Compression Performance of Grayscale-based Image Encryption for Encryption-then-Compression Systems

TL;DR

This paper introduces a new grayscale-based image encryption method for Encryption-then-Compression systems with JPEG, proposing a novel quantization table and analyzing its impact on compression efficiency and image quality on social media platforms.

Contribution

The paper proposes a new grayscale-based encryption method with a specialized JPEG quantization table to enhance compression performance in EtC systems.

Findings

Improved compression performance with the new quantization table.

Enhanced image quality after social media upload and download.

Color space selection significantly affects compression efficiency.

Abstract

This paper considers a new grayscale-based image encryption for Encryption-then-Compression (EtC) systems with JPEG compression. Firstly, generation methods of grayscale-based images are discussed in terms of the selection of color space. In addition, a new JPEG quantization table for the grayscale-based images is proposed to provide a better compression performance. Moreover, the quality of both images uploaded to Social Network Services (SNS) and downloaded from SNS, are discussed and evaluated. In the experiments, encrypted images are compressed using various compression parameters and quantization tables, and uploaded to Twitter and Facebook. The results proved that the selection of color space and the proposed quantization table can improve the compression performances of not only uploaded images but also downloaded ones.