sparray - sparse n-dimensional arrays in Python
Yesterday I wrote about sparse arrays for Python using dictionaries. I couldn't get it out of my head so tonight I actually made a complete module containing a class for sparse n-dimensional arrays....
View ArticleComputer Vision and the New iPhone SDK
A look at the newly released iPhone SDK for iPhone OS 4 shows some very interesting new features for people building computer vision and augmented reality applications. Video playback & Capture"You...
View ArticleComputational Mathematics with Python
Posting has been a little slow the last months. I have been busy at Polar Rose and in parallel I've been teaching a course in computational mathematics with python. I hope to increase posting soon as I...
View ArticleInstalling Numpy and Matplotlib on Mac OS X 10.6 Snow Leopard
This is partly an update to my previous post on installing for Leopard, partly a note to myself. After upgrading to Snow Leopard (and 64bit) I could still use my MacPort installs but not upgrade or...
View ArticleGeo Data from Twitter using Python
I wanted to write an example of plotting geo data with maps but I didn't have any good example data. Having played around with Twitter's API before, I decided to use that. There are several Python...
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Plotting Geo Data using Basemap
Matplotlib has an interesting toolkit called Basemap for plotting geo data and maps. Basemap handles all the possible map projections and uses Matplotlib to do the plotting. Basemap also includes data...
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Transparent figures
Matplotlib (Pylab) has an interesting option in the savefig() command; the figure background can be set to be transparent. Very useful if you want to put your figures on any non-white background (e.g....
View ArticleOpenCV with Python on Mac OS X
Open source computer vision library OpenCV is gaining a lot of traction and now comes with what looks like a pretty good Python interface. There are installers for Windows and Linux but Mac OS X...
View ArticleConverting video to NumPy arrays
Using OpenCV it is possible to read video frames from a file and convert them to NumPy arrays. Frames returned by QueryFrame() are in OpenCV's IplImage format where the pixels are stored as arrays of...
View ArticleInstalling LibSVM
LibSVM is a good Support Vector Machine (SVM) implementation which works well with Python. The current release of LibSVM is version 3.0 (released September 2010). Download the zip file from the LibSVM...
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3D plotting with Matplotlib
Earlier, Matplotlib (and Python) lacked proper support for 3D plotting. This is no longer the case as the mplot3d toolkit provides 3D plotting of points, lines, contours, surfaces and all other basic...
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Multidimensional meshgrid with Python
Looking for an easy way to plot cubes in 3D I found NumPy's mgrid that can do meshgrid in any number of dimensions. The syntax is a bit confusing but once you understand the trick, it works.Here's a...
View ArticleRQ Factorization of Camera Matrices
A common operation on camera matrices is to use RQ factorization to obtain the camera calibration matrix given a 3*4 projection matrix. The simple example below shows how to do this using the...
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Adjacency matrix for image pixel graphs
One of my favorite NumPy functions is roll(). Here's an example of using this function to get neighborhood indices to create adjacency matrices for images.An adjacency matrix is a way of representing a...
View ArticleRead/Write World
Last week at ARE2011 Blaise Aguera y Arcas and Avi Bar-Zeev gave two talks that got my attention. The Read/Write World initiative from Bing. This is interesting from a number of angles:RML - Reality...
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Another Python Interface for SIFT
I previously wrote about using David Lowe's SIFT code from Python here. There is a good open source alternative for those on Windows or Mac OS (Lowe's binaries are Linux only) called VLFeat. The...
View ArticleBook draft
The other night I put up the first early draft of my upcoming book "Programming Computer Vision with Python". The book is meant as an entry point to hands-on computer vision for students, researchers...
View ArticleInstalling the OpenCV Python Interface on Lion
On some machines I ran into "Segmentation fault 11" when I use the OpenCV Python interface on Mac OS X 10.7 Lion. These problem machines were all upgraded from Snow Leopard which had Python 2.6 (Lion...
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Polar panoramas with Python
Today I saw (again) Filipe Calegario's nice photos and instructions for making polar panoramas. To show how to warp images with Python I wrote a Python version of the polar warp. Here's a complete code...
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Isomap with scikit-learn
The scikit-learn project for Python contains many machine learning algorithms neatly packaged. There are several manifold learning algorithms in the manifold module. Here's a simple example of Isomap...
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