Henri Bruno Razafindradina

Henri Bruno Razafindradina, Paul Auguste Randriamitantsoa, Nicolas Raft Razafindrakoto

Digital image compression is a technique that allows to reduce the size of an image in order to increase the capacity storage devices and to optimize the use of network bandwidth. The quality of compressed images with the techniques based on the discrete cosine transform or the wavelet transform is generally measured with PSNR or SSIM. Theses metrics are not suitable to images compressed with the singular values decomposition. This paper presents a new metric based on the energy ratio to measure the quality of the images coded with the SVD. A series of tests on 512 * 512 pixels images show that, for a rank k = 40 corresponding to a SSIM = 0,94 or PSNR = 35 dB, 99,9% of the energy are restored. Three areas of image quality assessments were identified. This new metric is also very accurate and could overcome the weaknesses of PSNR and SSIM.

Henri Bruno Razafindradina, Attoumani Mohamed Karim

This paper gives a new scheme of watermarking technique related to insert the mark by adding edge in HH sub-band of the host image after wavelet decomposition. Contrary to most of the watermarking algorithms in wavelet domain, our method is blind and results show that it is robust against the JPEG and GIF compression, histogram and spectrum spreading, noise adding and small rotation. Its robustness against compression is better than others watermarking algorithms reported in the literature. The algorithm is flexible because its capacity or robustness can be improved by modifying some parameters.

Tahina Ezéchiel Rakotondraina, Henri Bruno Razafindradina

This paper presents a new approach to securing information stored in a database. It has three components including: an operation for indexing images using Singular Value Decomposition (SVD), which will constitute the reference images, asymmetric encryption operation using Elliptic Curve Cryptosystem (ECC), aiming to make confidential these reference images stored and a technique for comparing these images to a query image using the Euclidian Distance.

Henri Bruno Razafindradina, Nicolas Raft Razafindrakoto, Paul Auguste Randriamitantsoa

Watermarking is a technique which consists in introducing a brand, the name or the logo of the author, in an image in order to protect it against illegal copy. The capacity of the existing watermark channel is often limited. We propose in this paper a new robust method which consists in adding the triangular matrix of the mark obtained after the Schur decomposition to the DCT transform of the host image. The unitary matrix acts as secret key for the extraction of the mark. Unlike most watermarking algorithms, the host image and the mark have the same size. The results show that our method is robust against attack techniques as : JPEG compression, colors reducing, adding noise, filtering, cropping, low rotations, and histogram spreading.