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Abstracts
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Shift-Map
Image Editing
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Yael Pritch, Eitam Kav-Venaki, Shmuel Peleg - HUJI
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Geometric rearrangement of images includes operations such
as image retargeting, object removal, or object rearrangement. Each such
operation can be characterized by a shift-map: the relative shift of every
pixel in the output image from its source in an input image.
We describe a new representation of these operations as
an optimal graph labeling, where the shift-map represents the selected label
for each output pixel. Two terms are used in computing the optimal shift-map:
(i) A data term which indicates constraints such as
the change in image size, object rearrangement, a possible saliency map, etc.
(ii) A smoothness term, minimizing the new discontinuities in the output
image caused by discontinuities in the shift-map.
This graph labeling problem can be solved using graph
cuts. Since the optimization is global and discrete, it outperforms state of
the art methods in most cases. Efficient hierarchical solutions for
graph-cuts are presented, and operations on 1M images can take only a few
seconds.
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Fourier
to the rescue of Photography and Image Synthesis
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Fredo Durand - MIT
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New analysis of light transport and image formation
enables novel imaging strategies that reduce motion blur and depth of field
as well as acceleration algorithms for computer graphics.
We analyze phenomena such as light transport in a scene,
integration during the shutter interval and defocus blur with the Fourier
transform of the domain of light rays and space-time. For imaging
applications, this offers both new theoretical insights on upper bounds of
achievable sharpness and signal-noise ratio in the presence of motion blur
and depth of field as well as new lens and camera designs that, combined with
computation, can reduce blur. In image synthesis, similar analysis enables
algorithms that use adaptive sampling and novel reconstruction to simulate
effects such as motion blur and depth of field with dramatic speedups.
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PatchMatch:
A Randomized Correspondence Algorithm for Structural Image Editing
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Eli Shechtman,
Connelly Barnes, Adam Finkelstein, Dan Goldman – Adobe, Princeton
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We present a new randomized algorithm for quickly finding
approximate nearest neighbor matches between image patches for interactive
image editing. Previous research in graphics and vision has leveraged such
nearest-neighbor searches to provide a variety of high-level digital image
editing tools. However, the cost of computing a field of such matches for an
entire image has eluded previous efforts to provide interactive performance.
Our algorithm offers substantial performance improvements over the previous
state of the art (20-100x), enabling its use in interactive editing tools.
The key insights driving the algorithm are that some good patch matches can
be found via random sampling, and that natural coherence in the imagery
allows us to propagate such matches quickly to surrounding areas. We offer a
theoretical analysis of the convergence properties of the algorithm, as well
as empirical and practical evidence for its high quality and performance.
This one simple algorithm forms the basis for a variety of tools – image
retargeting, completion and reshuffling – that can be used together in the
context of a high-level image editing application. Finally, we provide
additional intuitive constraints on the synthesis process that offer the user
a level of control unavailable in previous methods.
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Super-Resolution
From a Single Image
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Daniel
Glasner, Shai Bagon, Michal Irani - Weizmann
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Methods for super-resolution (SR) can be broadly
classified into two families of methods: (i) The classical
multi-image super-resolution (combining images obtained at subpixel misalignments), and (ii) Example-Based
super-resolution (learning correspondence between low and high resolution
image patches from a database). In this work we propose a unified framework
for combining these two families of methods. We further show how this
combined approach can be applied to obtain super resolution from as little as
a single image (with no database or prior examples). Our approach is based on
the observation that patches in a natural image tend to redundantly recur
many times inside the image, both within the same scale, as well as across
different scales. Recurrence of patches within the same image scale (at subpixel misalignments) gives rise to the classical super-resolution,
whereas recurrence of patches across different scales of the same image gives
rise to example-based super-resolution. Our approach attempts to recover at
each pixel its best possible resolution increase based on its patch
redundancy within and across scales.
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Vanishing Points
Estimation by Self-Similarity
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Hadas Kogan, Ron Maurer, Renato Keshet - HP
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We propose a new self-similarity based approach for the
problem of vanishing point estimation in man-made scenes. A vanishing point (VP)
is the convergence point of a pencil (a concurrent line set), that is a
perspective projection of a corresponding parallel line set in the scene.
Unlike traditional VP detection that relies on extraction and grouping of
individual straight lines, our approach detects entire pencils based on a
property of 1D affine-similarity between parallel cross-sections of a pencil.
Our approach is not limited to real pencils. Under some conditions (normally
met in man-made scenes), our method can detect pencils made of virtual lines
passing through similar image features, and hence can detect VPs from
repeating patterns that do not contain straight edges. We demonstrate that
detecting entire pencils rather than individual lines improves the detection
robustness in that it improves VP detection in challenging conditions, such
as very-low resolution or weak edges, and simultaneously reduces VP
false-detection rate when only a small number of lines are detectable.
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Sketch2Photo:
Internet Image Montage
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Arik Shamir, Tao Chen, Ming-Ming Cheng, Shi-Min Hu, Ping
Tan – IDC,
Tsinghua University, University of Singapore
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We present a system that composes a realistic picture
from a simple freehand sketch annotated with text labels. The composed
picture is generated by seamlessly stitching several photographs in agreement
with the sketch and text labels; these are found by searching the Internet.
