diff --git a/jpegObj/__init__.py b/jpegObj/__init__.py
index 0b12853..297376e 100644
--- a/jpegObj/__init__.py
+++ b/jpegObj/__init__.py
@@ -30,6 +30,8 @@ colorCode = {
     "YCCK": 5
 }
 
+colorParam = ['Y', 'Cb', 'Cr']
+
 # The JPEG class
 # ==============
 
@@ -69,28 +71,35 @@ class Jpeg(Jsteg):
     # 1D Signal Representations
     # -------------------------
 
-    def rawsignal(self, mask=base.acMaskBlock):
+    def rawsignal(self, mask=base.acMaskBlock, channel="All"):
         """
           Return a 1D array of AC coefficients.
           (Most applications should use getsignal() rather than rawsignal().)
         """
         R = []
-        for X in self.coef_arrays:
+        if channel == "All":
+            for X in self.coef_arrays:
+                (h, w) = X.shape
+                A = base.acMask(h, w, mask)
+                R = np.hstack([R, X[A]])
+        else:
+            cID = self.getCompID(channel)
+            X = self.coef_arrays[cID]
             (h, w) = X.shape
             A = base.acMask(h, w, mask)
             R = np.hstack([R, X[A]])
         return R
 
-    def getsignal(self, mask=base.acMaskBlock):
+    def getsignal(self, mask=base.acMaskBlock, channel="All"):
         """Return a 1D array of AC coefficients in random order."""
-        R = self.rawsignal(mask)
+        R = self.rawsignal(mask, channel)
         if self.key == None:
             return R
         else:
             rnd.seed(self.key)
             return R[rnd.permutation(len(R))]
 
-    def setsignal(self, R0, mask=base.acMaskBlock):
+    def setsignal(self, R0, mask=base.acMaskBlock, channel="All"):
         """Reinserts AC coefficients from getitem in the correct positions."""
         if self.key != None:
             rnd.seed(self.key)
@@ -100,13 +109,40 @@ class Jpeg(Jsteg):
             R[P] = R0
         else:
             R = R0
-        for X in self.coef_arrays:
+        if channel == "All":
+            for cID in range(3):
+                X = self.coef_arrays[cID]
+                s = X.size * 63 / 64
+                (h, w) = X.shape
+                X[base.acMask(h, w, mask)] = R[fst:(fst + s)]
+                fst += s
+
+                # Jset
+                blocks = self.getCoefBlocks(channel=colorParam[cID])
+                xmax, ymax = self.Jgetcompdim(cID)
+                for y in range(ymax):
+                    for x in range(xmax):
+                        block = blocks[y, x]
+                        self.Jsetblock(x, y, cID, bytearray(block.astype(np.int16)))
+
+        else:
+            cID = self.getCompID(channel)
+            X = self.coef_arrays[cID]
             s = X.size * 63 / 64
             (h, w) = X.shape
             X[base.acMask(h, w, mask)] = R[fst:(fst + s)]
             fst += s
+
+            # Jset
+            blocks = self.getCoefBlocks(channel)
+            xmax, ymax = self.Jgetcompdim(cID)
+            for y in range(ymax):
+                for x in range(xmax):
+                    block = blocks[y, x]
+                    self.Jsetblock(x, y, cID, bytearray(block.astype(np.int16)))
+
         assert len(R) == fst
-        return;
+
 
     # Histogram and Image Statistics
     # ------------------------------
@@ -247,12 +283,12 @@ class Jpeg(Jsteg):
         assert blocks.shape[-2:] == (8, 8), "block is expected of size (8,8)"
         cID = self.getCompID(channel)
 
