Sridhar Srinivasan

Windows Media Video 9: overview and applications

Abstract Microsoft ® Windows Media 9 Series is a set of technologies that enables rich digital media experiences across many types of networks and devices. These technologies are widely used in the industry for media delivery over the internet and other media, and are also applied to broadcast, high definition DVDs, and digital projection in theaters. At the core of these technologies is a state-of-the-art video codec called Windows Media Video 9 (WMV-9), which provides highly competitive video quality for reasonable computational complexity. WMV-9 is currently under standardization by the Society of Motion Picture and Television Engineers (SMPTE) and the spec is at the CD (Committee Draft) stage. This paper includes a brief introduction to Windows Media technologies and their applications, with a focus on the compression algorithms used in WMV-9. We present analysis, experimental results, and independent studies that demonstrate quality benefits of WMV-9 over a variety of codecs, including optimized implementations of MPEG-2, MPEG-4, and H.264/AVC. We also discuss the complexity advantages of WMV-9 over H.264/AVC.

HD Photo: a new image coding technology for digital photography

This paper introduces the HD Photo coding technology developed by Microsoft Corporation. The storage format for this technology is now under consideration in the ITU-T/ISO/IEC JPEG committee as a candidate for standardization under the name JPEG XR. The technology was developed to address end-to-end digital imaging application requirements, particularly including the needs of digital photography. HD Photo includes features such as good compression capability, high dynamic range support, high image quality capability, lossless coding support, full-format 4:4:4 color sampling, simple thumbnail extraction, embedded bitstream scalability of resolution and fidelity, and degradation-free compressed domain support of key manipulations such as cropping, flipping and rotation. HD Photo has been designed to optimize image quality and compression efficiency while also enabling low-complexity encoding and decoding implementations. To ensure low complexity for implementations, the design features have been incorporated in a way that not only minimizes the computational requirements of the individual components (including consideration of such aspects as memory footprint, cache effects, and parallelization opportunities) but results in a self-consistent design that maximizes the commonality of functional processing components.

Lifting-based reversible color transformations for image compression

This paper reviews a set of color spaces that allow reversible mapping between red-green-blue and luma-chroma representations in integer arithmetic. The YCoCg transform and its reversible form YCoCg-R can improve coding gain by over 0.5 dB with respect to the popular YCrCb transform, while achieving much lower computational complexity. We also present extensions of the YCoCg transform for four-channel CMYK pixel data. Thanks to their reversibility under integer arithmetic, these transforms are useful for both lossy and lossless compression. Versions of these transforms are used in the HD Photo image coding technology (which is the basis for the upcoming JPEG XR standard) and in recent editions of the H.264/MPEG-4 AVC video coding standard.

Extracting Structure from Optical Flow Using the Fast Error Search Technique

AbstractIn this paper, we present a globally optimal and computationally efficient technique for estimating the focus of expansion (FOE) of an optical flow field, using fast partial search. For each candidate location on a discrete sampling of the image area, we generate a linear system of equations for determining the remaining unknowns, viz. rotation and inverse depth. We compute the least squares error of the system without actually solving the equations, to generate an error surface that describes the goodness of fit across the hypotheses. Using Fourier techniques, we prove that given an N × N flow field, the FOE, and subsequently rotation and structure, can be estimated in

Structure from motion: sparse versus dense correspondence methods

\mathcal{O}(N^2 \log N)

Computationally efficient transforms for video coding

operations. Since the resulting system is linear, bounded perturbations in the data lead to bounded errors.We support the theoretical development and proof of our technique with experiments on synthetic and real data. Through a series of experiments on synthetic data, we prove the correctness, robustness and operating envelope of our algorithm. We demonstrate the utility of our technique by applying it for detecting obstacles from a monocular sequence of images.

Techniques for enhancing JPEG XR / HD Photo rate-distortion performance for particular fidelity metrics

JPEG XR is a draft international standard undergoing standardization within the JPEG committee, based on a Microsoft technology known as HD Photo. One of the key innovations in the draft JPEG XR standard is its integer-reversible hierarchical lapped transform. The transform can provide both bit-exact lossless and lossy compression in the same signal flow path. The transform requires only a small memory footprint while providing the compression benefits of a larger block transform. The hierarchical nature of the transform naturally provides three levels of multi-resolution signal representation. Its small dynamic range expansion, use of only integer arithmetic and its amenability to parallelized implementation lead to reduced computational complexity. This paper provides an overview of the key ideas behind the transform design in JPEG XR, and describes how the transform is constructed from simple building blocks.

Reversible image rotations with modulo transforms

Researchers in image processing and computer vision fields have agonized over the last twenty-five years, to come up with robust methods for the structure from motion (SFM) problem. Two dominant approaches, based on flow and feature correspondences have been pursued. Despite tremendous efforts, only limited success in special cases can be claimed. We feel that with the availability of newer, general, robust methods for computing optical flow, fast methods for estimating the focus of expansion (FOE), inexpensive cameras, and inertial information, robust, real-time solutions to this problem may be possible in the near future. Some of our recent work in these areas is presented.