Stteganography: General Block Diagram Of Steganography
CHAPTER 1
INTRODUCTION
INTRODUCTION TO STEGANOGRAPHY
Steganography is the science of writing hidden messages in such a way that no one apart from the sender and intended recipient realizes there is a hidden message. In this technique, a secret message is hidden within an ordinary message and the extraction of it is done at its destination. The term steganography combines the two Ancient Greek words Steganos and graphein, where “steganos” means “covered, concealed, or protected” and “graphein” means “writing or drawing”. Thus, steganography is covered writing. The main purpose of steganography is to hide the fact of communication. The need to ensure that only the right people have authorization to high-security accesses, has led to the …show more content…
However, reformatting the text destroys the embedded content, hence the technique is not robust.
Image Steganography - Image Steganography is a technique of hiding the required message in an image. This technique is prevalent as almost no perceivable change occurs in the image after hiding a large amount of data along with wide variety of available images. Depending on the data hidden in the pixels directly or in the coefficients obtained after a suitable transform domain like FFT, DFT or DWT leads to spatial domain Steganography and frequency domain Steganography. Some of the commonly used methods of embedding payload in cover image are least Significant Bits (LSB) substitution in which the LSBs of cover image pixel are altered to hide the payload and more data can be hidden in …show more content…
Both take a set of points from the spatial domain and transform them into an equivalent representation in the frequency domain. The difference is that while the DFT takes a discrete signal in one spatial dimension and transforms it into a set of points in one frequency dimension and the Discrete Cosine Transform (for an 8x8 block of values) takes a 64-point discrete signal, which can be thought of as a function of two spatial dimensions x and y, and turns them into 64 DCT coefficients which are in terms of the 64 unique orthogonal 2D spectrum as shown in Fig. 1.19.
The DCT coefficient values are the relative amounts of the 64 spatial frequencies present in the original 64-point input. The element in the upper most left corresponding to zero frequency in both directions is the “DC coefficient” and the rest are called “AC coefficients.”
Fig. 1.19: 64 two-dimensional spatial frequencies
Because pixel values typically change vary slowly from point to point across an image, the FDCT processing step lays the foundation for achieving data compression by concentrating most of the signal in the lower spatial frequencies. For a typical 8x8 sample block from a typical source image, most of the spatial frequencies have zero or near-zero amplitude and need not be
INTRODUCTION
INTRODUCTION TO STEGANOGRAPHY
Steganography is the science of writing hidden messages in such a way that no one apart from the sender and intended recipient realizes there is a hidden message. In this technique, a secret message is hidden within an ordinary message and the extraction of it is done at its destination. The term steganography combines the two Ancient Greek words Steganos and graphein, where “steganos” means “covered, concealed, or protected” and “graphein” means “writing or drawing”. Thus, steganography is covered writing. The main purpose of steganography is to hide the fact of communication. The need to ensure that only the right people have authorization to high-security accesses, has led to the …show more content…
However, reformatting the text destroys the embedded content, hence the technique is not robust.
Image Steganography - Image Steganography is a technique of hiding the required message in an image. This technique is prevalent as almost no perceivable change occurs in the image after hiding a large amount of data along with wide variety of available images. Depending on the data hidden in the pixels directly or in the coefficients obtained after a suitable transform domain like FFT, DFT or DWT leads to spatial domain Steganography and frequency domain Steganography. Some of the commonly used methods of embedding payload in cover image are least Significant Bits (LSB) substitution in which the LSBs of cover image pixel are altered to hide the payload and more data can be hidden in …show more content…
Both take a set of points from the spatial domain and transform them into an equivalent representation in the frequency domain. The difference is that while the DFT takes a discrete signal in one spatial dimension and transforms it into a set of points in one frequency dimension and the Discrete Cosine Transform (for an 8x8 block of values) takes a 64-point discrete signal, which can be thought of as a function of two spatial dimensions x and y, and turns them into 64 DCT coefficients which are in terms of the 64 unique orthogonal 2D spectrum as shown in Fig. 1.19.
The DCT coefficient values are the relative amounts of the 64 spatial frequencies present in the original 64-point input. The element in the upper most left corresponding to zero frequency in both directions is the “DC coefficient” and the rest are called “AC coefficients.”
Fig. 1.19: 64 two-dimensional spatial frequencies
Because pixel values typically change vary slowly from point to point across an image, the FDCT processing step lays the foundation for achieving data compression by concentrating most of the signal in the lower spatial frequencies. For a typical 8x8 sample block from a typical source image, most of the spatial frequencies have zero or near-zero amplitude and need not be