Adaptive AC-Coefficient Prediction for Image Compression and Blind Watermarking

Abstract

In this work, an adaptive image compression algorithm is proposed based on the prediction of AC coefficients in Discrete Cosine Transform (DCT) block during reconstruction of image. In the prediction phase, DC values of the nearest neighbour DCT blocks is utilized to predict the AC coefficients of centre block. Surrounding DC values of a DCT blocks are adaptively weighed for AC coefficients prediction. Linear programming is used to calculate the weights with respect to the image content. Results show that this method is good in terms of good Peak Signal to Noise Ratio (PSNR) and less blocking artifacts. The proposed scheme has been demonstrated through several experiments including Lena. Reconstructed image is of good quality with same compression ratio compared to the existing technique in the literature. In addition, an image watermarking algorithm is proposed using DCT AC coefficients obtained. The performance of the proposed watermarking scheme is measured in terms of PSNR and Normalized Cross Correlation (NCC). Further, this algorithm is robust for various attacks including JPEG compression on watermarked image.