Analysis of the DCT coefficient distributions for document coding

It is known that the distribution of the discrete cosine transform (DCT) coefficients of most natural images follow a Laplacian distribution, and this knowledge has been employed to improve decoder design. However, such is not the case for text documents. In this letter, we present an analysis of their DCT coefficient distributions, and show that a Gaussian distribution can be a realistic model. Furthermore, we can use a generalized Gaussian model to incorporate the Laplacian distribution found for natural images.published_or_final_versio

JPEG compression of monochrome 2D-barcode images using DCT coefficient distributions

Two dimensional (2D) barcodes are becoming a pervasive interface for mobile devices, such as camera phones. Often, only monochrome 2D-barcodes are used due to their robustness in an uncontrolled operating environment of camera phones. Most camera phones capture and store such 2D-barcode images in the baseline JPEG format. As a lossy compression technique, JPEG does introduce a fair amount of error in the decoding of captured 2D-barcode images. In this paper, we introduce an improved JPEG compression scheme for such barcode images. By altering the JPEG compression parameters based on the DCT coefficient distribution of such barcode images, the improved compression scheme produces JPEG images with higher PSNR value as compared to the baseline implementation. We have also applied our improved scheme to a real 2D-barcode system - the QR Code and analyzed its performance against the baseline JPEG scheme

Compound document compression with model-based biased reconstruction

The usefulness of electronic document delivery and archives rests in large part on advances in compression technology. Documents can contain complex layouts with different data types, such as text and images, having different statistical characteristics. To achieve better image quality, it is important to make use of such characteristics in compression. We exploit the transform coefficient distributions for text and images. We show that the scheme in base-line JPEG does not lead to minimum mean-square error if we have models of these coefficients. Instead, we discuss an algorithm designed for this performance that involves first classifying the blocks, and then estimating the parameters to enable a biased reconstruction in the decompression value. Simulation results are shown to validate the advantages of this method. © 2004 SPIE and IS&T.published_or_final_versio

Improving mobile color 2D-barcode JPEG image readability using DCT coefficient distributions

Two dimensional (2D) barcodes are becoming a pervasive interface for mobile devices, such as camera smartphones. Often, only monochrome 2D-barcodes are used due to their robustness in an uncontrolled operating environment of smartphones. Nonetheless, we are seeing an emerging use of color 2D-barcodes for camera smartphones. Most smartphones capture and store such 2D-barcode images in the baseline JPEG format. As a lossy compression technique, JPEG does introduce a fair amount of error in the captured 2D-barcode images. In this paper, we analyzed the Discrete Cosine Transform (DCT) coefficient distributions of generalized 2D-barcodes using colored data cells, each comprising of 4, 8 and 10 colors. Using these DCT distributions, we improved the JPEG compression of such mobile barcode images. By altering the JPEG compression parameters based on the DCT coefficient distribution of the barcode images, our improved compression scheme produces JPEG images with higher PSNR value as compared to the baseline implementation. We have also applied our improved scheme to a 10 colors 2D-barcode system; and analyzed its performance in comparison to the default and alternative JPEG schemes. We have found that our improved scheme does provide a marked improvement for the successful decoding of the 10 colors 2D-barcode system

Cryptanalysis of an MPEG-Video Encryption Scheme Based on Secret Huffman Tables

This paper studies the security of a recently-proposed MPEG-video encryption scheme based on secret Huffman tables. Our cryptanalysis shows that: 1) the key space of the encryption scheme is not sufficiently large against divide-and-conquer (DAC) attack and known-plaintext attack; 2) it is possible to decrypt a cipher-video with a partially-known key, thus dramatically reducing the complexity of the DAC brute-force attack in some cases; 3) its security against the chosen-plaintext attack is very weak. Some experimental results are included to support the cryptanalytic results with a brief discuss on how to improve this MPEG-video encryption scheme.Comment: 8 pages, 4 figure