geometric distortions
It is a challenging work to solve the geometric attack in the field of digital watermarking. In order to solve the synchronization between the host image and the watermark, image normalization is introduced. Firstly, the geometrically invariant space of image is constructed by using image normalization, and a region of interest (ROI) is obtained from the normalized image by utilizing the invariant centroid theory. Then, the contourlet transform is performed on the ROI. Low-pass sub-band coefficients are divided into non-overlapping blocks.
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The subjective assessment of the generalized perspective projection (parameterized with projection center d) was conducted using eight omnidirectional images, in equirectangular format, taken from the Salient360! dataset [1]. The Stimulus Comparison Adjectival Categorical Judgment (SCACJ) was selected as an evaluation method. More details about generalized perspective projection, rendered viewport images, and the subjective assessment procedure can be found in [2].
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A crowdsourcing-based subjective evaluation of viewport images, rendered from ten omnidirectional images in equirectangular format (ERI), obtained with Pannini projection was conducted, aiming to assess the perceptual impact of the object shape deformation, introduced due to sphere-to-plane projections. More details on the Pannini projection, rendered viewports, and subjective test procedure can be found in [1].
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