Although online image search generates many inappropriate results, our system
is able to automatically select suitable photographs to generate a high
quality composition, using a filtering scheme to exclude undesirable images.
We also provide a novel image blending algorithm to allow seamless image
composition. Each blending result is given a numeric score, allowing us to
find an optimal combination of discovered images. Experimental results show
the method is very successful; we also evaluate our system using the results
from two user studies.
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Fast and Robust
Earth Mover's Distances
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Ofir Pele, Michael Werman
- HUJI
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We present a new Earth Mover's Distance (EMD) variant. We
show that it is a metric (unlike the original EMD) which is a metric only for
normalized histograms). Moreover, it is a natural extension of the L1 metric.
We propose a linear time algorithm for the computation of the EMD variant,
with a robust ground distance for oriented gradients.
We also present a new algorithm for a robust family of
Earth Mover's Distances - EMDs with thresholded ground distances. We compute the EMD by
an order of magnitude faster than the original algorithm, which makes it
possible to compute the EMD on large histograms and databases. In addition,
we show that EMDs with thresholded
ground distances have many desirable properties. First, they correspond to
the way humans perceive distances. Second, they are robust to outlier noise
and quantization effects. Third, they are metrics. Finally, experimental
results show that thresholding the ground distance
of the EMD improves both accuracy and speed.
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Understanding and
evaluating blind deconvolution algorithms
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Anat Levin, Yair
Weiss, Fredo Durand, Bill Freeman – Weizmann, HUJI,
MIT
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Blind deconvolution is the
recovery of a sharp version of a blurred image when the blur kernel is
unknown. Recent algorithms have afforded dramatic progress, yet many aspects
of the problem remain challenging and hard to understand. The goal of our
work is to analyze and evaluate recent blind deconvolution
algorithms both theoretically and experimentally. We explain the previously
reported failure of the naive MAP approach by demonstrating that it mostly
favors no-blur explanations. On the other hand we show that since the kernel
size is often smaller than the image size a MAP estimation of the kernel
alone can be well constrained and accurately recover the true blur.
The plethora of recent deconvolution
techniques makes an experimental evaluation on ground-truth data important.
We have collected blur data with ground truth and compared recent algorithms
under equal settings. Additionally, our data demonstrates that the
shift-invariant blur assumption made by most algorithms is often violated.
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Multiple One-Shots
for Utilizing Class Label Information
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Tal Hassner, Lior
Wolf, Yaniv Taigman - OpenU, TAU, face.com
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The One-Shot Similarity measure has
recently been introduced as a means of boosting the performance of face
recognition systems. Given two vectors, their One-Shot Similarity score
reflects the likelihood of each vector belonging to the same class as the other
vector and not in a class defined by a fixed set of ``negative'' examples. An
appealing aspect of this approach is that it does not require class labeled
training data. This talk will explain how the One-Shot Similarity may
nevertheless benefit from the availability of such labels. We claim the
following contributions: (a) We present a system utilizing subject and pose
information to improve facial image pair-matching performance using multiple
One-Shot scores; (b) we show how separating pose and identity may lead to
better face recognition rates in unconstrained, ``wild'' facial images; (c)
we explore how far we can get using a single descriptor with different
similarity tests as opposed to the popular multiple descriptor approaches;
and (d) we demonstrate the benefit of learned metrics for improved One-Shot
performance. We test the performance of our system on the challenging Labeled
Faces in the Wild unrestricted benchmark and present results that exceed by a
large margin the best results reported to date for this test.
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Automatically
Identifying Join Candidates in the Cairo
Genizah
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Lior Wolf, Rotem
Littman, Naama Mayer, Nachum
Dershowitz, R. Shweka, Y.
Choueka - TAU Genizah
Project
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A join is a set of manuscript-fragments
that are known to originate from the same original work. The Cairo Genizah is a collection containing approximately 250,000
fragments of mainly Jewish texts discovered in the late 19th century. The
fragments are today spread out in libraries and private collections
worldwide, and there is an ongoing effort to document and catalogue all
extant fragments. The task of finding joins is currently conducted manually
by experts, and presumably only a small fraction of the existing joins have
been discovered. In this work, we study the problem of automatically finding
candidate joins, so as to streamline the task. The proposed method is based
on a combination of local descriptors and learning techniques. To evaluate
the performance of various join-finding methods, without relying on the
availability of human experts, we construct a benchmark dataset that is
modeled on the Labeled Faces in the Wild benchmark for face recognition.
Using this benchmark, we evaluate several alternative image representations
and learning techniques. Finally, a set of newly-discovered join-candidates
have been identified using our method and validated by a human expert.
