University of Surrey

Test tubes in the lab Research in the ATI Dance Research

Fast recovery of unknown coefficients in DCT-transformed images

Ong, Simying, Li, Shujun, Wong, KokSheik and Tan, KuanYew (2017) Fast recovery of unknown coefficients in DCT-transformed images Signal Processing: Image Communication, 58. pp. 1-13.

Fast Recovery of Unknown Coefficients in DCT Transformed Images.pdf - Accepted version Manuscript

Download (9MB) | Preview


The advancement of cryptography and cryptanalysis has driven numerous innovations over years. Among them is the treatment of cryptanalysis on selectively encrypted content as a recovery problem. Recent research has shown that linear programming is a powerful tool to recover unknown coefficients in DCT-transformed images. While the time complexity is polynomial, it is still too high for large images so faster methods are still desired. In this Letter, we propose a fast hierarchical DCT coefficients recovery method by combining image segmentation and linear programming. In theory the proposed method can reduce the overall time complexity by a linear factor which is the number of image segments used. Our experimental results showed that, for 100 test images of different sizes and using a naive image segmentation method based on Otsu’s thresholding algorithm, the proposed method is faster for more than 92% cases and the maximum improvement observed is more than 19 times faster. While being mostly faster, results also showed that the proposed method can roughly maintain the visual quality of recovered images in both objective and subjective terms.

Item Type: Article
Divisions : Faculty of Engineering and Physical Sciences > Computing Science
Authors :
Ong, Simying
Wong, KokSheik
Tan, KuanYew
Date : 30 June 2017
DOI : 10.1016/j.image.2017.06.002
Copyright Disclaimer : © 2017 Elsevier Ltd. All rights reserved.
Uncontrolled Keywords : DCT transform; Image recovery; Selective encryption; Visual quality; Image segmentation; Hierarchical
Depositing User : Clive Harris
Date Deposited : 11 Jul 2017 13:14
Last Modified : 06 Jun 2019 02:08

Actions (login required)

View Item View Item


Downloads per month over past year

Information about this web site

© The University of Surrey, Guildford, Surrey, GU2 7XH, United Kingdom.
+44 (0)1483 300800