Abstract

A stereopair consists of two pictures related to the same subject taken by two different points of view. Since the two images contain a high amount of redundant information, new compression approaches and data formats are continuously proposed, which aim to reduce the space needed to store a stereoscopic image while preserving its quality. A standard for multi-picture image encoding is represented by the MPO format (Multi-Picture Object). The classic stereoscopic image compression approaches compute a disparity map between the two views, which is stored with one of the two views together with a residual image. An alternative approach, named adaptive stereoscopic image compression, encodes just the two views independently with different quality factors. Then, the redundancy between the two views is exploited to enhance the low quality image. In this paper, the problem of stereoscopic image compression is presented, with a focus on the adaptive stereoscopic compression approach, which allows us to obtain a standardized format of the compressed data. The paper presents a benchmark evaluation on large and standardized datasets including 60 stereopairs that differ by resolution and acquisition technique. The method is evaluated by varying the amount of compression, as well as the matching and optimization methods resulting in 16 different settings. The adaptive approach is also compared with other MPO-compliant methods. The paper also presents an Human Visual System (HVS)-based assessment experiment which involved 116 people in order to verify the perceived quality of the decoded images.

Highlights

  • A stereoscopic image, or stereopair, is composed by a pair of images, named left and right views, taken at the same time on the same scene by two cameras from different points of view

  • For each Multi Picture Object (MPO) image and for each value of JPEG compression factor used to compress the low quality image (i.e., 65 or 70) Table 1 reports the dimensions of the blocks used in decoding, and the lossy computed on the reconstructed image obtained after the enhancing procedure

  • The paper presents an evaluation of the adaptive stereo compression method under different settings, taking into account the compressed image quality, two different optimization methods, and two keypoints extraction techniques

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Summary

Introduction

A stereoscopic image, or stereopair, is composed by a pair of images, named left and right views, taken at the same time on the same scene by two cameras from different points of view. Compared with respect to previous methods, the methods in [19,20] are explicitly designed for the MPO format, formalizing a proper coding/decoding pipeline that can be implemented directly on acquisition devices They support the standardization, and work indifferently on stereoscopic images acquired using both a parallel or a convergent stereo camera system. It presents a comparative evaluation with other MPO-compliant methods, as well as an HVS-based experiment aimed to evaluate the perceived quality of the reconstructed images.

Motivations
Evaluated Pipeline
Encoding Pipeline
NCC-Based Decoding Approach
Geometry-Based Decoding Approach
Epipolar Geometry
Image Blocking
Matching Approach
Block Matching
Partial Matching
Image Enhancing
NCC-Based Complexity
Geometry-Based Complexity
Experiments
Comparative Evaluation
Subjective Assessment
Findings
Conclusions and Future Works
Full Text
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