ABSTRACT
One of the most important factors of information technology and communication has been the security of the information. For security purpose the concept of Steganography is being used. Imperceptibility and hiding capacity are very important aspects for efficient secret communication. In this paper a new steganography approach proposed based on LSB technique by using ALPHA channel on JPG cover images. for this method first the secrete image decomposed to bit streams and the data encrypted using an encryption method. On the cover side, an alpha channel is attached to the cover image and the data embedded into LSBs of RGBA channels.
Steganographic methods can be broadly classified based on the embedding domain, digital steganography techniques are classified into (i) spatial domain, (ii) frequency domain. In Spatial domain image steganography, cover image is first decomposed in to its bits planes and then LSB’s (Least Significant Bits) of the bits planes are replaced with the secret data bits. As LSB’s are redundant bits and contributes very less to overall appearance of the pixel, replacing it has no perceptible effect on the cover-image. Advantages are high embedding capacity, ease of implementation and imperceptibility of hidden data. The major drawback is its vulnerability to various simple statistical analysis methods.The most direct way to represent pixel's colour is by giving an ordered triple of numbers: red (R), green (G), and blue (B) that comprises that particular colour. The other way is to use a table known as palette to store the triples, and use a reference into the table for each pixel. For transparent images, extra channel called the Alpha value is stored along with the RGB channels. RGBA image stands for Red, Green, Blue, and Alpha. It extends the RGB colour model with the alpha value representing the transparency of pixels. The A value varies from 0 to 255, in which 0 means completely transparent while 255 means opaque. PNG images follow the RGBA colour model. Bit-plane slicing decomposition highlighting the contribution made to the total image appearance by specific bits. Assuming that each pixel is represented by 8-bits, the image is composed of eight 1-bit planes. Plane (0) contains the least significant bit and plane contains the most significant bit. Only the higher order bits (top four) contain the majority visually significant data. The other bit planes contribute the more subtle details.There are many researches in each of the steganography techniques, and a brief description of some of this research is presented. In this work an alpha channel is attached to a cover image with RGB colour system ( 24 bits depth ), the resulting image is a PNG (Portable Network Graphics ) image with RGBA colour system ( 32 bits depth ), on the other hand, using Bit-plane Slicing decomposition on the secrete image to compress it and transform the gray-level secrete image to a binary bit stream, then the secrete message bit streams will encrypted with a key and embedded in the four colour planes of the cover image.
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Mr. Roshan P. Helonde
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