-        vmax,hmax = blocks.shape[:2]
+        vmax, hmax = blocks.shape[:2]
         for i in range(vmax):
             for j in range(hmax):
                 v, h = i * 8, j * 8
-                self.coef_arrays[cID][v:v + 8, h:h + 8] = blocks[i,j]
-                self.Jsetblock(j, i, cID, bytearray(blocks[i,j].astype(np.int16)))
+                self.coef_arrays[cID][v:v + 8, h:h + 8] = blocks[i, j]
+                self.Jsetblock(j, i, cID, bytearray(blocks[i, j].astype(np.int16)))
 
     # Decompression
     # -------------
diff --git a/jpegObj/__init__.pyc b/jpegObj/__init__.pyc
index 6d5efc9..e6e4406 100644
Binary files a/jpegObj/__init__.pyc and b/jpegObj/__init__.pyc differ
diff --git a/msteg/StegBase.py b/msteg/StegBase.py
index b920464..e970b28 100644
--- a/msteg/StegBase.py
+++ b/msteg/StegBase.py
@@ -1,15 +1,6 @@
-"""
-This module implements a common base class of the steganographic
-algorithms which embed data into JPEG files.
-In order to run plugins inheriting from this class
-you must build the rw_dct.so library which interfaces with libjpeg.
-To do so, just run
-% python setup.py build
-in stegotool/util and copy the rw_dct.so
-library (which can be found somewhere in the build-directory to
-stegotool/util.
-
-"""
+__author__ = 'chunk'
+
+
 import numpy as np
 import time
 import os
@@ -21,6 +12,7 @@ import mjsteg
 import jpegObj
 from common import *
 
+sample_key = [46812L, 20559L, 31360L, 16681L, 27536L, 39553L, 5427L, 63029L, 56572L, 36476L, 25695L, 61908L, 63014L, 5908L, 59816L, 56765L]
 
 class StegBase(object):
     """
@@ -36,12 +28,14 @@ class StegBase(object):
         self.cov_jpeg = None
         self.cov_data = None
         self.hid_data = None
+        self.key = None
 
     def _get_cov_data(self, img_path):
         """
         Returns DCT coefficients of the cover image.
         """
         self.cov_jpeg = jpegObj.Jpeg(img_path)
+        self.key = self.cov_jpeg.getkey()
         self.cov_data = self.cov_jpeg.getCoefBlocks()
         return self.cov_data
 
@@ -150,7 +144,7 @@ class StegBase(object):
              float(emb_size) / cov_size))
 
     # dummy functions to please pylint
-    def _raw_embed(self, cov_data, hid_data, status_begin=0):
+    def _raw_embed(self, cov_data, hid_data):
         pass
 
     def _raw_extract(self, steg_data, num_bits):
diff --git a/msteg/StegBase.pyc b/msteg/StegBase.pyc
index 2de9c1f..918b89d 100644
Binary files a/msteg/StegBase.pyc and b/msteg/StegBase.pyc differ
diff --git a/msteg/steganography/F3.py b/msteg/steganography/F3.py
index d42c541..cfbc781 100644
--- a/msteg/steganography/F3.py
+++ b/msteg/steganography/F3.py
@@ -1,14 +1,6 @@
-"""
-<p>This module implements the F3 steganography algorithm invented by
-Andreas Westfeld.</p>
-
-It embeds a secret message in JPEG DCT coefficients.
-It differs from simpler algorithms such as JSteg by subtracting the
-absolute DCT value if the currently embedded bit and the LSB of the DCT
-value are not equal. DCT coefficients with value 0 are ignored.<br />
-If a DCT coefficient is equal to 1 or -1 the current bit
-is embedded repeatedly in order to make non-ambiguous extraction possible.
-"""
+__author__ = 'chunk'
+
+
 import time
 import math
 import numpy as np
@@ -42,7 +34,7 @@ class F3(StegBase):
         lossy compression.
         """
         self.t0 = time.time()
-        StegBase._post_embed_actions(self, src_cover, src_hidden, tgt_stego)
+        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
@@ -53,9 +45,9 @@ class F3(StegBase):
         tgt_hidden - A pathname denoting where the extracted data should be saved to.
         """
         self.t0 = time.time()
-        StegBase._post_extract_actions(self, src_steg, tgt_hidden)
+        self._post_extract_actions(src_steg, tgt_hidden)
 
