A Recursive Algorithm to Hide Three Secret Images In One Image Using Wavelet Transform


This paper presents an algorithm based on wavelet transform to hide threesecret colored or gray-scale images with different sizes in one colored coverimage. The algorithm takes level1 wavelet transformation for the cover image andlevel2 wavelet transformation for the coefficients resultant from level1. Thealgorithm begins to divide and transpose the secret images into multiple sub bands,then imbedding them into the coefficient parts resulting from level2. Theembedding depends upon a variable threshold which begins with a very smallvalue. Here the algorithm ensures the embedding of all the pixels values of the subband, if it is not, the operation will be repeated with a larger threshold value untilall the pixels are embedded. Also the pixel's value will not be embedded directly,the difference between the cover and the secret pixel value will be embeddedinstead of it after some manipulation (mathematical operations). All of thesefactors (divide and transpose the secret images, the variable threshold for each subband and changes on the embedded pixels) increase the robustness and quality ofthe algorithm. The resultant stego image and the extracted secret images are veryclose to the original one with high PSNR, high Correlation, low Normal AbsoluteError and low Maximum Difference.