Abstract

In contrast with traditional images, omnidirectional image (OI) has a higher resolution and provides the user with an interactive wide field of view. OI with equirectangular projection (ERP) format, as the default for encoding and transmitting omnidirectional visual contents, is not suitable for quality assessment of OI because of serious geometric distortion in the bipolar regions, especially for blind image quality assessment. In this paper, a segmented spherical projection (SSP) based blind omnidirectional image quality assessment (SSP-BOIQA) method is proposed. The OI with ERP format is first converted into that with SSP format, so as to solve the problem of stretching distortion in the bipolar regions of ERP format, but retain the equatorial region of ERP format. On the one hand, considering that the bipolar regions of the SSP format are circular, a local/global perceptual features extraction scheme with fan-shaped window is proposed for estimating the distortion in the bipolar regions of OI. On the other hand, the perceptual features of the equatorial region are extracted with heat map as weighting factor to reflect users' visual behavior. Then, the features extracted from the OI's bipolar and equatorial regions are pooled to predict the quality of distorted OIs. The experiments on two databases, namely CVIQD2018 and MVAQD databases, demonstrate that the proposed SSP-BOIQA method outperforms the state-of-the-art blind quality assessment methods, and is more consistent with human visual perception.

Highlights

  • With the rapid development of virtual reality (VR) technologies, omnidirectional visual contents play an important role in VR systems and are used in multimedia, industry, medical care and business fields [1]

  • (1) Considering that omnidirectional image (OI) are with spherical form, and there are serious stretching distortion in the bipolar regions of the equirectangular projection (ERP)-image which decreases the accuracy of quality assessment of OI, especially for blind quality assessment, even though ERP format is the default for OI’s encoding and transmission, the assessment is implemented on OI with segmented spherical projection (SSP) format instead of ERP format because SSP format is more in line with the real feeling of the user through head mounted display (HMD)

  • In this paper, a segmented spherical projection based blind omnidirectional image quality assessment (SSP-BOIQA) method is proposed for virtual reality systems

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Summary

INTRODUCTION

With the rapid development of virtual reality (VR) technologies, omnidirectional visual contents play an important role in VR systems and are used in multimedia, industry, medical care and business fields [1]. A new segmented spherical projection based blind omnidirectional image quality assessment (SSP-BOIQA) method is proposed in this paper. (1) Considering that OIs are with spherical form, and there are serious stretching distortion in the bipolar regions of the ERP-image which decreases the accuracy of quality assessment of OI, especially for blind quality assessment, even though ERP format is the default for OI’s encoding and transmission, the assessment is implemented on OI with SSP format instead of ERP format because SSP format is more in line with the real feeling of the user through HMD.

RELATE WORKS
THE EQUATORIAL REGION FEATURES OF SSP-IMAGE
QUALITY PREDICTION OF OI
CONCLUSION
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