-    def _raw_embed(self, cov_data, hid_data, status_begin=0):
+    def _raw_embed(self, cov_data, hid_data):
         """
         cov_data - 4-D numpy.int32 array
         hid_data - 1-D numpy.uint8 array
diff --git a/msteg/steganography/F3.pyc b/msteg/steganography/F3.pyc
index 07241ed..b3f2d1b 100644
Binary files a/msteg/steganography/F3.pyc and b/msteg/steganography/F3.pyc differ
diff --git a/msteg/steganography/F4.py b/msteg/steganography/F4.py
index 3fb0483..215324a 100644
--- a/msteg/steganography/F4.py
+++ b/msteg/steganography/F4.py
@@ -1,15 +1,11 @@
-"""
-<p>This module implements a slight variant of the F4 steganography algorithm
-invented by Andreas Westfeld. It embeds a secret message in JPEG
-DCT coefficients.</p>
-It differs from F3 in that even negative and odd positive DCT
-coefficients represent a 1 and odd negative and even positive
-DCT coefficients represent a 0. It also supports permutative strattling
-which is not included in the original description of F4.
-"""
+__author__ = 'chunk'
+
 import time
 import numpy as np
-from msteg.StegBase import StegBase
+import numpy.random as rnd
+from msteg.StegBase import *
+import mjsteg
+import jpegObj
 from common import *
 
 
@@ -18,51 +14,105 @@ class F4(StegBase):
     with the F3 algorithm and <i>extract_raw_data</i> to extract data
     which was embedded previously. """
 
-    def __init__(self):
+    def __init__(self, key=sample_key):
         """
         Constructor of the F3 class.
         """
         StegBase.__init__(self)
+        self.key = key
 
-    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.
+    def _get_cov_data(self, img_path):
+        """
+        Returns DCT coefficients of the cover image.
+        """
+        self.cov_jpeg = jpegObj.Jpeg(img_path, key=self.key)
 
-        src_cover - A valid pathname to an image file which serves as cover image
-        (the image which the secret image is embedded into).
+        cov_data = self.cov_jpeg.getsignal(channel='Y')
+        self.cov_data = np.array(cov_data, dtype=np.int16)
+        return self.cov_data
 
-        src_hidden - A valid pathname to an arbitrary file that is supposed to be
-        embedded into the cover image.
+    def embed_raw_data(self, src_cover, src_hidden, tgt_stego):
 
-        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()
-        StegBase._post_embed_actions(self, 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.
+        try:
+            cov_data = self._get_cov_data(src_cover)
+            hid_data = self._get_hid_data(src_hidden)
+            # print hid_data.dtype,type(hid_data),hid_data.tolist()
 
-        src_stego - A valid pathname to an image file which serves as stego image.
+            cov_data, bits_cnt = self._raw_embed(cov_data, hid_data)
+
+            if bits_cnt != np.size(hid_data) * 8:
+                raise Exception("Expected embedded size is %db but actually %db." % (
+                    np.size(hid_data) * 8, bits_cnt))
+
+            self.cov_jpeg.setsignal(cov_data, channel='Y')
+            self.cov_jpeg.Jwrite(tgt_stego)
+
+            # size_cov = os.path.getsize(tgt_stego)
+            size_cov = np.size(cov_data) / 8
+            size_embedded = np.size(hid_data)
+
+            self._display_stats("embedded", size_cov, size_embedded,
+                                time.time() - self.t0)
+
+        except TypeError as e:
+            raise e
+        except Exception as expt:
+            print "Exception when embedding!"
+            raise
+
+    def extract_raw_data(self, src_steg, tgt_hidden):
 