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A system for
recognizing instances from a large set of object classes using a novel shape model
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Simon Polak , Amnon
Shashua - HUJI
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We propose a model for classification and
detection of object classes where the number of classes may be large and
where multiple instances of object classes may be present in an image. The
algorithm combines a bottom-up, low-level, procedure of a bag-of-words naive Bayes phase for winnowing out unlikely object classes
with a high-level procedure for detection and classification. The high-level
process is a hybrid of a voting method where votes are filtered using beliefs
computed by a class-specific graphical model (using sum-TRBP). In that sense,
shape is both explicit (determining the voting pattern) and implicit (each
object part votes independently) --- hence we call our approach the
"semi-explicit shape model".
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Piecewise-consistent
Color Mappings of Images Acquired Under Various Conditions
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Sefy Kagarlitsky,
Yael Moses, Yacov Hel-Or - IDC
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Many applications in computer vision require comparisons
between two images of the same scene. Comparison applications usually assume
that corresponding regions in the two images have similar colors. However,
this assumption is not always true. One way to deal with this problem is to
apply a color mapping to one of the images. We address the challenge of
computing color mappings between pairs of images acquired under different
acquisition conditions, and possibly by different cameras. For images taken
from different viewpoints, our proposed method overcomes the lack of pixel
correspondence. For images taken under different illumination, we show that
no single color mapping exists, and we address and solve a new problem of
computing a minimal set of piecewise color mappings. When both viewpoint and
illumination vary, our method can only handle planar regions of the scene. In
this case, the scene planar regions are simultaneously co-segmented in the
two images, and piecewise color mappings for these regions are calculated. We
demonstrate applications of the proposed method for each of these cases.
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On Edge Detection
On surfaces
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Michael Kolomenkin, Ilan
Shimshoni, Ayellet Tal – Haifa, Technion
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Edge detection in images has been a
fundamental problem in computer vision from its early days. Edge detection on
surfaces, on the other hand, has received much less attention. The most common
edges on surfaces are ridges and valleys, used for processing range images in
computer vision, as well as for non-photorealistic rendering in computer
graphics. We propose a new type of edges on surfaces, termed relief edges.
Intuitively, the surface can be considered as an unknown smooth manifold, on
top of which a local height image is placed. Relief edges are the edges of
this local image. We show how to compute these edges from the local
differential geometric surface properties, by fitting a local edge model to
the surface. We also show how the underlying manifold and the local images
can be roughly approximated and exploited in the edge detection process. Last
but not least, we demonstrate the application of relief edges to artifact
illustration in archaeology.
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Optically Compressed Sensing by Undersampling the polar Fourier plane
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Adrian Stern, Ofer Levi - BGU
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The recently introduced theory of
compressed sensing (CS) has attracted the interest of theoreticians and
practitioners alike and has initiated a fast emerging research field. CS
theory shows that one can recover certain signals and images from far fewer
samples or measurements that traditional methods use. CS provides a new
framework for simultaneous sampling and compression of signals. Optically
compressed sensing is a natural implementation of CS theory because of high
redundancy typical to most optical data.
In a previous work we presented a compressed imaging approach that
uses a linear rotating sensor to capture indirectly polar strips of the
Fourier transform of the image. Here we present further developments of this
technique and present new results. The advantages of our technique, compared
to other optically compressed imaging techniques, is that its optical implementation
is relatively easy, it does not require complicate calibrations and that it
can be implemented in near-real time.
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Edge-Avoiding
Wavelets and their Applications
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Raanan Fattal -
HUJI
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We propose a new family of second-generation wavelets constructed
using a robust data-prediction lifting scheme. The support of these new
wavelets is constructed based on the edge content of the image and avoids
having pixels from both sides of an edge. Multi-resolution analysis, based on
these new edge-avoiding wavelets, shows a better decorrelation
of the data compared to common linear translation-invariant multi-resolution
analyses. The reduced inter-scale correlation allows us to avoid halo
artifacts in band-independent multi-scale processing without taking any
special precautions. We thus achieve nonlinear data-dependent multi-scale
edge-preserving image filtering and processing at computation times which are
linear in the number of image pixels. The new wavelets encode, in their
shape, the smoothness information of the image at every scale. We use this to
derive a new edge-aware interpolation scheme that achieves results,
previously computed by an inhomogeneous Laplace
equation, through an explicit computation. We thus avoid the difficulties in
solving large and poorly-conditioned systems of equations.
We demonstrate the effectiveness of the new wavelet basis
for various computational photography applications such as multi-scale
dynamic-range compression, edge-preserving smoothing and detail enhancement,
and image colorization.
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Energy-Based
Shape Deformation
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Daniel Freedman, Zachi Karni,
Craig Gotsman – HP, Technion
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The talk will present a general approach to energy-based
shape deformation, and applications of this approach to the problems of 2D shape
deformation and image resizing. The expression for the deformation energy
generalizes that found in the prior art, while still admitting an efficient
"local-global" algorithm for its optimization. The key advantage of
the energy function is the flexibility with which the set of "legal
transformations" may be expressed; these transformations are the ones
which are not considered to be distorting. This flexibility allows to pose
the problem of 2D shape deformation (possibly within an image), as well as image
resizing, in sensible ways, and generate minimally distorted results. Results
of both algorithms show the effectiveness of this approach.
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