Cryptography Reference
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and the value of the complexity threshold value input by the operator. The
default extraction mode is As it is. It extracts the whole folder structure
just as it was when embedding, and it is output in a temporary folder. Link
to Web extraction mode extracts the whole folder structure first, and then
searches for an index.html file directly under the top folder. If it is found, the
program instantly starts running it, and No other folders and files are shown.
Throughout all our experiments using variety of data, all embedded data
(folders and files) were extracted exactly. In As it is mode the extracting
times regarding the two BMP test images (Image-1 and Image-2) are listed in
Table 8.6. Extractions from PNG images took a little more time (less then 0.2
sec). The PC we used for extracting was the same as we used for embedding.
A Link to Web extracting mode took a longer time to go through all the
extracting processes. Fig. 8.22 illustrates a Link to Web extraction from the
stego Image-1 in PNG format.
Table 8.6. Extraction time (BMP stego image).
Image-1 Image-2
2.8 sec (approx) 1.5 sec (approx)
JPEG Embedding and Extracting
The vessel images for JPEG experiment were the same images that we used
for BPCS experiments. Two BMP images (Image-1 and Image-2) were con-
verted to JPEG images in two ways, i.e., high quality and low quality. JPG-
1-high.jpg and JPG-1-low.jpg are high and low quality JPEG images, and
JPG-2-high.jpg and JPG-2-low.jpg are the similar JPEG files converted
from Image-2-bef. There was no obvious degradation in BMP to JPG conver-
sion. The file sizes of these JPEG images are listed in Table 8.7.
Table 8.7. Size of the JPEG vessel image files.
JPG file name JPG-1-high.jpg JPG-1-low.jpg JPG-2-high.jpg JPG-2-low.jpg
File size (KB)
482
99
176
46
As for the data to embed, we prepared four bare text files (see Table
8.8). 1.highJPG.txt is for JPG-1-high.jpg, 1.lowJPG.txt is for JPG-1-low.jpg,
and two other text files are for two other JPG-2 images. These files were the
largest data amount that each JPEG image could embed. So, the compressed
files sizes are the respective embedding capacities. The file compression was
executed by a LHA program incorporated in the embedding program.
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