- Covell, Baluja, "LSH Banding
for Large-Scale Retrieval with Memory and Recall
Constraints," Proc. IEEE International Conference on
Acoustics, Speech, and Signal Processing, Taipei, April
2009.
Locality Sensitive Hashing (LSH) is widely used for
efficient retrieval of candidate matches in very large
audio, video, and image systems. However, extremely large
reference databases necessitate a guaranteed limit on the
memory used by the table lookup itself, no matter how the
entries crowd different parts of the signature space, a
guarantee that LSH does not give. In this paper, we provide
such guaranteed limits, primarily through the design of the
LSH bands. When combined with data-adaptive bin splitting
(needed on only 0.04% of the occupied bins), this approach
provides the required guarantee on memory usage. At the
same time, it avoids the reduced recall that more extensive
use of bin splitting would give.
- Baluja,
Covell, Ioffe, "Permutation Grouping: Intelligent Hash
Function Design for Audio and Image Retrieval," Proc. IEEE
International Conference on Acoustics, Speech, and Signal
Processing, Las Vegas, April 2008.
Locality-sensitive hashing (LSH) is used in many
applications that require retrieval and evaluation of
approximate nearest neighbors. The uniformity of the
signature distributions has a strong effect on the number of
candidates that must be considered. The effects of this
uneven distribution are squared, since retrieval probes are
taken from the same uneven distribution that resulted in
uneven occupancy in the table itself. In this study, we
introduce the idea of dimension grouping to intelligently
design the hash functions that are used to index the LSH
tables. This reduces the inefficiencies introduced by
hashing real-world data that is noisy, structured, and most
importantly is not independently or identically
distributed. Through large-scale tests, we find that
permutation-grouping dramatically increases the efficiency
of the overall retrieval system by lowering the number of
low-probability candidates that must be examined by 30-50%.
- Baluja, Covell,
"Learning to Hash: Forgiving Hash Functions and Applications,"
Data Mining and Knowledge Discovery, (Springer Netherlands) 2008.
- Baluja, Covell,
"Learning 'Forgiving' Hash Functions: Algorithms and
Large-Scale Tests," International Joint Conference on
AI, Hyderabad, January 2007.
We want to be able to efficiently find similar items
in large, high-dimensional datasets, for things like music,
image, and video retrieval. Scaling lookups for any large
corpus tends to lead to tree or hash-based
approaches. Correctly structuring such trees or hash
functions is made more difficult than in other large-corpus
domains by an imprecise definition of similarity. In this
work, we found a method to learn a similarity function from
only weakly labeled positive examples. We used this
similarity function as the basis of a hash function to
severely constrain the number of points considered for each
lookup. In testing on a large real-world audio dataset, only
a tiny fraction of the points (~0.27%) were ever considered
for each lookup. To increase efficiency, we did no
comparisons in the original high-dimensional space of points,
yet still achieve nearly 99% accuracy on 5-second-long probes.
- Covell, Baluja,
"Known-Audio Detection using Waveprint: Spectrogram Fingerprinting
by Wavelet Hashing," Proc. IEEE International Conference
on Acoustics, Speech, and Signal Processing, Hawaii, April 2007.
This paper extends the previous work on Waveprint
(see below) to handle open-set detection and identification. To do
this, we re-examine the best-ranked matches from Waveprint using
temporal-ordering-based processing. The resulting system has
excellent detection capabilities for small snippets of audio that
have been degraded in various ways, including competing noise, poor
recording quality, and cell-phone playback. The system is more
accurate than the previous state-of-the-art system while being more
efficient and flexible in memory usage and computation.
- Baluja, Covell,
"Waveprint: Efficient Wavelet-Based Audio Fingerprinting," Pattern Recognition 41(11): 3467-3480, November 2008.
- Baluja, Covell,
"Content Fingerprinting Using Wavelets," Proc. IET Conference
on Multimedia, London England, November 2006.
(invited paper)
- Baluja, Covell,
"Audio Fingerprinting: Combining Computer Vision and
Data-Stream Processing," Proc. IEEE International Conference
on Acoustics, Speech, and Signal Processing, Hawaii, April 2007.
In this paper, we introduce Waveprint, a novel
method for audio identification. Waveprint uses a
combination of computer-vision techniques and
large-scale-data-stream processing algorithms to create
compact fingerprints of audio data that can be efficiently
matched. The resulting system has excellent identification
capabilities for small snippets of audio that have been
degraded in a variety of manners, including competing noise,
poor recording quality, and cell-phone playback. We
explicitly measure the tradeoffs between performance, memory
usage, and computation through extensive experimentation.
