An intensity range reduction method for the image trading system with digital fingerprinting in visually protected domain

This paper proposes an intensity range reduction method for amplitude-only images (AOIs) which are inversely transformed amplitude components of images and are used in the digital fingerprinting-based image trading system. The conventional method using two dimensional discrete Fourier transformation (2D DFT) causes intensity range (IR) of AOIs too large to store and/or transmit, and random sign assignment (RSA) is needed in the conventional method to reduce the IR of AOIs. The proposed method uses one dimensional discrete cosine transformation (1D DCT) to generate AOIs with low IRs. In the proposed method, RSA is not needed, and the computational complexity is reduced by using 1D frequency transformation instead of 2D frequency transformation. By using DCT signs instead of DFT phases, a binary image can be used for storing and transmitting DCT signs of a purchased image from a content provider to a consumer; memory and bandwidth consumption is significantly reduced in the proposed method. In addition, a series of inverse DCT, quantization, inverse quantization, and DCT is not needed to handle DCT signs in the proposed method. That is, not only process reduction but also perfect handling of DCT signs which leads to high quality of fingerprinted images is achieved by the proposed method. Experimental results confirm the effectiveness of the proposed method in terms of both quality of fingerprinted images and fingerprinting performance.