John Y. A. Wang

Representing moving images with layers

We describe a system for representing moving images with sets of overlapping layers. Each layer contains an intensity map that defines the additive values of each pixel, along with an alpha map that serves as a mask indicating the transparency. The layers are ordered in depth and they occlude each other in accord with the rules of compositing. Velocity maps define how the layers are to be warped over time. The layered representation is more flexible than standard image transforms and can capture many important properties of natural image sequences. We describe some methods for decomposing image sequences into layers using motion analysis, and we discuss how the representation may be used for image coding and other applications.

Single lens stereo with a plenoptic camera

Ordinary cameras gather light across the area of their lens aperture, and the light striking a given subregion of the aperture is structured somewhat differently than the light striking an adjacent subregion. By analyzing this optical structure, one can infer the depths of the objects in the scene, i.e. one can achieve single lens stereo. The authors describe a camera for performing this analysis. It incorporates a single main lens along with a lenticular array placed at the sensor plane. The resulting plenoptic camera provides information about how the scene would look when viewed from a continuum of possible viewpoints bounded by the main lens aperture. Deriving depth information is simpler than in a binocular stereo system because the correspondence problem is minimized. The camera extracts information about both horizontal and vertical parallax, which improves the reliability of the depth estimates. >

Layered representation for motion analysis

Standard approaches to motion analysis assume that the optic flow is smooth; such techniques have trouble dealing with occlusion boundaries. The image sequence can be decomposed into a set of overlapping layers, where each layers motion is described by a smooth flow field. The discontinuities in the description are then attributed to object opacities rather than to the flow itself, mirroring the structure of the scene. A set of techniques is devised for segmenting images into coherently moving regions using affine motion analysis and clustering techniques. It is possible to decompose an image into a set of layers along with information about occlusion and depth ordering. The techniques are applied to a flower garden sequence. The scene can be analyzed into four layers, and, the entire 30-frame sequence can be represented with a single image of each layer, along with associated motion parameters.<<ETX>>

Spatio-temporal segmentation of video data

Image segmentation provides a powerful semantic description of video imagery essential in image understanding and efficient manipulation of image data. In particular, segmentation based on image motion defines regions undergoing similar motion allowing an image coding system to more efficiently represent video sequences. This paper describes a general iterative framework for segmentation of video data. The objective of our spatiotemporal segmentation is to produce a layered image representation of the video for image coding applications whereby video data is simply described as a set of moving layers.

A high-frequency fully differential BiCMOS operational amplifier

A high-frequency fully differential BiCMOS operational amplifier design for use in switched-capacitor circuits is presented. The operational amplifier is integrated in a 3.0-GHz, 2- mu m BiCMOS process with an active die area of 1.0 mm*1.2 mm. This BiCMOS op amp offers an infinite input resistance, a DC gain of 100 dB, a unity-gain frequency of 90 MHz with 45 degrees phase margin, and a slew rate of 150 V/ mu s. The differential output range is 12 V. The circuit is operated from a +or-5-V power supply and dissipates 125 mW. The op amp is unity-gain stable with 7 pF of capacitive loading at each output. The op amp is a two-stage, pole-split frequency compensated design that uses a PMOS input stage for infinite input resistance and an n-p-n bipolar second stage for high gain and high bandwidth. The frequency compensation network serves both the differential- and common-mode amplifiers so the differential- and common-mode amplifier dynamics are similar. A dynamic switched-capacitor common-mode feedback scheme is used to set the output common-mode level of the first and second stages. >

Layered representation for image sequence coding

A sequence is decomposed into a set of overlapping 2-D regions, each region occupying a depth-ordered layer with specified transparency, intensity, and motion. The resulting representation is efficient and flexible. While synthesis is straightforward, the analysis problem is challenging. The authors introduce a set of analysis techniques and demonstrate their use on some of the MPEG (Motion Picture Experts Group) sequences. The MPEG flower garden sequence is decomposed into a set of four static layer images. Given these four images and a small number of motion parameters, one can resynthesize the original 30-frame sequence remarkably well.<<ETX>>

A high frequency fully differential BiCMOS operational amplifier

A BiCMOS differential operational amplifier designed for use in switched-capacitor circuits is presented. This BiCMOS op-amp offers an infinite input resistance, a DC gain of 100 dB, a unity-gain frequency of 90 MHz with 45 degrees phase margin, and a slew rate of 150 V/ mu s. The op-amp is unity gain stable with 7 pF of capacitive loading. The circuit is operated from a +or-5-V power supply and dissipates 125 mW. The op-amp is integrated in the 3.0-GHz, 2-RGmm MIT BiCMOS process with an active die area of 1.0 mm*1.2 mm.<<ETX>>

A stereoscopic camera employing a single main lens

A camera for extracting depth information from a scene is described. It incorporates a single main lens along with a lenticular array placed at the sensor plane. The resulting plenoptic camera provides information about how the scene would look when viewed from a continuum of possible viewpoints bounded by the main lens aperture. Deriving depth information is simpler than in a binocular stereo system because the correspondence problem is minimized. The camera extracts information about both horizontal and vertical parallax, which improves the reliability of the depth estimates.<<ETX>>