- Covell, Baluja, Fink,
"Advertisement Detection and Replacement using Acoustic and
Visual Repetition," IEEE Workshop on Multimedia Signal
Processing, Victoria BC, October 2006.
- Covell, Baluja, Fink,
"Detecting Ads in Video Streams Using Acoustic and Visual Cues,"
IEEE Computer Magazine, December 2006.
We propose a method for detecting and
precisely segmenting repeated sections of broadcast
streams. The detection stage starts from acoustic matches
and validates the hypothesized matches using the visual
channel. The precise segmentation uses fine-grain acoustic
match profiles to determine start and end-points. The approach
is both efficient and robust to broadcast noise and
differences in broadcaster signals. Our final results is
nearly perfect, with better than 99% precision, at a recall
rate of 95% for repeated advertisements.
- Fink, Covell, Baluja, "Social- and Interactive-Television Applications Based on Real-Time Ambient-Audio Identification," EuroITV Athens Greece, May 2006. (best-paper award)
- Fink, Covell, Baluja, "Mass Personalization: Social and Interactive Applications using Sound-Track Identification," Multimedia Tools and Applications 2008. (invited paper)
We describe mass personalization, a framework for
combining mass media with a highly personalized Web-based experience.
We introduce four applications for mass personalization: personalized
content layers, ad hoc social communities, real-time popularity
ratings and virtual media library services. Using the ambient audio
originating from the television, the four applications are available
with no more effort than simple television channel surfing. Our audio
identification system does not use dedicated interactive TV hardware
and does not compromise the user's privacy. Feasibility tests of the
proposed applications are provided both with controlled conversational
interference and with "living-room" evaluations.
- Covell, Roy, Shen, Huve,
"Time-Scale Modification for 3G-Telephony Video," IEEE
Workshop on Multimedia Signal Processing Victoria BC,
October 2006. (with demo video)
Streaming video to mobile devices like cellular phones
is an important emerging application. However, mobile thin clients
and telephony-infrastructure constraints limit the capabilities
and interfaces available to the end user. This paper describes our
design of an end-to-end interactive video telephony service. The
challenges of providing interactive services is to remain compliant
with the telco signaling and data protocols, without requiring
software downloads onto the handset, while providing responsive,
interactive controls. Our service provides VCR-like control of
telephony video, maintains audio-video synchronization, and respects
the video frame and bit-rate contracts of the telephony channel.
This research was completed at HP Labs.
- Covell, Roy, Seo, "Predictive Modeling of Streaming Servers," SIGMETRICS Workshop
on Mathematical Performance Modeling and Analysis, Banff Canada, June 2005.
This paper describes a mathematical approach to deriving predictive
models of streaming-server saturation (saturating/non-saturating)
through hidden-variable estimation. We use a 240-dimensional
measurement vector to estimate
a low-dimensional vector of continuous valued hidden variables, with
each hidden-variable dimension corresponding to a
"discovered" resource on which the streaming server depends. The
discovery process uses labelled calibration
data, along with a POCS-like alternation of constraints, to create the
best (in a total-least squares sense) predictors
for server saturation, both under the current (unknown) set of client
sessions and under some (proposed)
increase in the client sessions. These models allow us to make
admission-control decisions as well as to indicate which types of
additional clients the streaming server can currently
handle. (A description of the
data-collection regime is available here.. A longer version of these two papers is
available here.)
This research was completed at HP Labs.
- Karlsson, Covell, "Dynamic Black-Box Performance-Model Estimation for Self-Tuning Regulators," International Conference on Autonomic Computing, Seattle WA, June 2005.
Methods for automatically managing the performance of
computing services must estimate a performance model of that service. This paper explores properties that are necessary
for performance model estimation of black-box computer systems when used together with adaptive feedback
loops. It shows that the standard method of least-squares estimation often gives rise to models that make the control
loop perform the opposite action of what is desired. This produces large oscillations and bad tracking performance.
The paper evaluates what combination of input and output data provides models with the best properties for the control
loop. Plus, it proposes three extensions to the controller that makes it perform well, even when the model estimated
would have degraded performance.
Our proposed techniques are evaluated with an adaptive
controller that provides latency targets for workloads on black-box computer services under a variety of conditions.
The techniques are evaluated on two systems: a three-tier ecommerce site and a web server. Experimental results show
that our best estimation approach improves the ability of the controller to meet the latency goals significantly.
