[OpenCV] detectMultiScale: output detection score

OpenCV provides quite decent implementation of the Viola-Jones Face detector. A quick example looks like this (OpenCV 2.4.5 tested): // File: main.cc #include using namespace cv; int main(int argc, char **argv) { CascadeClassifier cascade; const float scale_factor(1.2f); const int min_neighbors(3); if (cascade.load(“./lbpcascade_frontalface.xml”)) { for (int i = 1; i < argc; i++) { Mat img […]

On 2 dimensional array of C++

I was asked about this today. In practice, I rarely use 2-dimensional array, instead I use vector of vectors. To allocate a 2-d array on the stack, a C-style array is int d[2][3]; Then to refer to an element it is like d[i][j]; To make a dynamical allocation, one can NOT write his code like […]

[OpenCV]detectMultiScale

I met a problem when using the interface ‘detectMultiScale’ of OpenCV. The rectangles it gives out may not be fully inside the frame of the original image. As a result, if these rectangles are applied directly on the original image to crop out the detected objects, your programs crash. These are the interfaces virtual void […]

SSE2 Vector Operation by Vlfeat

If you are writing something involving the math between vectors in C/C++, you may want to check out Vlfeat (http://vlfeat.org). It is designed to be a library for Computer Vision related stuff, but it also bring you a wrapper for SSE2 acceleration for vector computation. Say your original code for the calculation of vectors product […]

Setup dropbox without X

Assume you are accessing your server remotely through SSH. 1. Download the package, say you are using Ubuntu $wget https://www.dropbox.com/download?dl=packages/ubuntu/dropbox_1.4.0_amd64.deb 2. Install the package $sudo dpkg -i *dropbox_1.4.0_amd64.deb 3. Start Dropbox $dropbox start 4. You will get an url to link your computer here, copy-and-paste into your web-browser. Restart your dropbox, all set :] $dropbox […]

fstream issue under 64-bits cygwin

This is a question I posted on StackOverflow: fstream issue under 64-bits cygwin, glad to get help from Nemo on Stackflow, all credits goes to him. The problem is when I use 64-bits g++ to compile the same piece of code, I get unexpected different result. The source code looks like this: #include #include using […]

Use a different delimiter in sed

Think about this, you want to replace “XXX” with a path like “/path/to/YYY” in a file. Your file looks like this: XXX AAA XXX Your bash script looks like this: NEW_PATH=”/path/to/YYY” VAR=”XXX” sed -e ‘{s/$VAR/$NEW_PATH/g}’ your_file Well, it won’t work, since single quotes ‘ will force bash to keep variables as-is. Ok, we try to […]

Project-Specific Vim Configuration

Usually, we have our own vim configuration in the file ~/.vimrc What if we want one for our project? For example, we are working on certain project which needs to read in a tags file. Well, here is a possible solution. You put a line at then end of your ~/.vimrc file source ./.project.vim Then […]