Abstract
In this paper, we propose a viewing direction based least significant bit (LSB) data hiding method for 360° videos. The distributions of viewing direction frequency for latitude and longitude are used to control the amount of secret data to be hidden at the latitude, longitude, or both latitude and longitude of 360° videos. Normalized Gaussian mixture models mimicking the viewing behavior of humans are formulated to define data hiding weight functions for latitude, longitude, and both latitude and longitude. On this basis, analytical expressions for the capacity offered by the proposed method to hide secret data in 360° cover videos are derived. Numerical results for the capacity using different numbers of bit planes and popular 360° video resolutions for data hiding are provided. The fidelity of the proposed method is assessed in terms of the peak signal-to-noise ratio (PSNR), weighted-to-spherically uniform PSNR (WS-PSNR), and non-content-based perceptual PSNR (NCP-PSNR). The experimental results illustrate that NCP-PSNR returns the highest fidelity because it gives lower weights to the impact of LSB data hiding on fidelity outside the front regions near the equator. The visual quality of the proposed method as perceived by humans is assessed using the structural similarity (SSIM) index and the non-content-based perceptual SSIM (NCP-SSIM) index. The experimental results show that both SSIM-based metrics are able to account for the spatial perceptual information of different scenes while the PSNR-based fidelity metrics cannot exploit this information. Furthermore, NCP-SSIM reflects much better the impact of the proposed method on visual quality with respect to viewing directions compared to SSIM.
Highlights
Immersive digital media such as virtual reality (VR) and augmented reality (AR) together with head-mounted displays (HMDs) have seen rapid development in recent years.In particular, 360◦ videos offering 360◦ × 180◦ viewing directions with respect to longitude and latitude are reported in [1] to account for the majority of VR content
The number of bit planes used for least significant bit (LSB) data hiding is varied from b = 1 bit to b = 6 bits
It can be observed that the fidelity in terms of all three metrics becomes more severe when b > 3 bits are used for LSB data hiding and is significant for b = 6 bits
Summary
Immersive digital media such as virtual reality (VR) and augmented reality (AR) together with head-mounted displays (HMDs) have seen rapid development in recent years. Hiding secret information in digital audio, images, and videos exploits the fact that the human auditory system and human visual system are rather insensitive to small changes in digital media. To keep computational load associated with data hiding in digital media low, especially for networked services, least significant bit (LSB) data hiding methods may be used. A comprehensive survey on LSB data hiding methods for digital images and videos can be found in [8]. Providing a classification of hiding data in the spatial, transform, and quantum domain of digital images, and the raw and compressed domain of digital videos. As for new digital media such as high-definition images and 360◦ videos, some LSB data hiding methods are reported in [8]. Steganography for new digital media is much less developed compared to conventional digital media because the different types of immersive digital media themselves are subject to further development
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