26-11-2012, 12:48 PM
An Analysis of LSB & DCT based Steganography
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Abstract-
This paper presents analysis of Least Significant Bit (LSB) based Steganography and Discrete Cosine Transform (DCT) based Steganography. LSB based Steganography embed the text message in least significant bits of digital picture. Least significant bit (LSB) insertion is a common, simple approach to embedding information in a cover file. Unfortunately, it is vulnerable to even a small image manipulation. Converting an image from a format like GIF or BMP, which reconstructs the original message exactly (lossless compression) to a JPEG, which does not (lossy compression), and then back could destroy the information hidden in the LSBs. DCT based Steganography embed the text message in least significant bits of the Discrete Cosine (DC) coefficient of digital picture. When information is hidden inside video, the program hiding the information usually performs the DCT. DCT works by slightly changing each of the images in the video, only to the extent that is not noticeable by the human eye. An implementation of both these methods and their performance analysis has been done in this paper.
INTRODUCTION
Steganography comes from the Greek words Steganós (Covered) and Graptos (Writing). Steganography in these days refers to information or a file that has been concealed inside a digital picture, video or audio file. If a person or persons view the object that the information is hidden inside, he or she will have no idea that there is any hidden information; therefore the person will not attempt to decrypt the information.
Discrete Cosine Transform (Dct)
DCT coefficients are used for JPEG compression. It
separates the image into parts of differing importance. It
transforms a signal or image from the spatial domain to the
frequency domain. It can separate the image into high,
middle and low frequency components.
LITERATURE SURVEY
A lot of Research has been carried out on Steganography
because it is important to know how much data can be
concealed without image distortion. Their description is as
follows:
Ken Cabeen and Peter Gent [1] have discussed the
mathematical equations of Discrete Cosine Transform
(DCT) and its uses in image compression. Andrew B.
Watson [2] has discussed Discrete Cosine Transform (DCT)
technique for converting a signal into elementary frequency
component. He developed simple function to compute DCT
and show how it is used for image compression. Jessica
Fridrich et. al [3] have discussed a reliable and accurate
method for detecting least significant bit (LSB) non
sequential embedding in digital images. The secret message
length is derived by inspecting the lossless capacity in the
LSB and shifted LSB plane. Mohesen Ashourian, R.C. Jain
and Yo-Sung Ho [4] have proposed a data hiding scheme to
embed a signature image in the host image. They selected a
gray scale host image of 512×512 pixels and signature
image of 256×256 pixels. They developed image data hiding
scheme on dithered quantization and a modified baseline
JPEG coding scheme.
PERFORMANCE & RESULTS
Comparative analysis of LSB based and DCT based
steganography has been done on basis of parameters like
PSNR. Both grayscale and colored images have been used
for experiments. Peak signal to noise ratio is used to
compute how well the methods perform.
PSNR computes the peak signal to noise ratio, in decibels,
between two images. This ratio is used as a quality
measurement between two images. If PSNR ratio is high
then images are best of quality.
CONCLUSION
LSB based steganography embed the text message in LSB of cover image. DCT based steganography embed the text message in LSB of DC coefficients. This paper implements LSB based steganography, DCT based steganography and computes PSNR ratio. PSNR is the peak signal to noise ratio, in decibels, between two images. This ratio is used as a quality measurement between two images. If PSNR ratio is high then images are better of quality. Comparison of LSB based and DCT based stego images using PSNR ratio shows that PSNR ratio of DCT based steganography scheme is high as compared to LSB based steganography scheme for all types of images- (Grayscale as well as Color). DCT based steganography scheme works perfectly with minimal distortion of the image quality as compared to LSB based steganography scheme. Even though the amount of secret data that can be hidden using this technique is very small as compared to LSB based steganography scheme still, DCT based steganography scheme is recommended because of the minimum distortion of image quality.