None, width=8, height=8):
        self.width = width
        self.height = height

        if path is None and data is None:
            raise IOError

        try:
            if path is not None:
                self.image = Image.open(path)
            else:
                self.image = Image.open(io.BytesIO(data))
        except Exception:
            logger.exception("Image data seems corrupted!")
            # just generate a bogus image
            self.image = Image.new("L", (1, 1))

    def average_hash(self):
        try:
            image = self.image.resize((self.width, self.height), Image.ANTIALIAS).convert("L")
        except Exception:
            logger.exception("average_hash error")
            return int(0)

        pixels = list(image.getdata())
        avg = sum(pixels) / len(pixels)

        def compare_value_to_avg(i):
            return 1 if i > avg else 0

        bitlist = list(map(compare_value_to_avg, pixels))

        # build up an int value from the bit list, one bit at a time
        def set_bit(x, idx_val):
            (idx, val) = idx_val
            return x | (val << idx)

        result = reduce(set_bit, enumerate(bitlist), 0)

        # print("{0:016x}".format(result))
        return result

    def average_hash2(self):
        """
        # Got this one from somewhere on the net.  Not a clue how the 'convolve2d'
        # works!

        from numpy import array
        from scipy.signal import convolve2d

        im = self.image.resize((self.width, self.height), Image.ANTIALIAS).convert('L')

        in_data = array((im.getdata())).reshape(self.width, self.height)
        filt = array([[0,1,0],[1,-4,1],[0,1,0]])
        filt_data = convolve2d(in_data,filt,mode='same',boundary='symm').flatten()

        result = reduce(lambda x, (y, z): x | (z << y),
                         enumerate(map(lambda i: 0 if i < 0 else 1, filt_data)),
                         0)
        #print("{0:016x}".format(result))
        return result
        """

    def dct_average_hash(self):
        """
        # Algorithm source: http://syntaxcandy.blogspot.com/2012/08/perceptual-hash.html

        1. Reduce size. Like Average Hash, pHash starts with a small image.
        However, the image is larger than 8x8; 32x32 is a     good size. This
        is really done to simplify the DCT computation and not because it
        is needed to reduce the high frequencies.

        2. Reduce color. The image is reduced to a grayscale just to further
        simplify the number of computations.

        3. Compute the DCT. The DCT separates the image into a collection of
        frequencies and scalars. While JPEG uses     an 8x8 DCT, this algorithm
        uses a 32x32 DCT.

        4. Reduce the DCT. This is the magic step. While the DCT is 32x32,
        just keep the top-left 8x8. Those represent the lowest frequencies in
        the picture.

        5. Compute the average value. Like the Average Hash, compute the mean DCT
        value (using only the 8x8 DCT low-frequency values and excluding the first
        term since the DC coefficient can be significantly different     from the other
        values and will throw off the average). Thanks to David Starkweather for the
        added information about pHash. He wrote: "the dct hash is based on the low 2D
        DCT coefficients starting at the second from lowest, leaving out the first DC
        term. This excludes completely flat image information (i.e. solid colors) from
        being included in the hash description."

        6. Further reduce the DCT. This is the magic step. Set the 64 hash bits to 0 or
        1 depending on whether     each of the 64 DCT values is above or below the average
        value. The result doesn't tell us the actual low frequencies; it just tells us
        the very-rough relative scale of the frequencies to the mean. The result will not
        vary as long as the overall structure of the image remains the same; this can
        survive gamma and color histogram adjustments without a problem.

        7. Construct the hash. Set the 64 bits into a 64-bit integer. The order does not
        matter, just as long as you are consistent.


        import numpy
        import scipy.fftpack
        numpy.set_printoptions(threshold=10000, linewidth=200, precision=2, suppress=True)

        # Step 1,2
        im = self.image.resize((32, 32), Image.ANTIALIAS).convert("L")
        in_data = numpy.asarray(im)

        # Step 3
        dct = scipy.fftpack.dct(in_data.astype(float))

        # Step 4
        # Just skip the top and left rows when slicing, as suggested somewhere else...
        lofreq_dct = dct[1:9, 1:9].flatten()

        # Step 5
        avg = (lofreq_dct.sum()) / (lofreq_dct.size)
        median = numpy.median(lofreq_dct)

        thresh = avg

        # Step 6
        def compare_value_to_thresh(i):
            return (1 if i > thresh else 0)

        bitlist = map(compare_value_to_thresh, lofreq_dct)

        #Step 7
        def set_bit(x, (idx, val)):
            return (x | (val << idx))

        result = reduce(set_bit, enumerate(bitlist), long(0))


        #print("{0:016x}".format(result))
        return result
        """

    # accepts 2 hashes (longs or hex strings) and returns the hamming distance

    @staticmethod
    def hamming_distance(h1, h2):
        if isinstance(h1, int) or isinstance(h2, int):
            n1 = h1
            n2 = h2
        else:
            # convert hex strings to ints
            n1 = int(h1, 16)
            n2 = int(h2, 16)

        # xor the two numbers
        n = n1 ^ n2

        # count up the 1's in the binary string
        return sum(b == "1" for b in bin(n)[2:])