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Rabu, 03 Juli 2013

[CVPR 2013] Three Trending Computer Vision Research Areas

As I walked through the large poster-filled hall at CVPR 2013, I asked myself, “Quo vadis Computer Vision?" (Where are you going, computer vision?)  I see lots of papers which exploit last year’s ideas, copious amounts of incremental research, and an overabundance of off-the-shelf computational techniques being recombined in seemingly novel ways.  When you are active in computer vision research for several years, it is not rare to find oneself becoming bored by a significant fraction of papers at research conferences.  Right after the main CVPR conference, I felt mentally drained and needed to get a breath of fresh air, so I spent several days checking out the sights in Oregon.  Here is one picture -- proof that the CVPR2013 had more to offer than ideas!



When I returned from sight-seeing, I took a more circumspect look at the field of computer vision.  I immediately noticed that vision research is actually advancing and growing in a healthy way.  (Unfortunately, most junior students have a hard determining which research papers are actually novel and/or significant.)  A handful of new research themes arise each year, and today I’d like to briefly discuss three new computer vision research themes which are likely to rise in popularity in the foreseeable future (2-5 years).

1) RGB-D input data is trending.  

Many of this year’s papers take a single 2.5D RGB-D image as input and try to parse the image into its constituent objects.  The number of papers doing this with RGBD data is seemingly infinite.  Some other CVPR 2013 approaches don’t try to parse the image, but instead do something else like: fit cuboids, reason about affordances in 3D, or reason about illumination.  The reason why such inputs are becoming more popular is simple: RGB-D images can be obtained via cheap and readily available sensors such as Microsoft’s Kinect.  Depth measurements used to be obtained by expensive time of flight sensors (in the late 90s and early 00s), but as of 2013, $150 can buy you one these depth sensing bad-boys!  In fact, I had bought a Kinect just because I thought that it might come in handy one day -- and since I’ve joined MIT, I’ve been delving into the RGB-D reconstruction domain on my own.  It is just a matter of time until the newest iPhone has an on-board depth sensor, so the current line of research which relies on RGB-D input is likely to become the norm within a few years.










2) Mid-level patch discovery is a hot research topic.
Saurabh Singh from CMU introduced this idea in his seminal ECCV 2012 paper, and Carl Doersch applied this idea to large-scale Google Street-View imagery in the “What makes Paris look like Paris?” SIGGRAPH 2012 paper.  The idea is to automatically extract mid-level patches (which could be objects, object parts, or just chunks of stuff) from images with the constraint that those are the most informative patches.  Regarding the SIGGRAPH paper, see the video below.






Unsupervised Discovery of Mid-Level Discriminative Patches Saurabh Singh, Abhinav Gupta, Alexei A. Efros. In ECCV, 2012.








Carl DoerschSaurabh Singh, Abhinav Gupta, Josef Sivic, and Alexei A. Efros. What Makes Paris Look like Paris? In SIGGRAPH 2012. [pdf]

At CVPR 2013, it was evident that the idea of "learning mid-level parts for scenes" is being pursued by other top-tier computer vision research groups.  Here are some CVPR 2013 papers which capitalize on this idea:

Blocks that Shout: Distinctive Parts for Scene Classification. Mayank Juneja, Andrea Vedaldi, CV Jawahar, Andrew Zisserman. In CVPR, 2013. [pdf]

Representing Videos using Mid-level Discriminative Patches. Arpit Jain, Abhinav Gupta, Mikel Rodriguez, Larry Davis. CVPR, 2013. [pdf]

Part Discovery from Partial Correspondence. Subhransu Maji, Gregory Shakhnarovich. In CVPR, 2013. [pdf]

3) Deep-learning and feature learning are on the rise within the Computer Vision community.
It seems that everybody at Google Research is working on Deep-learning.  Will it solve all vision problems?  Is it the one computational ring to rule them all?  Personally, I doubt it, but the rising presence of deep learning is forcing every researcher to brush up on their l33t backprop skillz.  In other words, if you don't know who Geoff Hinton is, then you are in trouble.

Rabu, 20 Juni 2012

CVPR 2012 Day 2: optimize, optimize, optimize

Due to popular request, here is my overview of some of the coolest stuff from Day 2 of CVPR 2012 in Providence, RI.  While the Lobster dinner was the highlight for many of us, there were also some serious learning/optimization-based papers presented during Day 2 worthy of sharing.  Here are some of the papers which left me with a very positive impression.


Dennis Strelow of Google Research in Mountain View presented a general framework for Wiberg minimization.  This is a strategy for minimizing objective functions with multiple variables -- objectives which are typically tackled in an EM-style fashion.  The idea is to express one of the variables as a linear function of the other variable, effectively making the problem depend on only one set of variables.  The technique is quite general and has been shown to produce state-of-the-art results on a bundle adjustment problem.  I know Dennis from my second internship at Google where we worked on some sparse-coding problems.  If you perform lots of matrix decomposition problems, check out his paper!


Dennis Strelow
General and Nested Wiberg Minimization
CVPR 2012


Another cool paper which is all about learning is Hossein Mobahi's algorithm for optimizing objectives by smoothing them to avoiding getting stuck in local minima.  This paper is not about blurry images, but about applying Gaussians to objective functions.  In fact, for the problem of image alignment, Hossein provides closed form versions of image operators.  Now when you apply these operators to images, you efficiently smooth the underlying cross-correlation alignment objective.  You decrease the blur, while following the optimum path, and get much nicer answers that doing naive image alignment.


Hossein Mobahi, C. Lawrence Zitnick, Yi Ma
Seeing through the Blur
CVPR 2012


Ira Kemelmacher-Shlizerman, of Photobios fame, showed a really cool algorithm for computing optical flow between two different faces based on learning a subspace (using a large database of faces).  The ideas is quite simple and allows for flowing between two very different faces where the underlying operation produces a sequence of intermediate faces in an interpolation-like manner.  She shared this video with us during her presentation, but it is on Youtube, so now you can enjoy it for yourself.


Ira Kemelmacher-Shlizerman, Steven M. Seitz
Collection Flow
CVPR 2012



Now talk about cool ideas!  Pyry, of CMU fame, presented a recommendation engine for classifiers.  The idea is to take techniques from collaborative filtering (think Netflix!) and apply then to the classifier selection problem.  Pyry has been working on action recognition and the ideas presented in this work are not only quite general, but have are quite intuitive and likely to benefit anybody working with large collections of classifiers.

Pyry Matikainen, Rahul Sukthankar, Martial Hebert
Model Recommendation for Action Recognition
CVPR 2012


And finally, a super-easy algorithm presented for metric learning by Martin Köstinger had me intrigued!  This a Mahalanobis distance metric learning paper which uses equivalence relationships.  This means that you are given pairs of similar items and pairs of dissimilar items.  The underlying algorithm is really not much more than fitting two covariance matrices, one to the positive equivalence relations, and another to the non-equivalence relations.  They have lots of code online, and if you don't believe that such a simple algorithm can beat LMNN (Large-Margin Nearest Neighbor from Killian Weinberger), then get their code and hack away!

Martin Köstinger, Martin Hirzer, Paul Wohlhart, Peter M. Roth, Horst Bischof
Large Scale Metric Learning from Equivalence Constraints
CVPR 2012



CVPR 2012 gave us many very math-oriented papers, and while I cannot list of all of them, I hope you found my short list useful.