Previously oscillating workload latencies are with our techniques smooth around the latency targets.
This research was completed at HP Labs.
- Harville, Covell, Wee, "An Architecture for Componentized, Network-Based Media Services," Proc. IEEE International Conference on Multimedia and Expo, Baltimore, MD, July 2003.
This
paper presents Media Services Architecture (MSA). MSA is a flexible,
general architecture for requesting, configuring, and running services
that operate on streaming audio and video as it flows through the
network. MSA decomposes requested media services into modular
processing components that may be distributed to servers throughout the
network and which intercommunicate via standard streaming protocols.
Use of standard protocols also affords seamless inter-operability
between MSA and media content delivery networks. MSA manages media
services by monitoring the networked servers and assigning service
components to them in a manner that uses available computational and
network resources efficiently. We describe some implemented example
services to illustrate the concepts and benefits of the architecture.
This research was completed at HP Labs.
- Roy, Covell, et al. "A System Architecture for Managing Mobile Streaming Media Services," Proc. IEEE Mobile Distributed Computing Workshop, Providence, RI, May 2003.
Current
mobile devices and wireless access allows delivery of video streams to
a wide range of cellular devices. The wide range and variability of the
network, processor, and display conditions on these devices will
effectively require streaming video to be dynamically tailored to each
client's changing constraints. Real-time compressed-domain video
transcoding allows each live streaming session to be tailored to these
changing environment in a practical and affordable manner. However,
even with new advances in the video-transcoding efficiency, the
computational, bandwidth, and scheduling requirements of live video
processing results in the need for managed placement of these tasks,
for best used of the distributed resources available with the network.
In this paper, we discuss our approach to service-location management (SLM).
We compare the performance alternative implementations of SLM resource
monitoring. Finally, we present our conclusions on which of these
alternate implementations is both most reliable and most extensible to
the service of large numbers of mobile client requests.
This research was completed at HP Labs.
- Covell, Ahmad, "Analysis-by-Synthesis Dissolve Detection," Proc. IEEE International Conference on Image Processing, Rochester, NY, Sept 23-25 2002.
This paper presents a novel, real-time,
minimal-latency technique for dissolve detection which
handles the widely varying camera techniques, expertise,
and overall video quality seen in amateur,
semi-professional, and professional video footage. We
achieve 88% recall and 93% precision for dissolve
detection. In contrast, on the same data set, at a similar
recall rate (87%), DCD has more than 3 times the number of
false positives, giving a precision of only 81% for
dissolve detection. This research was completed at
YesVideo, Inc.
- Covell, Slaney, Rothstein, "FastMPEG: Time-scale modification of Bit-Compressed Audio Information," Proc. IEEE International Conference on Acoustics, Speech, and Signal Processing, 2001.
This
paper describes techniques to change the playback speed of
MPEG-compressed audio, without first decompressing the audio file.
There are two primary contributions in this paper. 1) We describe three
techniques to perform time-scale modification in the maximally
decimated domain. 2) We show how to infer the output of the auditory
masking model on the new audio stream, using the information in the
original file. This new FastMPEG algorithm is more than an order of
magnitude more efficient then decompressing the audio, performing
time-scale modification in the conventional time-domain, and then
recompressing. Samples of our results can be found here .
This research was completed at Interval Research Corporation.
- Darrell, Covell, "Correspondence with Cumulative Similarity Transforms," IEEE Trans. on Pattern Analysis and Machine Interactions 23(2):222-227, Feb 2001.
This
paper defines a local image transform based on cumulative similarity
measures and shows it to enable efficient correspondence and tracking
near occluding boundaries. Unlike traditional methods, this transform
allows correspondences to be found when the only contrast present is
the occluding boundary itself and when the sign of contrast along the
boundary is possibly reversed. The transform is based on the idea of a
cumulative similarity measure which characterizes the shape of local
image homogeneity; both the value of an image at a particular point and
the shape of the region with locally similar and connected values is
captured. This representation is insensitive to structure beyond an
occluding boundary but is sensitive to the shape of the boundary
itself, which is often an important cue. We show results comparing this
method to traditional least-squares and robust correspondence matching.
This research was completed at Interval Research Corporation.