-        tgt_hidden - A pathname denoting where the extracted data should be saved to.
-        """
         self.t0 = time.time()
-        StegBase._post_extract_actions(self, src_steg, tgt_hidden)
 
-    def _raw_embed(self, cov_data, hid_data, status_begin=0):
+        try:
+            steg_data = self._get_cov_data(src_steg)
+            # emb_size = os.path.getsize(src_steg)
+            emb_size = np.size(steg_data) / 8
+
+
+            # recovering file size
+            header_size = 4 * 8
+            size_data, bits_cnt = self._raw_extract(steg_data, header_size)
+            size_data = bits2bytes(size_data)
+            print size_data
+
+            size_hd = 0
+            for i in xrange(4):
+                size_hd += size_data[i] * 256 ** i
+
+            raw_size = size_hd * 8
+
+            if raw_size > np.size(steg_data):
+                raise Exception("Supposed secret data too large for stego image.")
+
+            hid_data, bits_cnt = self._raw_extract(steg_data, raw_size)
+
+            if bits_cnt != raw_size:
+                raise Exception("Expected embedded size is %db but actually %db." % (
+                    raw_size, bits_cnt))
+
+            hid_data = bits2bytes(hid_data)
+            # print hid_data.dtype,type(hid_data),hid_data.tolist()
+            hid_data[4:].tofile(tgt_hidden)
+
+            self._display_stats("extracted", emb_size,
+                                np.size(hid_data),
+                                time.time() - self.t0)
+        except Exception as expt:
+            print "Exception when extracting!"
+            raise
+
+    def _raw_embed(self, cov_data, hid_data):
         """
-        cov_data - 4-D numpy.int32 array
+        cov_data - 1-D numpy.int16 array (permunated)
         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
+            if x == 0: continue
 
             m = (hid_data[i] & 1)
             if x > 0 and x & 1 != m:
@@ -72,19 +122,17 @@ class F4(StegBase):
             if x == 0: continue
             i += 1
             if i == hid_data.size: break
-
-        return cov_data
+        return cov_data, i
 
     def _raw_extract(self, steg_data, num_bits):
         """
         Just a small helper function to extract hidden data.
+        steg_data - 1-D numpy.int16 array (permunated)
         """
         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
+        for x in steg_data:
+            if x == 0: continue
             if j >= num_bits: break
             if x > 0:
                 hid_data[j] = x & 1
@@ -93,7 +141,7 @@ class F4(StegBase):
 
             j = j + 1
 
-        return hid_data
+        return hid_data, j
 
     def __str__(self):
         return "F4'"
diff --git a/msteg/steganography/F4.pyc b/msteg/steganography/F4.pyc
index a4586e4..d1fc8c5 100644
Binary files a/msteg/steganography/F4.pyc and b/msteg/steganography/F4.pyc differ
diff --git a/msteg/steganography/LSB.py b/msteg/steganography/LSB.py
index 4bb097b..5be5721 100644
--- a/msteg/steganography/LSB.py
+++ b/msteg/steganography/LSB.py
@@ -1,12 +1,6 @@
-"""
-<p>This plugin implements two variants of a well-known steganographic
-procedure commonly referred to as LSB algorithm.</p>
-The general idea is to
-overwrite some portion (usually the k least significant bits) of each byte
-in the cover image. The below methods specify the number of overwritten
-bits a parameter named word_size. Thus --- in this context --- word means
-\"a group of bits of a fixed size\".
-"""
+__author__ = 'chunk'
+
+
 import time
 import numpy as np
 import scipy as sp
@@ -53,7 +47,7 @@ class LSB(StegBase):
         self.t0 = time.time()
         StegBase._post_extract_actions(self, src_steg, tgt_hidden)
 
