Variable complexity DCT approximations driven by an HVQ-based analyzer

Fast JPEG Encoding for Color Fax Using HVQ

We derive a JPEG compliant image compressor which is based on hierarchical vector quantization (HVQ). The goal is to reduce complexity while increasing compression speed. For each block, the DCT DC coefficient is encoded in the regular way while the residual is mapped through HVQ to a pre-computed bit-stream corresponding to the compressed DCT AC coefficients. Approximation quality is generally...

Reduced DCT approximations for low bit rate coding

Transform approximations are explored for speeding up the software compression of images and video. Faster approximations are used to replace the regular DCT whenever only few DCT coefficients are actually encoded. In one instantiation we employ a data analyzer to drive a bank of coders by switching to the fastest coder depending on the image contents or on the output demand. The compression sp...

DCT Computation based on Variable Complexity Fast Approximations

A Class of DCT Approximations Based on the Feig-Winograd Algorithm

A new class of matrices based on a parametrization of the Feig-Winograd factorization of 8-point DCT is proposed. Such parametrization induces a matrix subspace, which unifies a number of existing methods for DCT approximation. By solving a comprehensive multicriteria optimization problem, we identified several new DCT approximations. Obtained solutions were sought to possess the following prop...

Energy-efficient 8-point DCT Approximations: Theory and Hardware Architectures

Due to its remarkable energy compaction properties, the discrete cosine transform (DCT) is employed in a multitude of compression standards, such as JPEG and H.265/HEVC. Several low-complexity integer approximations for the DCT have been proposed for both 1-D and 2-D signal analysis. The increasing demand for low-complexity, energy efficient methods require algorithms with even lower computatio...