- Slaney, Covell, "Face Synch: a Linear Operator for Measuring Synchronization of Video Facial Images and Audio Tracks," Proc. Neural Information Processing Society 13 , MIT Press, 2001. (presented at NIPS 2000)
This
paper develops an optimal linear algorithm that finds the degree of
synchronization between the audio and image recordings of a human
speaker. Using canonical correlation, it finds the best direction to
combine all the audio and image data, projecting them onto a single
axis. FaceSync uses Pearson's correlation to measure the degree of
synchronization between the audio and image data. We derive the optimal
linear transform to combine the audio and visual information and
describe an implementation that avoids the numerical problems caused by
computing the correlation matrices.
This research was completed at Interval Research Corporation.
- Covell, Rahimi, Harville, Darrell, "Articulated-Pose Estimation using Brightness- and Depth-Constancy Constraints," Proc. IEEE Computer Vision and Pattern Recognition, Hilton Head Island SC, June 2000.
This
paper explores several approaches for articulated-pose estimation,
assuming that video-rate depth information is available, from either
stereo cameras or other sensors. We use these depth measurements in the
traditional linear brightness constraint equation, as well as in a
depth constraint equation. To capture the joint constraints, we combine
the brightness and depth constraints with twist mathematics. We address
several important issues in the formation of the constraint equations,
including updating the body rotation matrix without using a first-order
matrix approximation and removing the coupling between the rotation and
translation updates. The resulting constraint equations are linear on a
modified parameter set. After solving these linear constraints, there
is a single closed-form non-linear transformation to return the updates
to the original pose parameters. We show results for tracking body pose
in oblique views of synthetic walking sequences and in moving-camera
views of synthetic jumping-jack sequences. We also show results for
tracking body pose in side views of a real walking sequence.
This research was completed at Interval Research Corporation.
- Covell, Darrell, "Dynamic Occluding Contours: A New External-Energy Term for Snakes," Proc. IEEE Computer Vision and Pattern Recognition, Fort Collins CO, June 1999, vol 2, p 232-238.
Dynamic
countours, or snakes, provide an effective method for tracking complex
moving objects for segmentation and recognition tasks, but have
difficulty tracking occluding boundaries on cluttered backgrounds. To
compensate for this shortcoming, dynamic contours often rely on
detailed object-shape or -motion models to distinguish between the
boundary of the tracked object and other boundaries in the background.
In this paper, we present a complementary approach to detailed object
models: We improve the discriminative power of the local image
measurements that drive the tracking process. We describe a new robust
external-energy term for dynamic contours that can track occluding
boundaries without detailed object models. We show how our image model
improves tracking in cluttered scenes, and describe how a fine-grained
image-segmentation mask is created directly from the local image
measurements used for tracking.
This research was completed at Interval Research Corporation.
- Covell, Slaney, Bregler, Withgott, "Modification of Audible and Visual Speech," Signal Processing for Multimedia. 1998 (invited)
Speech
is one of the most common and richest methods that people use to
communicate with one another. Our facility with this communication form
makes speech a good interface for communicating with or via computers.
At the same time, our familarity with speech makes it difficult to
generate synthetic but natural-sounding speech and synthetic but
natural-looking lip-synced faces. One way to reduce the apparent
unnaturalness of synthetic audible and visual speech is to modify
natural (human-produced) speech. This approach relies on examples of
natural speech and on simple models of how to take those examples apart
and to put them back together to create new utterances.
We discuss two such techniques in depth. The first technique, Mach1,
changes the overall timing of an utterance, with little loss in
comprehensibility and with no change in the wording of or emphasis
within what was said or in the identity of the voice. This ability to
speed up (or slow down) speech will make speech a more malleable
channel of communication. It gives the listener control over the amount
of time that she spends listening to a given oration, even if the
presentation of that material is prerecorded. The second technique, Video Rewrite,
synthesizes images of faces, lip synced to a given utterance. This tool
could be useful for reducing the data rate for video conferencing
[Rao98], as well as for providing photorealistic avatars.
This research was completed at Interval Research Corporation.
- Covell, Withgott, Slaney, "Mach1 for Nonuniform Time-Scale Modification of Speech: Theory, Technique, and Comparisons," IRC TR 1997-061, Interval Research Corporation, 1997.
- Covell, Withgott, Slaney, "Mach1: Nonuniform Time-Scale Modification of Speech," Proc. IEEE International Conference on Acoustics, Speech, and Signal Processing, Seattle WA, May 12-15 1998, vol 1 p 349-352.
