Category Archives: Uncategorized

OpenCV kmeans in MATLAB

Data clustering is one of unsupervised learning techniques that attempts to find some structure in the data. Given some dataset, we may be interested to see if there are some natural clusters. This is where the classic k-means algorithm kicks … Continue reading

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OpenCV matrix types

OpenCV is a framework for image processing, machine learning and related convenience processing of images and other data. One of the central data structures is the famous matrix, the Mat type. It can store multiple channel data, different color spaces … Continue reading

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Extracting FREAK descriptor in MATLAB (OpenCV interface)

In Computer Vision applications the local keypoint descriptors are well known. They encode in a vector some visual information contained around a selected keypoint in the image. We outline “some” since there are many assumptions and information types that can … Continue reading

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[MAC] How to compile MATLAB MEX with Intel Composer XE Compiler

With new things, the good old working things may break. This was the case for Matlab [WWW] MEX [WWW] compilation after migration from Snow Leopard [WWW] to Lion [WWW]. For those who don’t know, Matlab is an advanced scientific computation … Continue reading

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Efficient computation of element presence in a set of windows

It seems trivial to verify presence of an element (x,y) in a rectangle window. Now imagine that you have millions of elements and many thousands or more of windows. Your problem quickly gets unwieldy as it scales as badly as … Continue reading

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OpenCV 2.4.0 + IPP + TBB: Compilation instructions on Mac OS X (Snow Leopard)

In Computer Vision the OpenCV [WWW] framework is a well known collection of high-quality and real-time functions performing image processing, feature extraction, matrix operations, object detection and many many more ready to use routines.┬áThe framework is in active development and … Continue reading

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Bag of Visual Words – Efficient window histogram computation (MEX)

Bag of Visual Words (also known as Bag-of-Words) [LINKS] is a well known technique describing visual content in Pattern Recognition and Computer Vision. Idea is to represent an image or an object as a histogram of visual word occurrences. Here … Continue reading

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Embedding fonts in PDF

PDF stands for Portable Document Format [WIKI]. Not in all cases this format is that portable. Sometimes this is due to some special fonts that are not so widespread and are not included or embedded in the PDF file. To … Continue reading

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MATLAB: Sliding window – easy and painless

When doing advanced stuff such as image processing, it is very wasteful to re-invent a wheel. ┬áThis time this is about a very common operation as a sliding window operation. Imagine that we have an image I and a small … Continue reading

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MATLAB: Simple TF-IDF implementation

Term-Frequency word weighting scheme [WWW] is one of most used in normalization of document-term matrices in text mining and information retrieval. This down-weights the very frequent or called stop-words. The idea is that stop-words are very often non-informative e.g. “and”, … Continue reading

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