-    def _raw_embed(self, cov_data, hid_data, status_begin=0):
+    def _raw_embed(self, cov_data, hid_data):
         """
         cov_data - 4-D numpy.int32 array
         hid_data - 1-D numpy.uint8 array
diff --git a/msteg/steganography/LSB.pyc b/msteg/steganography/LSB.pyc
index 0c06f26..7cdbd23 100644
Binary files a/msteg/steganography/LSB.pyc and b/msteg/steganography/LSB.pyc differ
diff --git a/res/steged.jpg b/res/steged.jpg
index 7a84a41..f3f6c05 100644
Binary files a/res/steged.jpg and b/res/steged.jpg differ
diff --git a/test_jpeg.py b/test_jpeg.py
index 9996435..7a05a7f 100644
--- a/test_jpeg.py
+++ b/test_jpeg.py
@@ -3,6 +3,7 @@ __author__ = 'chunk'
 import numpy as np
 import mjsteg
 import jpegObj
+from jpegObj import base
 from common import *
 
 timer = Timer()
@@ -16,6 +17,7 @@ sample = [[7, 12, 14, -12, 1, 0, -1, 0],
           [0, 0, 0, 0, 0, 0, 0, 0],
           [0, 0, 0, 0, 0, 0, 0, 0]]
 
+sample_key = [46812L, 20559L, 31360L, 16681L, 27536L, 39553L, 5427L, 63029L, 56572L, 36476L, 25695L, 61908L, 63014L, 5908L, 59816L, 56765L]
 
 def diffblock(c1, c2):
     diff = False
@@ -184,16 +186,28 @@ if __name__ == '__main__':
 
     # test_bitbyte()
 
-    ima = jpegObj.Jpeg("res/test3.jpg")
-    imb = jpegObj.Jpeg("res/steged.jpg")
+    ima = jpegObj.Jpeg("res/test3.jpg",key=sample_key)
+    imb = jpegObj.Jpeg("res/new.jpg",key=sample_key)
+    imc = jpegObj.Jpeg("res/steged.jpg",key=sample_key)
     print ima.Jgetcompdim(0)
-    diffblocks(ima, imb)
-
-    c1 = ima.getCoefBlocks()
-    c2 =  imb.getCoefBlocks()
-
-    print c1[0],c2[0]
+    print ima.getkey(),imb.getkey()
+    diffblocks(imb, ima)
 
+    # c1 = ima.getCoefBlocks()
+    # c2 =  imb.getCoefBlocks()
+    #
+    # # print c1[0],c2[0]
+    # s1 = imb.getsignal(channel='Y')
+    # s2 = ima.getsignal(channel='Y')
+    # imb.setsignal(s2,channel='Y')
+    # imb.Jwrite('res/new.jpg')
+
+
+    # print base.acMask(8,16)
+    # mmask = base.acMaskBlock
+    # print mmask
+    # sample = np.array(sample)[mmask]
+    # print np.hstack([[],sample])
     pass
 
 
diff --git a/test_steg.py b/test_steg.py
index d7eb5bb..ab6c50d 100644
--- a/test_steg.py
+++ b/test_steg.py
@@ -22,10 +22,12 @@ sample = [[7, 12, 14, -12, 1, 0, -1, 0],
           [0, 0, 0, 0, 0, 0, 0, 0],
           [0, 0, 0, 0, 0, 0, 0, 0]]
 
+sample_key = [46812L, 20559L, 31360L, 16681L, 27536L, 39553L, 5427L, 63029L, 56572L, 36476L, 25695L, 61908L, 63014L, 5908L, 59816L, 56765L]
+
 txtsample = [116, 104, 105, 115, 32, 105, 115, 32, 116, 111, 32, 98, 101, 32, 101, 109, 98, 101, 100, 101, 100, 46, 10]
 
 if __name__ == '__main__':
-    f3test = F3.F3()
+    f3test = F4.F4()
     f3test.embed_raw_data("res/test3.jpg", "res/embeded", "res/steged.jpg")
     f3test.extract_raw_data("res/steged.jpg", "res/extracted")
 
--
libgit2 0.21.2