6th European Conference - Academic Conferences

M
M
M
Su−2 Sv
∑∑
u= 1 v=
1
h(,
i j)
=
Su−1 Sv
Su Sv−2
∑∑
u= 1 v=
1
Kesav Kancherla and Srinivas Mukkamala
δ(
Fh( u, v) = i, Fh( u+ 1, v) = j)
∑∑
u= 1 v=
1
v(,
i j)
=
Su Sv−1
Su−2 Sv−2
∑ ∑
u= 1 v=
1
δ(
Fh( u, v) = i)
δ(
Fv( uv , ) = iF , v(
uv , + 1) = j)
∑∑
u= 1 v=
1
d (, i j)
=
Su−1 Sv−1
M
Su−2 Sv−2
∑∑
u= 1 v=
1
δ(
Fuv v(
, ) = i)
δ ( Fd( uv , ) = iF , d(
u+ 1, v+ 1) = j)
∑∑
u= 1 v=
1
m(,
i j)
=
Su−1 Sv−1
u= 1 v=
1
δ ( Fd( u, v) = i)
δ(
Fm( u+ 1, v) = i, Fm( u, v+ 1) = j)
∑∑
δ(
Fm( u, v) = i)
Where Su and Sv are the dimensions of the image and δ (condition) = 1 if only if the conditions are
satisfied. The final features will be the average of the above 4 transition matrix.
5. Results
We used 2000 images in our experiment. From these 2000 images we used 1400 images for training
SVM and 600 images for testing. Each data point consists of 274 features, of which 193 are DCT
features and 81 are Markov features. We used the following parameters for embedding data using
YASS
Three different quality factor modes 50/50, 50/75 and 75/75
Four different block sizes 9, 10, 12 and 14
Low frequency DCT coefficients used for embedding 12 (low) and 19 (high)
We selected block sizes less than 14 as the block size increases the amount of data that can be
embedded decreases. We choose the number coefficients used for embedding 19 because it is used
in YASS (Solanki, Sarkar and Manjunath, 2007: 16-31) paper and value 12 to show the performance
of our steganalysis scheme at low embedding rates. Table 1 and Table 2 give the accuracies
obtained for different parameters at high data and low data respectively.
Table 1: Accuracy obtained for different block sizes, compression rates and coefficients used equal to
19
Advertised-Design Compression rate/ Block Size 9 10 12 14
50-50 99.8 99.7 99.75 99.7506
50-75 97.1737 97.584 97.5894 96.0881
75-75 97.5973 97.6725 97.0075 96.0881
Table 2: Accuracy obtained for different block sizes, compression rates and coefficients used equal to
12
Advertised-Design Compression rate/ Block Size 9 10 12 14
50-50 99.8337 99.5012 99.335 99.47
50-75 96.5087 96.7581 96.84 95.59
75-75 96.59 96.68 95.6775 94.55
We obtained an accuracy of about 99.5 % for 50-50 setting even when we used only 12 coefficients
for embedding. There is a decrease in accuracy as the block size increases for all compression
setting. This is due to the fact that as size of the block increases the embedding capacity decreases.
We obtained an accuracy of above 95% for all setting even when block size is 14 and embedding
147
(5)
(6)
(7)
(8)