Effectiveness of Ciphering Approximate Sub-band of Wavelet Transformed Image

Abstract

Image encryption plays a more and more important role in today's multimedia world. Image/video encryption algorithms working in wavelet domain attract some attention due to the prevalence of wavelet compression. In this paper, two partial stream encryption methods, based on transposition or substitution, have been studied to assess their effectiveness in concealing the perceptual content of images. To achieve the above goal, the wavelet domain, specifically the approximation coefficients, has been adopted as plaintext media. The set of conducted tests indicated that the use of substitution is more effective than transposition, and the encryption of Y-component alone is more powerful than encrypting RGB bands. The increase in wavelet passes reduces the image concealment capabilities. The ciphering of two most significant bits of approximate Y-subband reduces the image cipher space to %6.25 while the concealment level remains acceptable.