An improved DC recovery method from AC coefficients of DCTtransformed images

Motivated by the work of Uehara et al. [1], an im-proved method to recover DC coefficients from AC coeffi-cients of DCT-transformed images is investigated in this work, which finds applications in cryptanalysis of selec-tive multimedia encryption. The proposed under/over-flow rate minimization (FRM) method employs an op-timization process to get a statistically more accurate estimation of unknown DC coefficients, thus achieving a better recovery performance. It was shown by exper-imental results based on 200 test images that the pro-posed 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 qual-ity assessment (IQA) metrics such as SSIM and MS-SSIM.