2013 Volume E96.A Issue 6 Pages 1323-1330
In this paper, 1) it is shown that amplitude-only images (AOIs) have quite wide intensity ranges (IRs), and 2) an IR reduction method for AOIs is proposed. An AOI is the inversely transformed amplitude spectra of an image, and it is used in the privacy- and copyright-protected image trading system because of its invisibility. Since an AOI is the coherent summation of cosine waves with the same phase, the IR of the AOI is too large to be stored and/or transmitted. In the proposed method, random signs are applied to discrete Fourier transformed amplitude coefficients to obtained AOIs with significantly lower IRs without distortion while keeping the invisibility of images. With reasonable processing time, high correct watermark extracting rates, inversely quantized AOIs with low mean squared errors, and reconstructed images with high peak signal-to-noise ratios are obtained by a linear quantizer in the proposed method.
