F3.py
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__author__ = 'chunk'
import math
import numpy as np
from msteg import *
from common import *
class F3(StegBase):
""" This module has two methods: <i>embed_raw_data</i> to embed data
with the F3 algorithm and <i>extract_raw_data</i> to extract data
which was embedded previously. """
def __init__(self):
"""
Constructor of the F3 class.
"""
StegBase.__init__(self)
def embed_raw_data(self, src_cover, src_hidden, tgt_stego):
""" This method embeds arbitrary data into a cover image.
The cover image must be a JPEG.
src_cover - A valid pathname to an image file which serves as cover image
(the image which the secret image is embedded into).
src_hidden - A valid pathname to an arbitrary file that is supposed to be
embedded into the cover image.
tgt_stego - Target pathname of the resulting stego image. You should save to a
PNG or another lossless format, because many LSBs don't survive
lossy compression.
"""
self.t0 = time.time()
self._post_embed_actions(src_cover, src_hidden, tgt_stego)
def extract_raw_data(self, src_steg, tgt_hidden):
""" This method extracts secret data from a stego image. It is
(obviously) the inverse operation of embed_raw_data.
src_stego - A valid pathname to an image file which serves as stego image.
tgt_hidden - A pathname denoting where the extracted data should be saved to.
"""
self.t0 = time.time()
self._post_extract_actions(src_steg, tgt_hidden)
def _raw_embed(self, cov_data, hid_data):
"""
cov_data - 4-D numpy.int32 array
hid_data - 1-D numpy.uint8 array
"""
hid_data = bytes2bits(hid_data)
i = 0
cnt = -1
for x in np.nditer(cov_data, op_flags=['readwrite']):
cnt = cnt + 1
if x == 0 or cnt % 64 == 0: continue
m = (hid_data[i] & 1)
if x & 1 != m:
x[...] -= math.copysign(1, x)
if x == 0: continue
i += 1
if i == hid_data.size: break
return cov_data,i
def _raw_extract(self, steg_data, num_bits):
"""
Just a small helper function to extract hidden data.
"""
hid_data = np.zeros(num_bits, np.uint8)
j = 0
cnt = -1
for x in np.nditer(steg_data):
cnt = cnt + 1
if x == 0 or cnt % 64 == 0: continue
if j >= num_bits: break
hid_data[j] = x & 1
j = j + 1
return hid_data,j
def __str__(self):
return 'F3'