This
paper describes Mach1 , a new approach to nonuniform time compression
for speech. Mach1 was designed to mimic the natural timing of fast
speech. At identical overall compression rates, listener comprehension
for Mach1-compressed speech increased between 5 and 31 percentage
points over that for linearly compressed speech, and response times
dropped by 15%. For rates between 2.5 and 4.2 times real time, there
was no significant comprehension loss with increasing Mach1 compression
rates. In A-B preference tests, Mach1-compressed speech was chosen 95%
of the time. This paper describes the Mach1 technique and our
listener-test results. Audio examples are provided on the web page
referenced above.
This research was completed at Interval Research Corporation.
- Bregler, Covell, Slaney, "Video Rewrite: Driving Visual Speech with Audio," ACM Computer Graphics Proc. SIGGRAPH 97, Los Angeles, CA, Aug 3-8 1997, p 353-360.
- Bregler, Covell, Slaney, "Video Rewrite: Visual Speech Synthesis from Video," Proc. ESCA Workshop on Audio-Visual Speech Processing, Rhodes, Greece, Sept 26-27 1997, p 153-156.
- Bregler, Covell, Slaney, "Video Rewrite: Photorealistic Synthetic Lip Sync," Proc. INA Imagina, Monte Carlo, Monaco, March 4-6 1998, p 193-203. (invited)
Video
Rewrite uses existing footage to create automatically new video of a
person mouthing words that she did not speak in the original footage.
This technique is useful in movie dubbing, for example, where the movie
sequence can be modified to sync the actors' lip motions to the new
soundtrack.
Video Rewrite uses
computer-vision techniques to track points on the speaker's mouth in
the training footage, and morphing techniques to combine these mouth
gestures into the final video sequence. The new video combines the
dynamics of the original actor's articulations with the mannerisms and
setting dictated by the background footage. Video Rewrite is the first
facial-animation system to automate all the labeling and assembly tasks
required to resync existing footage to a new soundtrack.
This research was completed at Interval Research Corporation.
- Covell, "Eigen-points: control-point location using principal component analyses," Proc. IEEE International Conference on Automatic Face and Gesture Recognition, Killington VT, Oct 14-16 1996, p 122-127.
- Covell, Bregler, "Eigen-points," Proc. IEEE International Conference on Image Processing, Lausanne, Switzerland, Sept 16-19 1996, vol 3 p 471-474.
Eigen-points
estimates the image-plane locations of fiduciary points on an objects.
By estimating multiple locations simultaneously, eigen-points exploits
the inter-dependence between these locations. This is done by
associating neighboring, inter-dependent control-points with a model of
the local appearance. The model of local appearance is used to find the
feature in new unlabeled images. Control-point locations are then
estimated from the appearance of this feature in the unlabeled image.
The estimation is done using an affine manifold model of the coupling
between the local appearance and the local shape.
Eigen-points uses models aimed
specifically at recovering shape from image appearance. The estimation
equations are solved non-iteratively, in a way that accounts for noise
in the training data and the unlabeled images and that accounts for
uncertainty in the distribution and dependencies within these noise
sources.
This research was completed at Interval Research Corporation.
- Slaney, Covell, Lassiter, "Automatic Audio Morphing," Proc. IEEE International Conference on Acoustics, Speech, and Signal Processing, Atlanta GA, May 7-10 1996, vol 2 p 1001-1004.
This
paper describes techniques to automatically morph from one sound to
another. Audio morphing is accomplished by representing the sound in a
multi-dimensional space that is warped or modified to produce a desired
result. The multi-dimensional space encodes the spectral shape and
pitch on orthogonal axes. After matching components of the sound, a
morph smoothly interpolates the amplitudes to describe a new sound in
the same perceptual space. Finally, the representation is inverted to
produce a sound. This paper describes representations for morphing,
techniques for matching, and algorithms for interpolating and morphing
each sound component. Spectrographic images of a complete morph are
shown at the end of the paper.
This research was completed at Interval Research Corporation.
- Covell, "Autocorrespondence: Feature-based Match Estimation for Image Metamorphosis," Proc. IEEE Workshop on Image and Multi-dimensional Signal Processing, Belize City, Belize, March 3-6 1996, p 120-121.
- Covell, "Autocorrespondence: Feature-based Match Estimation and Image Metamorphosis," Proc. IEEE International Conference on Systems, Man and Cybernetics, Vancouver BC, Oct 22-25 1995, vol 3 p 2736-2741.
These
papers address the problem of matching distinct but related objects
across images, for applications such as view-based model capture,
virtual presence, and morphing special effects. A new approach to match
estimation is presented for estimating correspondances between distinct
objects. This approach minimizes the effects of lighting variations and
non-rigid deformations. A sparse set of features are used for
alignment, followed by image-plane warping, or morphing, based on these
constraints.
