Multi-bit watermarking of high dynamic range images based on perceptual models

A blind multi-bit watermarking method, specifically designed for high dynamic range (HDR) images, is introduced in this work. The presented embedding strategy takes into account several properties of the human visual system in order to guarantee proper imperceptibility of the embedded watermarks, as well as robustness against tone-mapping operators (TMOs) employed to derive low dynamic range (LDR) representations of the marked HDR content. Specifically, binary marks are embedded into the discrete wavelet transform (DWT) of the just-noticeable difference domain. Additionally, embedding locations are preferably selected in correspondence of the detail parts of an HDR image, determined by exploiting the properties of bilateral filtering. Furthermore, the watermark strength adopted in each DWT subband is modulated depending on a contrast sensitivity function, depending of the subband scale and orientation, to improve the visual quality of the watermarked image. In order to verify the effectiveness of the proposed approach, in terms of both mark imperceptibility and robustness, several experimental tests are carried out on a database comprising 15 HDR images. Specifically, robustness is evaluated by blindly extracting the embedded messages from both HDR marked images and from their LDR counterparts, thus investigating the effects of TMOs on message recovery. Copyright (c) 2015 John Wiley & Sons, Ltd.