An Improved DC Recovery Method from AC Coefficients of DCT-Transformed Images

TL;DR

This paper introduces an improved method for recovering DC coefficients from AC coefficients in DCT-transformed images, enhancing image quality in cryptanalysis applications through an optimization-based approach.

Contribution

It proposes a novel under/over-flow rate minimization (FRM) method that statistically improves DC coefficient estimation over previous techniques.

Findings

Significant PSNR improvements in recovered images.

Enhanced SSIM and MS-SSIM scores over existing methods.

Validated on 200 test images with consistent performance gains.

Abstract

Motivated by the work of Uehara et al. [1], an improved method to recover DC coefficients from AC coefficients of DCT-transformed images is investigated in this work, which finds applications in cryptanalysis of selective multimedia encryption. The proposed under/over-flow rate minimization (FRM) method employs an optimization process to get a statistically more accurate estimation of unknown DC coefficients, thus achieving a better recovery performance. It was shown by experimental results based on 200 test images that the proposed DC recovery method significantly improves the quality of most recovered images in terms of the PSNR values and several state-of-the-art objective image quality assessment (IQA) metrics such as SSIM and MS-SSIM.