This research was completed at Interval Research Corporation.
- Covell, Withgott, "Spanning the Gap between Motion Estimation and Morphing," Proc. IEEE International Conference on Acoustics, Speech, and Signal Processing, Adelaide, Australia, April 19-22 1994, vol 5 p 213-216.
Motion
estimation is an important and well-studied method for determining
correspondences between images in video processing. In contrast with
motion estimation, the use of image warping on image sequences is a new
and developing field. To provide image warping effects, morphing
algorithms rely on mesh points to align two images. The selection of
these mesh points is a labor-intensive, manual process. This paper
presents one approach to automating the selection of mesh points for
morphing by recognizing this problem as one of determining image
correspondences. Applications include video compression, animation
sequence generation and high-quality time dilation of video.
This research was completed at Interval Research Corporation.
- Covell, Myers, Oppenheim, Computer-Aided Algorithm Design and Rearrangement, Chapter 2 (p 30-87) in Symbolic and Knowledge-Based Signal Processing, Oppenheim & Nawab (eds.), Prentice-Hall, 1992.
- Covell, "An Algorithm Design Environment for Signal Processing," Proc. IEEE International Conference on Acoustics, Speech, and Signal Processing, Albuquerque NM, April 3-6 1990, vol 3 p 1779-1782.
- Covell, "An Algorithm Design Environment for Signal Processing, " MIT RLE TR 549, MIT, 1989.
Traditional
signal processing by computer has relied on numerical methods. This
chapter explores how symbolic representation and manipulation methods
may be incorporated in the numerical processing of signals and how
these methods may be used in the design and analysis of signal
processing systems. Using symbolic manipulation, a high-level compiler
was developed to exploit the underlying mathematics of the DSP systems.
This compiler uncovered a new, unconventional approach to implementing
a modulated filter bank. The details of this newly discovered algorithm
were published independently (see the next paper). This chapter also
describes one approach to recording and propagating computational cost
within a DSP system.
This research was completed at MIT, with
funding from the National Science Foundation Fellowship Program, from
the Advanced Research Projects Agency, and from Sanders Associates, Inc.
- Covell, Richardson, "A New, Efficient Structure for the Short-Time Fourier Transform, with an Application in Code-Division Sonar Imaging, " Proc. IEEE International Conference on Acoustics, Speech, and Signal Processing, Toronto, Canada, May 14-17 1991, vol 3 p 2041-2044.
An
implementation of a modulated filter bank is presented which, under
some operating conditions, reduces the computational complexity from O(N log N) to O(N). The
new structure is efficient when the application requires dense temporal
(or spatial) sampling of the STFT output. One example of such an
application is code-division, multiple-beam sonar. The computational
complexity of this new approach is slightly lower than of the extended
Goertzel algorithm. Unlike the extended Goertzel algorithm, which is
only marginally stable, the new structure is unconditionally stable.
This research was completed at MIT, with funding from the National
Science Foundation Fellowship Program, from the Advanced Research
Projects Agency, and from Sanders Associates, Inc.
- Covell, Lim. "Low data-rate video conferencing," Proc. SPIE - The International Society for Optical Engineering, Cambridge MA, Sept 15-16 1986, vol 707 p 75-90.
A
system is presented which enforces very low data rates, insures a low
maximum system delay, and allows for inexpensive decoders. To achieve
this, the gray-scale video conferencing sequences were converted to
binary (black/white) images. Spatial and temporal differencing and
statistical coding were then used for compression as were
"focus-of-attention" methods of partial update. In this manner, faces
and scenes were successfully encoded and decoded using simple
processors at data rates below 19.2 kbaud (hard maximum) with no more
than two frames of delay.
This research was completed at MIT, with funding from the National Science Foundation Fellowship Program.
- Covell, et al. "Automated analysis of multiple performance characteristics in magnetic resonance imaging systems," Medical Physics, 13(6): 815-823, Nov-Dec 1986.
An
imaging and analysis regime is presented for automatically estimating
MRI quality measures, such as slice thickness, separation, orientation,
and focus. Results of the automated analysis for MRI system examples
are in good agreement with expectations from theory and with more
manual tests.
This research was completed at U. Michigan Department of Radiological Physics and Engineering.
- Covell, "Likelihood Ratio Approximation for Mixed Gaussian and Poisson Processes, " MIT-LL TR 27L-0019, MIT-Lincoln Laboratory, 1986.
